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Scrubbing??

Posted: Mon Nov 01, 2010 8:53 pm
by JGLambourne
Page 1 and slide 9 from today’s morning meeting talk about 'scrubbing'.

http://lhc-commissioning.web.cern.ch/lh ... rning.pptx

I'm guessing this is some special kind of fill to clean out the vacuum chamber and fix the UFOs. Does anyone have any more details on this? Do they deliberately defocus the beam so it hits the sides of the beam tube? Are they using protons or ions?

Re: Scrubbing??

Posted: Tue Nov 02, 2010 1:21 am
by Harbles
Here is a paper on Scrubbing. http://cdsweb.cern.ch/record/386682/files/tha6.pdf

The Synopsis.
" An adequate dose of photoelectrons, accelerated by lowintensity
proton bunches and hitting the LHC beam screen
wall, will substantially reduce secondary emission and
avoid the fast build-up of an electron cloud for the nominal
LHC beam. The conditioning period of the liner surface
can be considerably shortened thanks to secondary electrons,
provided heat load and beam stability can be kept
under control; for example this may be possible using a
special proton beam, including satellite bunches with an
intensity of 15-20% of the nominal bunch intensity and a
spacing of one or two RF wavelengths. Based on recent
measurements of secondary electron emission, on multipacting
tests and simulation results, we discuss possible
‘beam scrubbing’ scenarios in the LHC and present an update
of electron cloud effects."

I assume this will be a handy thing to do before operating with ion beams and more intense proton beams in the new year.

Re: Scrubbing??

Posted: Tue Nov 02, 2010 10:34 pm
by amiso
Because of the large collision cross section of heavy ions, I guess this is very important to have extremely good vacuum here: electrons too.

Re: Scrubbing??

Posted: Fri Dec 07, 2012 2:47 pm
by chriwi
Why is scrubbing for 2 days in a row now necessary before they can stat to do proton-proton physics with 25ms spacing of the bunches?
.

Re: Scrubbing??

Posted: Fri Dec 07, 2012 9:02 pm
by Kasuha
Because 25 ns beam was found to have worse electron cloud problems than originally anticipated.

Re: Scrubbing??

Posted: Mon Dec 10, 2012 8:31 am
by chriwi
I understand that, but I wonder what the long time scrubbing is for, is there really so much time neded to clean out the electrons or is that time for test and adjustment to find the right settings?

Re: Scrubbing??

Posted: Mon Dec 10, 2012 9:42 am
by Kasuha