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Definition of total bootstrap current in tokamaks

Description: Alternative definitions of the total bootstrap current are compared. An analogous comparison is given for the ohmic and auxiliary currents. It is argued that different definitions than those usually employed lead to simpler analyses of tokamak operating scenarios.
Date: June 16, 1995
Creator: Ross, D.W.
Partner: UNT Libraries Government Documents Department

Numerical Calculation of Neoclassical Distribution Functions and Current Profiles in Low Collisionality, Axisymmetric Plasmas

Description: A new code, the Neoclassical Ion-Electron Solver (NIES), has been written to solve for stationary, axisymmetric distribution functions (f ) in the conventional banana regime for both ions and elec trons using a set of drift-kinetic equations (DKEs) with linearized Fokker-Planck-Landau collision operators. Solvability conditions on the DKEs determine the relevant non-adiabatic pieces of f (called h ). We work in a 4D phase space in which Ψ defines a flux surface, θ is the poloidal angle, v is the total velocity referenced to the mean flow velocity, and λ is the dimensionless magnetic moment parameter. We expand h in finite elements in both v and λ#21; . The Rosenbluth potentials, φ#8; and ψ, which define the integral part of the collision operator, are expanded in Legendre series in cos χ , where #31;χ is the pitch angle, Fourier series in cos #18;θ , and finite elements in v . At each ψ , we solve a block tridiagonal system for hi (independent of fe ), then solve another block tridiagonal system for he (dependent on fi ). We demonstrate that such a formulation can be accurately and efficiently solved. NIES is coupled to the MHD equilibrium code JSOLVER [J. DeLucia, et al., J. Comput. Phys. 37 , pp 183-204 (1980).] allowing us to work with realistic magnetic geometries. The bootstrap current is calculated as a simple moment of the distribution function. Results are benchmarked against the Sauter analytic formulas and can be used as a kinetic closure for an MHD code (e.g., M3D-C1 [S.C. Jardin, et al ., Computational Science & Discovery, 4 (2012).]).
Date: June 28, 2012
Creator: B.C. Lyons, S.C. Jardin, and J.J. Ramos
Partner: UNT Libraries Government Documents Department

Plasma Physics Regimes in Tokamaks with Li Walls

Description: Low recycling regimes with a plasma limited by a lithium wall surface suggest enhanced stability and energy confinement, both necessary for tokamak reactors. These regimes could make ignition feasible in compact tokamaks. Ignited Spherical Tokamaks (IST), self-sufficient in the bootstrap current, are introduced as a necessary step for development of the physics and technology of power reactors.
Date: August 21, 2003
Creator: Zakharo, L.E.; Gorelenkov, N.N.; White, R.B.; Krasheninnikov, S.I. & Pereverzev, G.V.
Partner: UNT Libraries Government Documents Department

Aspect Ratio Scaling of Ideal No-wall Stability Limits in High Bootstrap Fraction Tokamak Plasmas

Description: Recent experiments in the low aspect ratio National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 (2000) 557] have achieved normalized beta values twice the conventional tokamak limit at low internal inductance and with significant bootstrap current. These experimental results have motivated a computational re-examination of the plasma aspect ratio dependence of ideal no-wall magnetohydrodynamic stability limits. These calculations find that the profile-optimized no-wall stability limit in high bootstrap fraction regimes is well described by a nearly aspect ratio invariant normalized beta parameter utilizing the total magnetic field energy density inside the plasma. However, the scaling of normalized beta with internal inductance is found to be strongly aspect ratio dependent at sufficiently low aspect ratio. These calculations and detailed stability analyses of experimental equilibria indicate that the nonrotating plasma no-wall stability limit has been exceeded by as much as 30% in NSTX in a high bootstrap fraction regime.
Date: November 25, 2003
Creator: Menard, J. E.; Bell, M. G.; Bell, R. E.; Gates, D. A.; Kaye, S. M.; LeBlanc, B. P. et al.
Partner: UNT Libraries Government Documents Department


