Results from MD week 45

1
Results from MD week 45 Views of extracted
liners and RF shields
M. Taborelli for SPSU team
2
Pressure measurements after coating the RF
shields between coated magnets

• Start of beam
• Pumping speed from p decay?
• P change from 1 to 2 batches
• P at different bunch spacing

3
Start of MD week 33 and week 45
MDw33
co-co un-un co-un
Pressure mbar
No main difference in pressure rise after coating
the RF-shields Amplitude is lower for coated
(why?)
MDw45
1x72, 26GeV
450GeV
4
Effect of acceleration on the shape of the
pressure curve
450GeV
26GeV
Pressure mbar
5
Is the pressure recovery different in coated and
uncoated magnets ?
1x72 450GeV
Pressure mbar
1x12 450GeV
Assume there is no effect of outgassing from the
12 bunches. Then it
would be linear on the ln(p) plot if it is only
emptying a volume and constant outgassing
Ppoexp(-S.t/V)q
subtract q
6
after q subtraction.almost linear with same
slope for both
Pressure mbar
-from the slope of ln(p) and a volume of 49l we
get S0.15 l/s??? -the value is too low it
means possibly that we are looking at a part of
the curve where the degassing is not constant
during time
7
again on another time period (beam off)
Subtract q
Pressure mbar
Also here the slope gives only S0.6 l/s,
influenced by outgassing and not just emptying a
volume

(nominal 17 l/s at the RF-shield, which should
give a 1/e decay in 2.9s)
8
Look on the fast decay part
Pressure mbar

• Normalize the pressure to equal the values of
  both magnets (should not affect the exponent of
  the decay or 1/t behaviour for outgassing)
• in the steepest part the decay is quite similar
  for both magnets, but changes after few seconds

9
From 1 to 2 batches, 72 bunches 450GeV
Pressure mbar
With a very weak second batch the p decreases
the reason is the cleaning of the ring from
protons circulating out of the buckets (
e-cloud also decreases)
10
Effect of bunch spacing
3batches 25 ns
1batch 25ns long bunches
3b 50ns
1b 50ns
4b 50 ns
11
Effect of bunch spacing summary
12
Liners and RF shields extracted from SPS
13
CKr4 liner cut open used in scrubbing run
w24/2008
Uncoated regions
14
CNe8 liner cut open used in MD run w28/2008
15
StSt liners (run w24 and w28 or w3341)
Not sure that the visible line is really due to
e-cloud
16
RF shield with antenna holes 24mm, extracted from
SPS on 6/10/2009 from 51540 (between coated
magnets)
156 mm
6mm
Shields were inserted in SPS in March 2009, after
drilling the holes and chemical cleaning The
width is 5 mm, comparable with the most intense
region of e-cloud measured for low field (0.4A
20Gauss nominal) in the monitors
11/01/2010
Holger Neupert TE/VSC
17
Side without antenna holes
Holger Neupert TE/VSC
18

• Conclusions
• ?We still do not understand the too small
  difference in dynamic pressure between coated
  and uncoated magnets it does not correspond to
  the expectation from e-cloud monitors and
  dynamic degassing data from a-C coatings (slides
  Paolo)
• ? There is e-cloud also in RF shields (visible
  traces)
• ? The bad result of the first carbon coating in
  the scrubbing run of 2008 was due to uncoated
  regions
• Looking toward 2010
• -Magnetic field measurements outside the MBB
  (J.Bauche)
• -New setup for degassing measurements of a-C
  (optimize degassing, since we believe that SEY
  is sufficiently good)
• -What to do with SPS tests in 2010?
• - coat liners in MBB geometry
• - mass spectrometer?....few chances
• - longer section of coated magnets?
• - simulate the p behaviour more precisely?