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
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
To commission some of the hard and software for the RHIC electron lenses (e-lenses), a test bench was built based on the EBIS test stand at BNL. After several months of operation, the electron gun, collector, high-voltage gun modulator, instrumentation, partial control system, and several software applications have been tested. The nominal DC beam current of 0.85 A was demonstrated and the electron beam transverse profiles were verified to be Gaussian. Some e-lens power supplies and the electronics for current measurement were also evaluated on the test bench. The properties of the cathode and the profile of the beam are measured. In this paper, we will present some 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.
BNL, Upton, Long Island, New York, USA
Mechanical analysis of the RHIC beam dump window has shown that present heavy ion beam intensities are close to the tolerable limit, and will likely exceed that limit in future runs. Different approaches to upgrade the abort system for those projected higher intensities have been studied, namely replacing the existing window, and adding a vertical kicker that distributes the individual bunches more evenly across the window, thus reducing the heat load. We present the results of these studies and the present status of the upgrade project.