J. Tuozzolo

The RHIC beam abort kicker system

The energy stored in the RHIC beam is about 200 kJ per ring at design energy and intensity. To prevent quenching of the superconducting magnets or material damage, the beam will be safely disposed of by an internal beam abort system, which includes the kicker magnets, the pulsed power supplies, and the dump absorber. Disposal of heavy ions, such as gold, imposes design constraints more severe than those for proton beams of equal intensity. In order to minimize the thermal shock in the carbon-fiber dump block, the bunches must be laterally dispersed. The nominal horizontal beam deflection angle is required to vary from /spl sim/1.7 to 2.5 mrad, which is obtained from five 1.22 m long kicker modules operating at a magnetic field of /spl sim/3.5 T. The kickers are constructed as window frame magnets with an 50.8 by 76.2 mm aperture and are operated in the ring vacuum. The pulsed power supplies run at 33 kV and deliver the 12.8 /spl mu/s long pulse. The peak current required is /spl sim/21 kA and the 50% modulation is generated by means of a pulse forming network with non-uniform characteristic impedance.

The RHIC injection kicker

Beam transfer from the AGS to RHIC is performed in single-bunch mode. Close spacing of the bunches in the collider requires an injection kicker with a rise time of <90 nsec, suggesting adoption of a travelling wave structure. The required vertical kick of 0.186 T/spl middot/m is provided by 4 magnets, each 1.12 m long with a 48.4/spl times/48.4 mm aperture and operated at 1.6 kA. The kicker is constructed as a C cross section magnet, in which ferrite and high-permittivity dielectric sections alternate. The dielectric blocks provide the capacity necessary for the nominally 25 /spl Omega/ characteristic impedance of the travelling wave structure, but impose the practical limit on the peak voltage, and thus current, achievable. Computer studies to minimize local electric field enhancements resulted in a configuration capable of holding /spl sim/50 kV, with adequate safety margin over the nominal 40 kV. Equivalent circuit analysis indicated the possibility of lowering the nominal voltage by operating mismatched into 20 /spl Omega/ terminations without degrading the pulse shape. In this paper, the experience gained in the fabrication of the production units and the results from various single-unit tests and operation of four kickers with beam in the Sextant Test are reported.

Unique features in magnet designs for R&D energy recovery linac at BNL

In this paper we describe the unique features and analysis techniques used on the magnets for a R&D Energy Recovery Linac (ERL) [1] under construction at the Collider Accelerator Department at BNL. The R&D ERL serves as a test-bed for future BNL ERLs, such as an electron-cooler-ERL at RHIC [2] and a future 20 GeV ERL electron-hadron at eRHIC [3]. Here we present select designs of various dipole and quadrupole magnets which are used in Z-bend merging systems [4] and the returning loop, 3-D simulations of the fields in aforementioned magnets, particle tracking analysis, and the magnets influence on beam parameters. We discuss an unconventional method of setting requirements on the quality of magnetic field and transferring them into measurable parameters as well as into manufacturing tolerances. We compare selected simulation with results of magnetic measurements.

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.

Principle design of 300 KHz meco RF kicker bipolar solid state modulator

A high speed, high repetition rate, bipolar solid-state high voltage modulator is under development at Brookhaven National Laboratory for muon electron conversion (MECO) experiment. The modulator will be used to drive a RF kicker consisting of a pair of parallel deflecting plates. The principle design is based on the inductive-adder topology. This system requires a fast pulse rise and fall time of approximately 20 ns, a pulse width of 100ns, a pulse repetition rate of 300 kHz, and a 60 kHz sinewave amplitude modulation. Fast high voltage MOSFETs are used as main switching devices. Different magnetic materials are being investigated for the adder core magnets. The main circuit design, critical subsystems, and major technical issues will be discussed. The circuit simulation, component selection and evaluation, and preliminary test results will be presented

Metal and elastomer seal tests for accelerator applications

Abstract In excess of a thousand metal vacuum seals are used in the vacuum system of the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. Numerous elastomer seals are used throughout the AGS to seal large beam component chambers. An accelerator upgrade program is being implemented to reduce the AGS operating pressure by a factor of 100 and improve the reliability of the vacuum system. This paper describes work in progress on metal and elastomer vacuum seals to help meet these two objectives. Tests are reported on the sealing properties of a variety of metal seals used with different sealing surfaces. Results are also given on reversible sorption properties of certain elastomers.

Status of head-on beam-beam compensation in RHIC

In polarized proton operation, the performance of the Relativistic Heavy Ion Collider (RHIC) is limited by the head-on beam-beam effect. To overcome this limitation, two electron lenses are under commissioning. We give an overview of head-on beam-beam compensation in general and in the specific design for RHIC, which is based on electron lenses. The status of installation and commissioning are presented along with plans for the future.

High power fast kicker system for SNS beam extraction

A Blumlein topology based high peak power, high repetition rate, and low beam impedance fast extraction kicker system for ORNL Spallation Neutron Source (SNS) is being developed at Brookhaven National Laboratory. The large magnet window size, large deflecting angle, low beam impedance termination and fast deflecting field rise time demand a very strong pulsed power source to drive the SNS extraction fast kicker magnet. This system consists of fourteen high voltage modulators and fourteen lumped kicker magnet sections. All modulators will be located in a service building outside the beam tunnel, which is a revised design requirement adopted in the mid 2000. The high current pulses generated by the high power modulators will be delivered through high voltage pulsed transmission cables to each kicker magnet sections. The designed output capacity of this system is in multiple GVA. Its first article modulator has been constructed and is being tested. In this paper, we present the system overview, project status and the advantages of this new conceptual design.

Design of a high-bunch-charge 112-MHz superconducting RF photoemission electron source

High-bunch-charge photoemission electron-sources operating in a continuous wave (CW) mode are required for many advanced applications of particle accelerators, such as electron coolers for hadron beams, electron-ion colliders, and free-electron lasers. Superconducting RF (SRF) has several advantages over other electron-gun technologies in CW mode as it offers higher acceleration rate and potentially can generate higher bunch charges and average beam currents. A 112 MHz SRF electron photoinjector (gun) was developed at Brookhaven National Laboratory to produce high-brightness and high-bunch-charge bunches for the coherent electron cooling proof-of-principle experiment. The gun utilizes a quarter-wave resonator geometry for assuring beam dynamics and uses high quantum efficiency multi-alkali photocathodes for generating electrons.

SNS extraction fast kicker system development

The SNS extraction fast kicker system is a very high power, high repetition rate pulsed power system. It was design and developed at Brookhaven national laboratory. This system will consist of fourteen identical high voltage, high current modulators, and their auxiliary control and charging systems. The modulators will drive fourteen extraction magnet sections located inside of the SNS accumulator ring. The required kicker field rise time is 200 ns, a pulse flattop of 700 ns, a pulse repetition rate of 60 pulse-per-second. A 2500 Ampere per modulator output is required to reach the extraction kicker magnetic field strength. This design features a Blumlein pulse-forming-network based topology, a low beam impedance termination, a fast current switching thyratron, and low inductance capacitor banks. It has a maximum charging voltage of 50 kV, an open circuit output of l00 kV, and a designed maximum pulsed current output of 4 kA per modulator. The overall system output will be multiple GVA with 60 pulse-per-second repetition rate. A prototype modulator has been successfully built and tested well above the SNS requirement. The modulator system production is in progress.