BNL, Upton, Long Island, New York, USA
In the 2013 RHIC polarized proton run, it was found that the RHIC bunch intensity has reached a limit due to the head-on beam-beam interaction at 2x1011, as expected by simulations. To overcome this limitation, two electron lenses will be used for compensation. We report on the commissioning of new lattices that reduce beam-beam driven resonance driving terms, and bunch-by-bunch proton diagnostic during 2013 run. The effect of electron beam transport solenoids on the proton orbit was tested. The instrumentation for Blue electron lens was tested and electron beam was propagated from the gun to the collector. A timing system was implemented for the electron beam. Control software, machine protection and synoptic display were developed and tested during commissioning. Both Blue and Yellow electron lens superconducting magnets are installed and their field straightness was measured and corrected in the tunnel using a magnetic needle. The Yellow vacuum system and backscattered electron detectors installation are also completed now.
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.
BNL, Upton, Long Island, New York, USA
A code for determining the beam emittance from a multi-slit image has been developed. To verify its validity, we simulated a beam distribution in 4D phase space at the multi-slit position and the resulting image at a downstream profile measurement device. We applied the algorithm to this image pattern to recover the beam emittance at the slit position. The dependence of the relative difference of the inferred emittance and the input emittance on the slit width and drift length are studied in detail and presented in this report.
BNL, Upton, Long Island, New York, USA
The signal cables from the beam position monitors (BPMs) in the cryogenic sections of RHIC need to satisfy somewhat conflicting requirements. On the one hand, the cryogenic load due to heat conduction along the cable needs to be small, which led to the use of stainless steel jacketed cables with Tefzel insulation. On the other hand, radio frequency losses need to be reasonably small to reduce heating due to dissipated signal power. As the beam intensity in RHIC increased over the years, and the bunches become shorter, a point is being rapidly approached where these cables will soon become a performance limiting factor. Here we describe an extensive study of this problem including cable loss measurements as a function of temperature and frequency, characterization of the copper center conductor, and Particle Studio and ANSYS simulations.