Description: OAK A271 OPTIMUM PLASMA STATES FOR NEXT STEP TOKAMAKS. The dependence of the ideal ballooning {beta} limit on aspect ratio, A, and elongation {kappa} is systematically explored for nearly 100% bootstrap current driven tokamak equilibria in a wide range of the shape parameters (A = 1.2-7.0, {kappa} = 1.5-6.0 with triangularity {delta} = 0.5). The critical {beta}{sub N} is shown to be optimal at {kappa} = 3.0-4.0 for all A studied and increases as A decreases with a dependence close to A{sup -0.5}. The results obtained can be used as a theoretical basis for the choice of optimum aspect ratio and elongation of next step burning plasma tokamaks or tokamak reactors.
Date: November 1, 2002
Partner: UNT Libraries Government Documents Department

Discharges with high bootstrap current fraction on Tore Supra

Description: Bootstrap current is regarded as a serious candidate for non-inductively driving a significant fraction of the total current. High bootstrap fraction discharges have already been achieved and analysed in several tokamaks, including JT-60, DIII-D and TFTR. Tore Supra (R=2. 36 m, a=0.80 m) is particularly suited for the study of non-inductive discharges and long pulse operation. It is equipped with several of non-inductive current drive/heating systems including Lower Hybrid Current Drive (LHCD), Fast Wave Electron Heating (FWEH), and in the future Electron Cyclotron Heating. Fully non-inductive discharges with enhanced confinement (LHEP mode) have already been obtained in Tore Supra with LHCD. High {Beta}p ({le}1.6) regimes current nave also been achieved in the presence of FWEH. In particular, a discharge with 70% of the total current generated by the bootstrap current was observed. In this context, non-inductive current density profile determination is essential for understanding current drive experiments and ultimately for implementing current profile control. This paper briefly describes two methods developed on Tore Supra to determine the non-inductive current density profiles. The agreement between the two methods has been tested by applying them to ohmic discharges. These methods are then applied to the high bootstrap fraction discharges heated by FWEH. The non-inductive current density profile of these discharges are carried out. and the results are finally compared to several models of bootstrap current including Hirsman`s with low collisionality, matrix formulation and both Kessel and Houlberg matrix formulation.
Date: December 31, 1995
Creator: Joffrin, E.; Saoutic, B.; Basiuk, V.; Forest, C. & Houlberg, W.A.
Partner: UNT Libraries Government Documents Department

Bootstrap current close to magnetic axis in tokamaks

Description: It is shown that the bootstrap current density close to the magnetic axis in tokamaks does not vanish in simple electron-ion plasmas because the fraction of the trapped particles is finite. The magnitude of the current density could be comparable to that in the outer core region. This may reduce or even eliminate the need of the seed current.
Date: December 1, 1996
Creator: Shaing, K.C. & Hazeltine, R.D.
Partner: UNT Libraries Government Documents Department

Stable bootstrap-current driven equilibria for low aspect ratio tokamaks

Description: Low aspect ratio tokamaks can potentially provide a high ratio of plasma pressure to magnetic pressure {beta} and high plasma current I at a modest size, ultimately leading to a high power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current. A high value of the Troyon factor {beta}{sub N} and strong shaping are required to allow simultaneous operation at high {beta} and high bootstrap current fraction. Ideal magnetohydrodynamic stability of a range of equilibria at aspect ratio 1.4 is systematically explored by varying the pressure profile and shape. The pressure and current profiles are constrained in such a way as to assure complete bootstrap current alignment. Both {beta}{sub N} and {beta} are defined in terms of the vacuum toroidal field. Equilibria with {beta}{sub N} {ge} 8 and {beta} - 35% to 55% exist which are stable to n = {infinity} ballooning modes, and stable to n = 0, 1,2,3 kink modes with a conducting wall. The dependence of {beta} and {beta}{sub N} with respect to aspect ratio is also considered.
Date: August 1, 1996
Creator: Miller, R.L.; Lin-Liu, Y.R.; Turnbull, A.D.; Chan, V.S.; Pearlstein, L.D.; Sauter, O. et al.
Partner: UNT Libraries Government Documents Department

Investigation of the Spherical Stellarator Concept - Final Report

Description: This document is a final report of the U.S. DOE grant entitled ''Investigation of the Spherical Stellarator Concept'' which supported theoretical and numerical investigation of a novel fusion concept, the ultra-low-aspect-ratio stellarator system called Spherical Stellarator (SS). The research was concentrated on (a) search for principally different types of SS configurations, (b) optimization of SS configurations by varying the parameters of the coil systems, (c) finite beta and finite plasma current (including bootstrap current) equilibria in the SS, and (d) Monte Carlo particle transport simulations for the SS.
Date: October 15, 2000
Creator: Moroz, P.E.
Partner: UNT Libraries Government Documents Department

