J. van Zeijts

RHIC third generation PLL tune system

During the RHIC 2000 run a prototype PLL tune measurement system was implemented using commercial off-the-shelf hardware. To meet the requirements for tune feedback during RHIC 2001/2002, this system was migrated into RHIC BPM modules, whose flexible DSP/FPGA architecture permitted the specialized processing needed for tune tracking and feedback during acceleration, and whose existing firewire interface provided communication with the Control System. For RHIC 2003 this system has migrated yet again, to state-of-the-art DSPs in VME. We report here on various improvements, extending from the pickup through the analog electronics and digital processing into the Controls interface, and on the performance gains that resulted from these improvements.

Tune feedback at RHIC

Preliminary phase-locked loop betatron tune measurement results were obtained during RHIC 2000 with a resonant Beam Position Monitor. These results suggested the possibility of incorporating PLL tune measurement into a tune feedback system for RHIC 2001. Tune feedback is useful in a superconducting accelerator, where the machine cycle time is long and inefficient acceleration due to resonance crossing is not comfortably tolerated. This is particularly true with the higher beam intensities planned for RHIC 2001. We present descriptions of a PLL tune measurement system implemented in the DSP/FPGA environment of a RHIC BPM electronics module and the feedback system into which the measurement is incorporated to regulate tune. In addition, we present results from the commissioning of this system during RHIC 2001.

Commissioning of RHIC deuteron-gold collisions

Deuteron and gold beams have been accelerated to a collision energy of /spl radic/s = 200 GeV/u in the Relativistic Heavy Ion Collider (RHIC), providing the first asymmetric-species collisions of this complex. Necessary changes for this mode of operation include new ramping software and asymmetric crossing angle geometries. This paper reviews machine performance, problems encountered and their solutions, and accomplishments during the 16 weeks of ramp-up and operations.

Commissioning and future plans for polarized protons in RHIC

Polarized protons were injected and accelerated in the clockwise ring of RHIC to commission the first full helical Siberian snake ever used in an accelerator. With the snake turned on, the stable spin direction is in the horizontal plane. Vertically polarized protons were injected with the snake off. The snake was adiabatically ramped to give a spin rotation of 180/spl deg/ around a horizontal rotation axis about 13/spl deg/ from the longitudinal. When the beam was accelerated from injection G/spl gamma/ = 46.5 to G/spl gamma/ = 48 the spin flipped sign as expected and polarization was preserved. At G/spl gamma/ = 48 without the snake, no polarization was observed since several spin resonances were crossed. Eventually polarized beam was accelerated to G/spl gamma/ = 55.7 (29.1 GeV). In the next proton running period we plan to run with two full helical snakes in each ring and collide both transversely and longitudinally polarized protons at an energy around 100 GeV per beam.

Commissioning spin rotators in RHIC

During the summer of 2002, eight superconducting helical spin rotators were installed into RHIC in order to control the polarization directions independently at the STAR and PHENIX experiments. Without the rotators, the orientation of polarization at the interaction points would only be vertical. With four rotators around each of the two experiments, we can rotate either or both beams from vertical into the horizontal plane through the interaction region and then back to vertical on the other side. This allows independent control for each beam with vertical, longitudinal, or radial polarization at the experiment. In this paper, we present results from the first run using the new spin rotators at PHENIX.

Beam lifetime and emittance growth measurements of gold beams in RHIC at storage

During stores of gold beams, longitudinal and transverse beam sizes were recorded., Longitudinal profiles were obtained with a wall current monitor. Transverse profiles were reconstructed from gold-gold collision rates at various relative transverse beam positions. The total beam lifetime was measured with a beam current transformer, the bunched beam lifetime with the wall current monitor. Diffusion rates in the beam halo were determined from the change in the loss rate when a scraper is retracted. The measurements are used to determine the lifetime limiting effects. Beam growth measurements are compared with computations of beam-growth times from intra-beam scattering.

Tune Measurement in RHIC

Three basic tune measurement methods are employed in RHIC; kicked beam, Schottky, and phase‐locked loop. The kicked beam and 2GHz Schottky systems have been in operation since the first commissioning of circulating beam in RHIC in 1999. Preliminary PLL measurements utilizing a commercial off‐the‐shelf lockin amplifier were completed during that run, and the resonant BPM used in that system also delivered 230MHz Schottky spectra. With encouraging preliminary results and the thought of tune feedback in mind, a PLL tune system was implemented in the FPGA/DSP environment of the RHIC BPM system for the RHIC 2001 run. During that run this system functioned at the level of the present state‐of‐the‐art in tune measurement accuracy and resolution, and was successfully incorporated into a tune feedback system for use during acceleration. Each of the tune measurement systems has particular strengths and weaknesses. We present specific and comparative details of systems design and operation. In addition, we present d...

High luminosity /spl beta/*=0.5 m RHIC insertions

An increase in RHIC collision luminosity is possible by reducing the beam size at the interaction point (IP). We present a method for reducing the IP beta function, /spl beta/*, from the design minimum of 1 m to 0.5 m. We demonstrate that this /spl beta/*=0.5 m configuration is achievable with existing RHIC power supplies for 100 GeV protons. We discuss the correction of the higher order IR multi-poles and the second order chromaticity.

Commissioning results and applications

Abstract This section describes both: successful commissioning of RHIC and the state of the art RHIC accelerator physics tools/applications. The commissioning provided collisions of the fully stripped gold ions at a beam energy of 65 GeV/nucleon in all four experiments “STAR”, “PHENIX”, “PHOBOS”, and “BRAHMS”. They collected more than 3 μb −1 of data. Measurements of betatron and dispersion functions have shown excellent agreement with predictions. Diagnostic results from tune-meter, wall current monitor, chromaticity, decoupling measurements, ionization beam profile monitor, Schottky monitors, etc. are shown. Progress towards stable gold ion beam stores with optimized luminosity is described [Proceedings of the HEACC2001 The 18th International Conference On High Energy Accelerators, March 26–30, 2001, Tsukuba, Japan, March, 2001]. Few major commissioning challenges are described first. The most important results, from some of the RHIC systems, are shown in the next section. In the following section bringing beams from two separate “blue” and “yellow” rings into collisions and measurements during long beam stores are described. In the summary part necessary steps and commissioning of additional systems during the next RHIC-2001 run are mentioned.