ISSN:0031-9171    

DOI:10.1063/1.1711085

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

In the absence of collisions one must attribute the interaction between plasmas of different speeds in a shock front to collective mechanisms of energy and momentum transfer, such as growing plasma oscillations, ion waves, hydromagnetic waves, etc. Numerical one‐dimensional plasma models have produced evidence that nonlinear wave interaction provides an efficient alternative to collisions for creating shock fronts between two interpenetrating streams of noncolliding particles and, specifically, that the conservation of entropy normally associated with collision‐free conditions will, in a practical sense, be violated.

ISSN:0031-9171    

DOI:10.1063/1.1711088

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An adiabatic two‐fluid model is used to discuss generalized solutions for the structure of a plane bounded current sheet in a plasma. The current sheet is advancing in a region with no magnetic field. Numerical results for time‐independent solutions are given for different values of the ratio of the velocity of the sheet to the Alfve´n velocity referred to the magnetic field at a large distance behind the sheet.

ISSN:0031-9171    

DOI:10.1063/1.1711096

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A parametric study of the speeds of the current sheet and center‐of‐gravity of current in a magnetic annular shock tube has been carried out. The parameters varied include: (1) the drive current, (2) the polarity of the inner electrode, (3) the gas pressure, (4) the nature of the gas, (5) the radius of the inner electrode and (6) the material of the inner electrode. The most interesting result of the investigation was the observation of limiting speeds for the current sheet and center‐of‐gravity of current of approximately 8 cm/&mgr;sec and 3 cm/&mgr;sec, respectively. These speeds were not exceeded even under conditions where the magnetic pressure exceeded the dynamic pressure by a factor of 10. The most probable explanation of the limiting speed is that it is due to the inertial drag of material ablated from the insulator at the driver end of the shock tube.

ISSN:0031-9171    

DOI:10.1063/1.1711084

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The amount of deuterium gas admitted to a short center electrode (1 cm) coaxial plasma gun delineates two regions of operation, depending on whether the gas is localized near the inlet port or allowed to diffuse throughout the gun length. In the former, fast deuterium ions with energy in excess of the applied voltage (V0= 15 kV) emerge from the gun muzzle whereas in the latter, the accelerated plasma which initially starts at the breech end reaches an axial velocity of ∼2.5 × 107cm/sec at the muzzle end and forms a high‐density plasma focus on the axis in front of the central electrode. Neutron measurements show that this dense plasma is not in contact with the electrode and is most probably stagnated by the high ambient gas pressure downstream. Particle momentum analysis of the fast ion (>V0) distribution and neutron measurements downstream of the gun suggest two accelerated groups of fast ions, (1) a group of ∼1016particles which diverge from the gun muzzle and (2) a group of ∼1014particles which stream primarily along the axis with a radial distribution of ∼3 cm width. Multiple probes (B&thgr;) show an asymmetric angular distribution of the discharge current that varies as a function of time during a given discharge. A sharp break in the total gas current is accompanied by large inductive voltages. In the high‐energy mode, inductive voltages up to 7V0have been recorded at the breech end.

ISSN:0031-9171    

DOI:10.1063/1.1711086

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Photographic evidence is presented for the presence of an azimuthal component of the plasmoid motion in a coaxial source of small aspect ratio when operated with an appliedBzfield comparable in magnitude to the mean, self‐inducedB&thgr;field. The series of displaced images obtained suggests that the rotation is of the correct sense, and that restrikes of the source rotate in alternate directions with the current reversal in the source every half‐wave. Photographs taken without bias field confirm the fact that the plasmoid does not form a continuous torus, and the theoretical consequences of this upon the simple hydromagnetic model are examined. This model is used also to derive an approximate equation of azimuthal motion which predicts an amount of rotation about three times larger than that observed. The amount of rotation does, nevertheless, scale with the bias field strength, as predicted by the model.

ISSN:0031-9171    

DOI:10.1063/1.1711087

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An experimental study of the acceleration of plasma between two coaxial electrodes is described. A high current radial discharge is obtained that is highly reproducible and axisymmetric. Particular attention has been given to the study of current distribution in the plasma. It has been found that the current layer has a complicated conical structure exhibiting closed current loops in the plasma. No pressure wave propagating in front of the current layer has been observed.

ISSN:0031-9171    

DOI:10.1063/1.1711089

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An experimental study of the plasma leaving a coaxial gun is described. The plasma shows a conical shape with a central axial pinch. When a radial magnetic field is applied at the muzzle of the gun, magnetized plasma rings are formed. Under certain conditions the central pinch shows a helical instability, resulting in a considerable increase of the poloidal magnetic flux in the plasma rings. Different types of discharges are described, associated with the occurrence of a ``short‐circuit'' in the gun. During the decay of the plasma, magnetoacoustic oscillations are observed.

ISSN:0031-9171    

DOI:10.1063/1.1711090

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A coaxial plasma gun experiment is described. The gun has an azimuthal bias magnetic field, which is strong compared to the field from the discharge current. The discharge voltage is shown to depend linearly on the bias field, thus defining a velocity that is found to be almost independent of the pressure and the discharge current. This velocity is close to the ``critical velocity'' which has been found in rotating‐plasma experiments. The velocity of the current layer is also measured; it is always smaller than or equal to the critical velocity and it decreases with increasing pressure and decreasing magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1711091

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The current layer formed in a coaxial pulsed plasma accelerator has been examined with magnetic and electric field probes. The mappings ofEandBindicate that if electrons are assumed to carry the plasma conduction current, the advancing current sheet cannot act as an impermeable piston; rather, it has the character of a strong ionizing shock which imparts some forward momentum to the gas, but does not bring plasma up to its own speed.

ISSN:0031-9171    

DOI:10.1063/1.1711092

出版商:AIP    

年代:1964

数据来源: AIP