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

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