BNL, Upton, Long Island, New York
ALBA, Bellaterra (Cerdanyola del Valles)
Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises – including pressure instabilities, a reduction of the stability threshold for bunches crossing the transition energy, and possibly slow emittance growth. We report on the main observations in operation and dedicated experiments, as well as the effect of various countermeasures including baking, NEG coated warm pipes, pre-pumped cold pipes, bunch patterns, scrubbing, and anti-grazing rings.
BNL, Upton, Long Island, New York
A beam-based method was proposed and applied to check the polarities of the arc sextupoles in the Relativistic Heavy Ion Collider (RHIC) with repetitive local horizontal bumps. Wrong sextupole polarities can be easily identified from mismatched signs and amplitudes of the horizontal and vertical tune shifts from bump to bump and/or from arc to arc. This check takes less than 2 hours for both RHIC Blue and Yellow rings. Tune shifts in both planes during this study were tracked with a high-resolution baseband tunemeter (BBQ) system. This method was successfully used to the sextupole polarity check in the RHIC run06.
BNL, Upton, Long Island, New York
We explore the possibility of using two non-scaling FFAG with a smaller number of distributed RF cavities for a high power heavy ion driver. The pulsed heavy ion source would consist of an Electron Beam Ion Source (EBIS), fed continuously from a high charge state Electron Cyclotron Resonance (ECR) source. The Radio Frequency Quadrupole (RFQ) and a short 10 MeV/u linac would follow the ion source. Microseconds long heavy ion beam bunches from the EBIS would be injected in a single turn into a multi-pass small aperture non-scaling Fixed Field Alternating Gradient (FFAG) accelerator. The heavy ion maximum kinetic energy is assumed to be 400 MeV/u with a total of 400 kW power for uranium ion beams. Partially stripped heavy ions would be accelerated from 10 MeV/u to 67 MeV/u with a first non-scaling FFAG, while, after further stripping, a second non-scaling FFAG would accelerate from 67 to 400 MeV/u.
BNL, Upton, Long Island, New York
There are three main sources of the experimental background at RHIC. The beam-gas induced background is associated with the vacuum pressure, the beam-chamber-interaction induced background can be improved by collimations, and the beam-beam induced background is somewhat inherent, and probably harmless for the experimental data taking. The zero degree calorimeter (ZDC) is an essential luminosity detector for heavy ion operations in RHIC. It is shown that, however, the ratio of ZDC singles (background) and coincident rate is also useful in proton runs for background evaluations. In this article, the experimental background problem in RHIC polarized proton runs is reported.
BNL, Upton, Long Island, New York
A hydrogen jet polarimeter was developed for the RHIC accelerator to improve the process of measuring polarization. Particle beams intersecting with gas molecules can produce light by the process known as luminescence. This light can then be focused, collected, and processed giving important information such as size, position, emittance, motion, and other parameters. The RHIC hydrogen jet polarimeter was modified in 2005 with specialized optics, vacuum windows, light transport, and camera system making it possible to monitor the luminescence produced by polarized protons intersecting the hydrogen beam. This paper will describe the configuration and preliminary measurements taken using the RHIC hydrogen jet polarimeter as a luminescence monitor.
BNL, Upton, Long Island, New York
After the last successful RHIC Au-Au run in 2004 (Run-4), RHIC experiments now require significantly enhanced luminosity to study very rare events in heavy ion collisions. RHIC has demonstrated its capability to operate routinely above its design average luminosity per store of 2x1026 cm-2 s-1. In Run-4 we already achieved 2.5 times the design luminosity in RHIC. This luminosity was achieved with only 40% of bunches filled, and with β* = 1 m. However, the goal is to reach 4 times the design luminosity, 8x1026 cm-2 s-1, by reducing the beta* value and increasing the number of bunches to the accelerator maximum of 111. In addition, the average time in store should be increased by a factor of 1.1 to about 60% of calendar time. We present an overview of the changes that increased the instantaneous luminosity and luminosity lifetime, raised the reliability, and improved the operational efficiency of RHIC Au-Au operations during Run-7.
BNL, Upton, Long Island, New York
ITEP, Moscow
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 250GeV. It has been providing collisions at a beam energy of 100GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100GeV with careful control of the betatron tunes and the vertical orbit distortions. However, the intrinsic spin resonances beyond 100GeV are about a factor of two stronger than those below 100GeV 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 250GeV in RHIC with a polarization of 45\% measured at top energy in 2006. The polarization measurement as a function of beam energy also shows some polarization loss around 136GeV, the first strong intrinsic resonance above 100GeV. This paper presents the results and discusses the sensitivity of the polarization survival to orbit distortions.
