Phase A.12: Beam Commissioning with Experimental Magnets

Description:

Summary of the experimental magnets and their effect on Beam (c/o ML - main reference W.Herr's : The effect of solenoids and dipole magnets of LHC experiment [1])

	Description	Coupling	Orbit	Commissioning conclusion
ATLAS solenoid	Magnet length ~ 5.3 m. Max. field 2T. Integrated field ~ 12 T.m Max. radial field 5 e-4 T	Negligible	Can be neglected (1 microrad from crossing angle at 450 GeV)	Bring on and leave on after prefunctory checks at 450 GeV
ATLAS toroid	No effect on beam			As required by Atlas.

ALICE solenoid	Central field 0.5 T Max Radial field 20 e-4 T Magnet Length ~ 12 m.	"The maximum field is ~ 0.5 T and it can be neglected."	Orbit kick from crossing angle at 450 GeV about 1 microrad - negligible. Need radial field distribution to be sure but integrated field strength likely to be negligible. (12 m x 20 Gauss gives 16 microrad at 450 GeV).	Bring on and leave on after prefunctory checks at 450 GeV. Don't worry about polarity changes.
ALICE dipole spectrometer	field direction H kick V B.dl ~ 3 T.m ~ 130 microrad at 7 TeV	-	Strong orbit distortion around the machine. Compensation provided by 3 dedicated magnets -> closed, antisymmetric bump	Dedicated commissioning at 450 GeV and in ramp.

CMS solenoid	Magnetic length ~ 13.2 m Max. field 4 T ("significantly stronger that ATLAS") Integrated field ~ 52 Tm Radial field ~ 20 e-4 T at 1 mm from axis	At 450 GeV: delta cminus ~ -5i e-3 compared with tolerance of 0.03. Contribution relevant when solenoid is at full field at injection.	With crossing angle on - vertical kick of ~ 5 microrad Integrated Bdl from radial field - negligible	Measure and correct coupling at 450 GeV. Turn off for first ramp attempts - want to minimise effect of coupling on tune measurement. Check orbit when we bring on crossing angles.

LHCb dipole field direction V kick H	B.dl ~ 4.2 T.m ~ 180 microrad at 7 TeV	-	Strong orbit distortion around the machine. Compensation provided by 3 dedicated magnets -> closed, antisymmetric bump	Dedicated commissioning at 450 GeV and in ramp. Have to repeat for operation with crossing angle and on change of polarity.

The procedure is split in 2 parts :

    Commissioning of beam with the solenoids ON:
            The solenoids have to be ramped to full current at 450 GeV and their effects on the beam coupling and the beam orbit have to be measured and corrected.

The predicted coupling effects of Atlas and Alice solenoids are small. Given the time it takes to ramp a solenoid, the coupling will also vary due to other effects (orbit drifts, etc) during its ramping. If we add that the measurement resolution may not be optimal at the first stages of the commissioning, it could be impossible to measure the coupling effects due to Alice and Atlas solenoids.

    Commissioning of beam with the dipoles ON:
            The dipoles and the dedicated compensators have to be switched ON, and gradually put to their full strength. The bump closure and induced beam losses have to be measured and corrected before increasing the bump amplitude.