CLAS12 Torus Magnetic Field Mapping - qualitative look at the field distribution How well do we need to know the B-field? - momentum resolution with ideal torus What are the effects of construction inaccuracies? - misplacement of coils  distortion of Bfield How can we measure the distortions? - measure distortion field know coil position calculate true field I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Credit for this idea goes to Bernhard Mecking Jan. 7, 2013 CLAS12 Torus B-field Distortions

Where are the Strictest Tracking Requirements? Here I show the trajectory* of an electron (p = 10.1 GeV/c, q = 7o) - elastic scattering from 11 GeV beam (highest momentum particle at 7o ) fractional dp/p most important at high momentum radius ~ 42 cm * Note: plot courtesy of ced (Dave Heddle) I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

CLAS12 Tracking Resolution Momentum Resolution: Ideal B-Field DC resolution ~ 300 mm Ideal DC alignment Best at small theta highest B-field dp/p Goal: ~ 0.3%   Simulation & Reconstruction 10/30/2008 S.Procureur

Torus Coil Dimensional Tolerances Most critical point for tracking Radius ~ 50 cm Most critical dimension Large radius of inner coil Aug. 12, 2014 CLAS12 Torus B-field Distortions

Torus Mapping Location Magnetic mapping Points Radius = 50 cm, 100 cm Angle = -15, 0, 15o     measure B-field to 0.1% need to measure radius to 0.1% 0.5 mm at 50 cm Aug. 12, 2014 CLAS12 Torus B-field Distortions

Torus Magnetic Mapping vs. Z Measurement Tubes non-magnetic metal ~ 1” diameter Rotating Coil ~ 2.5 X 2.5 cm 100 turns, 10 Hz  1V measure ~ every 5cm in Z Digital Voltage Integrator   Jan. 7, 2013 CLAS12 Torus B-field Distortions

Torus Mapping: Next Steps need very good survey and good mapping accelerator group is currently developing a mapping device similar to what we need set up meeting with Ken Bagget, Joe Meyers (accelerator mag-mapping) Chris Curtis (head of metrology) Hall B representation Jan. 7, 2013 CLAS12 Torus B-field Distortions

Magnetic Field Change in Mid-plane % Change in B-field: plotted vs. radius coil stack too large by 2mm coil moved down, centered, up 2 mm increase in stack size ok if coil is moved inward to compensate large radius surface of inner coil is most critical dimension survey of total stack height important adjust (shim) to compensate I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

Effect of Change in Coil Stack Height of 1 mm ~ 18 Gauss change in field; ~ 0.1 % Aug. 12, 2014 CLAS12 Torus B-field Distortions

Effect of Coil Motion in Bore Jan. 7, 2013 CLAS12 Torus B-field Distortions

CLAS12 Torus B-field Distortions Recommendations Torus Construction - concentrate on critical dimensions radial placement: < 1 mm out-of-plane: < 1cm (preliminary) Plan a Magnetic Mapping Strategy - measure distortion field in bore for radial displacement - sample points in fiducial area?  measure coil displacements  calculate true field I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

CLAS12 Torus Magnetic Field Mapping Mac Mestayer I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which causes shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature, and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error on the calculated momentum. Jan. 7, 2013 CLAS12 Torus B-field Distortions

Calculations using “RADIA” This field map was calculated by Burin Asavapibhop using the program “RADIA” * and a description of the coils as four straight lines and four circular arcs *(supplied by Lionel Quettier) Preliminary (received Jan.2) I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

CLAS12 Torus B-field Distortions Goal: ≤ 0.2% dB/B at R = 40 cm Coil Inner Radial position tolerance ~ 0.5 mm Aug. 12, 2014 CLAS12 Torus B-field Distortions

Ideal Torus Magnetic Field This field map was calculated with nominal geometry. beam direction I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

Distortion Calculation using RADIA Coil moved radially by 2 mm Field changes by ~ 1% at 42 cm (need a better graph) - agrees roughly with my calculation I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions

Magnetic Field Change in Bore Radial component of the B-field measured at radii = 4, 2, 0 cm Black: ideal (no offset) Light: one coil offset 2mm (rad) 40 Gauss dipole field on axis azimuth determines which coil I am going to outline a strategy for dealing with non-ideal torus geometry. The non-ideal geometry results in a non-ideal magnetic field which in turn results in shifts in track parameters; particularly the momentum. This is easy to see: if you reconstruct a track to obtain its emission angles (phi and theta) and its curvature and you multiply the inverse curvature (“stiffness”) by the integral B-dl, you obtain the momentum. If you make a 1% mistake on the integral B-dl you have a 1% error Jan. 7, 2013 CLAS12 Torus B-field Distortions