Accelerating polarized beams at the AGS

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:137301

Roser, T

The acceleration of polarized beams in circular accelerators is complicated by the presence of numerous depolarizing resonances. During acceleration, a depolarizing resonance is crossed whenever the spin precession frequency equals the frequency with which spin-perturbing magnetic fields are encountered. There are two main types of depolarizing resonances corresponding to the possible sources of such fields: imperfection resonances, which are driven by magnet errors and misalignments, and intrinsic resonances, driven by the focusing fields. The resonance conditions are usually expressed in terms of the spin tune {nu}{sub s}, which is defined as the number of spin precessions per revolution. For an ideal planar accelerator, where orbiting particles experience only the vertical guide field, the spin tune is equal to G{gamma}, where G = 1.7928 is the anomalous magnetic moment of the proton and {gamma} is the relativistic Lorentz factor. The resonance condition for imperfection depolarizing resonances arise when {nu}{sub s} = G{gamma} = n, where n is an integer. Imperfection resonances are therefore separated by only 523 MeV energy steps. The condition for intrinsic resonances is {nu}{sub s} = G{gamma} = kP {+-} {nu}{sub y}, where k is an integer, {nu}{sub y} is the vertical betatron tune and P is the superperiodicity. For the AGS, P = 12 and {nu}{sub y} {approx} 8.8. For most of the time during the acceleration cycle, the precession direction, or stable spin direction, coincides with the main vertical magnetic field. Close to a resonance, the stable spin direction is perturbed away from the vertical direction by the resonance driving fields. When a polarized beam is accelerated through an isolated resonance, the final polarization can be calculated analytically.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 137301
• Report Number(s): BNL--61688; CONF-950299--2; ON: DE96002742
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ACCELERATION
BROOKHAVEN AGS
DEPOLARIZATION
POLARIZED BEAMS
PROTON BEAMS