DIII-D Advanced Tokamak Research Overview

Description: This paper reviews recent progress in the development of long-pulse, high performance discharges on the DIII-D tokamak. It is highlighted by a discharge achieving simultaneously {beta}{sub N}H of 9, bootstrap current fraction of 0.5, noninductive current fraction of 0.75, and sustained for 16 energy confinement times. The physics challenge has changed in the long-pulse regime. Non-ideal MHD modes are limiting the stability, fast ion driven modes may play a role in fast ion transport which limits the stored energy and plasma edge behavior can affect the global performance. New control tools are being developed to address these issues.
Date: December 1, 1999
Creator: Chan, V.S.; Greenfield, C.M.; Lao, L.L.; Luce, T.C.; Petty, C.C. & Staebler, G.M.
Partner: UNT Libraries Government Documents Department

Report for collisional and chaotic transport of energetic particles in toroidal plasma

Description: The authors have made progress in two general areas of confinement plasma physics. (1) We studies a new loss mechanism of the toroidally trapped particles related to the up-down asymmetry of ripple in a tokamak. (2) We estimated the bootstrap current of the particles making transitions between the toroidally and locally states in non-axisymmetric tori, stellarators and tokamaks.
Date: April 1, 1995
Creator: Cary, J.R. & Shasharina, S.G.
Partner: UNT Libraries Government Documents Department

Time-Scales for Non-Inductive Current Buildup in Low-Aspect-Ratio Toroidal Geometry

Description: The fundamental differences between inductive and non-inductive current buildup are clarified and the associated time-scales and other implications are discussed. A simulation is presented whereby the plasma current in a low-aspect-ratio torus is increased primarily by the self-generated bootstrap current with only 10% coming from external current drive. The maximum obtainable plasma current by this process is shown to scale with the toroidal field strength. The basic physics setting the time-scales can be obtained from a 1D analysis. Comparisons are made between the timescales found here and those reported in the experimental literature.
Date: November 1, 1999
Creator: Jardin, S.C.
Partner: UNT Libraries Government Documents Department

Stability of bootstrap current driven magnetic islands in stellarators

Description: The stability of magnetic island producing perturbations due to fluctuations in the bootstrap current in stellarator configuration is examined. The stability criterion depends on the sign of the derivative of the rotational transform, the pressure gradient and the direction of the equilibrium bootstrap current which is determined by the structure of {parallel}B{parallel}. It is found that quasi-helically symmetric stellarator configurations with p{prime}/{tau}{prime} < 0 are unstable to the formation of bootstrap current driven magnetic islands. The stability of conventional stellarator configurations depends upon the field structure.
Date: March 1, 1994
Creator: Hegna, C.C. & Callen, J.D.
Partner: UNT Libraries Government Documents Department

Calculation of the Non-Inductive Current Profile in High-Performance NSTX Plasmas

Description: The constituents of the current profile have been computed for a wide range of high-performance plasmas in NSTX [M. Ono, et al., Nuclear Fusion 40, 557 (2000)]; these include cases designed to maximize the non-inductive fraction, pulse length, toroidal-β, or stored energy. In the absence of low-frequency MHD activity, good agreement is found between the reconstructed current profile and that predicted by summing the independently calculated inductive, pressure-driven, and neutral beam currents, without the need to invoke any anomalous beam ion diffusion. Exceptions occur, for instance, when there are toroidal Alfven eigenmode avalanches or coupled m/n=1/1+2/1 kink-tearing modes. In these cases, the addition of a spatially and temporally dependent fast ion diffusivity can reduce the core beam current drive, restoring agreement between the reconstructed profile and the summed constituents, as well as bringing better agreement between the simulated and measured neutron emission rate. An upper bound on the fast ion diffusivity of ~0.5-1 m2/sec is found in “MHD-free” discharges, based on the neutron emission, time rate of change of the neutron signal when a neutral beam is stepped, and reconstructed on-axis current density.
Date: February 9, 2011
Creator: Gerhardt, S P; Gates, D; Kaye, S; Menard, J; Bell, M G; Bell, R E et al.
Partner: UNT Libraries Government Documents Department

