Sheila, Georgia

 

Just an update: I’ve been working towards some scripts to measure the alpha, beta, beta_2, and gamma co-efficients of test masses using the optical lever. This is similar to the measurements Sheila has done longitudinally, see lho alog 38656. This measurement will give more information than the usual Veff measurements, which is one combination of these four parameters, and will help us localise charge (eventually) quadrant-by-quadrant. 

 

By driving different combinations of the signal electrodes and bias electrodes, with and without signal and bias offsets, we think we can work out all 4 parameters for pitch and yaw, helping us localise charge on the optic. We can drive these electrodes hard enough to see a signal on the optical lever. Stay tuned for an alog full of maths about how we calculate the parameters.

 

The scripts I’m working on are works in progress, and are not fit to be run at the moment, but reside in /userapps/sus/common/scripts/quad/opLevChargeMeasurements

 

I’ve been testing the scripts out on ETMY. Note: to avoid driving the LR quadrant and introducing coupling between pitch and yaw I’ve changed the EUL2ESD matrix. Normally this is:

 

P = sqrt(2) UL + sqrt(2) UR - sqrt(2) LL - sqrt(2) LR

Y = - sqrt(2) UL + sqrt(2) UR - sqrt(2) LL - sqrt(2) LR

 

I’ve made the LL and LR elements 0 for pitch, and the UR and LR elements 0 for yaw. I assume we'll want to leave it this way until the LR quadrant is fixed.