M. Ross

USING A FAST-GATED CAMERA FOR MEASUREMENTS OF TRANSVERSE BEAM DISTRIBUTIONS AND DAMPING TIMES*

With a fast‐gated camera, synchrotron light was used for studying the transverse beam distributions and damping times in the Stanford Linear Collider (SLC) damping rings. By digitizing the image in the camera signal, the turn‐by‐turn time evolution of the transverse beam distribution was monitored and analyzed. The projections of the digitized image were fit with Gaussian functions to determine the moments of the distribution. Practical applications include the determination of injection matching parameters and the transverse damping times. In this report we describe a synchrotron light monitor and present experimental data obtained in the SLC damping rings.

Vibration studies of the Stanford Linear Accelerator

Vibration measurements of the linear accelerator structures in the SLC linac show a 1 micron RMS vertical motion. This motion reduces to 0.2 micron RMS motion when the cooling water to the accelerator structures is turned off. The quadrupoles have 250 nanometer RMS vertical motion with the accelerator structure cooling water on and 60 nanometer motion with it off. These results together with measurements of the correlations as a function of frequency between the motions of various components are presented.

Proposing a laser based beam size monitor for the future linear collider

Compton scattering techniques for the measurement of the transverse beam size of particle beams at future linear colliders (FLC) are proposed. At several locations of the beam delivery system (BDS) of the FLC, beam spot sizes ranging from several hundreds to a few micrometers have to be measured. This is necessary to verify beam optics, to obtain the transverse beam emittance, and to achieve the highest possible luminosity. The large demagnification of the beam in the BDS and the high beam power puts extreme conditions on any measuring device. With conventional techniques at their operational limit in FLC scenarios, new methods for the detection of the transverse beam size have to be developed. For this laser based techniques are proposed capable of measuring high power beams with sizes in the micrometer range. In this paper general aspects and critical issues of a generic device are outlined and specific solutions proposed. Plans to install a laser wire experiment at an accelerator test facility are presented.

Wire breakage in SLC wire profile monitors

Wire-scanning beam profile monitors are used at the Stanford Linear Collider (SLC) for emittance preservation control and beam optics optimization. Twenty such scanners have proven most useful for this purpose and have performed a total of 1.5 million scans in the 4 to 6 years since their installation. Most of the essential scanners are equipped with 20 to 40 μm tungsten wires. SLC bunch intensities and sizes often exceed 2×107particles/μm2 (3C/m2). We believe that this has caused a number of tungsten wire failures that appear at the ends of the wire, near the wire support points, after a few hundred scans are accumulated. Carbon fibers, also widely used at SLAC (1), have been substituted in several scanners and have performed well. In this paper, we present theories for the wire failure mechanism and techniques learned in reducing the failures.

Experience with wire scanners at SLC

Fifty wire scanners are in use at SLC for phase space and beam optics monitoring. A large number of failures of the 50 μm wire used in the scanners have occurred. Studies of these show strong electro‐magnetic fields produced by the beam to be the probable cause. The problem has been cured with the adoption of a ceramic mounting scheme. Other improvements including very high dynamic range scans and scans of non‐gaussian beams are described.

Availability and reliability issues for ILC

The International Linear Collider (ILC) will be the largest most complicated accelerator ever built. For this reason extensive work is being done early in the design phase to ensure that it will be reliable enough. This includes gathering failure mode data from existing accelerators and simulating the failures and repair times of the ILC. This simulation has been written in a general fashion using MATLAB and could be used for other accelerators. Results from the simulation tool have been used in making some of the major ILC design decisions and an unavailability budget has been developed.

Precise system stabilization at SLC using dither techniques

A data acquisition method has been developed at the SLAC Linear Collider (SLC) that provides accurate beam parameter information using sub-tolerance excitation and synchronized detection. This is being applied to several SLC sub-systems to provide high speed feedback on beam parameters such as linac output energy spread. The method has significantly improved control of the linac energy spread. The linac average phase offset (/spl phi/), used to compensate the effects of longitudinal wakefields, is adjusted /spl plusmn/1 control bit (about 0.18/sup ./ S-band or 20% of tolerance), in a continuous fashion. Properly coordinated beam energy measurements provide a measure of the derivative of the accelerating voltage (dE/d/spl phi/). The position of the beam on the RF wave can thus be determined to /spl plusmn/0.3/sup ./ in about 5 seconds. The dithering does not contribute significantly to the energy jitter of the SLC and therefore does not adversely affect routine operation. Future applications include control of the interaction region beam size and orientation.<<ETX>>

Performance of the PEP-II B-Factory Collider at SLAC

PEP-II is an e+e-asymmetric B-Factory Collider located at SLAC operating at the Upsilon 4S resonance (3.1 GeV x 9 GeV). It has reached a luminosity of 9.21×1033/cm2/s and has delivered an integrated luminosity of 710 pb-1in one day. PEP-II has delivered, over the past six years, an integrated luminosity to the BaBar detector of over 262 fb-1. PEP-II operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 2.45 A in 1588 bunches. Steady progress is being made in reaching higher luminosity. The goal over the next several years is to reach a luminosity of 2.1x1034/cm2/s. The accelerator physics issues being addressed in PEP-II to reach this goal include the electron cloud instability, beam-beam effects, parasitic beam-beam effects, high RF beam loading, shorter bunches, loweryinteraction region operation, and coupling control. Figure 1 shows the PEP-II tunnel.

The NLC injector system

The Next Linear Collider (NLC) injector system is designed to produce low emittance, 10 GeV electron and positron beams at 120 hertz for injection into the NLC main linacs. Each beam consists of a train of 95 bunches spaced by 2.8 ns; each bunch has a population of 1.15/spl times/10/sup 10/ particles. At injection into the main linacs, the horizontal and vertical emittances are specified to be /spl gamma//spl isin//sub x/=3/spl times/10/sup 16/ m-rad and /spl gamma//spl isin//sub y/=3/spl times/10/sup -8/ m-rad and the bunch length is 100 /spl mu/m. Electron polarization of greater than 80% is required. Electron and positron beams are generated in separate accelerator complexes each of which contain the source, damping ring systems, L-band, S-band, and X-band linacs, bunch length compressors, and collimation regions. The need for low technical risk, reliable injector subsystems is a major consideration in the design effort. This paper presents an overview of the NLC injector systems.

The Next Linear Collider damping ring complex

We report progress on the design of the Next Linear Collider (NLC) damping rings complex (DRC). The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs. It consists of two 1.98 GeV main damping rings, one positron pre-damping ring, two pairs of bunch length and energy compressor systems and interconnecting transport lines. The 2 main damping rings store up to 0.8 amp in 3 trains of 95 bunches each and have normalized extracted beam emittances /spl gamma//spl isin//sub x/=3 /spl mu/m-rad and /spl gamma//spl isin//sub y/=0.03 /spl mu/m-rad. The preliminary optical design, performance specifications and tolerances are given. Key subsystems include: 1) the 714 MHz RF system, 2) the 60 ns risetime injection/extraction pulsed kicker magnets, 3) the 44 m wiggler magnet system, 4) the arc and wiggler vacuum system, 5) the radiation management system, 6) the beam diagnostic instrumentation, 7) special systems used for downstream machine protection and 8) feedback-based stabilization systems.