FRC 2001: A White Paper on FRC Development
in the Next Five Years

March 1996

Executive Summary

This document expresses the consensus of a worldwide community of fusion energy researchers on directions for research on the field-reversed configuration (FRC) over the next five years.

The FRC, a variety of compact torus, occupies a unique position in the parameter space of magnetically confined plasmas. It differs markedly from other toroidal systems: no mechanical structure in the center of the torus; no appreciable toroidal field; and engineering beta near unity; no rotational transform; and scrape-off layer exhausting outside the coil system. FRCs range from small gyro-radius to large-orbit ion ring- dominated plasmas. Because of these peculiar features FRC research adds unique insight into the physics of tokamaks and similar fusion systems. Moreover, FRC research offers a means of exploring fundamental plasma physics questions unrelated to fusion.

Review panels have repeatedly called for fusion system improvements in order to project economical fusion energy. However, even improved tokamaks may not overcome the shortcomings of low power density, high complexity, large unit size, and high development cost. Among alternative concepts based on low-density magnetic confinement, the FRC offers arguably the best reactor potential because of high power density, simple structural and magnetic topology, simple heat exhaust handling, and potential for advanced fuels. Projected FRC reactors are much smaller than those based on the tokamak. Small size leads to lower costs. The enormous potential payoff as a reactor justifies a broad and sustained program on FRC stability and confinement.

Several FRC-related facilities are in operation around the world as well as other small theory efforts. Favorable results from theory and experiments have raised hopes for ultimate development into a practical fusion system. Parameters achieved include densities ranging from 5*10^13 to 5*10^15 cm^-3, temperatures up to 3 keV (ions) and 500 eV (electrons); and beta ~ 0.75-0.95. Noteworthy achievements include: formation by theta- pinch and by counter-helicity merging; simulation of large-orbit ion ring injection and trapping; stabilization of rotational instability; detection of global internal modes; tilting mode theory; global translation along a guide field; identification of transport anomalies; and demonstration of the convective nature of energy loss.

In view of the foregoing, five action items are recommended. (1) FRC research should be continued and expanded both as an adjunct to mainline fusion research and as a stand-alone alternative fusion concept. (2) Existing FRC-related resources should be exploited in an expanded program: including both facilities and the intellectual capital established in institutions and individuals with a long commitment to FRCs. (3) New FRC facilities or upgrades of existing facilities should be considered on the merits of how they address the directions offered in this document. This should include consideration of a jointly-operated international FRC research facility. (4) Researchers and institutions with a history of activity on the tokamak should be encouraged to broaden their research to include FRC theory, diagnostic development, and systems studies. (5) Vigorous international collaboration on FRC research should be encouraged, including, at the least, annual workshops and long-term exchange visits.


Full Text of "FRC 2001" (5 February 1996)

Fusion offers a nearly inexhaustible source of energy. Developing this energy source depends on more than just acclaimed progress in plasma physics: it also requires public support. Such support demands an environmentally sound final product that is superior to competing energy sources. Moreover, in the present economic environment, the development path must be consistent with an austere budget. This White Paper focuses on the field reversed configuration (FRC). Given its present state of development, the FRC has good prospects for a desirable end product. In particular, among all conventional low-density magnetic confinement concepts, the FRC probably offers the best vista for an attractive fusion power reactor due to its potential for high power density, reduced complexity and lower development cost. Moreover, continued FRC research offers unique insights into the physics of tokamaks, the present leading fusion concept, and other plasma configurations. This paper reflects the consensus of a worldwide community of researchers that are knowledgeable in FRC physics and interested in furthering fusion energy. The contents of the document identify the leading issues for FRC research over the next five years, and concludes with a roadmap for FRC development to guide this research.

I. MANDATE FOR FRC RESEARCH

A. DEFINITION

FRCs belong to the family of compact toroids. "Compact" implies the absence of internal material structures (e.g. magnet coils) allowing plasma to extend to the geometric axis. "Toroid" implies a topology of nested closed donut-shaped magnetic surfaces. FRCs are differentiated from other compact toroids by the absence of appreciable toroidal field within the plasma. In common with toroidal systems FRCs have plasma pressure comparable to the poloidal magnetic pressure (poloidal beta of order unity). However they differ markedly from toroidal systems in several respects: 1) the engineering beta (pressure / magnetic pressure supplied by the coils) is near unity; 2) magnetic field lines close (or nearly so) after a single circuit of the magnetic axis (no rotational transform); and 3) the scrape-off layer connects to spindle-like jets at each end, which freely exhaust outside the coil system. The term FRC only specifies the magnetic configuration. The plasma itself may take a variety of forms, from MHD (small gyro-radius) to "hybrid" (MHD plus a large orbit ion-ring component) to ion ring-dominated. An ion ring is composed of energetic ions with orbits comparable to the major radius. Each variation has its own attractive features.

B. CONTRIBUTION TO PLASMA SCIENCE

The importance of broadening the knowledge base of fusion plasma science beyond toroidal plasma physics has long been recognized. Major improvements in the stability and transport of conventional tokamaks have been achieved by confinement field shaping and a variety of other techniques. Fusion review panels have consistently recommended that further improvements are necessary to make a tokamak economically viable for fusion energy. One approach is to pursue high-beta tokamaks and spherical tokamaks, where a leading objective with recognized economic benefits is to reduce the toroidal field. In pursuing such improvements FRC research occupies a unique position in the parameter space of magnetically toroidal plasmas. In particular, FRCs offer vital insights into the physics of truly high-beta plasmas. Further, since FRCs lack a toroidal field, they offer insight into a kind of stability that may be independent of the standard ideal-MHD paradigm, which demands a large toroidal field. Besides its usefulness in advancing toroidal plasma science in general, FRCs can also play valuable ancillary roles in support of other confinement concepts: e.g. FRCs can be accelerated to high speed and injected into a tokamak to provide deep refueling.

Because of its extreme nature FRC research advances plasma science in ways that may be unrelated to tokamaks. Regarding the general topic of high-beta plasmas, FRCs are unique. They offer a magnetic topology that is singular for its lack of a rotational transform and magnetic shear. They also offer a means of researching fundamental plasma questions unrelated to fusion applications. Most notable among these is the reconnection of magnetic field lines, but other geophysical and astrophysical phenomena might be addressed as well.

C. FRC REACTOR PROSPECTS

One approach to fusion concept improvement is through incremental improvements such as offered by reverse-shear profiles in a tokamak. However, even improved tokamaks may not overcome the shortcomings of low power density, high complexity, large unit size, and high development cost. Therefore a step change away from the tokamak concept may be necessary. The FRC offers such a step change. Although the FRC concept is not new, it has not yet been investigated in a reactor relevant regime. Nevertheless, despite uncertainties about its stability and confinement, the enormous potential payoff justifies researching the FRC as its own reactor concept.

