Magnet Measurementfor the Hall A Compton Dipole

Ken Baggett

baggett@jlab.org

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.

Rotating Coil System

SW System

5.5m Stepper Stand 3m Stepper Stand

MMF Measurement Systems

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

100 150 200 250 300 350 400-0.20%

-0.10%

0.00%

0.10%

0.20%

Measurement RepeatabilityHall A Compton (in situ)

Current (A)

Dif

fere

nce

Bet

wee

n R

uns

(%)

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.

50 100 150 200 250 300 350 400-1.00%

-0.50%

0.00%

0.50%

1.00%New Maps vs. Saclay Map (no shim)

top down hystbottom up hyst

Current (A)

BL

Dif

fere

nce

(%)

0 50 100 150 200 250 300 350 400 4500.00%

0.20%

0.40%

0.60%

0.80%

1.00%

1.20%

Shimmed BL differences from No Shim

Short Shim

Long Shim

Current (A)

Dif

fere

nce

(%)

Questions?

SW Theory