Progress towards Steady State on NSTX

Description: In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal {beta} and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on the National Spherical Torus Experiment (NSTX) has been raised from {kappa} {approx} 2.1 to {kappa} {approx} 2.6--approximately a 25% increase. This increase in elongation has lead to a doubling increase in the toroidal {beta} for long-pulse discharges. The increase in {beta} is associated with an increase in plasma current at nearly fixed poloidal {beta}, which enables higher {beta}{sub t} with nearly constant bootstrap fraction. As a result, for the first time in a spherical torus, a discharge with a plasma current of 1 MA has been sustained for 1 second. Data is presented from NSTX correlating the increase in performance with increased plasma shaping capability. In addition to improved shaping, H-modes induced during the current ramp phase of the plasma discharge have been used to reduce flux consumption during and to delay the onset of MHD instabilities. A modeled integrated scenario, which has 100% non-inductive current drive with very high toroidal {beta}, will also be presented. The NSTX poloidal field coils are currently being modified to produce the plasma shape which is required for this scenario, which requires high triangularity ({delta} {approx} 0.8) at elevated elongation ({kappa} {approx} 2.5). The other main requirement for steady state on NSTX is the ability to drive a fraction of the total plasma current with radio-frequency waves. The results of High Harmonic Fast Wave heating and current drive studies as well as electron Bernstein Wave emission studies will be presented.
Date: January 24, 2005
Creator: Gates, D.A.; Kessel, C.; Menard, J.; Taylor, G.; Wilson, J.R. & co-authors, plus 94
Partner: UNT Libraries Government Documents Department

Analysis and Modeling of DIII-D Hybrid Discharges and their Extrapolation to ITER

Description: Recent experiments on tokamaks around the world [1-5] have demonstrated discharges with moderately high performance in which the q-profile remains stationary, as measured by the motional Stark effect diagnostic, for periods up to several {tau}{sub R}. Hybrid discharges are characterize by q{sub min} {approx} 1, high {beta}{sub N}, and good confinement. These discharges have been termed hybrid because of their intermediate nature between that of an ordinary H-mode and advanced tokamak discharges. They form an attractive scenario for ITER as the normalized fusion performance ({beta}{sub N}H{sub 89P}/q{sub 95}{sup 2}) is at or above that for the ITER baseline Q{sub fus} = 10 scenario, even for q{sub 95} as high as 4.6. The startup phase is thought to be crucial to the ultimate evolution of the hybrid discharge. An open question is how hybrid discharges achieve and maintain their stationary state during the initial startup phase. To investigate this aspect of hybrid discharges, we have used the CORSICA code to model the early stages of a discharge. Results clearly indicate that neoclassical current evolution alone is insufficient to account for the time evolution of the q-profile and that an addition of non-inductive current source must be incorporated into the model to reproduce the experimental time history. We include non-inductive neutral beam and bootstrap current sources in the model, and investigate the difference between simulations with these sources and the experimentally inferred q-profile. Further, we have made preliminary estimates of the spatial structure of the current needed to bring the simulation and experiment into agreement. This additional non-inductive source has not been tied to any physical mechanism as yet. We present these results and discuss the implications for hybrid startup on ITER.
Date: June 16, 2006
Creator: Makowski, M A; Casper, T A; Jayakumar, R J; Pearlstein, L D; Petty, C C & Wade, M R
Partner: UNT Libraries Government Documents Department


Description: OAK-B135 The authors have initiated an experimental program to address some of the questions associated with operation of a tokamak with high bootstrap current fraction under high performance conditions, without assistance from a transformer. In these discharges they have maintained stationary (or slowly improving) conditions for &gt; 2.2 s at {beta}{sub N} {approx} {beta}{sub p} {approx} 2.8. Significant current overdrive, with dI/dt &gt; 50 kA/s and zero or negative voltage, is sustained for over 0.7 s. The overdrive condition is usually ended with the appearance of MHD activity, which alters the profiles and reduces the bootstrap current. Characteristically these plasmas have 65%-80% bootstrap current, 25%-30% NBCD, and 5%-10% ECCD. Fully noninductive operation is essential for steady-state tokamaks. For efficient operation, the bootstrap current fraction must be close to 100%, allowing for a small additional ({approx} 10%) external current drive capability to be used for control. In such plasmas the current and pressure profiles are rightly coupled because J(r) is entirely determined by p(r) (or more accurately by the kinetic profiles). The pressure gradient in turn is determined by transport coefficients which depend on the poloidal field profile.
Date: July 1, 2003
Partner: UNT Libraries Government Documents Department