Among alternative fusion concepts based on conventional low- density magnetic confinement, the FRC offers arguably the best reactor potential for several reasons. (1) HIGH POWER DENSITY, with engineering beta of order unity. (2) GEOMETRIC SIMPLICITY: singly connected plasma; linear geometry; simple, maintainable fusion power core. (3) MAGNETIC SIMPLICITY: no toroidal field; no interlinking magnets; possibility of disruption-free plasma. (4) HEAT EXHAUST HANDLING: natural axial flow divertor with heat collection outside the core. (5) ADVANCED FUEL POTENTIAL: high-beta makes the FRC arguably the best magnetic- confinement system credibly capable of advanced fusion fuel operation. Collectively, the above features lead to reactors that are smaller than an advanced-fuel tokamak: small size leads to lower cost. (6) LOWER COST DEVELOPMENT PATH: if the FRC offers the potential for the simplest, lowest-cost magnetic confinement reactor, then its R&D path would be proportionately shorter and cheaper.

II. FRC ISSUES AND PROGRESS

A. FUNDAMENTAL ISSUES AT THE OUTSET

The following is a listing of FRC issues that one might perceive at the outset based on a general knowledge of fusion plasma physics and technology. The list emphasizes areas where FRCs possess attributes that are unique compared with other fusion concepts.

1) Stability According to the ideal-MHD stability paradigm, FRCs are unstable because of predominantly unfavorable magnetic curvature and the absence of a "stabilizing" toroidal field. Therefore the leading question is-- can FRCs be stabilized by factors excluded by the standard paradigm, whether naturally (phenomena arising of their own accord) or artificially (by external invervention)?

2) Start-up Since FRCs are generated in a singly-connected chamber and have inherently high beta, start-up is quite different from systems with toroidal plasma chambers and a large toroidal field. A major question is --can a suitable start-up method be developed, as it must be, more-or-less independently of techniques used in toroidal systems?

3) Current drive A consequence of high beta is that it may not be possible to simply borrow a current drive technique used in toroidal systems. Thus another question is--can a suitable current drive method be developed?

4) Transport Transport is a perennial issue for all fusion concepts. The uniqueness of the FRC implies that it may take different forms than in toroidal plasmas. Thus another question is--what are the dominant energy transport mechanisms that arise naturally, and do these extrapolate to an attractively small reactor? If inherent transport rates are too rapid, can they be reduced by reasonable and sustainable controls?

5) Technological burden The final issue is broader. The aforementioned "physics" issues introduce, in some cases, unique techniques that must be applied in FRCs. Thus a further question is--what are the technological burdens associated with unique FRC features, and are they surmountable? Examples include the unique start-up method, an artificial stabilization technique (if needed), and a specialized current drive method. High wall loading, which must be withstood to exploit high power densities, is an issue common to all compact devices.

B. PROGRESS IN FRC PHYSICS AND TECHNOLOGY

FRC experiment and theory results have been favorable, raising hopes for its ultimate development into a practical fusion system. Previous reviews of FRCs and FRC-related research include a review of FRC/Ion Ring research [1], a review of compact system physics and technology [2], a comprehensive review of FRC experiments and theory presented in 1988 [3], and a recent brief review of progress since then [4]. Experiments, primarily in theta pinches, have achieved the following ranges of FRC parameters:

density:	0.05-5x1015 cm-3

temperature:    ions, 50-3000 eV;  electrons, 50-500 eV

average beta    0.75-0.95

separatrix:     diameter, 3-20 cm;  length, 20-400 cm

poloidal magnetic flux   < 10 mWb
The following physics and technology achievements are noteworthy.

1) Formation by theta-pinch Using advanced formation techniques, the theta-pinch method has been improved to the point that the parameters listed in the table have been achieved. These include methods for improved gross symmetry of the pre-ionization plasma [5] and control of the axial shock dynamic process [6]. Note that since no auxiliary heating method was applied, the reported temperatures reflect heating intrinsic to the start-up process

2) Formation by counter-helicity merging This technique has been demonstrated on a small scale [7]. One of its features is the efficient conversion of initial toroidal field energy to ion energy.

3) Stabilization of the rotational mode The rotational mode that normally appears in FRC experiments has been stabilized by applying modest multipole fields, as demonstrated on several experiments in the early 1980's and confirmed by theory [8].

4) Detection of global internal modes The most feared instabilities have been disruption-threatening global ideal modes, particularly tilting. These are predicted to be internal modes in typical FRCs and thus difficult to detect. Although no non-intrusive internal diagnostic has been available, Mirnov probe array systems have been developed to detect the external signatures of internal modes. In two instances these were sufficient to distinguish between a range of global modes [9].

5) Tilting mode theory Many analytical and numerical treatments have addressed the tilting mode. All ideal-MHD theories predicted instability until a recent consideration of equilibria with more blunt separatrix shape and hollow current profile than achieved in experiments to date [10]. The most successful tilting theories have included finite larmor radius (FLR) effects, using either kinetic ions [11] or a gyroviscous fluid [12]. The latter led to the prediction of marginal stability conditions consistent with observed stable FRCs. The FLR stability explanation, however, fails to explain other evidences of robust stability, as will be discussed in Sec. IIC.

6) Translation Experiments on several facilities had demonstrated that an FRC can be formed inside a theta-pinch coil, translated along a guide field, and then stopped by a mirror field. Recent experiments have explored this procedure in detail [13] showing it to have great potential for equilibrium control (plasma radius, length, density) and heating (thermalization of the kinetic energy of translation). Remarkably these experiments ejected the initial FRCs at super-Alfvenic speeds into a chamber with a static magnetic field lower than in the source coil by factors up to 25 (magnetic pressure lower by factors over 600). Despite the extreme violence of the ejection, the FRC relaxed into a quiescent state with negligible magnetic flux loss, a remarkable demonstration of its robustness. The same robustness was also evident in experiments where an FRC, after translation through a tube with varied crossection, was compressed up to 1000 times (in volume) by a metal liner [14].

7) Identification of transport anomalies These include a) anomalous cross-field plasma transport rate, b) anomalous decay of the poloidal magnetic flux, and c) anomalously slow particle out flow along field lines in the scrape-off layer. In none of these instances does a satisfactory theory exist, except in the first where preliminary work has been done. A low-beta low-frequency-drift turbulence theory gave a reasonable prediction of plasma loss times for a limited experimental data base [15]. Empirical confinement scaling relations based on a data base including confinement results from most FRC experiments show an energy diffusivity in the range 3 - 7 m2/s in the largest experiments [16], and improving trend with increased size. Confinement properties in a translated and trapped FRC have proved better than empirical scaling relations from other facilities [17].

