HAPPEX Charge Asymmetry Feedback

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The HAPPEX DAQ is run to provide beam charge asymmetry feedback for the Polarized 3He experiments. This page will briefly describe the the system, and how to recover it if it does not work.

Introduction - The Feedback Loop

Feedback loop.png

Summary of the components (pink boxes):

  • Polarized Source - IA Cell

The electron beam is created by illuminating a GaAs Cathode with circularly polarized light. Before this light is circularly polarized (with a randomly flipped 30Hz Pockels Cell), the linearly polarized beam traverses through the "IA Cell". This system contains it's own Pockels Cell whose voltage is controlled at the same 30Hz random flip as the main Pockels Cell. It's purpose is to vary the intensity of the linearly polarized light, in a beam helicity correlated way. This provides the control to

  • Hall A - Beam Current Monitor
  • HAPPEX DAQ - Counting House Crate
  • Parity Analyzer (PAN) - compiled specifically for feedback

Summary of the communications (arrows)

  • CW Electron Beam
  • BCM Downconverter - TWINAX Cable
  • CODA - Event Transfer (ET)