Magnet Measurement for the Hall A Compton Dipole

1. Magnet Measurementfor the Hall A Compton Dipole Ken Baggett baggett@jlab.org

2. Measurement System Quality • The stretched wire measurement system utilizes hardware that are “industry standard” for the magnet measurement “world” • Stretched wire: Newport controllers • Positioning accuracy: 0.5μM • Voltage reading: HP3458A digital voltmeter with up to 100,000 point memory buffer. • dcV accuracy up to 8ppm • Power supplies: Danfysik or locally utilized powering system • 10 ppm stability • The system utilizes cross-checks to a stepper system to validate ∫Bdl: • Positioning: • Actual position is checked against set position and rotary encoder and calibrated using interferometer. • Hall probes: • NMR probes will be used on regular basis to accurately calibrate the Hall probe field strength curve. • Power supplies: • Currents checked with transducers Component quality, cross-checks, and process tests provide a high degree of confidence in the system’s performance.

3. MMF Measurement Systems SW System Rotating Coil System 3m Stepper Stand 5.5m Stepper Stand

4. Compton Mapping • Measurements were taken in the Hall A line using the stretched wire measurement system and the power supply used to power the magnet in the hall. • Testing was done to verify repeatability of the stretched wire system in situ. • SW measurements are sensitive to vibration and wind. • Results show acceptable performance based on the requirements

5. Compton Mapping • Both shim plates show increase in BL • Mapping along hysteresis curve shows that previous Saclay map used a “top-down” approach • “top-down” agreement ~0.2% • Differences possibly tied to different length mapping coverage.

6. Questions?

7. SW Theory