8) Convective thermal loss Experiments indicate that energy loss in FRCs is convective, both in the interior [16] and along the scrape-off layer [17], i.e. the energy transport rate is proportional to the plasma particle diffusion (or flow) rate. Two important implications follow from this: a) the burden of energy confinement is shifted to the question of plasma confinement; and b) the FRC is genuinely a thermally-isolated system, i.e. not in thermal contact with cold external boundaries.

C. CURRENT FRONTIERS IN FRC DEVELOPMENT

The frontiers described here are "hot" topics presently under investigation with favorable initial results and the potential of a major impact on FRC development.

1) Flow stabilization Flow, an important stabilizing influence [18], has largely been overlooked in stability analyses. Recent analyses of the effect of flow on stability has shown that the kink mode in z-pinches can be stabilized with a sufficiently sheared axial flow [19]. Sheared flow may also stabilize the sausage mode. Flow shear may provide stabilization by behaving like the magnetic shear arising from the axial field in a z- pinch, i.e. the conventional (Kruskal-Shafranov) method of stabilization. These results have important implications not only for z-pinches, but for related configurations as well, including tokamaks and FRCs. Sheared flow may cause both improved global stability and reduced transport.

2) Minimum energy state The possibility that the FRC may be a robust minimum energy state is under investigation [20]. The new theory employs a two-fluid model and extends the familiar one-fluid theory which postulates invariant magnetic helicity. The new theory postulates the invariance of both the ion and electron helicities: these generalizations of the magnetic helicity include the effect of mechanical momenta. This theory was motivated by experimental observations that suggest relaxation phenomena in FRCs: (1) transient global modes producing a restructuring rather than a disruption [21]; (2) quiescent FRCs exhibit profile consistency [22]; and (3) the relaxation of a spheromak (formed by merging) to an FRC, in which the toroidal field (and magnetic helicity) decays [7]. Minimum energy equilibria in simplified geometries display qualitative features of, depending on the parameters, laboratory FRCs and reversed- shear tokamaks. The essential ingredient in these minimum energy states is sheared flow. The finite-beta theory of minimum energy states may form the basis for a new stability paradigm.

3) Ion Ring supported FRC An Ion Ring system may be a "hybrid" system (Ring plus background plasma) [22] or a ring-dominated system (very little background) [23]. FRC stability questions might be resolved by the stiffening effect of an energetic ion ring carrying a substantial fraction of the current. Studies of plasmas with a significant fraction of large orbit ions has shown the stabilizing potential of such rings [24]. Moreover, there is evidence that energetic ring-like ions slow down and diffuse classically, leading to improved confinement properties. The recently completed FIREX facility (see Sec. III) extends previous ion-ring experiments [25]. It is designed to study Ion Rings as a means of forming and stabilizing an FRC. Ion-ring injection might also be used to sustain the current. It also offers a unique opportunity to study the peculiar phenomena associated with large orbit particles in magnetically confined plasmas.

4) New kinetic stabilization effect Kinetic effects associated with finite ion orbits are well known stabilizing influences, whether the orbits are relatively small (FLR) or large (ion rings). A new, recently discovered class of kinetic effects is driven by the electron grad-B drift, and is unrelated to orbits. In the high curvature regions near the ends of the FRC the electron grad-B drift frequency is much higher than the frequency of MHD-perturbations. Therefore, the electron response is strongly non-MHD. This produces the so called "charge uncovering" effect, which is a potentially important source of improved stability [26].

5) Rotating magnetic field (RMF) current drive RMF may offer a practical current drive method. Here a small transverse and rotating field component is generated by oscillating currents driven in four longitudinal conductors located near the wall. Under certain frequency and collisionality conditions, the transverse field penetrates the plasma and drives an electron current in a manner similar to an induction motor. In several small experiments, called rotomaks, RMF have transformed a magnetic-mirror confined plasma into one stably confined in an FRC. The RMF not only caused the reversal of the magnetic field on the axis, but sustained the FRC for times as long at the RMF drive was continued. The resulting FRCs have been relatively cold and roughly spherical. Recently, RMF has emerged as a promising current drive method that might be applied to a pre-existing hot FRC. In principle, RMF is an efficient current drive method since it drives the bulk electrons, and not just an energetic tail of the distribution. Proposed experiments on the LSX facility would apply RMF to demonstrate current drive on a pre-existing FRC [27]. Theoretical studies of RMF current drive are ongoing [28].

6) Traveling wave direct energy conversion An innovative method for direct conversion of 15-MeV fusion protons has been proposed [29] and is being investigated in theory and experiment [30]. A traveling wave is set up by a series of open grids; it is synchronized to extract energy from a fast stream of protons. In principle, highly efficient conversion is possible when the stream first passes through a properly phased pre-buncher grid. This concept exploits the fact that most of the fusion energy in an advanced fuel system is in the form of charged particles.

D. IMMEDIATE ISSUES FOR FRC DEVELOPMENT--THE NEXT FIVE YEARS

The maturation of a confinement concept causes an evolution of the issues to a more focussed and sophisticated form than at the outset. In view of progress in FRC research, the leading issues for realistic resolution in the next five years are listed in the following. Not listed here are issues that, though ultimately important, do not need resolution in the next five years. e.g. heating to fusion temperatures.

1) Demonstration of a long-lived, high-quality FRC This is the single most important issue in the next five years. By "long lived" is meant a configuration sustained for 1-10 msec, and by "high-quality" is meant ntau > 10^11 to 10^12 with Ti > 1keV, Te > 0.5keV. Achieving these goals raises associated issues related to current drive and possibly start-up, which are mentioned later.

2) Theory of global stability While FRCs have proved remarkably stable in experiments, a satisfactory theoretical explanation has not been found. A convincing stability theory is essential to gain confidence for extrapolation to the fusion regime. Such a theory should account for macroscopic plasma flows as well as the background "bath" of microturbulence. Such a new theory may require modification of the standard ideal-MHD paradigm.

3) Kinetic physics FRCs have an inherently low magnetic field core region, leading to highly kinetic and nonlocal behavior. Finite-orbit kinetic particles have a well known stabilizing influence. These effects are enhanced by the presence of a suprathermal component or an ion ring. Studies of plasmas with a significant fraction of large orbit ions has led to recognition of the unique advantages of Ion Rings. However much further work lies ahead to explore the ramifications of this concept. Kinetic physics studies also apply to fusion product behavior in a burning plasma.

