Search Results (15 total)

We present a new technique to continuously measure and compensate the global difference coupling coefficient through the continuous measurements of eigenmode projection parameters, using a high resolution phase-locked-loop tune meter. First, four eigenmode projection parameters are defined as the observables for weak difference coupling. Then, their analytical expressions are obtained using the strict matrix treatment and the Hamiltonian perturbation theory of linear coupling. From these parameters, the complex global coupling coefficient can be fully determined and compensated. This method was successfully demonstrated in the Relativistic Heavy Ion Collider (RHIC) 2006 run.

Simultaneous tune and coupling feedback were successfully implemented during RHIC run 6. In this paper we describe the measurement and control hardware and software used to accomplish this, present some of the results, discuss areas that require further investigation, and finally offer a few comments on possible implications of these results for LHC commissioning.

We describe a fast and robust global decoupling scheme, coupling angle modulation. This novel technique introduces an extra rotating coupling coefficient into the coupled optics to determine the global decoupling strengths. The eigentune split is used as the observable during the modulation. The two eigentunes are tracked with a high-resolution phase locked loop tune measurement system. In the article, the principle of coupling angle modulation is presented, followed by its application to the Relativistic Heavy Ion Collider (RHIC). Coupling angle modulation coupling correction has been used for the global coupling correction on the nonstop RHIC ramp.

Measurement of the residual betatron coupling with skew quadrupole modulation is a new diagnostics technique. It was developed and tested at the Relativistic Heavy Ion Collider (RHIC) as a promising method for measuring coupling on the ramp. By modulating the strengths of skew quadrupole families, the two tunes' responses are precisely measured with the phase lock loop system. The projection ratio of the residual coupling coefficient onto the coupling modulation direction can be determined. In this article, the analytical solution to the skew quadrupole modulation is given. Dedicated beam studies were carried out in RHIC Run'04 and the results are presented. The ability to measure coupling on the ramp opens the possibility of continuously correcting coupling during acceleration.

This paper summarizes the low-loss design for the Spallation Neutron Source accumulator ring [“Spallation Neutron Source Design Manual” (unpublished)]. A hybrid lattice consisting of FODO arcs and doublet straights provides optimum matching and flexibility for injection and collimation. For this lattice, optimization focuses on six design goals: a space-charge tune shift low enough (below 0.15) to avoid strong resonances, adequate transverse and momentum acceptance for efficient beam collimation, injection optimized for desired target beam shape and minimal halo development, compensation of magnet field errors, control of impedance and instability, and prevention against accidental system malfunction. With an expected collimation efficiency of more than 90%, the uncontrolled fractional beam loss is expected to be at the 10^-4 level.

A new type of spin depolarization resonance has been observed at the Brookhaven Alternating Gradient Synchrotron (AGS). This spin resonance is identified as a strong closed-orbit sideband around the dominant intrinsic spin resonance. The strength of the resonance was proportional to the 9th harmonic component of the horizontal closed orbit and proportional to the vertical betatron oscillation amplitude. This “hybrid” spin resonance cannot be overcome by the partial snake at the AGS, but it can be corrected by the harmonic orbit correctors.

A coherent spin resonance excited by an rf dipole was used to overcome depolarization due to intrinsic spin resonances at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. We found that our data are consistent with a full spin flip of a polarized proton beam, without emittance growth, at Gγ  =  12+ν_z and 36-ν_z, by adiabatically exciting a vertical coherent betatron oscillation using a single rf dipole magnet. The interference pattern observed between the intrinsic spin resonance and the coherent spin resonance agrees well with multiparticle spin simulations based on a simple two-resonance model. The interference pattern can be used for beam diagnostics.

