Analysis of rod-pinch-like radiography sources on a compact pulsed power generator

Abstract

Summary form only given. Radiography sources driven by a compact 800-kV, 7-kV pulsed power generator (the Hybrid Radiation Source) are analyzed with a rod-pinch diode model. The diode consists of a small diameter tungsten rod anode (1 to 4 mm diam) protruding through an annular stainless steel cathode. The rod-pinch model is applied to these diodes to understand the diode physics and to optimize radiographic performance. The measured diode voltage is used in the rod-pinch model to calculate the diode current. The formation and expansion of both cathode and anode plasma is included in the model. These diodes operate in the space-charge-limited (SCL) regime and do not achieve critical current. For a 4-mm diam anode, the model current fits the measured diode current for reasonable values of the cathode and anode plasma turn-on times, development times, and expansion velocities. The cathode plasma formation and ions from plasma drive the diode into a bipolar SCL mode at low impedance (<50 /spl Omega/) loading down the generator and leading to low voltage late in the pulse. For a 1-mm diam anode, the current approaches critical current near peak current, but not transition into the magnetically-limited regime. In the model. larger anode velocities (1.8-3.0 cm//spl mu/s) are required to fit the measured current late in time. However, heating the anode to 370/spl deg/C prior to the shot leads to smaller anode expansion velocities (/spl les/1 cm//spl mu/s) and increase the impedance lifetime.