review of “shaker” & “thumper” studies at various accelerators

Frank ZimmermannLHC UFO Study Meeting 14 September 2011

ISR dust & shaker

H. Frischholz, T. Wikberg, “Run 95, 9th August 1971, Test with a dust shaker in straight section 349”http://cdsweb.cern.ch/record/1131591/files/CM-P00072614.pdfdescribes experiments and shaker apparatus

Dust in the ISR and a dust shaker were first mentioned to me by Eberhard Keil in CERN resto 2 on 14 February 2011. He pointed me to

E Jones, H Schühback, „Dust and bakeout insulation,“ ISR Performance Report, 8 November 1973http://cdsweb.cern.ch/record/1130691/files/CM-P00071713.pdf

With the help of Kurt Hübner I retrieved the following related information:„Tore Wikberg (Herbert Schuhback was in his section) built an apparatus by which the vacuum chamber in a straight section could be made to vibrate. It was not compliacted, but rather a strong bell or relais fed with ac instead of dc current. I remember that an effect was seen with beam if the vibration was sufficiently strong.” Oswald Gröbner (email to Kurt Hubner) 26 March 2011

E Jones, H Schühback, „Dust and bakeout insulation,“ ISR Performance Report, 8 November 1973

H. Frischholz, T. Wikberg, “Run 95, 9th August 1971, Test with a dust shaker in straight section 349”.

ISR shaker

H. Frischholz, T. Wikberg, “Run 95, 9th August 1971, Test with a dust shaker in straight section 349”.

H. Frischholz, T. Wikberg, “Run 95, 9th August ‘71, Test with dust shaker in straight section 349”.

CERN AA chamber vibrations

A. Poncet, ‘Experience with ion and dust clearing in the CERN AA and EPA,” HHH ECL2 2007

CERN AA shutter

SLAC PEP-II thumper

U. Wienands, “Vacuum Performance and Beam Lifetime in the PEP II Storage Ring,” PAC2011

U. Wienands, “Vacuum Performance and Beam Lifetime in the PEP II Storage Ring,” PAC2011

SLAC PEP-II thumper“… no threshold beam current below which dust-trappingno longer occurs has been observed. With increased beamexposure of the vacuum system however, this effect hassubsided in frequency to the point where it is no longer a major operational concern.”

SLAC PEP-II thumper“The actual devices were small solenoids (commercially bought, not much larger than a few cm in all dimensions) and could be actuated using low dc voltage (up-to 30 Volts), which would exert a single knock, or ping, on the chamber. In this way we were able to provoke background events (what you call UFOs) and study their signature and verify that a knock upstream of the detector in IR 2 almost invariably provoked an SVT radiation abort. They make most sense in conjunction with a fast beam-loss monitoring system. I would think the LHC system (ion chambers) is fast enough, but that needs to be verified. The PEP-II cherenkov detectors certainly were.”

Uli Wienands, 14 September 2011

conclusions

• dust events can be provoked by mechanical vibrations• special thumpers and shakers have been built at

various machines (ISR, PEP-II)• at PEP-II the thumper confirmed dust as the origin of

background spikes• at the ISR it was hoped that the shaker would

improve the vacuum and allow higher beam currents (ISR shaker results look somewhat unclear)

• John Seeman has offered sending a PEP-II thumper to Ralph Assmann at CERN