9 October 2003S. DeBarger PEP-II Vacuum Status PEP-II Machine Advisory Committee

S. DeBarger 9 October 2003 S. Ecklund W. Kozanecki D. Kharakh A. Kulikov N. Kurita J. Langton S. Metcalfe A. Novokhatski J. Seeman M. Sullivan U. Wienands D. Wright

S. DeBarger 9 October 2003 Outline of Topics Introduction to HER & LER Vacuum Systems Present Performance Assessment Vacuum Failure Statistics from Run Future Performance Requirements

S. DeBarger 9 October 2003 Introduction to HER & LER Vacuum Systems High Energy Ring (HER) Arcs Copper vacuum chambers Distributed Ion Pumps (DIPs) in dipole chambers Conventional ion pumps located adjacent to quadrupoles Synchrotron Radiation absorbed along the length of the dipole chambers and at discrete masks in the quadrupole chambers Low Energy Ring (LER) Arcs Aluminum vacuum chambers Titanium Sublimation Pumps (TSPs) and conventional ion pumps located on pumping chambers Synchrotron Radiation absorbed on discrete photon stops located at the end of each pumping chamber

S. DeBarger 9 October 2003 Introduction to HER & LER Vacuum Systems Straight sections (HER & LER) Primarily stainless steel vacuum chambers with conventional ion pumps and discrete masks to absorb synchrotron radiation Interaction Region (IR-2) Primarily copper and stainless steel chambers Non-Evaporative Getter pumps (NEGs), Titanium Sublimation Pumps (TSPs) and conventional ion pumps Discrete masks to absorb synchrotron radiation Higher Order Mode (HOM) heating is a concern (due to the many changes in vacuum chamber cross section in this region)

S. DeBarger 9 October 2003 Present Performance Assessment Beam-gas interactions are not driving lifetime in either the HER or the LER, or backgrounds in BaBar, however a significant fraction (>50%) of the integrated radiation dose to BaBar comes from beam-gas interaction (W. Kozanecki et al,Sep-03) HER Lifetime 300 top of fill (1.1 A), 500 bottom of fill; Lifetime > 2000 low current (400 mA) LER Lifetime 100 top of fill (1.5 A), 200 bottom of fill: 1100 low current (100 mA) PEP TSPs flashed ~9 times during the run from Nov 02 to Jun 03

S. DeBarger 9 October 2003 Present Performance Assessment Vacuum pressure generally better than PEP-II Conceptual Design Report specified PEP-II CDR: 10 nTorr in Arcs, 1 nTorr in Straights Note: Pumps in the HER Arcs see scattered electrons, causing unrealistically high readings 1A 1.5 A

S. DeBarger 9 October 2003 Present Performance Assessment Temperatures at present currents are not globally an issue All LER bellows have had cooling fans added (summer 2003) 1A 1.5 A

S. DeBarger 9 October 2003 Vacuum Failure Statistics from Run There were 139 vacuum problems reported during the PEP-II Run. 23 of the 58 PEP ring vacuum reported problems were located in PR02 (Interaction Region). Most (85%) of PEP vacuum reported problems did not interrupt beam operations. Bad VACP power supplies, open TSP filaments, overheating bellows were all addressed through scheduled maintenance activities.

S. DeBarger 9 October 2003 Vacuum Failure Statistics from Run - Downtime 7 vacuum events resulted in loss of beam time in PEP-II Run. Total Beam Time lost and attributed to Vacuum Systems was hours. Actual negative impact on integrated luminosity is greater than this number suggests; does not count for periods of reduced current running or periods when PEP is running but BaBar cannot take data due to high backgrounds. Also, some follow-on activities become “Scheduled Off” time (i.e. NEG activation). Vacuum failures, while infrequent, generally require extended times to repair. This can be attributed to the relative inaccessibility of the devices, the necessity to transport and set-up leakchecking equipment, and the procedures followed when working with UHV systems.

S. DeBarger 9 October 2003 Vacuum Failures Causing Machine Downtime Elliptical Vacuum Valve Failure - Beam Time Lost hours LER Frangible Link - Beam Time Lost hours Mystery Pressure Bump Near IP - Beam Time Lost hours LER Arc 1 Pumping Chamber - Beam Time Lost hours Q2 Chamber - Beam Time Lost 50.1 hours These five incidents contributed of the hours of downtime attributed to vacuum failures during the PEP-II run

S. DeBarger 9 October 2003 Future Performance Requirements Existing devices were generally designed to operate at 3 Amps, 9 GeV HER and 3 Amps, 3.5 GeV LER In the Interaction Region this was not achieved – several items were designed for 2 A, 9 GeV HER and 2.1 A, 3.1 GeV LER Shorter bunch length will increase HOM heating New Interaction Region design could have new orbits and beam stay-clear values For operation at 3.6 A, 3.1 GeV LER, SR power will be 74% of CDR level For operation at 4.5 A, 3.1 GeV LER, SR power will be 92% of CDR level

S. DeBarger 9 October 2003 Future Performance Requirements Must reanalyze and potentially rebuild 17 vacuum chamber, mostly in the Interaction Region (see N. Kurita file V:\AD\Drop Boxes\Kurita- DeBarger\PEP-IIVacShortList.xls ) to survive higher LER currents LER bellows must be redesigned and replaced to reduce HOM heating at high currents LER Arc 3 HOM absorber (A. Novokhatski, J. Langton) has been effective, may need to deploy at more locations

S. DeBarger 9 October 2003 Future Performance Requirements Improve performance of RF sealed vacuum valves Reduce pressure in the LER upstream of BaBar? Improved vacuum instrumentation Residual Gas Analyzers More gauges Gauges which read at lower pressures

S. DeBarger 9 October 2003 Summary Both the HER and LER vacuum systems meet or exceed performance specified in the PEP-II CDR Moving to higher LER currents and shorter bunch lengths will require reanalysis and potential redesign of a significant number of vacuum chambers LER bellows will require a redesign for high current operation All vacuum designs must be robust, as vacuum failures lead to large losses in integrated luminosity