摘要:

Field reversed plasmas have been observed to spin up and develop a destructive rotatingm=2 instability. While the instability threshold has been reasonably well characterized, the cause of rotation remains obscure. Of the several mechanisms proposed, the following is treated; end shorting on open field lines spins up that portion of the plasma; viscous drag then spins up the plasma on closed field lines. Theoretical models are developed to describe these processes. The predicted behavior falls into three regimes. For low aspect ratio (≲2.8) the plasma is highly viscous, rotates as a rigid body, and spins up to instability in a few Alfve´n transit times. At intermediate aspect ratio (2.8 to 3.5) the plasma is weakly viscous; it reaches instability in the viscous transfer time which lengthens very rapidly for higher aspect ratio. At high aspect ratio (≳3.5 to 4) spin up is slower that the resistive decay of the plasma, and instability should not arise. Most recent experiments fall into the strongly viscous regime and correlate with its predicted characteristics. However, one series of experiments exhibited no apparent rotational instability, and also produced the large plasma radii characteristic of high aspect ratio. The present model in the high aspect ratio, weakly viscous regime is consistent with these observations.

ISSN:0031-9171    

DOI:10.1063/1.863363

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Analytical and numerical studies of an end‐plugged theta pinch are described. The analytical model treats the ablated plug plasma in the quasi‐static limit where radiation losses balance energy flowing from the main plasma. This model is used to calculate the enhancement in energy confinement due to an ablating end plug for various plug species. The numerical model employs a one‐dimensional, time‐dependent magnetohydro‐dynamic code. Results of calculations simulating the Scylla IV‐P end‐plugged theta pinch experiment are presented. The calculations achieve good agreement with the observed decay time of the energy line density. Moreover, the observed tendency toward longer decay times at lower atomic number is also predicted. However, certain notable discrepancies are found. For Si plugs, the calculations indicate a somewhat longer decay time than observed with SiO2plugs. In addition, an axial compression wave driven by plug ablation causes the calculated energy line density to rise after 15 to 20 &mgr;sec which was not observed in the experiments. This is believed to be a feature of the one radial cell model which forbids axial wave dispersion; such dispersion would tend to mute the appearance of such waves. For fusion reactor scale plasma, the calculations predict that higher atomic number leads to negligible enhancements in confinement time.

ISSN:0031-9171    

DOI:10.1063/1.863373

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The results are presented of a series of experiments investigating the mechanisms leading to the collective acceleration of protons occurring in electron beam propagation through evacuated drift tubes. Detailed measurements have been made of the electron and ion beam propagation and of the ion energy spectra. The results show that the acceleration cannot occur as a result of a beam head or deep potential well mechanism. It seems likely that the acceleration is due to the self‐excitation of a wave on the beam, possibly the electron‐ion two‐stream instability.

ISSN:0031-9171    

DOI:10.1063/1.863374

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The diocotron stability properties of a relativistic coaxial multi‐ring hollow electron beam are investigated using a macroscopic cold fluid description based on moment‐Maxwell equations. It is found that for a broad range of beam parameters and somewhat more general type beam profiles, the growth rate of instability has a sensitive dependence on fractional charge neutralization, relative position of the rings with conducting wall, and gap‐length of the rings. In the case of a sharp boundary density profile, the beam can easily be stabilized by a small fractional charge neutralization with appropriate gap‐length. The growth rate can be either enhanced or reduced depending on the position and gap‐length of the rings.

ISSN:0031-9171    

DOI:10.1063/1.863375

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The equation ∇×B−&lgr;B=0, where B is the magnetic field and &lgr; is constant, is solved analytically in toroidally curved cylindrical coordinates, assuming a large aspect ratio torus.

ISSN:0031-9171    

DOI:10.1063/1.863351

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The effect of a finite diffusion velocity on the stability of the resistive internal kink and reconnecting modes is investigated. It is shown that the diffusion velocity modifies the growth rate of only the second mode.

ISSN:0031-9171    

DOI:10.1063/1.863376

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A unified analytical model is presented for sinusoidal diverging nonlinear ion‐acoustic waves of plane, cylindrical, and spherical geometry. In contrast to plane waves, cylindrical and spherical waves do not show complete recurrence of the initial waveform.

ISSN:0031-9171    

DOI:10.1063/1.863377

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is shown that ion motion can significantly affect the magnetic field generated by an intense circularly polarized electromagnetic wave in a plasma. For extremely strong waves, the magnetic field induced by the electron current in an electron‐ion plasma can be nearly canceled by the ion current.

ISSN:0031-9171    

DOI:10.1063/1.863378

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Calculations of ion flux enhancement from overlap of many plasma‐channel‐transported beams onto inertial confinement fusion targets give factors of 10 with efficiencies around 85%. Scaling relations are presented for different beam parameters and overlap geometries.

ISSN:0031-9171    

DOI:10.1063/1.863379

出版商:AIP    

年代:1981

数据来源: AIP