Michael Blaskiewicz

Experience with low-energy gold-gold operations in RHIC during FY 2010

During Run-10, RHIC operated at several different Au-Au collision energies, as requested mainly by the STAR collaboration in a quest to search for the critical point in the QGP phase diagram. The center-of-mass energies {radical}s{sub NN} are listed in Table 1, together with the respective start and end dates and the duration of the respective run at each energy. While STAR defines low energy as anything below {radical}s{sub NN} = 39 GeV, we focus in the scope of this paper on energies below the regular RHIC injection energy of {radical}s{sub NN} {approx} 20 GeV, since this energy regime is particularly challenging for stable RHIC operations. Figures 1 and 2 show the evolution of beam intensity and luminosity during the course of the {radical}s{sub NN} = 7.7 GeV and 11.5 GeV run. In the following sections we will recapitulate the modifications during the run that led to significant performance improvements, and summarize what was learned at the various energies for possible application in future runs.

The fast loss electron proton instability

The fast loss electron proton instability is studied both experimentally and theoretically. It is shown that electron multi-pactoring is required for fast beam loss.

Beam Diagnostics for the BNL Energy Recovery Linac Test Facility

An Energy Recovery Linac (ERL) test facility is presently under construction at BNL. The goals of this test facility are first to demonstrate stable intense CW electron beam with parameters typical for the RHIC e-cooling project (and potentially for eRHIC), second to test novel elements of the ERL (high current CW photo-cathode, superconducting RF cavity with HOM dampers, and feedback systems), and finally to test lattice dependence of stability criteria. Planned diagnostics include position monitors, loss monitors, transverse profile monitors (both optical and wires), scrapers/halo monitors, a high resolution differential current monitor, phase monitors, an energy spread monitor, and a fast transverse monitor (for beam break-up studies and the energy feedback system). We discuss diagnostics challenges that are unique to this project, and present preliminary system specifications. In addition, we include a brief discussion of the timing system.

New methods to estimate the HOM generation and energy spread of SRF cavities in the eRHIC ERL design

High Order Mode (HOM) power is produced by high current linear accelerators. In this paper, we report a new method to estimate the HOM power generation and energy spread from multiple bunch patterns in the time domain on multiple HOMs. These methods can be used to evaluate the HOM power and energy spread induced by the HOM field, and to optimize the design of SRF cavities to minimize the HOM power and the energy spread induced by the HOMs.

Emittance Growth From Modulated Focusing and Bunched Beam Electron Cooling

The Low Energy electron Cooling (LEReC) project at Brookhaven employs an energy recovery linac to supply electrons in the 1.6 to 5 MeV range. Along with cooling the stored ion beam these bunches create a coherent space charge field which can cause emittance growth. This process is investigated both analytically and via simulation.

RHIC Performance with Stochastic Cooling for Ions and Head-on Beam-beam Compensation for Protons

The Relativistic Heavy Ion Collider (RHIC) has two main operating modes with heavy ions and polarized protons respectively. In addition to a continuous increase in the bunch intensity in all modes, two major new systems were completed recently mitigating the main luminosity limit and leading to significant performance improvements. For heavy ion operation stochastic cooling mitigates the effects of intrabeam scattering, and for polarized proton operation head-on beam-beam compensation mitigates the beam-beam effect. We present the performance increases with these upgrades to date, as well as an overview of all operating modes past and planned.

Higher Luminosity eRHIC Ring-Ring Options and Upgrade

Lower risk ring-ring alternatives to the BNL linac-ling [1] eRHIC electron ion collider (EIC) are discussed. The baseline from the Ring-Ring Working Group [2] has a peak proton-electron luminosity of ≈ 1.2 × 10 cm s. An option has final focus quadrupoles starting immediately after the detector at 4.5 m, instead of at 32 m in the baseline. This allows the use of lower βs. It also uses more, 720, lower intensity, bunches, giving reduced IBS emittance growth and requiring only low energy pre-cooling. It has a peak luminosity of ≈ 7 × 10 cm s. An upgrade of this option, requiring magnetic, or coherent, electron cooling, has 1440 bunches and peak luminosity of ≈ 15 × 10 cm s.

Novel techniques and devices for in-situ film coatings of long, small diameter tubes or elliptical and other surface contours

Devices and techniques that can, via physical vapor deposition, coat various surface contours or very long small aperture pipes, are described. Recently, a magnetron mole was developed in order to in-situ coat accelerator tube sections of the Brookhaven National Lab relativistic heavy ion collider that have 7.1u2009cm diameter with access points that are 500 m apart, for copper coat the accelerator vacuum tube in order to alleviate the problems of unacceptable ohmic heating and of electron clouds. A magnetron with a 50u2009cm long cathode was designed fabricated and successfully operated to copper coat a whole assembly containing a full-size, stainless steel, cold bore, of the accelerator magnet tubing connected to two types bellows, to which two additional pipes made of accelerator tubing were connected. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and ...

Beam-beam Interaction in the Asymmetric Energy Gold-gold Collision in RHIC

In this article, we study the beam-beam interaction in a possible future gold-gold collision with different particle energies in the Relativistic Heavy Ion Collider (RHIC). Since RF harmonic numbers are different for the two rings, bunches collide in 110 or 111 turn followedby 10 turns without collision. We will carry out 6-D numeric simulations to study the stability of bunch centers and the transverse emittance growth. The nonlinear beam-beam interaction force, chromaticities, and synchrotron motion are included. Both weak-strong and strong-strong simulation models are used.

Optics Setup in the AGS and AGS Booster for Polarized Helion Beam

Future RHIC physics program calls for polarized helion beam. The helion beam from the new EBIS source has a relative low rigidity which requires delicate control of injection and RF setup in the Booster. The strong depolarization resonance strength in both AGS and AGS Booster requires careful consideration of beam energy range and optics setup. Recently, the unpolarized helion beam was accelerated to 11GeV/n in the AGS. The optics with special tune path has been tested in both AGS and the Booster. The near term goal of 4×10/bunch at RHIC injection requires several RF bunch merges in both AGS and the Booster. The beam test results are presented in this paper.