Resistive heating in Z-pinches

Summary form only given. Power balance in Z pinches, especially moderate-Z plasmas, tends to be difficult to reconcile in a conventional interpretation in which the predominant energy source is the conversion of plasma kinetic energy to internal energy. In this case Spitzer resistive heating is small when uniform current flow through the plasma is assumed. Anomalous resistivity via a source like the ion acoustic instability is usually small because of the low growth rates and the short time scales involved in the implosion and stagnation. This problem has been examined in the light of data recently obtained on Sandia´s Saturn accelerator. These experiments generally show that the total X-ray emission from the pinch exceeds the calculated kinetic energy delivered to the pinch. Also, time-resolved X-ray pinhole photographs have shown that significant additional X-ray energy is radiated in the highest energy photons after peak compression during an expansion phase of the pinch. These data suggest that sources of energy other than kinetic heating exist. While the value for Spitzer resistivity for moderate-Z plasmas is low, heating can be large if the current is confined to a small volume on the surface of the pinch determined by the plasma skin depth. The continued heating during the expansion phase could be due to increased resistive heating because of the higher currents generated by the plasma doing work on the external fields (or equivalently, flux conservation).