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Calculations of alpha particle loss for reversed magnetic shear in the Tokamak Fusion Test Reactor

Description: Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma predict both total alpha losses and ripple diffusion losses to be greater than those from a comparable non-reversed magnetic shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. A simple ripple loss model, benchmarked against the guiding center code, is found to work satisfactorily in transport analysis modelling of reversed and monotonic shear scenarios. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. The 40% alpha particle loss predictions for TFTR suggest that reduction of toroidal field ripple will be a critical issue in the design of a reversed shear fusion reactor.
Date: March 1, 1997
Creator: Redi, M.H.; White, R.B.; Batha, S.H.; Levinton, F.M. & McCune, D.C.
Partner: UNT Libraries Government Documents Department

Ion heating in the field-reversed configuration (FRC) by rotating magnetic fields (RMF) near cyclotron resonance

Description: The trajectories of ions confined in a Solovev FRC equilibrium magnetic geometry and heated with a small-amplitude, odd-parity rotating magnetic field, have been studied with a Hamiltonian computer code. When the RMF frequency is in the ion-cyclotron range, explosive heating occurs. Higher-energy ions are found to have betatron-type orbits, preferentially localized near the FRC midplane. These results are relevant to a compact magnetic-fusion-reactor design.
Date: July 20, 2000
Creator: Cohen, Samuel A. & Glasser, Alan H.
Partner: UNT Libraries Government Documents Department

Maintaining the closed magnetic-field-line topology of a field-reversed configuration (FRC) with the addition of static transverse magnetic fields

Description: The effects on magnetic-field-line structure of adding various static transverse magnetic fields to a Solovev-equilibrium field-reversed configuration is examined. It is shown that adding fields that are anti-symmetric about the axial mid-plane maintains the closed field-line structure, while adding fields with planar or helical symmetry opens the field structure. Anti-symmetric modes also introduce pronounced shear.
Date: January 13, 2000
Creator: Cohen, S.A. & Milroy, R.D.
Partner: UNT Libraries Government Documents Department

Microstability theory for the field reversed configuration. Final report

Description: This report summarizes the work done in the last contract period. Previous work has been described in Annual Performance Reports. The work carried on under this Research Grant and not included in previous progress and annual reports includes two distinct items. One work is a study of the nonlocal high beta microstability of the FRC (Field Reversed Configuration), which they began sometime ago. This study identified the limiting beta (=4{pi}nT/B{sup 2}) for the mode to remain unstable. The study found that as beta increases, the wavenumbers (k{sub y}, K{sub z}) for maximum growth changes, so that the limiting beta is not the one found by fixing (k{sub y}, K{sub z}) and increasing beta. It also appears that the criterion for nonlocal terms to influence the result, as beta increases, is substantially weaker than might have been thought. The authors identify the parameter that determines this effect. This study is presented as Appendix 1 of this report. The second study is of the effect of collisions on the lower hybrid drift instability. The result is that the effect of collisions is substantially more important than might have been expected. These two studies are in different stages of completion. The second is in fact complete, and could be published virtually as is, although it would benefit from a small amount of numerical analysis. The first study is far richer than the second, in that it includes a variety of regimes and effects. The formulation presented in it could e used as the basis for a series of papers, although in its present stage it is not ready for publication. It is unfortunate, but the level of the research Grant, and its untimely end, did not permit further progress on that study.
Date: November 5, 1997
Creator: Krall, N.A.
Partner: UNT Libraries Government Documents Department

Numerical study of tilt stability of prolate field-reversed configurations

Description: Global stability of the Field-Reversed Configuration (FRC) has been investigated numerically using both 3D MHD and hybrid (fluid electron and delta f particle ion) simulations. The stabilizing effects of velocity shear and large ion orbits on the n = 1 internal tilt mode in the prolate FRCs have been studied. Sheared rotation is found to reduce the growth rate, however a large rotation rate with Mach number of M greater than or approximately equal to 1 is required in order for significant reduction in the instability growth rate to occur. Kinetic effects associated with large thermal ion orbits have been studied for different kinetic equilibria. These simulations show that there is a reduction in the tilt mode growth rate due to finite ion Larmor radius (FLR) effects, but complete linear stability has not been found, even when the thermal ion gyroradius is comparable to the distance between the field null and the separatrix. The instability existing beyond the FLR theory threshold could be due to the resonant interaction of the wave with ions whose Doppler shifted frequency matches the betatron frequency.
Date: June 21, 2000
Creator: Belova, E. V.; Jardin, S. C.; H. Ji, M. Yamada & Kulsrud, R.
Partner: UNT Libraries Government Documents Department

