November 16-18, 2004 Belle High Luminosity Workshop 1 M. Sullivan High Luminosity workshop (HL6) November 16-18, 2004 IR Vacuum Summary and Issues

November 16-18, 2004 Belle High Luminosity Workshop 2 Outline NEG story Vacuum modeling Conclusions

November 16-18, 2004 Belle High Luminosity Workshop 3 PEP-II Interaction Region and the BaBar Detector HER LER Collision point BaBar ee ee

November 16-18, 2004 Belle High Luminosity Workshop 4 Summary of the NEG story When we regenerated the NEGs in IR2 on March 24 we began to wonder if some of the NEGs were starting to heat up from HOM power. We confirmed that some were getting hot shortly thereafter but we did not get a full picture until the next ROD on June 3 when we instrumented every NEG in the upstream LER beam line. Regeneration temperature is about 750 °F

November 16-18, 2004 Belle High Luminosity Workshop 5 Upstream LER plan view 136F side 160F side 150F bot 130F bot 150F bot 150F bot Collimators Quad chambers Dipole chambers

November 16-18, 2004 Belle High Luminosity Workshop 6 Lab test data of NEG outgassing as a function of temperature LER NEG Pump Temperatures Upstream LER side 350 °F

November 16-18, 2004 Belle High Luminosity Workshop 7 NEG temperatures Pump pressure of The ion pump is between the two NEGs Data from the two hottest NEGs LER beam current

November 16-18, 2004 Belle High Luminosity Workshop 8                     Hydrogen Concentration Torr l/g Hydrogen Equilibrium Pressure (Torr) 200° C 300° C 400° C 600° C 500° C St707 Embrittlement Limit (20 Torr l/g) NEG heaters on NEG heaters off Ion pumps off Ion pumps on Heat NEGs for 1 hr degC Time 11:45-12:45 Tubro cart pump: 220 L/s Pressure at pump about Torr Some regeneration details

November 16-18, 2004 Belle High Luminosity Workshop 9 LER NEG Test chamber

November 16-18, 2004 Belle High Luminosity Workshop 10 Recent test NEG data We held the test NEG at our regen temperature for a month

November 16-18, 2004 Belle High Luminosity Workshop 11 Pressure in the test NEG Pressure as a function of time in the test NEG. Holding the NEG at the regen temperature of 725  F (400  C).

November 16-18, 2004 Belle High Luminosity Workshop 12 LER upstream NEG work This last summer: –Took out the nine NEGs with “c type” screens and installed a small HOM absorber in each cavity –The total length of NEG pumping removed is 5.5 m out of a total of 40.4 m –We have removed the Q4 LER NEG and replaced it with a HOM absorber (another 1.6 m) –We then added extra pumping at the port between the Q4 and Q5 chambers –In addition, we have added extra screening to the ion pumps in this region –We also removed the movable collimators

November 16-18, 2004 Belle High Luminosity Workshop 13 One of the NEGs that was removed last summer

November 16-18, 2004 Belle High Luminosity Workshop 14 One of the collimators that was removed The NEG in this chamber was one of the hottest

November 16-18, 2004 Belle High Luminosity Workshop 15 Vacuum model We have started building a vacuum model of straight 2 Had great help getting started by a summer student (Edward Young) We have a preliminary model of the LER upstream beam pipe Still need to check on screen conductances and on outgassing values from SR fans Nevertheless we can get some idea about what happens to the vacuum pressure profile with the above LER NEGs removed

November 16-18, 2004 Belle High Luminosity Workshop 16 Chamber Model Layout HER downstream LER upstream LER downstream HER upstream Support chamber Q5 NEG m m ST plot plot

November 16-18, 2004 Belle High Luminosity Workshop 17 Support tube Vacuum Design Model Vacuum pressure in the support tube. The model predicts a pressure peak at the IP of about 20 nTorr.

November 16-18, 2004 Belle High Luminosity Workshop 18 No radial ion pumps We lost these pumps a couple of years ago. One developed an Argon instability before it died. Both pumps do not work right now. We intend to replace these pumps this coming summer.

November 16-18, 2004 Belle High Luminosity Workshop 19 Upstream LER Ideal LER beam line from Q2 septum to about 63 m upstream

November 16-18, 2004 Belle High Luminosity Workshop 20 Upstream LER after summer down One can see the pressure bumps where the NEG pumps have been removed Keep in mind that we believe the vacuum pressure to be better than this due to the beam scrubbing from the high LER beam current.

November 16-18, 2004 Belle High Luminosity Workshop 21 HER scrubbing

November 16-18, 2004 Belle High Luminosity Workshop 22 HER Upstream Q5 chamber We plan to replace this chamber BaBar Deadtime Diamond BW (HER) NEG temp in Q5 chamber

November 16-18, 2004 Belle High Luminosity Workshop 23 Other upstream HER NEGs and heater instrumentation The upstream HER beam pipe is also blanketed with NEG pumps starting at 21 m and going up to up to about 45 m from the IP There are a total of 4 vacuum chambers in this region with NEG pumping (6 long NEGs). All of the pumps are below the beam chamber. The collimator at 35 m has a TSP The only chamber in this area without pumping is the fast kicker chamber The screen is very similar to the “c type” screen seen in the LER Stan instrumented one of these NEG heaters the last week (they all look like they have the same design) by putting a small current (10 mA ) through the heater circuit and measuring the heater resistance Next slide

November 16-18, 2004 Belle High Luminosity Workshop 24 HER upstream NEG screen This is a post at the center of the chamber

November 16-18, 2004 Belle High Luminosity Workshop 25 Conclusions This last run we discovered that NEG pumps in the upstream LER were heating up due to HOM power getting through the screens. The high beam current in the LER and high beam bunch currents increased the HOM power levels. In addition, we verified that the movable collimators were a significant source of HOM power. (These screens would have probably worked with the original PEP-II design parameters) This past summer we have fixed as many of the NEG heating problems as we could: –9 LER “ c type ” chambers have been modified –The upstream LER Q4 chamber NEG has been removed –The two LER upstream movable collimators have been removed –Intend to replace the HER upstream Q5 chamber this coming summer These fixes should make recovering from a NEG regen much faster The upstream HER NEGs will need to be watched more closely