1 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Title Field maps of the U17 PS magnet Alexander ASKLÖV Linköping University Régis Chritin CERN

2 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland PS extraction region adaptation needed for the LHC  New current operation → ejection unit must be better known  Effects of the metallic shims on ejected beam and circulating beam  Access limitation → new bench developed Alternated Gradient principle  Combined function units (Focusing and Defocusing)  C shaped magnets  10 blocks assembled, laminated  total geometrical length = 4260 mm U17 PS magnet

3 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland U17 magnet different coil schematics Main coil Pole face windings (pfw) Figure-of-eight loop Used to adjust the Tunes and Chromaticities (sextupolar component) modified by saturation Used to change the Tune (quadrupolar component) without affecting the curvature (integrated bending field) Combined function magnet Main coil Defocusing (5 blocks) Focusing (5 blocks) Figure of eight loop Pole face windings

4 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland PFW configuration To create pure quadrupole on hyperbolic profile: To create pure sextupole on hyperbolic profile: Windings configuration and field component: per pole = equation of equipotential

5 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Currents IpI8IpfwFIpfwD Cycle Test2500 A--- Cycle E669.2 A--- Cycle C A A200.7 A99.75 A Cycle LHC A A206.7 A86.9 A

6 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Measurement techniques 2D Field mapping Hall probes  KSY44 (Siemens)  Semiconductor mono-crystalline GaAs  Low temperature dependency β = %/°C  Hall current 3mA.  High sensitivity 200 V/A/T gives 600 mV/T  Low noise, less than 0.2 gauss (time span 2-20min)  Tiny active surface, mm 2  Resistance - Each probe: about 900 ohm at 1 T - 11 probes connected in series - Vary with induction and thus also the Hall current

7 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland - 11 Hall probes measured once during a power cycle → 481 ms for a scanning ms Flat-top → magnetic field not constant due to Eddy Current - 1 Hall probe measured 3 times → Eddy Current effects correction 11 Hall probes (calibrated in their fixed position) 116 mm 3 thermistors 19 mm Hall probes assembly

8 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Magnetic distances measurements With the PS magnet we can measure easily the individual magnetic distances between the probes with good precision. - Magnet gradient = A → small probe displacement = significant field change - Heidenhain ruler → precise measurement head displacement (micron resolution)

9 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Wanted precision Better than 1 per mille (for the induction B)  Absolute error smaller than 10 Gauss (Nominal field = 1.2 tesla (26 GeV)) Gradient 5.2 tesla/m  Position precision of 0.1 mm Other parameters  Hall current, 4 pulsed power currents, temperature, time evolution, measurement equipment (positioning errors) The whole installation 7 m Magnetic measurement stand which may be used to map ANY long magnet (up to 6.5 m) with closed gap (34 mm min).

10 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Bench synoptic diagram

11 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Kevlar thread Encoder Maxon motor Rubber wheel Sandpaper Molybdenum wheel Displacement system -Conceived to be as temperature independent as possible -Calibrated with respect to the molybdenum wheel radius -System based on a 7 meters long straight plastic arm -Movement regulated by the position encoder

12 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Procedure Array of 11 Hall probes  Scan (HP34970A + module 34901A multiplexer)  37 ms between each Hall probe measurement  3 thermistors for temperature compensation Steps  1 cm in longitudinal direction  Displacement precision. Kevlar® (-2 ppm/K) thread (diam. 0.6 mm) and Molybdenum wheel (+5 ppm/K). ROD 450 Encoder. Maxon motor DC.  500 steps + 4 more transversal positions (5 x 10 cm)  Total map with around points Relative changes  with and without magnetic shims to know their influences ® Dupont de Nemours

13 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Temperature corrections for the probes  Using β = %/°C (linear) Hall current corrections  Using linear correction. Hall probe calibration  15 degree polynomial as a function of the Hall tension.  Real magnetic distance between each Hall probe Position correction of the guiding rail  Using laser tracker measurements Time evolution corrections (mainly due to eddy currents)  Using a second order approximation function for correction  One probe measured three times on the flat top: in the beginning, the middle and the end.  For each longitudinal position Corrections applied

14 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Position measurements Position corrections approximating by linear lines the non rectitude of the guiding rail. After shims installation Made with a Laser Tracker system Rail movements Position reproducibility

15 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Field integral under new LHC conditions For consecutive measurements: 6*10 -5  No movement of the rail  No calibration deviation Mean absolute relative difference between first and final measurements are 5*10 -4  Rail movements during mechanical manipulations on the magnet  Long term calibration deviation Rem: the two longitudinal extremities, where the field drops quickly are neglected. The precision of the longitudinal coordinate (z) is too bad here (slipping checked with telescope < 0.4 mm). New PFW validation Maximum position difference between old and new PFW < 0.5 mm Magnetic shims (each block gap = 34 mm) Different radial positions between simulations and the physical installation: 198 gauss field drop instead of 105 gauss estimated. Results

16 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland With shims Magnetic shims  homogenize the field by shielding the ejected beam from a non linear fringe field  different radial position of the five different shims Shims Magnet blocks ← Focusing side with and without shims

17 / 17 Author CERN – Geneva – CH 14th International Magnetic Measurement Workshop September 2005, Geneva, Switzerland Future New field maps of U17 with 4 new PFW power supplies instead of 2, when narrow sides and wide sides will be powered independently. Use the bench for magnets with no lateral access (6.2 meter long SPS dipoles – magnets with small gaps) Verify measured B train in the PS  Strong Eddy currents at the end blocks, which are not taken into account in the actual B train coils located near the central blocks of the reference magnet.  Coils measuring the full integral, seeing the whole eddy current picture. Not very sensitive to transversal displacement (F and D halves compensate each other), but very sensitive to any yaw-angle though Thesis report on the web (  EDMS document  EDMS seminaire technique Measurement data  G:\Divisions\AT\Groups\MTM\MTM-RM\Technical_Students\AlexanderAsklov\Measure Data _____________________ P+ P+ ejected