Dynamo theory: can amplification of magnetic-field profiles arise from a cross-field alpha effect

Description: The answer to the title question is here provided in cylindrical geometry for an essentially arbitrary radial dependence of this alpha effect, except that it is subject to a simple, physically required constraint. The interest in this type of alpha effect derives from its connection with compressible turbulence, which is usually not considered in kinematic dynamo theory.
Date: April 1, 1982
Creator: Gerwin, R. & Keinigs, R.
Partner: UNT Libraries Government Documents Department

Conceptual physics design of a compact torus fusion reactor (CTOR)

Description: The general approach to fusion power embodied by field-reversed plasmoid configurations is reviewed within the context of a power reactor. A simple analytic formulation is developed and applied to the field-reversed theta pinch as a core plasma for a thermonuclear reactor. These calculations and results are based on a minimum power constraint and will serve as a basis for more exact and detailed reactor modeling.
Date: July 1, 1980
Creator: Hagenson, R.L. & Krakowski, R.A.
Partner: UNT Libraries Government Documents Department

Analytic model of the radiation-dominated decay of a compact toroid

Description: The coaxial-gun, compact-torus experiments at LLNL and LASNL are believed to be radiation-dominated, in the sense that most or all of the input energy is lost by impurity radiation. This paper presents a simple analytic model of the radiation-dominated decay of a compact torus, and demonstrates that several striking features of the experiment (finite lifetime, linear current decay, insensitivity of the lifetime to density or stored magnetic energy) may also be explained by the hypothesis that impurity radiation dominates the energy loss. The model incorporates the essential features of the more elaborate 1 1/2-D simulations of Shumaker et al., yet is simple enough to be solved exactly. Based on the analytic results, a simple criterion is given for the maximum tolerable impurity density.
Date: November 11, 1981
Creator: Auerbach, S.P.
Partner: UNT Libraries Government Documents Department

Overview of the data-acquisition system (including shielding, isolation and grounding) on the Beta II field-reversed plasma-gun experiment

Description: Computer-supported acquisition, analysis, and storage of mirror fusion experimental data requires the solution of several problems. The data must be gathered with a minimum amount of noise, and transients must be excluded from the computer so that it can function properly. On Beta II (which was an experiment to produce field-reversed plasma rings from a coaxial plasma gun) the diagnostic system was planned to provide the shielding and isolation necessary to solve these two problems. The Beta II system has been in operation for about two years and provides 300-channel capacity, CAMAC interfaced, to a Hewlett Packard 21MX computer. The system routinely handles signals ranging from 1 mV to 50 kV, with bandwidths from .05 Hz to 10 MHz. The data are captured by transient recorders during a shot, then transferred to the computer. The computer stores the data on disc for immediate processing and on tape for long-term storage. Processed data from any number of channels (usually 20 to 30) is plotted between shots for immediate review. The rest of the data is processed and plotted during off hours.
Date: July 1, 1981
Creator: Bell, H.H. Jr.
Partner: UNT Libraries Government Documents Department

Computational methods for reversed-field equilibrium

Description: Investigating the temporal evolution of reversed-field equilibrium caused by transport processes requires the solution of the Grad-Shafranov equation and computation of field-line-averaged quantities. The technique for field-line averaging and the computation of the Grad-Shafranov equation are presented. Application of Green's function to specify the Grad-Shafranov equation boundary condition is discussed. Hill's vortex formulas used to verify certain computations are detailed. Use of computer software to implement computational methods is described.
Date: April 15, 1980
Creator: Boyd, J.K.; Auerbach, S.P.; Willmann, P.A.; Berk, H.L. & McNamara, B.
Partner: UNT Libraries Government Documents Department

