摘要:

Experiments are described in which shock speeds up to 1% of the speed of light were achieved in gaseous hydrogen or deuterium. Separation between the transverse shock wave and the drive current are clearly observed. The density and magnetic field shock compressions are measured and the post‐shock electron temperature, determined from plasma x‐ray bremsstrahlung spectra, is found to be about107 °K. Neutron emission was detected from shocks in deuterium. The axial electric field in the shock structure is measured and interpreted as resulting from a combination of Hall effect and ion displacement current.

ISSN:0031-9171    

DOI:10.1063/1.1693304

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The isothermal assumption for electrons is removed from the continuum theory of the electrostatic probe. Asymptotic analyses based upon small Debye length are developed for both cold and warm ions with an appropriate electron energy equation. The structure of the asymptotic expansion is essentially changed from that of the isothermal theory. In particular, the current‐voltage characteristic is expressed as a series in which the leading term, obtained under quasineutral approximation, is of the order of unity and the subsequent terms are small in the asymptotic sense. The results may be used to explain the discrepancies between the isothermal theory and some experimental results of Little and Waymouth.

ISSN:0031-9171    

DOI:10.1063/1.1693305

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A nonlocal theory for the low‐frequency trapped particle instability in toroidal systems has been developed in a model field. The stability of the trapped particle mode is studied by using normal mode analyses with radial boundary conditions. In the absence of magnetic shear, the finite‐orbit effect is shown to be incapable of stabilizing the mode; large magnetic shear is needed for stabilization. The ratio of the localization width of the mode to the characteristic density length is of the order of(&Lgr;/r;)1/2&egr;1/4(&Lgr; is the charactistic “banana” size, r is the characteristic density length, and&egr;is the aspect ratio). An estimate of the nonlinear diffusion coefficient for the mode is given.

ISSN:0031-9171    

DOI:10.1063/1.1693306

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The stability of a magnetic pulse with respect to ion acoustic‐electron drift waves is studied, using a realistic magnetic profile instead of the local approximation customarily analyzed. The stabilizing effect of nonlocal corrections is noted, and the condition for validity of local approximation in this case is obtained.

ISSN:0031-9171    

DOI:10.1063/1.1693307

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A relativistic version of the one‐dimensional cloud‐in‐cell model for plasma simulation is developed. The model is physically self‐consistent despite the omission of transverse, electromagnetic waves. The conditions for the onset of relativistic electrostatic instabilities between two electron beams and between two identical counterstreaming plasmas are derived for the case in which the one‐dimensional and three‐dimensional results are identical. In particular, the ion‐ion instability can occur only for extremely high electron temperatures. Collisional effects in the model are discussed. Supraluminous waves are shown to be generated both by collisional effects and by nonlinear interactions in unstable plasmas. The results of the simulation of the instabilities are consistent with the theory. With the exception of the behavior of vortexes in position‐momentum phase space, the relativistic results correspond reasonably well to the nonrelativistic ones.

ISSN:0031-9171    

DOI:10.1063/1.1693308

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A closed set of equations relating the macroscopic variables are derived from the linearized kinetic equations with a Bhatnagar‐Gross‐Krook collision term. The collisional fluid limit of these expressions are in complete agreement with the most exact magnetohydromagnetic equations, including viscosity. The collisionless fluid limit provides an extension of the Chew‐Goldberger‐Low equations, now valid when the diamagnetic velocity is comparable to the electric drift. The generalized equations may be used to investigate the transition between the weakly collisional condition, where resonant particle effects are important, and the strongly collisional condition where viscosity becomes dominant.

ISSN:0031-9171    

DOI:10.1063/1.1693309

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An expression for the equilibrium diffusion rate is derived using the generalized equations previously published. Different limiting forms of this expression are compared with the intermediate collisional and highly collisional results derived earlier. The validity of these results are found to be more restricted than previously assumed. To cover the range of experimental interest, two new limiting conditions are considered. In both these the ambipolar diffusion is generally comparable to the Pfirsch‐Schlu¨ter rate. The generalized expression allows the diffusion to be evaluated in the transition zones between the different regimes.

ISSN:0031-9171    

DOI:10.1063/1.1693310

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The spectrum of electrostatic potential fluctuations was measured with a capacitive probe in a steady‐state, turbulent plasma confined in a magnetic mirror geometry. The plasma conditions ranged over5×107≤ne≤5×108/cm3,8≤Te≤38eV,350≤Ti≤930eV, andBmax = 1.0 T. When oscillation peaks were absent, the amplitude spectrum of electrostatic potential fluctuations had a power‐law dependence on frequency of the form&thgr;=&thgr;0&ngr;−nover the range 0.2‐1.0 MHz. The value of the spectral indexndepended on the probe position in the magnetic field, and, at a given position, depended on the plasma characteristics. The spectral index was generally below the valuen = 2.5predicted by some turbulence theories formulated inkspace. Enhancement of the turbulent spectrum on the high‐frequency side of oscillation peaks suggests that the direction of net energy flow in the turbulent spectrum is from low frequencies to high frequencies in this plasma. The effects on the amplitude spectrum of a sinusoidal external modulation of the anode voltage were assessed over the range 0‐100 kHz. The spectra exhibited several mode coupling phenomena, including enhanced harmonics of the externally imposed frequency, and sideband modulation of plasma generated oscillation peaks. External excitation of the plasma at frequencies below 50 kHz resulted in only a small degree of ion heating.

ISSN:0031-9171    

DOI:10.1063/1.1693311

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Analysis of a low‐&bgr; axisymmetric toroidal plasma is reported. This predicts shock structure in the presence of resistivity and viscosity. A one‐fluid model is considered which includes the Hall terms in Ohm's law and gyroviscous corrections to the pressure tensor. In analyzing this behavior two orderings are used. For typical stellarator parameters, the first ordering (in which the mean free path is less than the connection length but greater than a critical value) leads to a stable rotational equilibrium with a positive potential on axis. In the second ordering the mean free path is less than this critical value and a shock develops toward the inside of the torus, leading to diffusion an order of magnitude larger than the Pfirsch‐Schlu¨ter value. A Korteweg‐de Vries equation with an added dissipation term due to parallel viscosity, governs the azimuthal density variation in the shock region. Agreement is found between theory and the results of a two‐dimensional computer simulation of a toroidal plasma.

ISSN:0031-9171    

DOI:10.1063/1.1693312

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The neutrons emitted by a plasma focus were analyzed by using a time‐of‐flight method. Flight paths as large as 80 m were used to obtain better than 10% energy resolution. The energy spectrum of neutrons from d—d reactions in the plasma focus shows a sharp onset with average maximum energies of 2.8 and 3.2 MeV in the radial and the axial directions, respectively. The average half‐width of the energy spectrum was 270 keV with a shot‐to‐shot variation between 150 and 400 keV. Simultaneous measurements in the axial and radial directions showed no appreciable difference in the half‐widths and thus indicated randomly oriented ion velocities in the plasma. A converging ion model is described which is found to be in agreement with the measured quantities.

ISSN:0031-9171    

DOI:10.1063/1.1693313

出版商:AIP    

年代:1971

数据来源: AIP