Physics requirements  mapping spec’s Strategy: analyze measurements to get field Mapping plan: where/how to map Engineering design: sensor, fixtures, DAQ Fitting the data: method, software Work plan: schedule, progress Q & A CLAS12 Torus Magnetic Field Mapping Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 1

People Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 2 Physicists: Mac Mestayer, Joseph Newton Hall B Engineers: Renuka Ghoshal, Ruben Fair, Orlando Pastor, Probir Ghoshal Accelerator: Joe Meyers Survey, DAQ: Kelly Tremblay, Mark Taylor Shift Personnel: … + collaboration

Momentum Resolution vs. P,  Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 3 1 % 0.3 % Resolution is better at smaller angles because B-field is higher. 0.3 % Best resolution ~ 0.3 %.

CLAS12 Torus Magnetic Field Mapping Physics Requirement Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 4

Strategy for Mapping and Fitting the CLAS12 Torus Magnetic Field Two types of distortions: 1.expected from design, (e.g. shrinkage at low temperature ) and 2.those due to small manufacturing differences (like one coil being shifted in z, or one coil not being wound as tight as another, etc.). Strategy to map and adjust the magnetic field: 1.use best estimate of coil dimensions to calculate the nominal field 2.calculate the error B-field, i.e.(B distorted - B nominal ), for various anticipated distortions due to manufacturing tolerances 3.after mapping, fit (B measured - B nominal ) to a sum of these error B-fields scaled by adjustable coefficients 4.calculate B-field tables using the distorted, displaced coils Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 5

% Change in B-field: plotted vs. radius coil stack too large by 2mm coil moved down, centered, up  2 mm increase in stack size can cause field distortions of up to a few parts per thousand  large radius surface of inner coil is most critical dimension Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 6 Effect of Distortion in Coil-Winding (one example)

Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 7 Need to know radius to ~ 0.1mm Map Field Near Coils  sensitive to distortions

Effect of Change in Coil Stack Height of 1 mm Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 8 ~ 18 Gauss change in field; ~ 0.1 % Measure 5cm steps in z

Establishing Magnetic Centerline Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 9 Magnetic field ~ radius 5 Gradient = 3 Gauss/mm at 5 cm  need to measure where B exceeds a few Gauss  need to measure B in bore at 5 cm or greater

How Are We Going to Map? Digital Voltage Meter Hall Probes in Sensor Block Three 1-dimensional probes measure ~ every 5cm in Z Measurement Tubes non-magnetic ~ 2” diameter Carbon Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 10 linear stage

Hall Probe Holder Z Y X Direction of movement of hall probe holder 3 single axis transverse hall probes, (orange dot indicates ‘sweet spot’) Hall probe holder 5 cm Hall Probe Holder Design Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 11

Hall Probe Holder: machined Delrin Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 12

Hall Probe Holder Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 13 3 Hall Probes: X, Y, Z All assembled in magnet measuring lab

Hub OOPS limits radial position Moved to 30cm radial location to no interfere with hub OOPS Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 14 Hall Probe Holder

Torus Mapper Prototype Test magnet field strength of ~2 Tesla enlarge gap to accommodate one measurement tube and assembly Procure and build prototype - sensor cylindrical sensor head containing three 1-dimensional Hall probes connection to translation rod electrical connections - tube tube assembly attachment and survey points - translation system - analysis and display software - control system: motion, data-taking runs, interlocks, Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 15 Operational and calibrated

Torus Mapper Prototype: Test Test operation of prototype Do all systems work? placement and survey rotating and moving of sensor signal readout under various conditions; noise measurement quick ‘real-time’ analysis of results Do procedures make sense? How long does a scan take? Verify reproducibility to better than 0.1% many scans, no changes changing step size changing position within magnet; removing, replacing changing orientation with respect to gravity Calibration of Hall probes Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 16

Fitting the Measurements Number of measurements – 6 (sectors) x 4 (x-y posn’s) x 3 (dim.) x 50 (z posn’s) = 3600 Method – fit measured deviation from ideal to adjustable parameters which scale tables of calculated deviations from ideal due to ‘unit distortions’ Number of parameters – 6 (coils) x [ 2 (movements) + 1 (expansion) ] = 18 Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 17 6 total; is 2 enough?

Definition of  2 sum over measurement points and dimensions table of measurements minus ‘ideals’ pre-calculated table of ideal field minus fields due to ‘unit distortions’ adjustable parameters Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 18

Torus Mapping Timelines Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 19 SepOctNovDecJanFebMarAprMayJunJul Conceptual Design Prototype: Sensor, Tube, Stage, Magnet Design Fixture Build Mapper Torus Ready for Installation Install, SurveyMapper Torus Commissioned Mapping Build Fitting Software; Verify Procedure

Physics Requirements : measure field to 0.1% accuracy at a radius known to 0.1mm Strategy:  where to map field : 4 x-y locations each sector, ~25 – 50 pts in z  measure actual, calculate deviation from ideal model  fit deviation from ideal to error tables : with adjustable strength Design and Prototyping  sensor built, ready for survey, prototype tests  fixtures designed, almost ready for procurement  analysis software: fitting shell built; testing with toy model Collaboration Involvement  join analysis effort; data-taking Summary Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 20

Back-up Slides Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 21

Mapping Measurements to a B-field Table (will it really work?) Build ROOT shell around Minuit fitting: done Build toy model of magnetic field: done Fill table (3600 pts.) with ideal fields Choose a distortion (coil 3 too big, e.g.) and fill distortion table Create an ‘error table’ by subtracting the tables Simulate measured data by ‘smearing’ distorted table Fit simulated data to scaled ‘error tables’  do you find that coil 3 is the (only) culprit?? Feb 23, 2016 CLAS12 Torus Magnetic Field Mapping Mac Mestayer 22