Electron Clouds and Vacuum Pressure Rise in Rhic (original) (raw)
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Analysis of Electron Cloud at Rhic
2004
Pressure rises with high intense beams are among the main luminosity limitations at RHIC. Observations during the latest runs show beam induced electron multipacting as one of the causes for these pressure rises. Experimental studies are carried out at RHIC using devoted instrumentation to understand the mechanism leading to electron clouds. In the following, we report the experimental electron cloud data and the analyzed results using computer simulation codes.
Electron cloud observations and cures in RHIC
2007 IEEE Particle Accelerator Conference (PAC), 2007
The Relativistic Heavy Ion Collider (RHIC),. in operation since 2000, has collided species from gold ions, at energies up to 100 GeV/n, to polarized protons, at energies up to 100 GeV. Since 2001 dynamic pressure rises were observed that limited the beam intensity. At that time the cause of the dynamic pressure rise was not known. As possible causes were considered: electron impact desorption after electron cloud formation, ion-impact desorption after rest gas ionization and ion acceleration in the beam potential, and beam loss induced desorption [2]. It was later concluded that all operationally relevant pressure rises can be explained by electron clouds. Tab. 1 shows selected machine and beam parameters relevant to electron clouds for all species operated in RHIC so far. Since 200 1 RWIC has experienced electron cloud effects, .-40000' which have limited the beam intensity. These include dy-3 MOO. namic pressure risesincluding pressure instabilities, tune
Electron Cloud Observations at RHIC in Run-3 (2002/03)
2003
In the Run-2 (2001), an unexpected vacuum pressure was observed with increasing currents in both gold and proton operation at RHIC. This pressure increase due to molecular desorption is suspected to be induced mainly by electron multipacting, but other causes may coexist. In order to obtain a reliable diagnostic of the phenomenon, electron detectors have been designed, and finally installed in the RHIC ring. The use of solenoids as a possible cure for the phenomenon has also been evaluated. This report describes both instrumentation and measurements during Run-3 (2002/03) at RHIC.
Experience in Reducing Electron Cloud and dynamic Pressure Rise in warm and cold Regions in RHIC
2006
The large scale application of non-evaporable getter coating in RHIC has been effective in reducing the electron cloud. Since beams with higher intensity and smaller bunch spacing became possible in operation, the emittance growth is of concern. Study results are reported together with experiences of machine improvements: saturated NEG coatings, anti-grazing ridges in warm sections, and the pre-pumping in cryogenic regions.
Observation of Electron-Ion Effects at RHIC Transition
Proceedings of the 2005 Particle Accelerator Conference, 2005
Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electronion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition.
Beam Induced Pressure Rise in RHIC
Proceedings of the 2005 Particle Accelerator Conference, 2005
Phone: (800) 553-6847 Facsimile: (703) 605-6900 Online ordering: http://www.ntis.gov/ordering.htm Abstract Beam induced pressure rise in RHIC warm sections is one of the machine luminosity limits. The RHIC electron cloud and the beam transition pressure rise are discussed. Countermeasures and studies for RHIC pressure rise and RHIC upgrade are reported.
Electron Cloud Effects: Observations, Mitigation Measures, and Challenges in RHIC and SNS
Electron cloud is one of the leading mechanisms that limit the performance of high intensity circular accelerators and colliders. In the Relativistic Heavy Ion Collider, multibunch electron cloud effects are observed both in the warm region and super-conducting region when the number of ion bunches and their intensities are raised beyond the design values. Vacuum-pressure rises, transverse tune shifts, and electron detector signals are observed at injection, upon transition crossing, and at top energy. Transverse emittance growth, fast instabilities, and beam loss also occur upon transition crossing. With the Spallation Neutron Source Ring, single-bunch electron cloud effects are expected for the high intensity proton beam. A comprehensive list of mitigation measures are implemented both to reduce the production of electron cloud and to control the beam stability. This paper intends to provide an overview of observations, performance limitations, and beam dynamics challenges pertaining to electron cloud build-up in high intensity, circular hadron accelerators.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2000
Creating and probing high density matter at RHIC
2004
In the search for the Quark-Gluon Plasma, results from RHIC depict formation of a dense system at an energy density greater than 5 GeV/fm3, well above that where hadrons exist. Statistical models that describe RHIC data indicate a temperature and baryochemical potential at the deconfinement phase trasition boundary predicted by lattice QCD calculations. The anisotropic collective flow observed in collisions at RHIC provides direct evidence of strong pressure gradients in the highly interacting dense medium. Hardscattering, suppression of hsdrons at large transverse momentum, and quenching of di-jets are observed in central Au + Au collisions and provide evidence for large energy loss of partons traversing the high density matter created at RHIC.