摘要:

It is demonstrated how static magnetic field errors can resonantly drive low‐frequency electrostatic waves in a pure electron plasma column. The driving mechanism is identified as a charge bunching that results from the field error. It is found that the wave amplitude increases linearly with time.

ISSN:0031-9171    

DOI:10.1063/1.863446

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The ideal magnetohydrodynamic stability of high‐beta model equilibria in slab geometry withBz= 0 and containing elongated regions of closed field lines is investigated as an initial‐value problem and in terms of the energy principle. For moderate or larger elongations, flute (interchange) modes are found to be stable throughout the closed region. Co‐interchange modes with the character of anm= 1 kink mode, however, are found to be unstable. The growth rate of these modes initially increases rapidly withkzand then approaches a finite limit askz→∞. As the elongation of the closed region is increased, the growth rate decreases rapidly. Possible implications of these results for field‐reversed theta pinches are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863447

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Solutions are given for the characteristics of a warm plasma flowing axially through a magnetic mirror in the presence of a confined hot‐ion species. The warm plasma is assumed to have negligible effect on the magnetic field. The plasma is described by four moment equations for the density, velocity, parallel temperature, and perpendicular temperature of the ions, that are solved by a time‐dependent finite‐difference computer code. Two basic types of solutions occur corresponding to the warm‐ion density (nw) being less than the hot‐ion density (nh), andnw≳nh. In the first case, the flow is nearly stagnant between the warm‐ion source and the midplane, but the flow rapidly accelerates to a supersonic velocity just beyond the midplane. In the second case, the flow velocity profile is more symmetric about the midplane, and the sonic transition occurs at the mirror throat. Specific calculations are given for gas box and stream gun sources used to stabilize microstabilities and for a collisional tandem mirror.

ISSN:0031-9171    

DOI:10.1063/1.863448

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The effects of ion flow on the nonlinear development of resonantly driven electron plasma oscillations in a nonuniform plasma are investigated. The Lagrangian oscillator equation is generalized to include ion flow. A solution of the oscillator equation is obtained and is examined in detail for a model profile. Plasma flow through the critical surface is found to substantially reduce the energy of electrons at wave breaking when the flow velocity exceeds the oscillating velocity of electrons in the driver field.

ISSN:0031-9171    

DOI:10.1063/1.863449

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is found that a finite perturbations of the ion orbits leads to a nonlinear frequency shift that reduces the mode frequency and has a weak stabilizing effect on the lower‐hybrid drift instability. This result is obtained from a self‐consistent solution of the Vlasov–Poisson equations using perturbation theory in which the nonlinear dielectric function and the nonlinear temporal evolution of a single unstable mode in the low drift velocity regime are calculated analytically. The nonlinear frequency shift does not seem to be a potent saturation mechanism in a collisionless plasma, but may be more relevant when there are ion‐ion collisions.

ISSN:0031-9171    

DOI:10.1063/1.863458

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Solenoidal field linkage is explained and its application to magnetic helicity is discussed. A Green’s tensor function for the magnetic vector potential of a plasma current distribution bounded by a perfect conductor is derived. A hypothesis of incomplete relaxation of a turbulent discharge is then used to establish reversed‐field pinch configurations with finite beta.

ISSN:0031-9171    

DOI:10.1063/1.863459

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Computer simulations of the free‐electron laser have been carried out using a two‐and‐one‐half dimensional fully electromagnetic relativistic particle code. It has been found that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates and, therefore, mode competition is an important consideration in the design of free‐electron lasers. Furthermore, electromagnetic waves with group velocities opposite to the direction of electron beam propagation can be absolutely unstable. It is shown that the absolutely unstable waves can completely disrupt the electron beam and any laser oscillaton; therefore, they are extremely detrimental to the operation of free electron lasers. However, it has been found that one can stabilize the absolute instability by taking particular precautions in the design of free‐electron lasers.

ISSN:0031-9171    

DOI:10.1063/1.863460

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

In one spatial dimension, the effects of finite pump lengthLon the oscillating two‐stream instability are considered. In the absence of damping, a purely growing instability for very small pump extent is found. Under certain conditions, the finite system exhibits faster growth rates than the corresponding infinite system.

ISSN:0031-9171    

DOI:10.1063/1.863461

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Parametric excitation of drift waves and suppression of drift instabilities in a plasma by an oscillating field of low frequency has been studied. The role of such an oscillating field of frequency, much higher than the drift frequency in determining the stability properties of the waves, has been investigated.

ISSN:0031-9171    

DOI:10.1063/1.863462

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An investigation of the growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in a collisionless unmagnetized plasma is presented. The effect of the position and the width of the ripple on its growth has been studied in some detail. In a special case, the growth rate of the ripple is seen to be comparable to the growth rate of filamentation instability. In addition to the growth of the ripple, the effect of the presence of the ripple on the excitation of an electron plasma wave has also been studied.

ISSN:0031-9171    

DOI:10.1063/1.863463

出版商:AIP    

年代:1981

数据来源: AIP