High-Harmonic Fast Wave Driven H-mode Plasmas on NSTX

Description: The launch of High-Harmonic Fast Waves (HHFW) routinely provides auxiliary power to NSTX plasmas, where it is used to heat electrons and pursue drive current. H-mode transitions have been observed in deuterium discharges, where only HHFW and ohmic heating, and no neutral beam injection (NBI), were applied to the plasma. The usual H-mode signatures are observed. A drop of the Da light marks the start of a stored energy increase, which can double the energy content. These H-mode plasmas also have the expected kinetic profile signatures with steep edge density and electron temperature pedestal. Similar to its NBI driven counterpart--also observed on NSTX-- the HHFW H mode have density profiles that features ''ears'' in the peripheral region. These plasmas are likely candidates for long pulse operation because of the combination of bootstrap current, associated with H-mode kinetic profiles, and active current drive, which can be generated with HHFW power.
Date: May 2003
Creator: LeBlanc, B. P.; Bell, R. E.; Bernabei, S. I.; Indireshkumar, K.; Kaye, S. M.; Maingi, R. et al.
Partner: UNT Libraries Government Documents Department


Description: A271 COMPLETE SUPPRESSION OF THE M/N = 2/1 NEOCLASSICAL TEARING MODE USING RADIALLY LOCALIZED ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D AND THE REQUIREMENTS FOR ITER. DIII-D experiments demonstrate the first real-time feedback control of the relative location of a narrow beam of microwaves to completely suppress and eliminate a growing tearing mode at the q = 2 surface. long wavelength tearing modes such as the m/n = 2/1 instability are particularly deleterious to tokamak operation. Confinement is seriously degraded by the island, plasma rotation can cease (mode-lock) and disruption can occur. The neoclassical tearing mode (NTM) becomes unstable due to the presence of a helically-perturbed bootstrap current and can be stabilized by replacing the missing bootstrap current in the island O-point by precisely located co-electron cyclotron current drive (ECCD). The optimum position is found when the DIII-D plasma control system (PCS) is put into a search and suppress mode that makes small radial shifts (in about 1 cm steps) in the ECCD location based on minimizing the Mirnov amplitude. Requirements for ITER are addressed.
Date: July 1, 2003
Partner: UNT Libraries Government Documents Department

Plasma transport near the separatrix of a magnetic island

Description: The simplest non-trivial model of transport across a magnetic island chain in the presence of collisionless streaming along the magnetic field is solved by a Wiener-Hopf procedure. The solution found is valid provided the boundary layers about the island separatrix is narrow compared to the island width. The result demonstrates that when this assumption is satisfied the flattened profile region is reduced by the boundary layer width. The calculation is similar to the recent work by Fitzpatrick but is carried out in the collisionless, rather than the collisional, limit of parallel transport, and determines the plasma parameters on the separatrix self-consistently.
Date: December 1, 1996
Creator: Hazeltine, R.D.; Helander, P. & Catto, P.J.
Partner: UNT Libraries Government Documents Department

Results from D-T experiments on TFTR and implications for achieving an ignited plasma

Description: Progress in the performance of tokamak devices has enable not only the production of significant bursts of fusion energy from deuterium-tritium plasmas in the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) but, more importantly, the initial study of the physics of burning magnetically confined plasmas. As a result of the worldwide research on tokamaks, the scientific and technical issues for achieving an ignited plasma are better understood and the remaining questions more clearly defined. The principal research topics which have been studied on TFTR are transport, magnetohydrodynamic stability, and energetic particle confinement. The integration of separate solutions to problems in each of these research areas has also been of major interest. Although significant advances, such as the reduction of turbulent transport by means of internal transport barriers, identification of the theoretically predicted bootstrap current, and the study of the confinement of energetic fusion alpha-particles have been made, interesting and important scientific and technical issues remain. In this paper, the implications for the TFTR experiments for overcoming these remaining issues will be discussed.
Date: July 1, 1998
Creator: Hawryluk, R.J.; Blanchard, W. & Batha, S.
Partner: UNT Libraries Government Documents Department

