摘要:

Parametric excitation [wherein a Langmuir oscillation at(&ohgr; k)simultaneously drives an ion‐acoustic mode at(&ohgr;′, k′), one sideband Langmuir oscillation at(&ohgr; − &ohgr;′, k − k′), and possibly another at(&ohgr; + &ohgr;′, k + k′(]is considered. Steady‐state solutions are found for these systems in various limits, taking into account contributions which are third order and higher in the mode fields. Connections with experiment are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692530

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Computer experiments on plasma instabilities due to anisotropic velocity distributions are made to study nonlinear phenomena as well as the validity limit of linear theory using a sheet plasma model. Three kinds of anisotropic distributions are considered; type‐A, perpendicular (to an applied magnetic field) velocity distribution function having a hump atv⊥ ≠ 0, type‐B, bi‐Maxwellian distribution withT⊥ ≫ T‖, and type‐C, loss‐cone distribution. Results of the experiments show that instability due to type‐A distribution is generally very strong and resembles two‐beam instability. One of the characteristics of this is that the strength of the instability is relatively insensitive to the propagation angle. On the other hand, instability due to type‐B distribution is quite sensitive to the propagation angle. A particular feature of the type‐B instability is that, in addition to a growth that is predicted by linear theory, there exist several strong bursts which play an essential role in accelerating plasma along magnetic field lines. After the bursts, the plasma arrives at a stable state with a much reduced ratio ofT⊥/T‖compared with that at the initial state. Another interesting instability is the loss‐cone instability which is caused by the type‐C distribution, an inherent distribution in a mirror magnetic field. When a disturbance propagates almost perpendicularly to magnetic field, an instability is shown to develop due to a coupling of hot ions with cold electrons. With the development of the instability, ions are accelerated along the magnetic field lines and are gradually lost from the mirror field.

ISSN:0031-9171    

DOI:10.1063/1.1692531

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Collisional absorption and emission of longitudinal waves in a one‐species, one‐dimensional plasma are investigated by numerical experiments. The theory of Birmingham, Dawson, and Kulsrud for longitudinal bremsstrahlung is extended to the one‐dimensional case. The results of the numerical experiments are found to be in agreement with the theory. Low‐frequency electric field fluctuations for long‐wavelength modes are also found and are associated with the random motion of the particles.

ISSN:0031-9171    

DOI:10.1063/1.1692532

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A process of aborption of energy by a cold nonuniform collisionless plasma from an externally driven electric field is described using a linearized theory. With the example of a cylindrically symmetric plasma, power is shown to be absorbed whenever the maximum plasma frequency exceeds the driving frequency. The admittance of the plasma as seen by an external circuit is developed and found to be sensitively dependent upon the equilibrium density distribution near the wall, suggesting the use of this phenomenon to examine electron sheath structure. Experimental results are presented which support the theoretical prediction. The occurrence of this absorption in the presence of a magnetic field and its effect upon the propagation of surface modes along a nonmagnetized plasma column are also indicated.

ISSN:0031-9171    

DOI:10.1063/1.1692533

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Self‐consistent solutions for the problem of a collisionless plasma streaming across a magnetic field whose dimensions are small compared to(rcerci)1/2show that the electrons can accompany the ions across the field (over distances large compared torce) provided&ohgr;ce < &agr; &ohgr;pe, where&agr; ≤ 1is a function of the electron distribution function (&agr; = 1when the electron thermal velocities are neglected). This appears to explain the threshold,&ohgr;ce ≃ 0.9 &ohgr;pe, observed in recent experiments on plasma penetration across a radial magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1692534

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Detailed observations of 100‐eV hydrogen plasmas moving in a linear quadrupole and a toroidal octupole magnetic field show that the plasmas polarize and that the field lines quickly become equipotentials. The plasmasE × Bdrift with negligible diamagnetism in double vortex flow patterns similar to the self‐consistent solutions of Poukey. The agreement is not perfect presumably because the uniform field and steady state assumed in the theory are lacking in the experiments.

ISSN:0031-9171    

DOI:10.1063/1.1692535

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Neutral‐atom injection with Lorentz trapping is one of the most popular and successful methods of forming a “hot ion plasma.” It is suggested here that one could form a “hot electron plasma” by injecting ions with megaelectron volt energies and using Lorentz trapping. For example, build‐up calculations indicate that one could form in a mirror machine a 15‐keV “hot electron plasma” with a density of109 cm−3by using a 50‐&mgr; A beam ofH2+ at 60 MeV. TheH2+beam would be sent through a gas cell or foil to obtain some30 MeV H0atoms by dissociation. TheH0would then pass through the magnetic confinement field and some 15‐keV electrons would be trapped by Lorentz ionization of excitedH0. If the background gas pressure is below10−8Torr, electron‐electron scattering will determine the containment time forn ≈ 109 cm−3. Neutralization of the hot electrons can be accomplished by ionization of the residual gas as the ionization time constant is much shorter than the gasscattering time constant. Since typical scattering times are many seconds, dc operation is preferable. If one can obtain the necessary combination of ion energy and confining magnetic field strength, Lorentz electron stripping from theH−orHe−ground state can result in very high trapping efficiencies and higher plasma densities. Some advantages and uses for beam‐injected and Lorentz‐trapped hot electron plasmas are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692536

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An instability phenomenon in the form of a symmetrical pattern of vortices was found to exist at the edge of a rotating disk partially submerged in liquid in a vertical tank.

ISSN:0031-9171    

DOI:10.1063/1.1692537

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The spectral equation of nonstratified turbulent shear flow in the equilibrium range is solved analytically. A numerical example is computed and presented.

ISSN:0031-9171    

DOI:10.1063/1.1692538

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The influence of low‐pass filtering on measurement of odd‐order correlations of non‐Gaussian processes is investigated using digital harmonic analysis. These corrections are found to be negligible for the case considered.

ISSN:0031-9171    

DOI:10.1063/1.1692539

出版商:AIP    

年代:1969

数据来源: AIP