4) Fusion-relevant start-up method It is not clear whether the theta-pinch method used in most FRC experiments is suitable for fusion application because of the typically high voltages (e.g. 50 kV), and limitations on the achievable trapped magnetic flux (about 10 mWb). A better physical understanding of theta- pinch formation limitations is needed. Alternate "technologically friendly" start-up techniques should also be tested.

5) Current drive demonstration Except for low-temperature "rotomak" plasmas, current drive has never been attempted in an FRC. A current drive technique needs to be developed and applied to a hot, pre-existing FRC, sustaining the current in more or less steady state for longer that 1 msec (issue #1). This achievement has obvious technological as well as plasma physics aspects.

6) Transport mechanism Although certain aspects of the transport physics have been established, important unresolved questions remain, including: a) the plasma diffusion mechanism, particularly in the pivotal edge plasma (region between the high-beta core and separatrix); b) the effect of relaxation processes on plasma transport, particularly in the core; and c) the mechanism governing plasma flow along the scrape-off layer.

III. EXISTING FRC PROGRAM RESOURCES

A. LABORATORY RESOURCES

Several FRC-related facilities are in existence around the world. Each is supported by a group with two or three senior scientists. The following is a listing of these resources and their general capabilities.

BN (TRINITI research center, Troitsk, Russia). This multi-coil theta-pinch facility has been used to investigate improved formation control techniques, internal plasma parameters (magnetic field structure and local electron energy distribution) and other compact toroid systems (spheromak and tokamak-like). It is planned to modify BN to expand the regime of good-quality FRC formation. The BN group has emphasized formation using heating by nonadiabatic axial compression.

TL (TRINITI Research Ctr, Troitsk, Russia). This conical-coil theta-pinch employs independent active end-control coils for dynamic formation. It has recently been used to study start-up with varied time scales. It is presently being modified to add a confinement chamber.

TOR (TRINITI research center, Troitsk, Russia). This multi-coil theta-pinch facility has been used to study strong heating (intrinsic to the start-up process) up to "neutron"-producing ion temperatures, and formation procedures with magnetic insulation at the chamber wall.

NUCTE-3 (Nihon Un., Japan). This theta-pinch facility has been used to detect global modes with a Mirnov array, control the separatrix shape with auxiliary coils, and examine the effect of multipole fields on stability and confinement. It is presently being modified to include a translation section. The Nihon group has emphasized variations of the formation technique, and innovative controls.

FIX (Osaka Un., Japan). This formation-translation-trapping facility (theta-pinch source) has recently been used to study confinement properties, measure internal azimuthal fields, measure magnetic field fluctuations associated with microturbulence, examine the thermalization of translated FRCs, measure the particle and energy flow in the scrape- off layer, examine the heating potential of dissipative magneto-acoustic waves generated by magnetic pulses applied by auxiliary coils, and steer the moving FRC using a curved guide field. It is planned to install megawatt-class neutral beam injectors on FIX, operation of which is scheduled for 1996. The Osaka group has emphasized the application of innovative diagnostics and control techniques to FRCs.

TS-3 (Tokyo Un., Japan). The TS-3 facility uses paired z-theta- pinch discharges for start-up, generating FRCs, spheromaks, and ultra low- aspect ratio tokamaks. FRCs were formed by counter-helicity merging of two spheromaks. An OH current transformer is available to amplify currents in FRCs and other plasmas. TS-3 has also been used to study the physics of magnetic reconnection. Recent FRC-related themes at Tokyo include: (1) transition from merging low-beta spheromaks to a high-beta FRC and associated energy conversion processes; (2) heating and current amplification by merging and by OH transformer; and (3) relaxation bifurcation and its relation to FRC robustness. TS-3 will be upgraded to a larger device, TS-4, in 1996-97.

LSX/mod (Un. Washington, USA). This formation-translation facility (theta-pinch source) is the largest FRC device in the world. At present and for the last three years it has been used to accelerate FRCs to test a tokamak refueling concept. Such studies could be continued in the future. It is proposed to convert LSX/mod in 1996 for research tasks immediately germane to FRCs. These include 1) addition of a confinement chamber at the end of the translation section, 2) additional equilibrium coils in the confinement chamber for control of the separatrix shape, and 3) rotating magnetic fields for current drive and possibly start-up. The LSX group at Washington has emphasized diagnostics (e.g. internal structure, instability detection), formation controls, and translation.

MRX (Princeton, USA). This flux-core based facility has been built to perform three-dimensional magnetic reconnection experiments. It can generate spheromaks, low-aspect ratio tokamaks, and FRCs. It is planned to form a single FRC by merging two smaller spheromaks with opposite helicities. The ion gyro-radii are expected to be smaller than the separatrix radius by a factor of 10. Detailed tests of the global stability of FRCs can be carried out in a reactor-relevant MHD-like regime. A major question is whether such FRCs are susceptible to a tilt mode or not. If so, one can investigate the conditions under which it can be made stable.

FIREX (Cornell Un., USA). This recently completed facility (Field-reversed Ion Ring EXperiment) injects an ion beam from a diode through a magnetic cusp to form an ion-ring. It is a first step toward the realization of a field-reversed ion ring or FRC/Ion Ring hybrid in which a significant fraction of the azimuthal current is carried by large orbit ions. The ion ring can provide stability to an FRC. It also has the potential to provide a start-up technique, current drive, and equilibrium control for FRCs.

B. THEORY AND COMPUTATION

Small ongoing theory efforts (generally individual) are scattered around the world. Within the last three years active work has proceeded at (or publications have appeared from) institutions in the US (Cornell Un., Krall Associates, and Un. Washington), Japan (Niigata Un., Kyoto Un., and Nagoya Un.), Russia (TRINITI, Moscow State Technical Un.), and Brazil (Campinas Un.). Beside these, theorists elsewhere possess FRC-relevant expertises developed in previous years, though they are not presently active in FRC research. In addition to strictly plasma theory, ARTEMIS, a systems study of a D-3He FRC reactor, was carried out in Japan in the early 1990s. Most members of this multi-institutional team are still active in FRC research.

A major 3D nonlinear-MHD + Hall effect code was developed in the 1980s [31]. While this code has not been operated for several years, it remains a valuable resource for FRC studies. An attractive option for FRC kinetic modeling on ion orbit and transport timescales is the hybrid PIC code based on a fluid-electron, particle ion representation [11]. Recently, a sophisticated new object-oriented code designed to run on massively parallel computer architectures was developed and is in use to study FRC/Ion Ring systems [32]. In addition to these, there exist a wealth of tokamak codes that could, in principal, be adapted for use in FRC studies.

