L.G. Ratner

Polarized proton collider at RHIC

Abstract In addition to heavy ion collisions (RHIC Design Manual, Brookhaven National Laboratory), RHIC will also collide intense beams of polarized protons (I. Alekseev, et al., Design Manual Polarized Proton Collider at RHIC, Brookhaven National Laboratory, 1998 [2]), reaching transverse energies where the protons scatter as beams of polarized quarks and gluons. The study of high energy polarized protons beams has been a long term part of the program at BNL with the development of polarized beams in the Booster and AGS rings for fixed target experiments. We have extended this capability to the RHIC machine. In this paper we describe the design and methods for achieving collisions of both longitudinal and transverse polarized protons in RHIC at energies up to s =500 GeV .

Overcoming intrinsic spin resonance by using an AC dipole

Depolarization from an intrinsic spin resonance can be avoided by adiabatically exciting a coherent betatron oscillation. Experimental results of creating sustained coherent betatron oscillations in the Brookhaven National Laboratory AGS, and relevant spin tracking calculations are discussed.

Feasibility of a polarized deuteron beam in the AGS and RHIC

The possibility of accelerating polarized deuterons in the AGS and RHIC is discussed. In the AGS, the polarized deuteron can be accelerated up to 15 GeV/c/u without depolarization. In RHIC, the snakes designed for use in accelerating polarized protons are applicable as partial snakes in inducing spin flip to overcome the imperfection resonances. Gradient error resonances in RHIC are found to be negligible. Difficulties arise from intrinsic resonances in RHIC, which limit the polarized deuteron collision energy to γ ≤ 29 or to an energy less than 27.2 GeV/u, if corrections are not made. A type 3 snake is found to be impractical for a spin tune jump. Betatron tune jump by using quadrupoles or induced betatron oscillations may be used to jump through intrinsic resonances. The achievable luminosity is found to about 2 × 1030 cm−2 s−1 at γ ≈ 30. If intrinsic resonances can be overcome, one expects to obtain higher energy and higher luminosity.

Analyzing power measurements in high‐P2∥ p‐p elastic scattering

The analyzing power in 28 GeV/c proton/proton elastic scattering was measured at P2∥=5.95 and 6.56 (GeV/c)2 using a polarized proton target and an unpolarized proton beam at the Brookhaven National Laboratory AGS. Results indicate that the analyzing power, A, is rising sharply with P2∥.

Overcoming weak intrinsic depolarizing resonances with energy-jump

In the recent polarized proton runs in the AGS, a 5% partial snake was used successfully to overcome the imperfection depolarizing resonances. A polarized proton beam was accelerated up to the required RHIC injection energy of 25 GeV. However, a significant amount of polarization was lost at 0+/spl nu//sub y/, 12+/spl nu//sub y/ and 36+/spl nu//sub y/, which is believed to be partially due to the coupling resonances. To overcome the coupling resonance, an energy-jump was generated by rapidly changing the beam circumference using the powerful AGS RF system. It clearly demonstrates that the novel energy-jump method can successfully overcome coupling resonances and weak intrinsic resonances.

Partial Siberian snake experiment at the AGS

A 9° solenoidal spin rotator or 5% partial Siberian snake was used to successfully accelerate polarized protons for the first time to 10.8 GeV kinetic energy in the Brookhaven AGS. It was found that a 5% partial snake can effectively overcome 18 imperfection resonances in this energy range. We also observed an interference between the spin flip induced by an intrinsic resonance and linear coupling due to the solenoid field of the partial snake.

MINIMIZING LINEAR COUPLING IN THE AGS WITH SKEW QUADS

Skew quadrupoles and solenoids can introduce linear betatron coupling into the beam. Since the linear coupling causes emittance growth, it should be minimized. Linear coupling caused by a solenoid can be corrected with skew quadrupoles by minimizing the coupling coefficient. It requires two orthogonal skew quadrupole families. The major source of linear coupling arises from the 5% partial solenoidal snake to be installed in the section I10 of the AGS. To correct the effect of linear coupling, 4 families of skew quadrupoles are proposed. 3 figs.

Energy change of a depolarizing resonance due to a type-3 Siberian snake

The authors measured the photon beam polarization in the IUCF (Indiana University Cyclotron Facility) Cooler Ring at five energies. They found that the G/sub lambda /=2 imperfection depolarizing resonance occurred about 1.9 MeV below the expected resonance energy of 108.4 MeV. This energy shift could be due to a shift of about +0.0036 in the spin time, nu /sub s/, which is the number of spin rotations in each turn around the ring. It was then demonstrated that this spin tune shift is consistent with the cooler ring containing a partial type-3 Siberian snake, which is apparently caused by the magnets that confine the electron and proton beams in the cooling region.<<ETX>>

Measurement of Spin Effects in pp Elastic Scattering Using the Polarized Beam at the AGS

Using the recently developed 18.5 GeV/c AGS polarized proton beam and a polarized proton target we measured the analyzing power, A, and the spin-spin correlation parameter, Ann, in medium-P2 ⊥ proton-proton elastic scattering. We found sharp dips in both A and Ann, which occur at different P2 ⊥ values. The unexpected sharp structure in the spin-spin force occurs near P2 ⊥ = 2.3 [GeV/c]2 where the elastic cross-section has no apparent structure.

EDDY CURRENTS IN THE TRANSITION JUMP QUADRUPOLE VACUUM CHAMBERS

A fast transition jump is being installed in the AGS. Quadrupoles located in the 111711 straight sections of the A, C , E, G, I, and K superperiods will be excited with a 60 msec risetime. This will raise the AGS transition energy by about 3 GeV. The transition energy will then be abruptly lowered during a 500 psec deexcitation as the AGS itself passes through transition. The effect of these manipulations will be to speed up passage through transition by a factor of 30 to 100 if the magnetic fields in the quaddrupoles follow the excitation currents. This will drastically lower beam losses at this inherently unstable point. However, eddy currents induced in the vacuum chamber by the rapid de-excitation will reduce the aimount of speed up. The purpose of these studies was to investigate the effects of eddy currents in the vacuum chamber on the pulsed magnetic field in a transition jump quadrupole. 0