RHIC Vacuum Pressure Bump Page: 2 of 20
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RHIC Vacuum Pressure Bump
January 14, 2002
Effects of the beam loss, ion and electron gas desorption on the
RHIC vacuum pressure bump have been reviewed. The beam loss and
ion desorption are probably not the dominant factors in the RHIC
vacuum problem. On the other hand, electron desorption, given the
electron multipacting, can cause serious vacuum problem. In general,
the electron multipacting was not predicted for the RHIC according
to the present understanding of the mechanism. However, beam loss
created ions can extend electron lifetime during the bunch gap, and
electron multipacting becomes possible at the RHIC. Also, the pres-
sure rise in the RHIC Gold beam run was much worse than the usual
electron cloud induced vacuum pressure rise, which was observed in
many machines. One possibility is that the beam loss created ions
have raised the electron density saturation limit and, therefore, con-
tributed to further pressure rise. Some complications in diagnostics
of electron multipacting by coherent tune shift in bunches will be dis-
cussed. Electron collection may indicate the coincidence between the
electron multipacting and the pressure rise. It also can help to deter-
mine the electron density.
The vacuum pressure bump has been a problem for the high intensity RHIC
FY2001 gold beam run, in both 55 bunch and 110 bunch filling patterns.
The pressure bump was shown up at the warm beam sections, mostly at the
intersection regions. The relevant factors include the bunch intensity, bunch
spacing, beam loss, and the locations.
In this note, the following issues are discussed.
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Y., Zhang S. RHIC Vacuum Pressure Bump, report, January 1, 2002; United States. (digital.library.unt.edu/ark:/67531/metadc827893/m1/2/: accessed October 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.