BNL, Upton, Long Island, New York
Tech-X, Boulder, Colorado
ORNL, Oak Ridge, Tennessee
AES, Princeton, New Jersey
Fermilab, Batavia, Illinois
Jefferson Lab, Newport News, Virginia
BINP SB RAS, Novosibirsk
JINR, Dubna, Moscow Region
The physics interest in a luminosity upgrade of RHIC requires the development of a cooling-frontier facility. Detailed cooling calculations have been made to determine the efficacy of electron cooling of the stored RHIC beams. This has been followed by beam dynamics simulations to establish the feasibility of creating the necessary electron beam. Electron cooling of RHIC at collisions requires electron beam energy up to about 54 MeV at an average current of between 50 to 100 mA and a particularly bright electron beam. The accelerator chosen to generate this electron beam is a superconducting Energy Recovery Linac (ERL) with a superconducting RF gun with a laser-photocathode. An intensive experimental R&D program engages the various elements of the accelerator: Photocathodes of novel design, superconducting RF electron gun of a particularly high current and low emittance, a very high-current ERL cavity and a demonstration ERL using these components.
BNL, Upton, Long Island, New York
CERN, Geneva
LBNL, Berkeley, California
We report on improvements in the non-scaling Fixed Field Alternating Gradient (FFAG) gantry design. As we previously reported*, a major challenge of the carbon/proton cancer therapy facilities is isocentric gantry design. The weight of the isocentric gantry transport elements in the latest Heidelberg carbon/proton facility is 135 tons**. In this report we detail improvements to the previous non-scaling gantry design. We estimate that this non-scaling FFAG gantry would be almost hundred times lighter than traditional heavy ion gantries. Very strong focusing with small dispersion permits passage of different energies of carbon beams through the gantry's fixed magnetic field.*
BNL, Upton, Long Island, New York
Muon acceleration for muon collider or neutrino factory is still in the stage where further improvements are likely as a result of further study. This report presents a design of the racetrack non-scaling Fixed Field Alternating Gradient (NS-FFAG) accelerator to allow fast muon acceleration in small number of turns. The racetrack design is made of four arcs: two arcs at opposite sides have a smaller radius and are made of closely packed combined function magnets, while two additional arcs with a very large radius are used for muon extraction, injection, and RF accelerating cavities. The ends of the large radii arcs are geometrically matched at the connections to the arcs with smaller radii. The dispersion and both horizontal and vertical amplitude functions are matched at the central energy.
BNL, Upton, Long Island, New York
Acceleration of electrons up to 10 GeV for a future electron-ion collider eRHIC (Relativistic Heavy Ion Collider) could be performed with the energy recovery linac with multiple passes. An energy recovery scheme is required if a superconducting linac is used for acceleration. We report on an attempt to make a combination of a multi-pass linac with non-scaling Fixed Field Alternating Gradient (NS-FFAG) arcs. Two NS-FFAG arcs would allow electrons to pass through the same structure with different energies. The beam will be accelerated by the superconducting linac at the top of the sine function, and returned to the front of the linac by the non-scaling FFAG. This process is repeated until the total energy of 10 GeV is reached. After collisions the beam is brought back by the NS-FFAG and decelerated before being dumped.
BNL, Upton, Long Island, New York
With 8 arc sextupole families in each RHIC ring, the nonlinear chromaticities can be corrected on-line by matching the off-momentum tunes onto the wanted off-momentum tunes with linear chromaticity only. The Newton method with singular value decomposition (SVD) technique is used for this multi-dimensional nonlinear optimization, where the off-momentum tune response matrix with respect to sextupole strength changes is adopted to simplify and fasten the on-line optimization process. The off-momentum tune response matrix can be calculated with the on-line accelerator optics model or directly measured with the real beam. This correction method will be verified and used in the coming RHIC run'07.
BNL, Upton, Long Island, New York
To further improve the the polarized proton (pp) luminosity in the Relativistic Heavy Ion Collider, the beta functions at the two interaction points (IPs) will be reduced from 1.0 m to 0.9m in 2007. In addition, it is planned to increase the bunch intensity from 1.5*1011 to 2.0*1011. To accommodate these changes, the nonlinear chromaticities and the third resonance driving term should be corrected. In 2007, the number of the arc sextupole power supplies will be doubled from 12 to 24, which allows nonlinear chromaticity correction. With the updated field errors in the interaction regions (IRs), detailed dynamic aperture studies are carried out to optimize the nonlinear correction schemes, and increase the available tune space in collision.