Preliminary Report on Solenoid Mapping

1. Preliminary Report on Solenoid Mapping • Field mapping completed in first week of August • Aim to measure field to 1 in 2000 (10 G in 2 T) • “Windmill” measuring machine with 4 arms • Driven by pneumatic motors • 12 Hall probes on each arm • 5 NMR probes, 4 permanent and one on machine • Field measured at 4 currents: 5000, 7000, 7730, 7850 A (twice at 7730 A) • Analysis at Manchester (Steve Snow and Paul Miyagawa), RAL (JCH) and CERN (Heidi Sandaker) John Hart RAL ATLAS physics meeting

2. Field Measuring Machine … undergoing tests in laboratory Hall probes mounted on 4 windmill arms Carriage Rails • Driven by pneumatic motors • Measurements scheduled for July/August John Hart RAL ATLAS physics meeting

3. Notes on the field mapping • Mapping originally scheduled for February, but slippage gave time for work on measuring machine and software • Accident after machine installed in solenoid necessitated re-survey and replacement of a few probes • 2 weeks set aside for measurement but further delays from cryogenics, CERN power failure … • Central NMR planned for normalisation failed • Normalise to average of Hall probes • Probe calibration to ~1 G up to 1.5 T but only ~10 G at higher fields • Hysteresis minimal, not more than a few gauss difference in cycling field • Solenoid current stable to within less than 0.1 A • Some problem with machine jamming near ends of solenoid • Aimed for a series of coarse scans rather than a few fine scans John Hart RAL ATLAS physics meeting

4. Points measured at 7730 A John Hart RAL ATLAS physics meeting

5. Analysis of the mapping data • Measuring machine output converted to Bz, Br and Bphi (including temperature correction) using calibration results • Need to correct for probe alignment errors (~1 mrad) and normalisation • Apply corrections from survey measurements including measuring arm axis directions • Further corrections for exact probe positions, skew in carriage positioning, … • Check consistency of the measurements • Combine data and perform geometrical or Fourier-Bessel fit • Generate field map for ATLAS analysis John Hart RAL ATLAS physics meeting

6. Plane zero scans • Measuring machine positioned so that each arm in turn is at z=0 and measurements made for 16 values of phi. • Possible to check agreement between corresponding probes on each arm • After corrections, differences are less than 5 G, often less than 2 G • Scan data from 2 August but probe alignments from 7 August, so evidence for stability in alignments. • Axis alignments from data (relative to field axis) agree with survey measurements (in IWV coordinates), so conclude field is parallel with IWV axis (to within ~0.2 mrad) John Hart RAL ATLAS physics meeting

7. Plane zero scans Br for outermost probes (12,24,36 & 48) versus phi John Hart RAL ATLAS physics meeting

8. Plane zero scans Bphi for outermost probes (12,24,36 & 48) versus phi John Hart RAL ATLAS physics meeting

9. Plane zero scans |B| for outermost probes (12,24,36 & 48) versus phi - structure not expected from “realistic” model John Hart RAL ATLAS physics meeting

10. Fine scan in phi Bphi for 3 outermost probes on arm 3 versus phi – after subtraction of return conductor field John Hart RAL ATLAS physics meeting

11. Plans • Continue checks on consistency of measurements: • between measurements (including different probes and different currents) • with Maxwell’s equations (using Fourier Bessel fits) • with geometrical model • Develop software to process measurements on unequally spaced z planes • Combine measurements and make a best fit (or fits) to the field • Generate a field map for ATLAS physics John Hart RAL ATLAS physics meeting

12. Conclusions The field mapping was completed successfully despite various difficulties Preliminary results indicate that a field map accurate to 1 in 2000 is possible Further work is required to understand the measured field and generate the map John Hart RAL ATLAS physics meeting