摘要:

The magnetohydrodynamic (MHD) equations are presented in an invariant form in flux variables and variational principles are formulated for these variables. These equations are then solved in Boozer coordinates in the small curvature expansion.

ISSN:0031-9171    

DOI:10.1063/1.866771

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A two‐ and one‐half‐dimensional electromagnetic particle code (PS2M) [H. Abe and S. Nakajima, J. Phys. Soc. Jpn.53, xxx (1987)] is used to study how an electric field applied parallel to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The parallel electric fieldE∥perturbs the electron velocityv∥parallel to the magnetic field and also induces a perpendicular magnetic field perturbationB⊥. The unstable growth of the flute mode in the absence of such a radio frequency electric field is first studied as a basis for comparison. The ponderomotive force originating from the time‐averaged product ⟨v∥B⊥⟩ is then shown to stabilize the flute modes. The stabilizing wave power threshold, the frequency dependency, and the dependence on ∇‖E∥‖ all agree with the theoretical predictions.

ISSN:0031-9171    

DOI:10.1063/1.866772

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The nature of a rigid, flutelikeM=1 instability as seen in the Tara tandem mirror [Nucl. Fusion22, 549 (1982);PlasmaPhysicsandControlledNuclearFusion1984(IAEA, Vienna, 1985), Vol. 2, p. 285] is discussed. Radial density and light emission profiles obtained by inverting chord measurements are compared to end loss radial profiles during the evolution of the mode to its nonlinear saturated state. This final state is characterized by a coherent, flutelike motion of the plasma as a whole about the machine axis.

ISSN:0031-9171    

DOI:10.1063/1.866773

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new particle simulation model has been developed to investigate Cˇerenkov masers. The novel aspects of the code are briefly described, and results of simulations of two types of Cˇerenkov masers are presented. The first device uses a conventional dielectric lining as its slow‐wave structure. The second is a new type of Cˇerenkov maser in which a circular waveguide is partially filled with a dense annular plasma instead of a dielectric layer. Both simulations agree well with experimental results and linear theory calculations. Saturation of the instability is shown to be due to trapping of the beam electrons. The relative merits of each system are discussed.

ISSN:0031-9171    

DOI:10.1063/1.866774

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The UCI modified betatron [Phys. Rev. Lett.53, 266 (1984)] was converted into a stellatron accelerator by the addition of helical quadrupole coils to the betatron configuration. An experimental study of the injection, trapping, acceleration, and disruption of a beam in this apparatus has been conducted. The stellarator field applied was of up to 10 kG and with a rotational transform of &igr;&slash;≃0.1– 0.15. Electrons were injected from a thermionic emitter typically operated by applying 20 kV, 2– 4 &mgr;sec pulses to the hot cathode, which emitted ∼3 A. A beam of ∼200 A was trapped in the torus and accelerated by the betatron field applied immediately after the injection. The beam life was extended by increasing the toroidal field. The beam current suffered a partial disruption after it reached its peak value. After that the beam lost electrons gradually, accompanied by generation of x rays, until the entire beam was lost close to the peak of the accelerating betatron field. Electron energies of up to ∼4 MeV were reached. The dependence of the beam current and its lifetime, upon the applied fields and injection conditions, was explored.

ISSN:0031-9171    

DOI:10.1063/1.866775

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Operation of the induced resonance electron cyclotron (IREC) maser [Appl. Phys. Lett.49, 1154 (1986); Nucl. Instrum. Methods Phys. A250, 36 (1986)] at Doppler upshifted cyclotron harmonics is studied. A set of fast‐time averaged nonlinear equations of motion is derived for the particle motion near an arbitrary harmonic at any index of refraction. The small signal efficiency is computed analytically and the minimum current to start the cavity oscillations is obtained. The nonlinear equations of motion are integrated numerically. The interaction efficiency at the first few harmonics is found to be comparable to the efficiency at the fundamental. The sensitivity of the efficiency to beam thermal spreads is minimized by proper selection of the index of refraction.

ISSN:0031-9171    

DOI:10.1063/1.866776

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A theoretical model of cathode plasma behavior in a planar, high current, space‐charge limited diode is presented. The model predicts the evolution of the cathode plasma to steady state when certain diode conditions are satisfied. This steady state corresponds to current extraction from a stationary plasma boundary with no diode impedance collapse. In order for the equilibrium to be achieved, the driving impedance of the external power supply circuit must be smaller than a critical value that depends only on diode voltage, gap spacing, and plasma electron temperature. The temporal evolution of the cathode plasma is described using both a discrete numerical simulation model and an approximate analytical solution to the transport equations. The dependence on plasma temperature, neutral gas density and composition, diode voltage, gap spacing, and extracted current density are investigated.

ISSN:0031-9171    

DOI:10.1063/1.866777

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A subgrid‐scale model recently derived by Yoshizawa [Phys. Fluids29, 2152 (1986)] for use in the large‐eddy simulation of compressible turbulent flows is examined from a fundamental theoretical and computational standpoint. It is demonstrated that this model, which is only applicable to compressible turbulent flows in the limit of small density fluctuations, correlates somewhat poorly with the results of direct numerical simulations of compressible isotropic turbulence at low Mach numbers. An alternative model, based on Favre‐filtered fields, is suggested which appears to reduce these limitations.

ISSN:0031-9171    

DOI:10.1063/1.866778

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A self‐consistent, one‐dimensional, quasilinear formulation is used to calculate the efficiency of current generation by whistler waves (&ohgr;ci≪&ohgr;≪&ohgr;ce) in the weak‐source regime. Estimates of the efficiency compare well with recent measurements in the ACT‐1 device [Phys. Rev. Lett.55, 1669 (1985)] and also in the Irvine Torus [Phys. Rev. Lett.56, 835 (1986)].

ISSN:0031-9171    

DOI:10.1063/1.866779

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A review of experimental data suggests that particle loss and end shorting contribute together to the rotation of field‐reversed configurations. Neither process can account for all available data by itself. An empirical scaling law based on both mechanisms is proposed that is consistent with all data.

ISSN:0031-9171    

DOI:10.1063/1.866780

出版商:AIP    

年代:1988

数据来源: AIP