Computational methods for reversed-field equilibrium

Description: Investigating the temporal evolution of reversed-field equilibrium caused by transport processes requires the solution of the Grad-Shafranov equation and computation of field-line-averaged quantities. The technique for field-line averaging and the computation of the Grad-Shafranov equation are presented. Application of Green's function to specify the Grad-Shafranov equation boundary condition is discussed. Hill's vortex formulas used to verify certain computations are detailed. Use of computer software to implement computational methods is described.
Date: April 15, 1980
Creator: Boyd, J.K.; Auerbach, S.P.; Willmann, P.A.; Berk, H.L. & McNamara, B.
Partner: UNT Libraries Government Documents Department

Studies of the formation of field reversed plasma by a magnetized co-axial plasma gun

Description: The gun injects axially into a drift tank followed by a magnetic mirror. For the experiments reported here, only the guide coils outside the vacuum vessel and solenoids on the plasma gun electrodes were used; the mirror coil was not energized. A stainless steel flux conserver is placed in the mirror throat to prevent the plasma from contacting the nonconducting vacuum wall in the region of the mirror. An axis encircling array of magnetic loop probes includes four diamagnetic loops and a loop which measures the azimuthally averaged outward pointing radial component of magnetic field. These loop probes are stainless steel jacketed and form a flux conserving boundary (at a radius = 30 cm) for plasma emitted from the gun. A five tip probe that can be positioned anywhere along the axis of the experiment is used to measure internal components of magnetic field.
Date: May 28, 1980
Creator: Turner, W.C.; Granneman, E.H.A.; Hartman, C.W.; Prono, D.S.; Taska, J. & Smith, A.C. Jr.
Partner: UNT Libraries Government Documents Department

Reversed-field pinch fusion reactor

Description: A conceptual engineering design of a fusion reactor based on plasma confinement in a toroidal Reversed-Field Pinch (RFP) configuration is described. The plasma is ohmically ignited by toroidal plasma currents which also inherently provide the confining magnetic fields in a toroidal chamber having major and minor radii of 12.7 and 1.5 m, respectively. The DT plasma ignites in 2 to 3 s and undergoes a transient, unrefueled burn at 10 to 20 keV for approx. 20 s to give a DT burnup of approx. 50%. The 5-s dwell period between burn pulses for plasma quench and refueling allows steady-state operation of all thermal systems outside the first wall; no auxiliary thermal capacity is required. Tritium breeding occurs in a granular Li/sub 2/O blanket which is packed around an array of radially oriented water/steam coolant tubes. The slightly superheated steam emerging from this blanket directly drives a turbine that produces electrical power at an efficiency of 30%. A borated-water shield is located immediately outside the thermal blanket to protect the superconducting magnet coils. Both the superconducting poloidal and toroidal field coils are energized by homopolar motor/generators. Accounting for all major energy sinks yields a cost-optimized system with a recirculating power fraction of 0.17; the power output is 750 MWe(net).
Date: January 1, 1980
Creator: Hagenson, R.L. & Krakowski, R.A.
Partner: UNT Libraries Government Documents Department

Estimation of neutral-beam-induced field reversal in MFTF by an approximate scaling law

Description: Scaling rules are derived for field-reversed plasmas whose dimensions are common multiples of the ion gyroradius in the vacuum field. These rules are then applied to the tandem MFTF configuration, and it is shown that field reversal appears to be possible for neutral beam currents of the order of 150 amperes, provided that the electron temperature is at least 500 eV.
Date: April 28, 1980
Creator: Shearer, J.W.
Partner: UNT Libraries Government Documents Department

Power-crowbar impacts on plasma characteristics in ZT-40

Description: Detailed analysis of the impact of I/sub phi/ and I/sub theta/ power crowbars on the ZT-40 plasma is presented for the operational period between shots 1620-3600. It is demonstrated that in both aided- and self-reversed modes the main effect of the I/sub phi/ power crowbar is to lengthen the time to l/e of peak current, whereas the main effect of the I/sub theta/ power crowbar is to extend the reversal of B/sub phi/ at the wall, primarily in self-reversed operation. It is shown that this extension has the effect of also decreasing the current decay rate to the point where no distinction is seen between the two modes. A saturation is seen in the decay time (tau/sub l/e/ less than or equal to 0.4 ms) once the field reversal in either mode exceeds approximately 0.3 ms. Possible physical explanations of these effects are discussed.
Date: July 1, 1981
Creator: Watt, R.G.
Partner: UNT Libraries Government Documents Department

