R. Wells

The STAR time projection chamber: a unique tool for studying high multiplicity events at RHIC

The STAR Time Projection Chamber (TPC) is used to record the collisions at the Relativistic Heavy Ion Collider (RHIC). The TPC is the central element in a suite of detectors that surrounds the interaction vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within ± 1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than

STAR TPC at RHIC

Design information, construction methods and testing results are given for the STAR TPC which will be installed at the BNL RHIC collider.

A recirculating linac-based facility for ultrafast x-ray science

We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac, in particular the incorporation of EUV and soft x-ray production. The project has been named LUX - Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10s fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-short-pulse photon production in the 1-10 keV range. High-brightness rf photocathodes produce electron bunches which are optimized either for coherent emission in free-electron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by four passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility.

Applications of the constant-current variable-voltage dc accelerator

Abstract Variable beam energy at constant current is useful for industrial applications such as surface hardening and passivation or semiconductor processing. We discuss a dc accelerator, under development for the DOE magnetic fusion energy program, which uses electrostatic quadrupole (ESQ) focusing to maintain constant current while the voltage is variable over a wide range. The use of ESQs also allows a conservative design that alleviates known causes of dc voltage breakdown. The beam is accelerated by a series of 100 kV ESQ modules, stackable to a megavolt or more. The energy is tunable to as low as 20 keV without reduction in current. Single-beam and multiple-beam systems have been designed, capable of accelerating typically 50 mA of N + or O + per beam.

The laser system for the STAR time projection chamber

Abstract The Time Projection Chamber (TPC) is the core tracking detector for the STAR experiment at RHIC. To determine spatial distortions, calibrate and monitor the TPC, a laser calibration system has been built. We developed a novel design to produce ∼500 thin laser beams simulating straight particle tracks in the TPC volume. The new approach is significantly simpler than the traditional ones, and provides a higher TPC coverage at a reduced cost. During RHIC 2000 and 2001 runs the laser system was used to monitor the TPC performance and measure drift velocity with ∼0.02% accuracy. Additional runs were recorded with and without magnetic field to check E×B corrections.

Design Studies for a VUV–Soft X-ray Free-Electron Laser Array

Several recent reports have identified the scientific requirements for a future soft X-ray light source [1, 2, 3, 4, 5], and a high-repetition-rate free-electron laser (FEL) facility responsive to them is being studied at Lawrence Berkeley National Laboratory (LBNL) [6]. The facility is based on a continuous-wave (CW) superconducting linear accelerator with beam supplied by a high-brightness, high-repetition-rate photocathode electron gun operating in CW mode, and on an array of FELs to which the accelerated beam is distributed, each operating at high repetition rate and with even pulse spacing. Dependent on the experimental requirements, the individual FELs may be configured for either self-amplified spontaneous emission (SASE), seeded high-gain harmonic generation (HGHG), echo-enabled harmonic generation (EEHG), or oscillator mode of operation, and will produce high peak and average brightness X-rays with a flexible pulse format ranging from sub-femtoseconds to hundreds of femtoseconds. This new light source would serve a broad community of scientists in many areas of research, similar to existing utilization of storage ring based light sources.

STAR TPC Gas System

The STAR TPC (Time Projection Chamber) Gas System supplies either of two mixtures, P10 (Ar 90% + CH4 10%) or C2H6 50% + He 50%, to the STAR TPC (STAR Project, Brookhaven, USA) at a controlled pressure. This system regulates the pressure and composition of the gas while monitoring gas temperature, O2 and H2O. A computer data acquisition system collects and logs the gas system parameters, controls the purification of the recirculating mixture. A separate alarm and interlock system prevents the TPC from operating under unsafe conditions.

Low‐energy injector design for SSC

An injector is being designed for SSC that will deliver 30 mA of H− at 35 keV, matched to the RFQ input. The H− ions are produced by a new rf‐driven multicusp source that uses no cesium. The ions are extracted by a high‐perveance accelerator designed to handle the large electron content of this type of source. The low‐energy beam transport system (LEBT) uses electrostatic focusing; gas‐neutralized magnetic focusing is ruled out because pulse lengths (7–35 μs) are shorter than plasma buildup times and because pulse intervals are longer than plasma decay times. Plasma buildup is prevented by the LEBT electric fields, so the system is noise free and stable. The advantages of electrostatic LEBTs were demonstrated by a previous design tested at LBL, which showed negligible emittance growth, confirming the results of computer modeling. The object of our new LEBT design is to preserve the emittance of the rf‐driven source, which is less than 0.01 πu2009mradu2009cm (normalized rms), and thereby produce a beam well within...

Mechanical design & analysis of a 200 MHz, bolt-together RFQ for the accelerator driven neutron source

A high-yield neutron source to screen sea-land cargo containers for shielded special nuclear materials (SNM) has been designed at LBNL. The Accelerator-Driven Neutron Source (ADNS) uses the D(d,n)3He reaction to create a forward directed neutron beam. Key components are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power target capable of producing a neutron flux of >107 n/(cm2.s) at a distance of 2.5 m. The mechanical design and analysis of the four-module, bolt-together RFQ will be presented here. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mA deuteron beam to 6 MeV. At a 5% duty factor, the time-average d+ beam current on target is 1.5 mA. Each of the 1.27 m long RFQ modules will consist of four solid OFHC copper vanes. A specially designed 3-D O-ring will provide vacuum sealing between both the vanes and the modules. RF connections are made with canted coil spring contacts. A series of 60 water-cooled pi-mode rods provides quadrupole mode stabilization. A set of 80 evenly spaced fixed slug tuners is used for final frequency adjustment and local field perturbation correction.

Laser calibration system for STAR TPC

The big tracking detector Time Projection Chamber (TPC) being constructed for the STAR experiment at RHIC requires an accurate calibration system to provide precision in crack reconstruction. The calibration system under construction uses a novel design of small mirror bundles to create /spl sim/500 thin laser beams. These beams simulate straight charge particles tracks in the TPC volume. The new approach is significantly simpler than the traditional ones, and provides a higher TPC coverage at a reduced cost. Results of test measurements and the system design will be presented.