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…