Production of field-reversed configurations with a magnetized coaxial plasma gun

Description: Compact toroids were generated which can be made to come to rest in a cylindrical resistive flux conserver. They are observed to rotate so that their major axis is perpendicular to the axis of the flux conserver. Subsequently they appear to remain stationary and decay with a time constant of about 100 ..mu..s. We have also generated compact toroids in an oblate geometry which remain aligned with the axis of the flux conserver and decay with a time constant of 150 ..mu..s. The magnetic field reconnection time for compact toroid formation is measured in the latter case to be much shorter than the decay time.
Date: January 1, 1980
Creator: Jarboe, T.R.; Henins, I.; Hoida, H.W.; Linford, R.K.; Marshali, J.; Platts, D.A. et al.
Partner: UNT Libraries Government Documents Department

Excluded flux analysis of a field reversed plasma

Description: A simple eigenvalue approach for mapping the vacuum field between an assumed separatrix and a conducting wall is described. This allows an improved determination of the plasma shape in Field Reversed Experiments (FRX) compared to previous estimates based on excluded flux radius measurements. It is also shown that an array of magnetic field diagnostics located outside the discharge tube cannot resolve features of the plasma shape that have scale length smaller than about a coil radius.
Date: September 1, 1980
Creator: Tuszewski, M.
Partner: UNT Libraries Government Documents Department

Computer simulation of kinetic properties of plasmas. Progress report, October 1, 1977--September 30, 1978

Description: The research is directed toward the development and testing of new numerical methods for particle and hybrid simulation of plasmas and their application to physical problems of current significance to Magnetic Fusion Energy. During the past year, research on the project has been concerned with the following specific problems: (1) analysis and computer simulations of the dissipative trapped-electron instability in tokamaks; (2) long-time-scale algorithms for numerical solutions of the drift-kinetic equation; and (3) computer simulation of field-reversed ion ring stability.
Date: January 1, 1978
Creator: Denavit, J.
Partner: UNT Libraries Government Documents Department

Evaluation of a relativistic electron ring system as a plasma target for buildup of compact-toroid configurations

Description: A review of the idea of using plasma-loaded electron rings as buildup targets for future compact-toroid machines is presented. Present experiments at Cornell University and Nagoya University are analyzed, and the need for auxiliary heating to reach interesting temperatures is described. Consideration of the effect of two-stream instability, toroidal field, and plasma containment are discussed.
Date: June 26, 1980
Creator: Condit, W.C.
Partner: UNT Libraries Government Documents Department

FRC studies on FRX-B

Description: Recent experimental studies of Field-Reversed Configurations (FRC) on the FRX-B device have included (1) characterization of FRC formation with regard to loss of bias flux, (2) examination of FRC equilibria through separatrix profiles, (3) formation of FRC's with different end-mirror configurations, and (4) extension of FRC parameter range. Studies on loss of bias flux during the pre-ionization (PI) phase of FRC formation are presented in another paper dedicated solely to PI considerations. Loss of bias flux during the reversal phase of FRC formation is reviewed in the first section of this paper. Use of barrier fields during the reversal phase to enhance trapping of bias flux is included in the third section of this paper. In addition to barrier field studies, results from different mirror configurations are also discussed in the third section. A critical diagnostic for interpretation of the results from the different machine modifications is the excluded-flux probe array. Analysis of excluded-flux measurements to obtain the FRC separatrix profile is described in the second section. Finally, preliminary results of FRX-B operation in an extended range of plasma parameters is briefly discussed in the fourth section.
Date: January 1, 1980
Creator: Armstrong, W.T.; Cochrane, J.C.; Lipson, J.; Linford, R.K.; McKenna, K.F.; Sgro, A.G. et al.
Partner: UNT Libraries Government Documents Department