S. Hamasaki

Self‐Consistent Calculation of an Explosive Instability

The effect of an explosive instability on the plasma distribution functions is calculated for a specific initial distribution. It is found that this change in the plasma distribution (a) limits the possible level of field energy and (b) greatly increases the time required for the field to approach this limit compared with the explosion time calculated by ignoring the change in the distribution.

Stable sheath thickness in collisionless high-beta plasmas

Fluid-numerical studies have been carried out to investigate the scaling of the stable magnetic sheath thickness ΔLs with β, Te/Ti, n0, etc., in a collisionless finite-β plasma column. The system is initially close to a two-fluid equilibrium with sheath width ΔL sufficiently narrow for the azimuthal current to trigger various cross-field instabilities (ion acoustic, modified two-stream, Buneman). The enhanced field fluctuations in the sheath region, in addition to heating the plasma locally, leads to a decrease in azimuthal current and a corresponding increase in sheath width to some stable value ΔLs, achieved as the system stabilizes and the field level saturates. The final sheath width in the numerical studies agrees well with the theoretical estimate.

Fluid-numerical studies of high-density theta-pinch implosion including classical and anomalous transport processes

For parameters appropriate to high-density pinch experiments (ne 1014 cm−3) it is shown that both classical transport processes and anomalous transport processes can play an important role during the implosion. The fluid-numerical model of Liewer and Krall has been modified and extended to include (in addition to turbulent transport) the effects of classical transport (e.g. frictional force, thermal force, heat conduction, heat convection, resistive heating and thermalization), as well as the effects of ionization, neutral-particle diffusion and charge exchange. Numerical studies of the early and intermediate stages of implosion are presented for parameters appropriate to Scylla 1-B and Scyllac. It is found that the relative importance of the various transport processes depends in detail on radial location, initial ionization level, bias field, etc. As a general remark, however, anomalous transport processes tend to dominate in the sheath region and behind the piston (where the current and temperature are relatively high), whereas classical transport processes are important in front of the piston (where the density is high and the temperature is relatively low). Moreover, for sufficiently large initial neutral density, the effects of charge exchange, neutral-particle diffusion, and ionization, are found to be significant during the implosion.

Calculation of Anomalous Resistance

The time development of a one‐dimensional electron‐positron plasma subjected to a weak applied electric field, E0 = const, is calculated through the quasilinear equations. The results are in good qualitative agreement with the computer simulation experiments of Boris et al.