C. INTERNATIONAL CONNECTIONS

International collaborations on FRC research have taken place between the US, Japan, Russia, Austria, Argentina, and Brazil. The most active interaction has been between the US and Japan. Indeed the well- established US-Japan interaction on FRCs might be listed among the accomplishments of FRC research. It has fostered perhaps a dozen US- Japan workshops in the last dozen years and a number of extended laboratory visits, and has led to the publication of perhaps 20 archival papers with a mixed US-Japan authorship. These collaborations survived even the five-year hiatus in alternate concepts research in the US.

IV. FRC RESEARCH DIRECTIONS OVER THE NEXT FIVE YEARS

Each issue raised in Sec. IID implies particular directions in both theory and experiment and, by extension, in technology development and systems studies. What follows is a definition of what needs to be done in these areas to address the immediate, five-year issues.

A. EXPERIMENT DIRECTIONS

1) Basic FRC structure and phenomena Much has been learned about the gross stability and confinement of FRCs as a result of increasingly sophisticated diagnostics. Even so, to a large extent the interior structure itself remains a "black hole" about which little is known beyond indirect inferences. In terms of the spatial structure only multichord interferometry, emission tomography, and internal magnetic probing of translating FRCs, have been applied, and these only in a limited way. Little or nothing is known about the internal magnetic structure, fluctuations, electrostatic potentials, and flows. A knowledge of these basic properties is essential to understand FRC physics with reasonable confidence. The core plasma, edge plasma, scrape-off layer, exhaust jet, and halo plasma properties all play key roles and need investigation. A reproducible, quiescent, long-lived FRC is the ideal environment for applying these diagnostics to the core plasma, although facilities that don't satisfy all these conditions are useful for applying specific diagnostics. Diagnostics heretofore applied on an introductory basis need more common use, including multichord interferometry and emission tomography (both radial and longitudinal). Internal magnetic structure diagnostics are needed, including both existing intrusive techniques (e.g. short-time probing of a translating FRC) and the development of non-intrusive techniques (e.g. motional Stark effect). Injection of pellets, beams, or tracer impurities may be attractive alternatives to expensive multi-point systems. Another is spectrally resolved Doppler shifts to detect flows. The most promising diagnostics for the edge plasma, scrape-off layer and jet are probably particle collecting probes. These are best applied to translated plasmas since they are incompatible with existing start-up methods.

2) Equilibrium modification and control a) Plasma shaping. Separatrix control by programming the equilibrium field coil system has been a fruitful avenue of research on tokamaks, producing both greater understanding of the physics as well as performance improvements. Typical FRCs have been confined in straight flux conservers, i.e. strictly passive equilibrium control. Equilibrium field controls should be applied to FRCs by adding auxiliary coils to supplement the basic flux conserver. By this means separatrix shape control could be demonstrated. Then the effect of modified separatrix shape on stability and transport can be investigated.

b) Structure and bulk parameter modification. No artificial controls have been applied to modify the internal structure of FRCs. Moreover, the electron and ion temperatures have been strictly the product of heating intrinsic to the start-up process and the natural thermal loss rates. Modifying these properties is essential to study the distinct effects of Ti, Te, current, and profile on confinement. One fruitful method for modifying these properties is injection and merger of ion rings with the FRC; another is RF heating; and a third is neutral beam (nb) injection. As repeatedly demonstrated on tokamaks powerful RF and nb injection can modify the internal structure, flows, and distribution function. Moreover, both ion ring and nb injection shed light on large- orbit particle effects. These methods also have potential for heating and current drive.

c) Large-s physics. FRC stability has often been ascribed to finite ion Larmor radius (FLR) effects, which weaken with increased size. >From the ideal-MHD theory of global modes FLR stability is achieved if s/E is less than some value (s is the minor radius divided by the average internal ion gyroradius and E is the separatrix elongation). Tilting-stable theta-pinch FRCs approached the predicted instability threshold. Limited merging-formed FRCs with s/E above the threshold were tilting unstable in the absence of a center column. Experiments are needed over a range of s/E that spans the predicted threshold. This can be done either by raising s or reducing E. The former requires either a larger theta-pinch, or one including significant formation enhancements. A more straightforward and cost-effective approach is to form a lower-E FRC, as might be done in a merging-formation facilities.

3) Ion Ring systems Although previous facilities have produced ion rings, they have never had the current producing capability to reverse the magnetic field. Therefore the first priority for Ion Rings is to demonstrate field reversal. Once this has been achieved and the conditions for field reversal characterized, studies can be initiated on the ring properties (its longitudinal dynamics, lifetime, and stability), ring manipulation (bulk translation, magnetic compression) and its effect on the background plasma (electron temperature, transport). Following that the next stage would be experiments merging ion rings with a pre-existing FRC. This would test the potential of ring merging as a means of (a) sustaining the internal flux (equivalent to current drive) and (b) heating.

4) Dense FRC's FRCs have interesting potential for "filling" centimeter-size imploding liners. This scheme can eventually lead to development of an extremely compact pulsed fusion reactor with attractive economics. The pre-implosion FRC should have a radius and the length of roughly 1 cm and 4-5 cm, respectively, plasma density 10^18 cm^-3, and temperature 50-100 eV. Studies of the formation and evolution of such FRC's would also considerably broaden the parametric domain of the experimental data base, and offer stronger validation of scaling laws.

5) Fusion-relevant start-up method The traditional FRC formation method uses theta-pinch technology. Alternative technologies might be more suitable for a fusion system. One such exploits the possibility that an ion ring (see Sec. IV-A-3) might be used as an armature on which to build up the plasma current for FRC start-up. Here, previously demonstrated start-up techniques, theta- pinches and two other methods, are discussed.

a) Theta-pinch formation. Although ostensibly a high-voltage technology, theta-pinches have been used to form hot, low-Z FRCs with lower-voltage ignitrona and somewhat slower start-up recipes. This technology may yet be suitable for a reactor. Further modifications that may enhance the basic theta-pinch approach include conical coils, and end- coil control methods, which offer an independent temperature control by exploiting the conversion of axial kinetic energy to thermal energy. The same might also be accomplished by merging two colliding FRCs.

b) Merging formation of FRCs. Oblate FRCs have been formed using counter-helicity merging of spheromaks. This low-voltage, slow-timescale technique may be attractive for start-up in a fusion system, but has only received limited investigation. Further formation studies are needed to characterize the limitations and determine the size and temperature scalability. At present, merging formation lacks a basic theoretical basis for predicting the temperatures and magnetic fluxes that can be achieved. A simple, perhaps "thermodynamic" theory is needed.

c) Rotating magnetic field (RMF) start-up. Low-voltage start-up has been demonstrated in several small experiments called "rotomaks". These FRCs have typically been quasi-spherical (confined in a Helmholtz coil) and low temperature (~10eV). This is a promising start-up method but it is only useful if plasmas temperatures (Ti and Te) somewhat above 100 eV can be produced. It may only be a matter of applying sufficient power (through the RMF) to pass the radiation barrier. The potential of higher-power RMF for burning through such barriers needs investigation both theoretically and, if that appears promising, experimentally. Alternatively, electron cyclotron heating (ECH) offers an established means to create an initial temperatures above radiation barriers.

