Positive polarity x-pinch operation

Abstract

Summary form only given. We present here the results of a series of experiments comparing the operation of an X-pinch in positive and negative polarity. Of particular interest are the X-ray yield, timing, radiating spot size, and the number of radiating spots in a given X-pinch. Conventionally, an X-pinch is operated in negative polarity resulting in electric field lines that terminate on the wires. This choice of polarity for the generator is due to the fact that breakdown in these machines is easier to prevent when they are operated in negative polarity. Previous experiments involving single wire explosions at low current (1-5 kA) have shown that more energy can be deposited in the wire cores when they are driven in positive as opposed to negative polarity. These results raised the question of what happens when pinch-type experiments are driven in positive polarity. Recently, it has become possible to use the 450 kA XP pulser at Cornell to drive X-pinches in positive polarity. The positive polarity condition is established by inserting a convolute before the load and this results in electric field lines that originate on the wires of the X-pinch. This arrangement added complexity and inductance to the positive polarity shots, making it difficult to directly compare results from positive and negative shots. More recently, the entire pulser was switched to positive polarity. This allows a more direct comparison between positive and negative polarity X-pinch operation