BNL, Upton, Long Island, New York, USA
To search for the critical point in the QCD phase diagram, Au-Au collisions at beam energies between 2.5 and 15 GeV are required. While RHIC has successfully operated at 3.85 and 5.75 GeV, the performance achieved at 2.5 GeV is not sufficient for a meaningful physics program. We report on dedicated beam experiments performed to understand and improve this situation.
IUCEEM, Bloomington, Indiana, USA
BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
Independent component analysis (ICA) was applied to the AC dipole based optics measurement at RHIC to extract beta functions as well as phase advances at each BPM. Existence of excessive beta-beat was observed in both rings of RHIC at store energy. A unique global optics correction scheme was then developed and tested successfully during the RHIC polarized proton run in 2013. The feasibility of using closed orbit bump and sextupole for arc beta-beat correction was also demonstrated. The technique and experimental results of optics correction are reported in this paper.
BNL, Upton, Long Island, New York, USA
In this report we describe and present experimental results from correction of the accelerator optics during acceleration and preparation for collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL. Past experiences with beam optics correction at RHIC have concentrated on measurements and corrections at store beam energies. While well-corrected beam optics is desirable for maximizing beam and polarization lifetime, well-corrected beam optics during the ramp is also desirable for example to reduce the strength of depolarizing resonances. With optics measurements on the ramp at every 2 or 4 seconds, corrections were computed for several fixed points on the ramp using a well-tested weighted Singular Value Decomposition algorithm. Successful implementation of correction on the second part of the ramp (rotator ramp), together with some observations on the first part of the ramp (the energy ramp) will be presented.
BNL, Upton, Long Island, New York, USA
Deviation of the optical functions from the model may result in reduced dynamic aperture, luminosity and beam polarization all of which are of particular interest in the polarized proton program at RHIC. Peak to peak beta-beats as large as ± 80% have been observed. In run-13, we demonstrated that the optical functions can be corrected globally by two different approaches, beta-beat and phase-beat corrections. The optics measurement, correction algorithm and beta-beat measurements before and after correction will be presented.
BNL, Upton, Long Island, New York, USA
We describe a new and minimally invasive method for near real-time measurement of the evolution of critical beam optical parameters during acceleration of beams to high energies in the Relativistic Heavy Ion Collider (RHIC) at BNL. The implementation uses existing hardware to periodically excite a single bunch in the beam and leverages off of improved precision and deterministic data delivery from the RHIC beam position monitors operating in turn-by-turn mode. The beam response to the external excitations was observed to decohere on a relatively short time scale so allowing near-simultaneous data acquisition in the horizontal and vertical planes. The excitations and acquisitions are carefully timed to allow coexistence with normal ramp orbit feedback operating at a 1 Hz rate. Respecting the limitations of the data transfer times, important parameters such as the beta functions, local phase advance, and betatron tune spread were measured in both accelerators and both transverse planes at a maximum rate of once every 2 seconds / 4 seconds in each of the two RHIC accelerators respectively. The measurement architecture is described together with select experimental results.