Study of explosive electron emission from a pin cathode using high resolution point-projection x-ray radiography

Summary form only given. Explosive electron emission (EE) is well-known phenomenon widely used in high-current electronics [1]. Most theories of EE are based on mechanism of cathode flares development after explosion of metal micropins on the cathode surface [2]. It was shown that the EE have a complicated inhomogeneous spatial and temporal structure, but experimental methods at that time were incapable of revealing the internal structure of the flame and could not adequately explain the processes occurring during pin explosion. The physical state of the pin material, the spatial structure of the flame and its origin are still a matter of conjecture. In this work we used high-resolution point projection x-ray radiography [3] with Hybrid X-pinch (HXP) as the source of radiation [4] to directly observe pin explosion in the high-current diode. Pins made from thin (10-25) Cu or Mo wires were soldered to the cathode of the diode placed in return current circuit of HXP in BIN pulser (250 kA current, 100 ns risetime). Radiograph images with x7.4 magnification were recorded on the Kodak DR film with 12.5 μm Ti filter. Pin length and pin-anode gap were varied in wide range. The diode current and voltage were measured. In experiments with small pin-anode gap (0.1-1 mm) development of the expanded dense core of the pin wire was observed except pin tip with length 100-200 μm. In experiments with bigger gap there was no visible wire core expansion within spatial resolution of the experimental technique (2 μm).