ALICE Magnets Ben Shepherd MaRS Group ASTeC STFC Daresbury Laboratory

Overview Magnet settings table Calibration / field maps for energy measurements Degaussing Controls Online field measurements

ALICE Magnets 66 magnets – a combination of new magnets (Danfysik) and some donated by Jefferson Lab Qty. Quadrupoles4317 from JLab, 26 new Sextupoles44 new Dipoles1910 from JLab, 9 new Magnet Total6627 from JLab, 42 new + air core magnets (solenoids, correctors) QD DA QA DD S S S S QA QD QE

Magnet Table Hall probe and integrating coil tests have been carried out on all the new magnets Field map produced for one of each type of the JLab magnets Results summarised in a table relating model magnet strengths to required currents Magnet_table Magnet_table

Magnetic hysteresis At the low fields used in these magnets, hysteresis can have an effect The field produced by a magnet will be slightly different depending on whether the current is being increased or decreased current field e.g. for INJ-MAG-DIP-01 (field directly measured): typical difference is about 8G (1% of nominal field) 0.3° change in angle: 7mm at the OTR screen The PSUs in use do not have the capability to bring the magnets to saturation For a reproducible field: Always increase the current If you need to reduce it, take it back to zero first A simple tool will be written to encapsulate this procedure Worst case is probably the JLab quadrupoles

Online field measurements Three dipoles are important for energy measurements: INJ-MAG-DIP-01 (first after booster) AR1-MAG-DIP-01 (first after main linac) ST1-MAG-DIP-01 (dump dipole) A Hall probe is attached to the pole of each of these Calibration has been carried out with respect to central field This provides a check on the field Should result in more accurate energy measurements

Energy measurements (1) INJ-MAG-DIP-01 Used for measuring energy after the booster We have a complete field map of this magnet Take measurements of: Initial angle and position (from YAG-03 and BPM-03 or YAG-02) Central field (pole-mounted Hall probe) Final angle (from YAG-03 and -04)

Energy measurements (2) AR1-MAG-DIP-01 Measure energy after the main linac For this magnet, we have integral fields along the nominal beam path and central fields To measure energy: Ensure the beam is going through the centre of ST1-OTR-04 and AR1-OTR-01 Measure the field (pole-mounted Hall probe)

Energy measurements (3) ST1-MAG-DIP-01 Measure energy post-deceleration Two beams go through this dipole When dumping the decelerated beam: DON’T change the dump dipole current! Record the field (pole-mounted Hall probe) Record the position on DMP-OTR-01

Magnet Controls Control panel on the control room Linux consoles Main Menu  Commissioning  Magnets Magnet controls for the entire machine