Computational modeling of neoclassical and resistive MHD tearing modes in tokamaks

Description: Numerical studies of the nonlinear evolution of MHD-type tearing modes in three-dimensional toroidal geometry with neoclassical effects are presented. The inclusion of neoclassical physics introduces an additional free-energy source for the nonlinear formation of magnetic islands through the effects of a bootstrap current in Ohm`s law. The neoclassical tearing mode is demonstrated to be destabilized in plasmas which are otherwise {Delta}` stable, albeit once an island width threshold is exceeded. The plasma pressure dynamics and neoclassical tearing growth is shown to be sensitive to the choice of the ratio of the parallel to perpendicular diffusivity ({Chi}{parallel}/{Chi}{perpendicular}). The study is completed with a demonstration and theoretical comparison of the threshold for single helicity neoclassical MHD tearing modes, which is described based on parameter scans of the local pressure gradient, the ratio of perpendicular to parallel pressure diffusivities {Chi}{perpendicular}/{Chi}{parallel}, and the magnitude of an initial seed magnetic perturbation.
Date: June 24, 1996
Creator: Gianakon, T.A.; Hegna, C.C. & Callen, J.D.
Partner: UNT Libraries Government Documents Department

Effects of plasma shape and profiles on edge stability in DIII-D

Description: The results of recent experimental and theoretical studies concerning the effects of plasma shape and current and pressure profiles on edge instabilities in DIII-D are presented. Magnetic oscillations with toroidal mode number n {approx} 2--9 and a fast growth time {gamma}{sup {minus}1} = 20--150 {micro}s are often observed prior to the first giant type 1 ELM in discharges with moderate squareness. High n ideal ballooning second stability access encourages edge instabilities by facilitating the buildup of the edge pressure gradient and bootstrap current density which destabilize the intermediate to low n modes. Analysis suggests that discharges with large edge pressure gradient and bootstrap current density are more unstable to n > 1 modes. Calculations and experimental results show that ELM amplitude and frequency can be varied by controlling access to the second ballooning stability regime at the edge through variation of the squareness of the discharge shape. A new method is proposed to control edge instabilities by reducing access to the second ballooning stability regime at the edge using high order local perturbation of the plasma shape in the outboard bad curvature region.
Date: December 1, 1998
Creator: Lao, L.L.; Chan, V.S. & Chen, L.
Partner: UNT Libraries Government Documents Department

FWEH Induced High Bootstrap Current on Tore Supra

Description: Bootstrap current is regarded as a good candidate to sustain a large fraction of the plasma current, in the so-called `advanced` regimes of a tokamak reactor. It is thus important to study the stability of such discharges and to control them. By means of fast wave electron heating (FWEH, up to 9.5 MW), stationary high bootstrap discharges (during 5 seconds, Angstrom 40 %) were routinely obtained on Tore Supra. The bootstrap profile is computed with a matrix formulation (1,2) and is directly compared to the calculation of the non-inductive current. The simulation of the loop voltage either with the code CRONOS (1D current diffusion code) using the profile of bootstrap current, or with the knowledge of the resistivity, allows also a self consistent determination of the bootstrap current. First results show that the energy enhancement factor H increases linearly with the fraction of bootstrap current. The bootstrap induced by the FWEH is mainly due to the central pressure electron gradient (the central power deposition strongly peaks the electronic temperature). A 0D study shows that the bootstrap current (I{sub bs}) varies linearly with the poloidal beta (I{sub bs}/I{sub p} = C{sub bs} x {beta}{sub p}). The effect of various plasma parameters (toroidal field B{sub t}, line-integrated density nI, ion and electron temperature, plasma current I{sub p}) on the bootstrap profile, fraction, C{sub bs} and on the confinement are analysed.
Date: January 1, 1997
Creator: Basiuk, V.; Aniel, T.; Becoulet, A.; Hoang, G. T.; Litaudon, X.; Hutter, T. et al.
Partner: UNT Libraries Government Documents Department