Beam Charge Measurement for the g2p/GEp experiments

TL;DR

This paper details the calibration and performance of beam charge measurement systems used in g2p/GEp experiments with polarized targets, focusing on low-current measurement techniques to ensure accurate physics cross sections.

Contribution

It introduces a calibration procedure for BCMs and evaluates their performance at low beam currents in polarized target experiments.

Findings

Successful calibration of BCMs at low currents

Accurate charge measurement improves cross section calculations

Enhanced understanding of beam current monitoring in polarized experiments

Abstract

The g2p/GEp experiments used a solid NH3 polarized target, where the polarization of the target is sensitive to temperature and radiation. The beam current was limited to 5-100 nA during the experiment to avoid too much depolarization of target (The typical Hall A running condition for beam current is 1 uA to 100 uA). The measured charge was further used to get the accurate physics cross sections. New BCM (Beam Current Monitor) receivers and a DAQ system were used to measure the beam current at such a low current range. A tungsten calorimeter was used to calibrate the BCMs. This technical note summarizes the calibration procedure and the performance of the BCMs.