1. Progress Report Nick Shipman - Thursday, 27 March 2014 1

2. Update I decided to rewrite the apparatus chapter and split some of it off to form a new chapter ‘Gap Measurment Techniques’ Downside I don’t have any more finished chapters, upside I have twice as many nearly finished chapters. It was Iaroslava’s last day tomorrow and the past two weeks I was obliged to spend more time helping in the lab then I would have liked. However some nice results came out of it which I may even include in the thesis.

3. Some recent plots included in the Apparatus re-write The power in the HRR circuits resistors and the current drawn form the resistor depends on the voltage, capacitance and pulse width. There are also power limitations which means at certain voltages we have to reduce the rep rate. These plots show the maximum save rep rate, as well as the power in the resistors and current drawn from the power supply at this rep rate. The capacitance of the FGS is much higher than in system I which means we have to reduce the rep rate at a lower voltage to stay within the power limitations. Exceeding these limitations would risk damage to the circuit.

4. Some recent plots included in the Apparatus re-write To study the effect of the pulse length on the BDR it was necessary to reduce the bleed resistance to make the voltage after the switch opens fall faster. If the bleed resistance is lower it dissipates more power for a given voltage. The choice was between 1 or 2 4k resistors and hence the power limit of the bleed resistance was half as big when using just one resistor. The graphs on the left show how the repetition rate varies with the voltage and pulse length. Although a 4k resistor would have given a faster fall time it was decided to use a 8k resistance so that we were not limited as much in repetition rate.

5. Pulse Width vs. BDR BDR [#BDs/pulse] Pulse Length us Defining Pulse Length at the 90% level Defining Pulse Length at the 95% level If these results prove to be repeatable they are quite remarkably close to the behavior observed in RF accelerating cavities. Despite the much longer pulse lengths and very different geometry. Before these experiments I was of the opinion that the BDR~t^6 scaling law observed in RF was somehow related to the number of RF cycles and we would therefore not see an effect in a DC experiment. This was a reasonable guess especially considering more than 90% of DC breakdowns happen right at the beginning of the pulse as opposed to in accelerating structures where they are more evenly spread.

6. Plan March Week4April Week 1April Week2April Week 3April Week 4May Week 1May Week 2May Week 3May Week 4 Introductioncomplete Theory50% Apparatus99% Gap Measurment60% ResultsAnalysis complete Magnetic field effect 50 % of Analysis completed Statistical Properties of BDs Analysis complete Summary and Conclusion not started I am now planning to have my draft finished by the end of May and I think this is realistic. Already by the end of next week it will look in a lot better shape as I should have 3 complete chapters. To make writing easier I am considering staying one more month in CERN until the end of May. This will allow me easier access to the data and analysis tools should I need them such as MATLAB and simulation suites including Maxwell and PSPICE in case I need to re- run any simulations to get the right plots.