6) Current drive Excepting the low-temperature rotomak devices, all previous FRC experiments have been decaying, unsustained plasmas. Since a method of sustaining the configuration is needed in a fusion plasma, the time has come for a current drive demonstration on an FRC. A suitable proof-of- principle demonstration would be to sustain the current for 1 ms.

a) Rotating magnetic field (RMF) current drive. RMF has been demonstrated as both a start-up and sustainment method in small rotomak plasmas. In order to be accepted as a current drive method it should be demonstrated on a pre-existing hot (>100eV) FRC plasma or a hot ECH- generated plasma in a static magnetic mirror. Principal issues in such an experiment include verifying the optimum RMF rotation frequencies and field amplitudes, observing initial RMF penetration and its timescale, and determining the power level needed for sustainment.

b) Neutral beam (nb) current drive. Intense nb injection as a means of modifying the internal structure and bulk parameters of an FRC was called for in Sec. IV-A-2-b. These experiments would also allow a preliminary assessment of the current drive potential of nb injection.

7) Direct conversion system Efficient direct conversion is essential for an advanced fuel reactor to be economically competitive. Conventional electrostatic conversion may be impractical as a stand-alone system because of high- voltage breakdown problems arising if such a system were expected to handle unthermalized fusion products. An innovative approach to this problem is the traveling wave direct energy conversion (TWDC) concept. A proof-of-principle experiment is needed to test this method at conditions that simulate fusion-like parameters. Important engineering issues related to the TWDC also should be addressed: minimizing power losses associated with the large recirculating high-frequency power in a TWDC; and the engineering feasibility of the high-transparency grid structure.

8) Heating Ultimately a heating method is needed to elevate the temperature from the post-start-up level (100s of eV to 1 keV) to fusion ignition. However, in terms of the next five years of FRC development, this issue has lower priority than the others described here. Nevertheless, some of the experiments called for here would also ancillary information on potential heating techniques. These include intense nb injection, ion-ring injection, resistive heating by RMF, ECH, and heating by the thermalization of dynamic energy produced by merging or translation.

B. THEORY DIRECTIONS

1) Equilibrium and stability theory. The theory of FRC or FRC/Ion Ring equilibrium and stability needs continued attention both in analytic and numerical studies. Analytic studies are particularly needed to extend the recent studies showing the important stabilizing influence of sheared flow. Also needed are studies of high-frequency modes and their effects in FRC/Ion Ring systems.

a) Equilibrium codes. Although a number of FRC equilibrium codes (Grad-Shafranov equation solvers) have been reported in past years, numerical solutions of FRC equilibria have proved troublesome. Needed is a more robust and flexible equilibrium code that also accepts flow. The flexibility is essential because more complex equilibrium field coils are anticipated in future experiments. A work-horse equilibrium code would form an effective basis for stability studies. Priority should be given to adapting existing codes developed for tokamaks rather than developing a completely new code.

b) Recommissioning MHD codes. A 3D-MHD code for simulating FRC global mode stability was last operated in the late 1980s. Since then considerable new information has become available about the current profiles, flows, and other features of FRC equilibria observed in actual experiments. In brief, the equilibria to which these codes were applied are not relevant to laboratory FRCs in several ways. Therefore the existing 3D-MHD code needs to be recommissioned and operated more-or-less continually as a check on analytical stability theories. In particular, the emergence of new stability concepts such as sheared flows and minimum energy states need testing with standard stability codes. The purpose for maintaining and operating such codes is to achieve sufficient agreement with experiment to promote the claim of predictive capability.

c) Advanced kinetic codes. Sophisticated 3D hybrid codes are needed for the study of equilibrium and low-frequency stability. One such, developed specifically to model FRC/Ion Ring systems is presently in use. This code needs continued development, and it or codes of like kind need to be applied to FRCs in a more general context. A global kinetic stability code provides another method for stability analysis that does not break down near the field null or the separatrix. The method is to expand the perturbed distribution function in eigenfunctions of the equilibrium Liouville operator.

3) Current drive theory The theory of RMF physics is relatively undeveloped. Needed is a 2D (r-theta) time-dependent two-fluid theory that accounts for particle and momentum balances as well as the energy balance. Important questions concern the transient penetration timescale of RMF, and the anomalous (or classical) nature of the resistivity (parallel and theta directions).

4) Transport a) Dominant transport mechanism. As in any magnetically confined plasma, transport in an FRC is complicated by the presence of multiple regions each of which may be governed by somewhat different phenomena. In an FRC, confinement may be dominated by the transport rate in the edge plasma (between the low-field core and separatrix). In none of the regions is the mechanism known with certainty (although low-frequency drift turbulence is a promising candidate in the edge plasma). The dominant transport mechanisms need to be established with reasonable confidence. This includes consideration of collisionality regimes and the extrapolation toward fusion conditions. Some aspects of FRC transport are being explored in studies with quite a different purpose, e.g. parts of the geomagnetosphere resemble the low magnetic field core of an FRC.

b) Nonlocal theory. There is an urgent need for a nonlocal theory of transport in view of the sharp gradients (ion gyroradius scale) that arise naturally in FRCs. The basic elements for such a theory have been formulated but not yet applied. With such work, analysis of the interplay between MHD and anomalous resistivity could be done, as well as a profile- consistent analysis of turbulent transport itself.

c) Scrape-off layer plasma and energy flow. Electron thermal loss in present experiments appears to be limited by ambipolar effects in the scrape-off layer. Electrostatic fields may also play a role in governing the outflow (anomalously slow) of plasma. This effect may be accentuated in the presence of suprathermal ions such as produced by an ion ring or unthermalized fusion products. Also of interest is the inference of a double-layer like plasma in the exhaust jet region of the scrape-off layer that isolates hot from cold plasmas. A theory accounting for finite ion gyroradius and self-consistent electric fields is needed to explain observed anomalies compared to fluid theories.

d) Nonlinear Theory. There is an urgent need to study single particle dynamics in FRCs, including the spectra of stochastic processes. This will allow formulation of boundary conditions for kinetic equations, and then the calculation of distribution functions of different species and a nonlocal dielectric tensor. With this it will become possible to study wave spectra and the spatial structure of eigenmodes for different wave branches. For unstable modes this will include nonlinear analysis of wave-particle-wave interactions, determination of the wave saturation level (if it exists), and the energy and particle fluxes.

