Table of Contents

Problem

Below is a sketch that Siqi made on the whiteboard about the setup. Here is my understanding of the problem (I'm not an expert in the field).

• The beam goes through the DMD
• it is then split
  • first view on the VCC - virtual cathode ?
  • second, after going through nonlinear cathode and its optics, on the YAG

The end goal is to shape and control the beam. To do this one needs to know what happens to the beam as it goes through the cathode.

The cathode creates a non linear gain map - some parts magnify, and some parts shrink. The problem is basically calibration, figuring out what the cathode does to the beam. You can't just let the whole beam through, you need to let a little bit of the beam through at a time and see what the cathode does by looking at the YAG.

• operators can control how big of a square to open up on the DMD to let beam go through.
• A scan across the DMD is just going row by row, opening a different square of DMD pixels to let beam go through.
• One want to measure two things
  • The location of the beam on the VCC
  • The charge of the beam on the YAG
• The charge will be the sum inside the box around the beem on the YAG, so you need to know location on YAG for this

For a given file, to accurately compute charge

• first subtract the background (upper row of above plot)
• Then figure out where the beam is for YAG (bottom row, when all DMD open to let beam through)
• when you sum charge in the YAG box, restrict to the region on the YAG open beam plot, 

Image Added

Screen Information

File 4 also contains the yag and vcc backgrounds, as well as shots where the entire beam is opened up (as opposed to just one location on the DMD). Here are those plots

Image Added

Notice the distortion on the yag. This is because the beam goes through the cathode and its nonlinear optics before showing up on the yag screen. 

Data

The page Accelerator Beam finding - Internal Notes talks about the data and code, page has restricted access.

...

• Files 1 and 2 have 142 samples. With file 4, the total number of 239 samples is.
• Each sample has a yag, vcc, and box for each - there are also backgrounds to subtract for file 4, and a oval like image of the entire beam region - one can use that  to narrow the search so as to not predict a box in a corner of the yag or vcc screen
  • File 4 also containts the bkg and beam shots above.
  • Files 1 and 2 already have the bkg subtracted.
• vcc values are in [0,255], and the boxed beam can get quite brite
• yag values go over 1000, I think, but the boxed value is always dim, like up to 14

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yag median+Guassian Blur