N. Tsoupas

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.

Commissioning of RHIC deuteron-gold collisions

Deuteron and gold beams have been accelerated to a collision energy of /spl radic/s = 200 GeV/u in the Relativistic Heavy Ion Collider (RHIC), providing the first asymmetric-species collisions of this complex. Necessary changes for this mode of operation include new ramping software and asymmetric crossing angle geometries. This paper reviews machine performance, problems encountered and their solutions, and accomplishments during the 16 weeks of ramp-up and operations.

Superconducting Helical Snake Magnet for the AGS

A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This “partial Snake” magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that the magnet can operate in the AGS cooled by several cryocoolers. The design, construction and performance of this unique magnet will be summarized.

Commissioning and future plans for polarized protons in RHIC

Polarized protons were injected and accelerated in the clockwise ring of RHIC to commission the first full helical Siberian snake ever used in an accelerator. With the snake turned on, the stable spin direction is in the horizontal plane. Vertically polarized protons were injected with the snake off. The snake was adiabatically ramped to give a spin rotation of 180/spl deg/ around a horizontal rotation axis about 13/spl deg/ from the longitudinal. When the beam was accelerated from injection G/spl gamma/ = 46.5 to G/spl gamma/ = 48 the spin flipped sign as expected and polarization was preserved. At G/spl gamma/ = 48 without the snake, no polarization was observed since several spin resonances were crossed. Eventually polarized beam was accelerated to G/spl gamma/ = 55.7 (29.1 GeV). In the next proton running period we plan to run with two full helical snakes in each ring and collide both transversely and longitudinally polarized protons at an energy around 100 GeV per beam.

Commissioning results of slow extraction of heavy ions from the AGS Booster

Brookhavens AGS Booster has been modified to deliver slow extracted beam to a new beam line, the NASA Space Radiation Laboratory (NSRL). This facility was constructed in collaboration with NASA for the purpose of performing radiation effect studies for the NASA space program. The design of the resonant extraction system has been described. A more detailed description, which includes predictions of the slow extracted beam time structure has been described. In this report we present results of the system commissioning and performance.

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.

Commissioning of the Relativistic Heavy Ion Collider

This report describes in detail steps performed in bringing the Relativistic Heavy Ion Collider (RHIC) from the commissioning into the operational stage when collisions between 60 bunches of fully striped gold ions, were routinely provided. Corrections of the few power supply connections by beam measurements are described. Beam lifetime improvements at injection, along the acceleration are shown. The beam diagnostic results such as the Schottky detector, beam profile monitor, beam position monitors, the tune meter and others, are shown.

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.

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.

Mechanical design of fast extraction kicker and PFN for SNS accumulator ring

Two kicker assemblies, seven pulsed magnet modules in each assembly, will be used in the SNS accumulator ring to kick the beam vertically to the extraction septum then to the target. These kickers are designed as window frame magnets housed inside a vacuum chamber. Fourteen pulse forming networks (PFN) housed in separate silicon fluid containers are designed to power each kicker module. A single module prototype kicker magnet and PFN modulator have been successfully assembled and tested. In this paper we discuss the mechanical design criteria of these kicker assemblies, the installation layout in the accumulator ring, the structural analysis of the kicker chamber, the magnetic field analysis of the ferrite magnet, the high voltage feedthrough design, the structural design of the modulator container, the cooling and the thermal expansion considerations of the silicon fluids.