The Chunk Code: HV Stability During an EDM Simulation

This Weekly Win is a celebration of my high voltage ramp test analysis suite, AKA Chunk Code. Let me break this down into ‘chunks,’ if you will:

Here is a plot of a high voltage ramp test the Spinlab RaEDM crew performed on 7-5-2017. The ramp test simulates the conditions that the electrodes will be subjected to during a real permanent EDM experiment. A high voltage square wave signal is applied to a pair of Niobium electrodes for a period of about 30 minutes. Every minute the voltage signal flips from a LO value—0 V—to a HI value—in this case 21 kV—and vice versa.

The Chunk Code scans the voltages over the duration of the test and automatically divides the LO and HI voltages into bins. Below I show a plot of the Chunk Code’s ability to distinguish between LO and HI voltages. Notice that the Chunk Code does not include the transient, or ‘in-between’ voltages that show up while the power supply is switching from LO to HI or HI to  LO. The Chunk Code is too smart to be fooled by such parlor tricks. The first and last few sets, or ‘chunks’, of code are ignored intentionally.

Once the HI and LO data points are sorted, each 60-second bin is condensed into singular “chunks.” The chunks are weighted averages. Finally, the Chunk Code computes weighted averages and standard deviations of the set of HI chunks and LO chunks.

In addition to high voltage parameters, these computations are carried through for current leaking between the 2 electrodes. The parameters reported by the Chunk Code help us analyze the stability of high voltage and leakage current over the course of the ramp test. In the graph below, I’ve plotted leakage current standard deviation against chunk # for both HI and LO chunks. We can see in this ramp test that the leakage current is on the order of 10 pA and does not appear to depend on the voltage. -RR