摘要:

The usual kinetic description of a plasma is extended to include variables to describe the nuclear spin. The distribution function, over phase space and the new spin variables, provides a sufficient description of a spin‐polarized plasma. The evolution for the distribution function is given. The equations derived are used to calculate depolarization caused by four processes: inhomogeneous fields, collisions, collisions in inhomogeneous fields, and waves. It is found that depolarization by field inhomogeneity on scales large compared with the gyroradius is totally negligible. The same is true for collisional depolarization. Collisions in inhomogeneous fields yield a depolarization rate of order 10−3sec−1for deuterons and a negligible rate for tritons in a typical fusion reactor design. This is still sufficiently small on reactor time scales. However, small‐amplitude magnetic fluctuations (of order 1 G) resonant with the spin precession frequency can lead to significant depolarization (depolarizes triton in 10 sec and deuteron in 100 sec).

ISSN:0031-9171    

DOI:10.1063/1.865726

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new analytical solution is obtained for an ion‐acoustic soliton, which is much closer to the exact solution than the Korteweg–de Vries (KdV) solution. The case of a two‐ion plasma is considered in detail, and the results are compared with those of the dressed soliton solution. The effect of multiple ionization of the ion species is also discussed.

ISSN:0031-9171    

DOI:10.1063/1.865727

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A self‐consistent analysis is given for the development of an air discharge produced by microwaves with powers above the breakdown threshold. The structure of the ionization wave is derived for planar geometry and for arbitrary initial conditions. The theoretical predictions are in excellent agreement with previous results obtained by numerical simulations.

ISSN:0031-9171    

DOI:10.1063/1.865728

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The equations of quasilinear theory are derived for a uniformly magnetized inhomogeneous plasma interacting with electromagnetic field fluctuations. The derivation avoids the use of the random phase approximation, and requires no assumption on the ratio of the Larmor radius to the fluctuation wavelength. These equations are used to obtain the transport equations for each plasma component. The latter satisfy the necessary conservation properties, and yield explicit expressions for various fluxes.

ISSN:0031-9171    

DOI:10.1063/1.865729

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The energy transfer between matter and radiation at very high temperatures is investigated. A previously presented formalism is applied to a mixture of electrons, positrons, and photons interacting through Compton scattering and pair creation and annihilation. The relaxation time toward thermal equilibrium and the bulk viscosity of the mixture are derived, and numerical results are presented for temperatures 3×108K≤T≤1011K. For temperaturesT≳8×108K pair creation and annihilation is found to be more efficient than Compton scattering in transferring energy between matter and radiation.

ISSN:0031-9171    

DOI:10.1063/1.865730

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new set of two‐fluid equations that are valid from collisional to weakly collisional limits is derived. Starting from gyrokinetic equations in flux coordinates with no zero‐order drifts, a set of moment equations describing plasma transport along the field lines of a space‐ and time‐dependent magnetic field is derived. No restriction on the anisotropy of the ion distribution function is imposed. In the highly collisional limit, these equations reduce to those of Braginskii, while in the weakly collisional limit they are similar to the double adiabatic or Chew, Goldberger, and Low (CGL) equations [Proc. R. Soc. London, Ser. A236, 112 (1956)]. The new set of equations also exhibits a physical singularity at the sound speed. This singularity is used to derive and compute the sound speed. Numerical examples comparing these equations with conventional transport equations show that in the limit where the ratio of the mean free path &lgr; to the scale length of the magnetic field gradientLBapproaches zero, there is no significant difference between the solution of the new and conventional transport equations. However, conventional fluid equations, ordinarily expected to be correct to the order (&lgr;/LB)2, are found to have errors of order (&lgr;/Lu)2=(&lgr;/LB)2/(1−M2)2, whereLuis the scale length of the flow velocity gradient andMis the Mach number. As such, the conventional equations may contain large errors near the sound speed (M≊1).

ISSN:0031-9171    

DOI:10.1063/1.865731

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In numerical simulations ofq=2 tearing modes, the maximum amplitude of the mode is found to increase rapidly as the safety factor on axisq(0) rises above 1.5. The associated magnetic islands grow to the center of the column, encompassing virtually the entire plasma cross section. As a result of the formation of these very large islands, the hot central plasma is rapidly convected out to the edge of the column, thereby destroying central confinement. Experimental evidence from several tokamaks linking the formation of these very large islands with major disruptions is presented. Typically, major disruptions are observed to occur in two (or more) stages. During the first stage(s)qrises on axis while the final stage, which terminates the discharge, is associated with the violent growth of anm=2 perturbation. Under some circumstancesq=2 sawteeth are predicted to occur. Evidence for such sawteeth in a divertor tokamak is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865433

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Collective features of accelerated ions in the plasma focus are investigated theoretically by using a computer simulation. It is shown that an effective heating of ions by the acceleration of ions occurs without collisions in the collapse phase. A hybrid plasma diode model is used for the particle accelerations after disruption of the focused plasma by them=0 mode instability. It is shown that ions are efficiently accelerated in the disrupted region toward the downstream direction with respect to the discharge current, and that the energy of the accelerated ions is spread rather widely over the scale of 100 keV, as was observed in experiments.

ISSN:0031-9171    

DOI:10.1063/1.865434

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

External excitation, propagation, and ion heating for the ion‐Bernstein wave (IBW) are studied for the single‐ion and two‐ion species plasmas, using particle simulation. It is found that the value of &ohgr;/&OHgr;inear the antenna position influences the excitation characteristics of the IBW. The wavelength and group velocity of the propagating IBW agree well with those calculated from the linear dispersion relation. Corresponding to the experiment done with the JIPP T‐II‐U device [Phys. Rev. Lett.54, 2339, (1985)], the 3&OHgr;Dheating process in the plasma composed of deuterium‐like and hydrogen‐like ions is investigated. The wave energy is deposited into the bulk and tail of the deuterium‐like ions because of third harmonic cyclotron resonance and the bulk of the hydrogen‐like ions because of 3/2 &OHgr;Hcyclotron subharmonic resonance.The possibility is also discussed that the heating efficiency may not depend on the concentration of the deuterium‐like ion in the 3&OHgr;Dheating in the actual tokamak experiment.

ISSN:0031-9171    

DOI:10.1063/1.865435

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Resistive tearing mode instabilities are driven by unfavorable current gradients at the position where the safety factorqis rational. Their dynamics in the presence of radio‐frequency (rf) power absorption in the electron‐cyclotron wavelength range is investigated by means of a hybrid transport‐magnetohydrodynamic (MHD) code and analytic considerations. A panorama of possibilities of stabilization and control of disruptions in tokamaks is presented.

ISSN:0031-9171    

DOI:10.1063/1.865436

出版商:AIP    

年代:1986

数据来源: AIP