摘要:

A Kerr‐cell shuttered spectrograph has been used to make measurements of the state of the plasma produced by an electric shock tube operating at high pressure (100 Torr of CO2). Relative line intensities have been used to measure the temperature and Stark broading has been used to obtain the electron densities. The free‐running plasma front is expected and found to be in local thermodynamic equilibrium. The complete state of the plasma flow is then deduced. Measured pressure, trajectory and density profiles approximate blast‐wave calculations with, however, higher‐pressure and lower‐density values at the front than calculated from the Rankine‐Hugoniot theory. The temperature profile does have a rising trend upstream, but the front temperature is much too high (a factor of four). Violent forward mixing of the arc gas, due to the deceleration of the front, accounts for this. An arc‐produced photon precursor is assumed to dissociate the CO2.

ISSN:0031-9171    

DOI:10.1063/1.1691782

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The phenomenon of convection is investigated in nonequilibrium plasmas where there are substantial nonuniformities in the plasma state. It is shown that a boundary‐value problem can be formulated to solve for the current stream function and the electron temperature including convective effects. The resulting equations are coupled and nonlinear so they are solved by an iteration technique. Two simple examples are chosen to illustrate the procedure. The first consists of a pair of electrodes in a straight channel, and the second is the entrance region of a parallel‐walled solid electrode device. In each case, only an applied electric field was considered. The calculations show the current streamlines and the electron temperature distribution displaced downstream for both uniform and nonuniform flows. It is also shown that as the flow velocity increases the voltage necessary to pass a specified amount of current increases.

ISSN:0031-9171    

DOI:10.1063/1.1691783

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Using the thirteen‐moment method of Grad, explicit expressions for the drift velocities and thermal flux vectors in a five‐component nonequilibrium plasma in the presence of electric and magnetic fields, and pressure, temperature (or concentration) gradients are presented. The results are valid over a wide range of the degree of ionization and in situations where charge neutrality does not hold. When terms of the order of the square root of the ratio of the mass of the electron to the mass of a heavy particle can be ignored, a direct and simple derivation of the generalized Ohm's law in a multicomponent plasma can be obtained. The influence of charge nonneutrality on the electrical conductivity is discussed.

ISSN:0031-9171    

DOI:10.1063/1.1691742

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A quantum‐mechanical description of a cold plasma in a strong magnetic field is developed from the hydrodynamic equations. The plasmon‐particle and plasmon‐plasmon interaction Hamiltonians are derived and expressed in terms of second quantized operators for plasmons and particles. The quantum‐mechanical plasmon growth rate due to stimulated emission is obtained. The classical limit is taken and compared with the growth rate predicated by the linearized Vlasov equations. The possibility of a spacial gradient instability, that of Mikhailovskii and Timofeev, arises and is interpreted in terms of emission and absorption of plasmons by the energetic particles. The plasmon‐particle interaction Hamiltonian is used to determine the time development of the particle distribution function. Finally, the plasmon‐plasmon coupling is included in the time development of the plasmon distribution.

ISSN:0031-9171    

DOI:10.1063/1.1691744

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Longitudinal waves were excited radially across a plasma column subjected to an axial magnetic field. A strip line placed externally to the column was the source of excitation. The wavelength and propagation direction were measured by a movable antenna immersed in the plasma. The measurements are compared with theory and with observations made with an externally situated receiving antenna. The following conclusions are drawn. (a) Contrary to the commonly accepted notion, the longitudinal waves are propagating rather than standing waves. The propagation is radial towards the axis of the plasma column. Since the waves are backward waves, the energy propagates radially outwards. (b) The internal and external measurements are related to good accuracy through the geometrical optics, “phase quantization” condition,∫ k dr ≈ 2m&pgr;, where k is the propagation constant, r is the radial coordinate, and m is an integer. The left‐hand side of the equation is deduced from measurements ofkmade with the movable antenna immersed in the plasma, and the right‐hand side of the equation is obtained from measurements of the signal received by the external antenna.

ISSN:0031-9171    

DOI:10.1063/1.1691745

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

It is shown that, if a longitudinal wave is excited in a collision‐free plasma and Landau‐damps away, and later a second wave is excited and also damps away, then a third wave will spontaneously appear in the plasma. This wave appears long after the first two waves have damped away at a time proportional to the interval between the first two waves, and is in that sense an echo. It is also shown that, if a wave is continuously excited at one point in a plasma and a second wave is continuously excited many Landau damping lengths from the first point, then a third wave will spontaneously appear many Landau damping lengths from the second point. Fundamentally, plasma wave echoes are possible because of the reversible nature of Landau damping. However, small‐angle Coulomb collisions are very effective in destroying the echo.

ISSN:0031-9171    

DOI:10.1063/1.1691746

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A simplified theoretical model for a phenomenon of fast randomization of an electron gas which was investigated experimentally is presented. It is assumed that a certain region in constricted electrical discharges, called “plasma sac” can become the siege of trapped electroacoustic waves generated by a beam‐plasma interaction. The interaction between those waves and the electron gas is treated by a pseudo‐collisional method leading to a generalization of Boltzmann'sH‐theorem. The velocity distribution, which is essentially Maxwellian with a significant deficiency in the fast electron tail, is deduced.

ISSN:0031-9171    

DOI:10.1063/1.1691747

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Longitudinal plane wave oscillations of electrons and ions described by the linearized Vlasov equation with no magnetic fields and coupled by Poisson's equation are examined for a wider class of distribution functions than previously analyzed. An expression is obtained for the time evolution of the electric field in terms of approximate wave contributions and a remainder. It is found that an electron plasma oscillation and an ion wave—either an ion acoustic wave or an ion plasma oscillation—are observable. For a short initial time interval coherent plasma oscillations are observable and persist if the ratio of Debye length to wavelength is small. For larger times, but not too large, ion waves are observable, and they persist for many periods if&rgr;−1 = {(T+/T−)[(k&lgr;−)2 + &ggr;0])12≪ 1, where&ggr;0is a positive constant of order unity determined by the electron distribution functions. The ion waves are thereafter exponentially damped into the incoherent background of the remaining contribution.

ISSN:0031-9171    

DOI:10.1063/1.1691749

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The propagation of ion‐acoustic waves in a weakly ionized, bounded plasma is investigated, typically with reference to discharge tubes, where a flow of plasma towards the walls is required to ensure the balance between volume ionization and surface recombination. A macroscopic description is used which accounts for effects of ion‐neutral collisions and finite ion temperature. Special attention is paid to the problem of the wave absorption at the plasma boundary. It results that the ion‐acoustic waves are strongly absorbed at the plasma boundary whenever the electrostatic boundary conditions require the formation of a space‐charge sheath near the walls (implying the existence of a transonic point of the plasma flow at the limit between the sheath and the plasma). The situation where no transonic point exists is also discussed.

ISSN:0031-9171    

DOI:10.1063/1.1691750

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

It has recently been discovered how to vary the electron temperature in a simple discharge‐tube plasma over large ranges in a controlled manner. Subsequent use of this technique to study the propagation characteristics of ion acoustic waves in the plasma, as a function of electron temperature, has made it possible to measure properties of both the waves and the plasma: (1) the theoretically predicted dependence of wave velocity on electron temperature has been verified; (2) good agreement was found between a strong damping of the waves occurring at low electron temperatures and a theoretically predicted Landau damping; and (3) an accurate means for measuring the plasma ion temperature has been found.

ISSN:0031-9171    

DOI:10.1063/1.1691751

出版商:AIP    

年代:1968

数据来源: AIP