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IR2 Vacuum Status
M. Sullivan forS. Ecklund, A Fisher, S. Novokhatski, F-J Decker, A. Kulikov, S. DeBarger, U. Wienands, S. Gierman, M. Petree,
many BaBarians
Feb. 8, 2006
2e34 meeting
Summary
• Last week we vented IR2 to remove the pumping plenum on the incoming LER beam pipe between at the Q4/Q5 location (5 m from the IP) – picture
• Work was done Thurs. and we regenerated the NEG pumps Fri.
• An excellent job. Thanks to everyone who helped: vacuum, MFD, controls, PEM, …
• The vacuum scrubbed so quickly we were able to get to high enough currents within hours after IR2 was searched. Saw our first vacuum event by 10pm Friday night -- 5 hrs after first beam.
• By Saturday morning we had had several vacuum spike events.
Interaction Region Layout
LER HER
7039 gauge
SIG11LER sensitive
2187 gauge
3044 pump
LER frangible link
Detector
7043 pump
8020 pump
3027 gauge
Support tube end bellows
4042 gauge
NEG pump
Backward Q2 NEG
Forward Q2 NEG
Typical event pressures
LER HER
1.9
1540
96
0
LER frangible link
Detector
0
1.9
630
Support tube end bellows
0.1
NEG pump
Backward Q2 NEG
Forward Q2 NEG
One of the highest pressure events
LER HER
2.5
1480
115
0
LER frangible link
Detector
0
2.2
1210
Support tube end bellows
0.3
NEG pump
Backward Q2 NEG
Forward Q2 NEG
Characteristics• Generally very fast single spike but we do have cases of precursors
and aftershocks• Pressure at highest gauge (3027) is about 500 nTorr• Next highest pressure is at 2187 gauge which is ten times lower • The spike threshold seems to have increased. Before last weeks
vacuum work the workable beam currents were 1350x900. Now they seem to be 1650x1050 with a fairly sharp threshold at 1700 for the LER.
• We sometimes get low pressure flurries• Some operators feel that there might be a thermal effect…seems
you have to back off in beam current for a while after a big spike• The events are more consistent – I get the same or very similar
pressure ratios• Rogues’ gallery…
First event that aborted the beam -- Friday evening at 21:42
Attempted to get above the threshold
Very slight increase in LER current generated a huge spike – 1000 nTorr
What’s been done this week
• Changed the RF voltage Monday. Because the character of the vacuum spikes had changed (threshold increased) we wanted to see if changing the RF voltage would make a difference. Changed the RF from 4.05 to 4.5 MV. No significant change seen in the vacuum spike behavior.
• LINAC trouble yesterday allowed us to add more tubes to the He checking system
• We also recalibrated the gauge responses by heating up the two Q2 NEG pumps as well as the backward side LER Q4 and Q5 NEGs
• This will help in getting the vacuum model properly tuned• Yesterday we did our first big He leak check with beam
present…
Helium hosing layout
LER HER
DetectorSupport tube end bellows
NEG pump
Known small vacuum leak
Signal from the known small leak about 20-25 m in the upstream LER
The flow meter says 2 SCFH for one tube
He flow turned on at 17:00. No signal yet.
The two ion pumps 8020 and 3044 were turned off
He flow still onNo signal when we get a vacuum spike at 17:37This spike reads 150 nTorr at 3027
He flow still onFirst He signal at 17:50
He signal getting stronger 10 min after first sign
He signal getting stronger 20 min after first signSome vacuum activity also seen on the gauges
He turned off at about 18:20, at left edge of plot
The two ion pumps 8020 and 3044 were turned on where the Argon trace drops
A spike is seen in the He trace when we get a vacuum spike at 18:50
Status and plans
• More external leak checking
• We need to try to understand the signal we have seen
• Presently installing a controlled leak at the 3044 ion pump location. We are using the pump out port located there.
• Concentrate on improving the analysis that pinpoints the z location– More events to H. Nicholson of BaBar– Work on the IR vacuum model to see if we can get a z location from it– Study and perhaps improve B. Peterson’s analysis
• Hooked up one of the BPMs at 3024 to a high speed cable – did this yesterday – nothing seen yet
• Review the borescope videos again – still to do
• More…
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