R. Michnoff

ARTUS: THE TUNE MEASUREMENT SYSTEM AT RHIC

The super-conducting Relativistic Heavy Ion Collider (RHIC) with two separate rings and six combined interaction regions will provide collisions between equal and unequal heavy ion species up to Au ions in typically 60 bunches. The betatron tunes of the two beams are among the most important parameters to be measured. The tunes have to be acquired at any moment during accelerator operation and in particular during the acceleration process. At RHIC the tune measurement device (ARTUS) consists of a fast horizontal and vertical kicker magnet and a dedicated beam position monitor in each ring. The system layout is described and first experiences from operation is reported.

Residual-Gas-Ionization Beam Profile Monitors in RHIC

Four ionization profile monitors (IPMs) in RHIC measure vertical and horizontal beam profiles in the two rings by measuring the distribution of electrons produced by beam ionization of residual gas. During the last three years both the collection accuracy and signal/noise ratio have been improved. An electron source is mounted across the beam pipe from the collector to monitor microchannel plate (MCP) aging and the signal electrons are gated to reduce MCP aging and to allow charge replenishment between single-turn measurements. Software upgrades permit simultaneous measurements of any number of individual bunches in the ring. This has been used to measure emittance growth rates on six bunches of varying intensities in a single store. Also the software supports FFT analysis of turn-by-turn profiles of a single bunch at injection to detect dipole and quadrupole oscillations.

Operations and Performance of RHIC as a Cu-Cu Collider

The 5thyear of RHIC operations, started in November 2004 and expected to last till June 2005, consists of a physics run with Cu-Cu collisions at 100 GeV/u followed by one with polarized protons (pp) at 100 GeV [1]. We will address here the overall performance of the RHIC complex used for the first time as a Cu-Cu collider, and compare it with previous operational experience with Au, PP and asymmetric d-Au collisions. We will also discuss operational improvements, such as a squeeze to 85cm in the high luminosity interaction regions from the design value of 1m, system improvements, machine performance and limitations, and address reliability and uptime issues.

RHIC BPM System Modifications and Performance

The RHIC beam position monitor (BPM) system provides independent average orbit and turn-by-turn (TBT) position measurements. In each ring, there are 162 measurement locations per plane (horizontal and vertical) for a total of 648 BPM planes in the RHIC machine. During 2003 and 2004 shutdowns, BPM processing electronics were moved from the RHIC tunnel to controls alcoves to reduce radiation impact, and the analog signal paths of several dozen modules were modified to eliminate gainswitching relays and improve signal stability. This paper presents results of improved system performance, including stability for interaction region beam-based alignment efforts. We also summarize performance of recently-added DSP profile scan capability, and improved million-turn TBT acquisition channels for 10 Hz triplet vibration, nonlinear dynamics, and echo studies.

Observation of Electron-Ion Effects at RHIC Transition

Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electron-ion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition.

The IPM as a Halo Measurement and Prevention Diagnostic

Four ionization beam profile monitors (IPM’s) are in RHIC to measure vertical and horizontal profiles in the two rings. Each IPM collects and measures the distribution of electrons in the beamline resulting from residual gas ionization during bunch passage. The ionized electron signal provides an accurate beam profile and the detectors are capable of measuring individual gold bunches. However the detectors are extremely sensitive and their performance has been limited by backgrounds from radiation spray, rf coupling to the beam, and secondary electrons. In 2002 two IPM’s were rebuilt using design changes which greatly reduced the backgrounds. During the summer 2003 shutdown another rebuild will increase the sweep electric field, make the electric field more uniform, and add a calibration system. The improvements in the electric field will increase the sensitivity to beam without increasing backgrounds and the calibration system will allow channel‐channel gain variations to be removed. These improvements s...

Enhancements To The Digital Transverse Dampers At The Brookhaven AGS

Since 1993, a digital transverse damper system has been used at the Brookhaven Alternating Gradient Synchrotron (AGS). The dampers are used to damp coherent oscillations and injection errors in both planes for protons and all species of Heavy Ions. Over nine years, several AGS improvements, the addition of the Relativistic Heavy Ion Collider (RHIC) operations, and our experience, created a critical need to improve the original system. Several enhancements have been made to the digital electronics including compatibility with harmonic numbers up to 24, an increase in the system resolution from eight to ten bits, and the conversion of the system interface to VME. The analog electronics were also modified to appropriately interface with the new digital electronics, as well as to provide an overall functional improvement. The pick‐up electrode (PUE) preamplifiers were redesigned to decrease the radiation susceptibility of the electronics. The concepts of the AGS Damper system can be utilized in developing a s...

RHIC data correlation methodology

A requirement for RHIC data plotting software and physics analysis is the correlation of data from all accelerator data gathering systems. Data correlation provides the capability for a user to request a plot of multiple data channels vs. time, and to make meaningful time-correlated data comparisons. The task of data correlation for RHIC requires careful consideration because data acquisition triggers are generated from various asynchronous sources including events from the RHIC Event Link, events from the two Beam Sync Links, and other unrelated clocks. In order to correlate data from asynchronous acquisition systems a common time reference is required. The RHIC data correlation methodology will allow all RHIC data to be converted to a common wall clock time, while still preserving native acquisition trigger information. A data correlation task force team, composed of the authors of this paper, has been formed to develop data correlation design details and provide guidelines for software developers. The overall data correlation methodology is presented.

Accelerating polarized protons to 250 GeV

The relativistic heavy ion collider (RHIC) as the first high energy polarized proton collider was designed to provide polarized proton collisions at a maximum beam energy of 250 GeV. It has been providing collisions at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100 GeV with careful control of the betatron tunes and the vertical orbit distortions. However, the intrinsic spin resonances beyond 100 GeV are about a factor of two stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were accelerated to the record energy of 250 GeV in RHIC with a polarization of 46% measured at top energy in 2006. The polarization measurement as a function of beam energy also shows some polarization loss around 136 GeV, the first strong intrinsic resonance above 100 GeV. This paper presents the results and discusses the sensitivity of the polarization survival to orbit distortions.

Fast IR Orbit Feedback at RHIC

Mechanical low-β triplet vibrations lead to horizontal jitter of RHIC beams at frequencies around 10Hz. The resulting beam offsets at the interaction points are considered detrimental to RHIC luminosity performance. To stabilize beam orbits at the interaction points, installation of a fast orbit feedback is foreseen. A prototype of this system is being developed and tested. Recent results will be presented.