1. 5 September 2006 John Hart RAL ATLAS physics meeting 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)

2. 5 September 2006 John Hart RAL ATLAS physics meeting 2 Field Measuring Machine … undergoing tests in laboratory Carriage Hall probes mounted on 4 windmill arms Rails Driven by pneumatic motors Measurements scheduled for July/August

3. 5 September 2006 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

4. 5 September 2006 John Hart RAL ATLAS physics meeting 4 Points measured at 7730 A

5. 5 September 2006 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

6. 5 September 2006 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)

7. 5 September 2006 John Hart RAL ATLAS physics meeting 7 Plane zero scans Br for outermost probes (12,24,36 & 48) versus phi

8. 5 September 2006 John Hart RAL ATLAS physics meeting 8 Plane zero scans Bphi for outermost probes (12,24,36 & 48) versus phi

9. 5 September 2006 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

10. 5 September 2006 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

11. 5 September 2006 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

12. 5 September 2006 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