Vacuum Spark Soft X-Ray Source


This page was begun on 16 January, 2012 and will be updated as the project progresses. Please use the Forum to ask questions and to provide feedback.


The vacuum spark is a plasma pinch discharge in the general category of z-pinches. My device is a relatively small scale vacuum spark apparatus with the energy source being several doorknob capacitors operating at up to about 80 kV.

The device consists of a tungsten anode electrode and a hollow cathode. Within the hollow cathode is a sliding spark trigger pin. After the triggering of the main discharge, the anode is bombarded by electrons thereby producing a burst of soft x-rays.

As is the case with the Mini-F plasma focus, I have used the work of S. Lee, C.S. Wong and others for this device. The presentation Research on Small Plasma Devices at University of Malaya by C.S. Wong includes photographs of a number of small vacuum spark devices (as well as other small scale pinch devices).

My Device

My current project is depicted in the illustration at the top of the page. It is built around an ISO63 cross. The high voltage insulator & feedthrough consists of a pyrex tube of 1.5 inches outside diameter with a central 3/8 inch inside diameter inner tube that supports the anode structure. The anode itself is a pure tungten pin, 3/32 inches in diameter. This was made from welding electrode stock. The cathode is a plate that is inserted into the opposing port. It has a conical hole. Behind the cathode plate is a sliding spark trigger that enters though the side of the cross.

The port on the cathode side will be equipped with any of several options. One is an x-ray spectrometer fashioned from BPX65 diodes. This is the same as what I am using on the Mini-F plasma focus. Alternatively, a mylar film may be placed on the port to pass x-rays into the room.

Vacuum is supplied by a Varian diffusion pump. Vacuum requirements are modest - 10-4 to 10-5 Torr are adequate.

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