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A single-frequency ECR ion source with a large uniformly distributed resonant plasma volume

Description: An innovative technique for increasing ion source intensity is described which, in principle, could lead to significant advances in ECR ion source technology for multiply charged ion beam formation. The advanced concept design uses a minimum-B magnetic mirror geometry which consists of a multi-cusp, magnetic field, to assist in confining the plasma radially, a flat central field for tuning to the ECR resonant condition, and specially tailored mirror fields in the end zones to confine the plasma in the axial direction. The magnetic field is designed to achieve an axially symmetric plasma {open_quotes}volume{close_quotes} with constant mod-B, which extends over the length of the central field region. This design, which strongly contrasts with the ECR {open_quotes}surfaces{close_quotes} characteristic of conventional ECR ion sources, results in dramatic increases in the absorption of RF power, thereby increasing the electron temperature and {open_quotes}hot{close_quotes} electron population within the ionization volume of the source.
Date: December 1, 1995
Creator: Alton, G.D. & Smithe, D.N.
Partner: UNT Libraries Government Documents Department

Fast Particle Destabilization of Toroidicity Induced Alfven Eigenmodes in National Spherical Torus Experiment

Description: Toroidicity induced Alfven Eigenmode (TAE) stability in National Spherical Torus Experiment (NSTX) is analyzed using the improved NOVA-K code, which includes finite orbit width and Larmor radius effects and is able to predicts the saturation amplitude for the mode using the quasilinear theory. Broad spectrum of unstable global TAEs with different toroidal mode numbers is predicted. Due to the strong poloidal field and the presence of the magnetic well in NSTX better particle confinement in the presence of TAEs in comparison with tokamaks is illustrated making use of the ORBIT code.
Date: December 10, 1999
Creator: Cheng, C.Z.; Fu, G.Y.; Gorelenkova, M.V.; Gorelenkov, N.N.; White, R. & Kaye, S.
Partner: UNT Libraries Government Documents Department

High Beta Tokamaks

Description: Perhaps the ideal tokamak would have high {beta} ({beta} {approx}> 1) and classical confinement. Such a tokamak has not been found, and we do not know if one does exist. We have searched for such a possibility, so far without success. In 1990, we obtained analytic equilibrium solutions for large aspect ratio tokamaks at {beta} {approx} {Omicron}(1) [1]. These solutions and the extension at high {beta} poloidal to finite aspect ratio [2] provided a basis for the study of high {beta} tokamaks. We have shown that these configurations can be stable to short scale MHD modes [3], and that they have reduced neoclassical transport [4]. Microinstabilities (such as the {del}T{sub i} mode) seem to be stabilized at high {beta} [5] - this is due to the large local shear [3] and the magnetic well. We have some concerns about modes associated with the compressional branch which may appear at high {beta}. Bill Dorland and Mike Kotschenreuther have studied this issue and our concerns may be unfounded. It is certainly tantalizing, especially given the lowered neoclassical transport values, that these configurations could have no microinstabilities and, one could assume, no anomalous transport. Unfortunately, while this work is encouraging, the key question for high {beta} tokamaks is the stability to large scale kink modes. The MHD {beta} limit (Troyon limit) for kink modes at large aspect ratio is problematically low. There is ample evidence from computations that the limit exists. However, it is not known if stable equilibria exist at much higher {beta}--none have been found. We have explored this question in the asymptotic high {beta} poloidal limit. Unfortunately, we are unable to find stable equilibrium and also unable to show that they don't exist. The results of these calculations will be published when a more definitive answer is found.
Date: November 14, 1998
Creator: Cowley, S.
Partner: UNT Libraries Government Documents Department


Description: A review of methods for static-field compression of an electron ring is shown to suggest advantages for a method in which there is no axial acceleration or deceleration of the ring. In the method proposed here the static magnetic field itself is o such a character that the electrons are neither focused nor defocused in the axial direction. The integrity and movement of the ring through the compressor is controlled by a small traveling magnetic well. The feasibility of creating such a traveling well is discussed, and an example is presented of a current distribution capable of producing the static magnetic field of the compressor.
Date: February 20, 1969
Creator: Laslett, L.Jackson & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department