5) Simulation of ongoing experiments A nonlinear 2D-MHD + Hall effect code is presently in active use to simulate ongoing experiments on LSX. This "workhorse" tool would be valuable for experimental interpretation at other facilities as well. In addition, the possibility of adapting existing tokamak codes should be considered. The availability of parallel computation has enabled the implementation of fairly realistic (3D, toroidal geometry) simulations from "first principles" (gyrokinetic particle models) on the turbulent timescale. Full cross section 2D fluid simulation of transport in toroidal geometry is also being developed. Some of these tools might be applied to FRC simulations, thus exploiting the large investment in code development and modeling.

6) Burning plasma physics The next five years do not call for extension of FRC experimental plasmas into the fusion temperature regime. Therefore the investigation of phenomena arising in a burning plasma has lower priority. Even so, certain topics should be addressed in anticipation of later experiments on FRCs in a more fusion-like regime.

a) Fusion product effects. Several topics need study. (i) Prompt losses of energetic particles (fusion products and energetic components of the basic plasma): this is needed to determine the distribution of high energy particles entering the direct converter and the proper boundary conditions for the kinetic equations for fusion products. (ii) Solution of kinetic equations for the fusion products plus the power deposition in the core plasma itself: this is an essential element in the power balance of a burning FRC plasma. (iii) Instabilities associated with non- Maxwellian distribution functions: in their saturation phase these may cause turbulent behavior and enhance transport.

b) Power flow analysis of a burning FRC. This includes several topics: power and particle balances based on kinetic/power models; estimation of the highest possible levels of power amplification; and formulation of the requirements for an FRC reactor (types and level of external heating power, injection currents, value of plasma beta, magnetic configuration).

c) Cyclotron radiation transport. Although cyclotron radiation losses are expected to be relatively low in an FRC because of high-beta, this needs confirmation by more detailed theory. In particular the transport of cyclotron radiation should be treated in a self-consistent manner, including a realistic magnetic structure, self-absorption, heating, radiation polarization, and wall reflection.

C. TECHNOLOGY DEVELOPMENT DIRECTIONS

1) Rotating magnetic field (RMF) source development The most efficient and technologically friendly method of generating an RMF needs to be determined and developed. A research program to address this question should incorporate the following tasks: (1) design and construction of a suitable high power RF source and drive coils capable of a sustained pulse longer than 1 msec; (2) demonstration of the RMF technique in a plasma column of moderate size (0.5-m diameter and 1.5-m length); (3) investigation of alternate methods for generating the RMF which are more efficient and capable of delivering higher power.

2) Ion Ring technology Ion rings have been successfully produced by injection through a magnetic cusp: consideration of improvements of the basic technology merits continued attention. In addition, new technologies associated with Ion Ring concepts need work on design of pulsed magnet coils, and power supplies suitable for ring compression and translation. Further, repetitively-pulsed power supplies are needed for multi-ring formation. In this area repetition rate technologies developed for ion beam driven ICF and material processing might be exploited.

D. SYSTEMS STUDY DIRECTIONS

Although the inherent features of an FRC endow it with great potential for an attractive reactor, it is needed to show this rationally and quantitatively. For an alternative fusion concept to be considered for extensive development, it should satisfy the following criteria. (1) REACTOR TEST--assuming that the physics "works", it must offer marked advantages over a tokamak, i.e. a step change improvement in cost and complexity; (2) PHYSICS TEST--based on the existing theoretical and experimental data base, the physics must be considered plausible; and (3) DEVELOPMENT PATH TEST--the development path, from physics-oriented experiments to ignition to an ETR facility to a DEMO, should offer significant advantages over a tokamak. FRC systems studies can elucidate at least the first and third of these tests.

1) FRC systems code An integrated study of critical physics and engineering issues is needed. Ideally, such an analysis is performed with a systems code. Such codes have proved invaluable in identifying interfacial problems that might otherwise be overlooked until late in research and development projects. A systems analysis facilitates the formulation of a quantitative reactor assessment using, e.g., system sizes, masses, costs, mass power densities, costs-of-electricity and economy of scale. Accordingly, an FRC-capable systems code should be developed. Since systems code shells already exist, this requires only the addition of FRC-relevant modules for plasma physics, engineering, fuel cycle, and costing. Regarding the plasma module: given the limited FRC physics database, the results can be formulated in terms of uncertainties in the input database. The engineering modules should include moderately detailed models for the several engineering systems (see Sec. IV-D-2 following). The use of an uncertainty analysis will highlight minimum performance requirements for major parameters such as confinement and stability in terms of their impact on the reactor product. A systems analysis can also help in formulating the FRC development path by quantifying the size/cost parametrics of the complex of machines leading to a DEMO. Although the FRC is an ideal candidate for advanced fuels burning, consideration should also be given to the D-T fuel cycle.

2) Engineering design Several crucial, long lead-time engineering issues exist, including radiation damage, activation, shielding, safety, environment, tritium-breeding blanket design, direct energy converter engineering, plasma-surface interactions, current drive, and maintenance. Some of these have aspects unique to FRCs that would not receive consideration in the mainline fusion development program.

3) FRC/Ion Ring system Detailed study has never been devoted to the potential of a FRC/Ion Ring Systems as a compact reactor. Although such a system has most of the features of a non-ring FRC system, its unique aspects need consideration with respect to their reactor implications.

4) International collaboration: advanced fuels In view of the recent Japanese ARTEMIS study of a commercial D-3He FRC reactor and the expertise built up there, the Japanese FRC design team should be close collaborators in any future reactor study. Although FRCs are expected to perform well in D-T power plants, the Japanese chose the D-3He fuel cycle for the ARTEMIS design for several reasons: because of the excellent match between D-3He fuel and FRCs; because of a desire for the most environmentally favorable concept; and because D-3He almost completely circumvents the neutron wall loading problem. The particular advantages of a D-3He FRC system are (1) the linear geometry facilitates direct conversion of the charged-particle power; (2) the increased power density arising from high beta somewhat compensates for lower fusion cross-section, and (3) despite the high charged-particle power, the surface heat flux is moderate because the axially flowing plasma carries most of the energy losses out the ends of the coil system.

V. ACTION ITEMS

This document, prepared by the world-wide FRC community, defends the value of the FRC to plasma science in general and its particular potential as a fusion reactor concept. It also summarizes the present state of the concept with respect to important issues, and gives fruitful directions for research in the next five years. As a result of these factors, the following five action items are recommended.

VI. REFERENCES

1. J.M. Finn and R.N. Sudan, Nucl. Fusion 22,1443, (1982).

2. R.Kh. Kurtmullaev et al., in Results of Science and Technology, Plasma Physics Ser., Vol. 7. V.D. Shafranov, ed., VINITI, Moscow, pp.80-135.

