Experimental Investigation of Vacuum Breakdown Triggering Mechanisms in a DC Electrode System

Peacock, Ruth and Burt, Graeme (2023) Experimental Investigation of Vacuum Breakdown Triggering Mechanisms in a DC Electrode System. PhD thesis, Lancaster University.

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Abstract

This thesis describes the testing and results of the two pulsed DC large electrode systems at CERN, as part of a collaborations with the Compact Linear Collider (CLIC) and Linear Accelerator 4 (Linac 4) projects. The pulsed DC systems consist of two precision machined electrodes placed parallel to one another, with a gap between 60 μm and 100 μm, under high vacuum to observe vacuum breakdown triggering mechanisms and conditioning. Descriptions of the setup with be given, as well as changes to the electrode drawings to improve reliability of machining with a reduced electric field enhancement. Additionally, a description of a new method of conditioning through pulses rather than breakdowns will be discussed. The new conditioning method was used to condition several different materials, including, TiAl6V4, CuCr1Zr, Nb, Cu OFE, Ta, and AlMgSi1, and observations of the characteristics observed are given. This is followed by the same materials except AlMgSi1 being irradiated by a H- beam, to observe the effects of irradiation on the electric field holding capabilities and breakdown locations throughout conditioning. Measurements of the field emission current for each pair of electrodes tested was conducted, using a constant DC supply. Analysis of the results gives the field enhancement factor, as well as comparisons between materials, polarity, and irradiation effects. During field emission measurements an optical spectrometer was attached to one window. The results are presented for the materials that produced light, showing the correlation between the light intensity at different wavelengths, with the voltage and field emission current. This can also be correlated with possible causes of light that would occur during field emission. Additionally fast fluctuations in the field emission current were measured and possible interpretations with respect to mobile dislocations are given.