Accelerating polarized protons to 22 GeV/c at the Brookhaven Alternating Gradient Synchro- tron required both extensive hardware modifications and a difficult commissioning process. We had to overcome 45 strong depolarizing resonances to maintain polarization up to 22 GeV/c in this strong-focusing synchrotron. At 18.5 GeV/c we measured the analyzing power A and the spin-spin correlation parameter A_nn in large- P_⊥² proton-proton elastic scattering, using the polarized proton beam and a polarized proton target. We also obtained a high-precision measurement of A at P_⊥²=0.3 (GeV/c)² at 13.3 GeV/c. At 18.5 GeV/c we found that A_nn=(-2±16)% at P_⊥²=4.7 (GeV/c)², where it was about 60% near 12 GeV at the Argonne Zero Gradient Synchrotron. This sharp change suggests that spin-spin forces may have a strong and unexpected energy dependence at high P_⊥².

We measured the analyzing power A and the spin-spin correlation parameter A_nn, in large-P_⊥² proton-proton elastic scattering, using a polarized-proton target and the polarized-proton beam at the Brookhaven Alternating-Gradient Synchrotron. We also used our polarimeter to measure A at small P_⊥² at 13 GeV with good precision and found some deviation from the expected 1 / P_lab behavior. At 18.5 GeV/c we found A_nn=(-2±16)% at P_⊥²=4.7 (GeV/c)². Comparison with lower-energy data from the Argonne Zero-Gradient Synchrotron shows a sharp and surprising energy dependence for A_nn at large P_⊥².

The spin analyzing power A in 28-GeV/c proton-proton elastic scattering was measured at P_⊥ ²=6.5 (GeV/c)² using a polarized proton target and a high-intensity unpolarized proton beam at the Brookhaven National Laboratory Alternating Gradient Synchrotron. The result of (24±8)% confirms that the analyzing power is large and rising in the large-P_⊥ ² region.

Using the new Brookhaven Alternating Gradient Synchrotron polarized proton beam and our polarized proton target, we measured the spin-spin correlation parameter A_nn in 16.5-GeV/c proton-proton elastic scattering. We found an A_nn of (6.1±3.0)% at P_⊥ ²=2.2 (GeV/c)². We also measured the analyzing power A in two independent ways, providing a good test of possible experimental errors. Comparing our new data with 12-GeV Argonne Zero Gradient Synchrotron data shows no evidence for strong energy dependence in A_nn in this medium-P_⊥ ² region.

The difference Δσ_T=σ(↓↑)-σ(↑↑) between the proton-proton total cross sections for protons in pure transverse-spin states, was measured at incident momenta 0.8 to 2.5 GeV/c in experiments performed at the Los Alamos Clinton P. Anderson Meson Physics Facility and the Argonne Zero Gradient Synchrotron. In agreement with other data, peaks were observed at center-of-mass energies of 2.14 and 2.43 GeV/c², where ¹D₂ and ¹G₄ dibaryon resonances have been proposed.

The analyzing power A in 28-GeV/c proton-proton elastic scattering was measured with a polarized proton target and a high-intensity unpolarized proton beam at the Brook-haven National Laboratory alternating-gradient synchrotron. The P_⊥² range of 2.85 to 5.95 (GeV/c)² was covered with good precision. A small dip of about -3.5% was found near P_⊥²=3.5 (GeV/c)² where a 24-GeV/c CERN experiment had reported a deep dip of about -16% with large errors. In the previously unexplored large-P_⊥² region near 6 (GeV/c)² these new large-error points suggest that A may be rising.

The analyzing power, A, was measured in proton-proton elastic scattering with use of a polarized proton target and 28-GeV/c primary protons from the alternating-gradient synchrotron. Over the P_⊥² range of 0.5 to 2.8 (GeV/c)², the data show interesting structure. There is a rather sharp dip at P_⊥²=0.8 (GeV/c)² corresponding to the break in the elastic differential cross section at the end of the diffraction peak.

We measured the differential cross section for proton-proton elastic scattering at 6 GeV/c, with both initial spins oriented normal to the scattering plane. The analyzing power A shows significant structure with a large broad peak reaching about 24% near P_⊥²=1.6 (GeV/c)². The spin-spin correlation parameter A_nn exhibits more dramatic structure, with a small but very sharp peak rising rapidly to about 13% at 90°_c.m.. This sharp peak may be caused by particle-identity effects.