3. M. Tuszewski, Nucl. Fusion 28, 2033 (1988).

4. L.C. Steinhauer, "Recent Advances in FRC Physics," in Proc. IEEE Symposium on Fusion Engineering, Champaign, Illinois, 1-6 October 1995.

5. J.T. Slough et al., Phys. Fluids B 2, 797 (1990).

6. B.B. Bogdanov, et al., in Plasma Physics and Controlled Nuclear Fusion Research, (IAEA, Vienna, 1991), Vol.2, p.739.

7. Y. Ono et al., in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1992), Vol. 2, p619; Y. Ono, Trans. Fusion Technol. 27, 369 (1995).

8. T. Minato et al. in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1983), Vol.II, p303; T. Ishimura, Phys. Fluids 27, 2139 (1984).

9. M. Tuszewski, et al., Phys. Fluids B 3, 2856 (1991); J.T. Slough and A.L. Hoffman, Phys. Fluids B 5, 4366 (1993).

10. J. Cobb et al., Phys. Fluids B 5, 3227 (1993); L.C. Steinhauer et al., Phys. Plasmas 1, 1523 (1994); R. Kanno et al., J. Phys. Soc. Jpn. 64, 463 (1995).

11. D.C. Barnes et al., Phys. Fluids 29, 2616 (1986).

12. A. Ishida et al., Phys. Fluids B 4, 1280 (1992).

13. H. Himura et al., Phys. Plasmas 2, 191 (1995).

14. A.G. Es'kov et al., in Proc. 10th European Conference on Controlled Fusion and Plasma Physics, Moscow, 1981, paper L-5.

15. N.A. Krall, Phys. FluidsB 1, 2213 (1989).

16. J.T. Slough et al., Phys. Plasmas 2, 2286 (1995).

17. L.C. Steinhauer, Phys. Fluids B 4, 4012 (1992).

18. R.N. Sudan,Phys. Rev. Lett. 42, 1277 (1979).

19. U. Shumlak and C.W. Hartman, Phys. Rev. Lett. 75, 3285 (1995).

20. L.C. Steinhauer and A. Ishida, "Finite-beta minimum energy states of a two-fluid flowing plasma," submitted to Phys. Plasmas, January 1996.

21. L.C. Steinhauer and A. Ishida, Phys. Fluids B 4, 645 (1992).

22. N. Rostoker, et al., Phys. Rev. Lett. 70, 1818 (1993).

23. R.N. Sudan, in Physics of High Energy Particles in Toroidal Systems (AIP Conf. Proc. 311, 1993), p.194.

24. C. Litwin and R.N. Sudan, Phys. Fluids 31, 423 (1988); and refs. therein.

25. J.B. Greenly et al., Phys. Fluids 29, 908 (1986); and refs. therein.

26. D.Ryutov. presented at the 1995 International Sherwood Fusion Theory Conference, April 3-5, 1995, Paper 3C26.

27. A.L. Hoffman, "A steady state FRC development program," presented at the Conference on Advanced Approaches to Economic Fusion Power, Monterey, 12-14 September 1995, unpublished.

28. M. Ohnishi and A. Ishida, Nucl. Fusion 36, January 1996 (in press).

29. H. Momota, Los Alamos Nation Laboratory report LA-11808-C (1989), p8; H. Momota, et al., in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1993), Vol.3, p319.

30. Y. Yasaka, "Experimental plan on travelling wave direct energy convertor", presented at the US-Japan Workshop on the Physics of D-3He Fusion, Nagoya, December 5-7, 1994.

31. R.D. Milroy et al., Phys. Fluids B 1, 1225 (1989).

32. Yu.A. Omelchenko and R.N. Sudan, Phys. Plasmas 2, 2773 (1995).

VII. LIST OF SIGNATORIES

We the undersigned are in significant agreement with the assessment of the status, key issues, and future directions in FRC research as expressed in this White Paper.

	Loren C. Steinhauer  (Un. Washington, USA), Editor
	Daniel C. Barnes (Los Alamos National Lab., USA)
	Michl Binderbauer (Un. California, Irvine, USA)
	Robert D. Brooks  (Un. Washington, USA)
	Chan Choi  (Purdue Un., USA)
	Roberto A. Clemente  (Campinas Un., Brazil)
	John W. Cobb  (Oak Ridge National Lab., USA)
	Edward A. Crawford,  (Un. Washington, consultant)
	Alexei Es'kov  (Triniti, Troitsk, Russia)
	Preston Geren  (The Boeing Co., USA)
	Seiichi Goto  (Osaka Un., Japan)
	John Greenly  (Cornell Un., USA)
	Alan L. Hoffman  (Un. Washington, USA)
	Akio Ishida  (Niigata Un., Japan)
	Winfried Kernbichler  (Technical Un. Graz, Austria)
	Vladimir Khvesyuk  (Moscow State Technical Un., Russia)
	Nicholas A. Krall  (Krall Assoc., USA)
	Andrei Kreshchuk  (Triniti, Troitsk, Russia)
	Alexander Kukushkin  (Kurchatov Inst., Russia)
	Rustam Kurtmullaev  (Triniti, Troitsk, Russia)
	Ricardo Maqueda  (Los Alamos National Lab., USA)
	George H. Miley  (Un. Illinois, USA)
	Hiromu Momota  (National Inst. Fusion Science, Japan)
	Kenneth G. Moses  (Fusion Physics and Technology, USA)
	Yasuyuki Nogi  (Nihon Un., Japan)
	Masami Ohnishi  (Inst. of Atomic Energy, Kyoto Un., Japan)
	Shigefumi Okada  (Osaka Un., Japan)
	Yasushi Ono  (Tokyo Un., Japan)
	L. John Perkins (Lawrence Livermore National Lab., USA)
	Norman Rostoker  (Un. California, Irvine, USA)
	Dmitri Ryutov  (Lawrence Livermore National Lab., USA)
	John F. Santarius  (Un. Wisconsin, USA)
	Tetsuya Sato  (National Inst. Fusion Science, Japan)
	John T. Slough  (Un. Washington, USA)
	Ravi Sudan (Cornell Un., USA)
	Toshi Tajima  (Inst. for Fusion Studies, Un. Texas, USA)
	Alfonso Tarditi  (Lawrence Livermore National Lab., USA)
	Yukihiro Tomita (National Inst. Fusion Science, Japan)
	Frank Wessel  (Un. California, Irvine, USA)
	Masaaki Yamada  (Princeton Plasma Physics Lab., USA)
This White Paper was drafted and revised using electronic mail during the period 20 December 1995 - 2 February 1996.