Description: A start-up scheme for producing a plasma in the biscusp field configuration of TORMAC which involves the radial injection and trapping of a toroidal gun plasma is described. The peloidal field of the external cusp coils acts as a barrier to the outward travel of the plasma ring. Interferometry and magnetic probe measurements observed the stopping of the expanding plasma ring which has a velocity of 17 cm/{micro}sec. Once stopped, the fields are arranged to hold the plasma in a magnetic well. Interferometry measurements observed a well defined outer boundary remaining stationary during the 20 {micro}sec of the measurement. The inner boundary was also in evidence as shown particularly by the particle flux distribution emanating from the cusp region. The indications are that a sheath exists having a width of 1 to 1.5 ion gyro radii in the poloidial field. Measurements of Thomson and interferometry give a T{sub e} of 15eV, a 15 {micro}sec density decay time, and a 5 {micro}sec energy decay time. These results show that this injection and trapping method is successful, and thus a higher gun plasma energy combined with a flux conserving barrier may lead to higher temperatures for testing containment in TORMAC.
Date: July 1, 1981
Creator: Pincosy, P.A.; Myers, B.R.; Levine, M.A.; Feinberg, B.; Niland, R.A. & Soroka, L.
Partner: UNT Libraries Government Documents Department

Continuum Edge Gyrokinetic Theory and Simulations

Description: The following results are presented from the development and application of TEMPEST, a fully nonlinear (full-f) five dimensional (3d2v) gyrokinetic continuum edge-plasma code. (1) As a test of the interaction of collisions and parallel streaming, TEMPEST is compared with published analytic and numerical results for endloss of particles confined by combined electrostatic and magnetic wells. Good agreement is found over a wide range of collisionality, confining potential, and mirror ratio; and the required velocity space resolution is modest. (2) In a large-aspect-ratio circular geometry, excellent agreement is found for a neoclassical equilibrium with parallel ion flow in the banana regime with zero temperature gradient and radial electric field. (3) The four-dimensional (2d2v) version of the code produces the first self-consistent simulation results of collisionless damping of geodesic acoustic modes and zonal flow (Rosenbluth-Hinton residual) with Boltzmann electrons using a full-f code. The electric field is also found to agree with the standard neoclassical expression for steep density and ion temperature gradients in the banana regime. In divertor geometry, it is found that the endloss of particles and energy induces parallel flow stronger than the core neoclassical predictions in the SOL. (5) Our 5D gyrokinetic formulation yields a set of nonlinear electrostatic gyrokinetic equations that are for both neoclassical and turbulence simulations.
Date: January 9, 2007
Creator: Xu, X Q; Xiong, Z; Dorr, M R; Hittinger, J A; Bodi, K; Candy, J et al.
Partner: UNT Libraries Government Documents Department

Physics of Substorm Growth Phase, Onset, and Dipolarization

Description: A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m{sup 2} as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization.
Date: October 22, 2003
Creator: Cheng, C.Z.
Partner: UNT Libraries Government Documents Department

Minimum-B mirrors plus EBT principles

Description: Electrons are heated at the minimum-B location(s) created by the multiple field and the toroidal field. Resulting hot electrons can assist plasma confinement by (i) providing mirror, (ii) creating azimuthally symmetric toroidal confinement, or (iii) creating a modified bumpy torus.
Date: August 1, 1983
Creator: Yoshikawa, S.
Partner: UNT Libraries Government Documents Department

ELMO Bumpy Torus

Description: The present understanding of equilibrium, stability, and transport in EBT suggests a sequence of research and development activities aimed at a full-scale reactor. The EBT program includes an aggressive development effort for high-power millimeter CW microwave sources based on the Cyclotron Resonant Maser principle. The existing physics evidence suggests that the EBT approach can be extended to confine steady-state, high-beta (toroidal) plasmas. If this extension is demonstrated, then EBT offers an attractive alternative to the tokamak and magnetic mirror for controlled thermonuclear fusion. Some of the critical scientific and technology factors that require resolution as preconditions to reactor feasibility are listed. (MHR)
Date: January 1, 1977
Creator: Dandl, R.A.; Dory, R.A. & Uckan, N.A.
Partner: UNT Libraries Government Documents Department

Magnetic mirror fusion systems: Characteristics and distinctive features

Description: A tutorial account is given of the main characteristics and distinctive features of conceptual magnetic fusion systems employing the magnetic mirror principle. These features are related to the potential advantages that mirror-based fusion systems may exhibit for the generation of economic fusion power.
Date: August 10, 1987
Creator: Post, R.F.
Partner: UNT Libraries Government Documents Department

The spheromak as a prototype for ultra-high-field superconducting magnets

Description: In view of current progress in the development of superconductor materials, the ultimate high-field limit of superconducting magnets is likely to be set by mechanical stress problems. Maximum field strength should be attainable by means of approximately force-free magnet windings having favorable ''MHD'' stability properties (so that small winding errors will not grow). Since a low-beta finite-flux-hole spheromak configuration qualifies as a suitable prototype, the theoretical and experimental spheromak research effort of the past decade has served to create a substantial technical basis for the design of ultra-high-field superconducting coils. 11 refs.
Date: August 1, 1987
Creator: Furth, H.P. & Jardin, S.C.
Partner: UNT Libraries Government Documents Department