M. Sullivan High Luminosity workshop (HL6) November 16-18, 2004

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

2. Outline • NEG story • Vacuum modeling • Conclusions

3. PEP-II Interaction Region and the BaBar Detector LER HER e+ e- BaBar Collision point

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

5. Upstream LER plan view Quad chambers Dipole chambers Collimators 130F bot 150F bot 136F side 160F side 150F bot 150F bot

6. 350 °F LER NEG Pump Temperatures Lab test data of NEG outgassing as a function of temperature Upstream LER side

7. LER beam current Data from the two hottest NEGs 3149 Pump pressure of 3147. The ion pump is between the two NEGs NEG temperatures 3142 3149

8. Some regeneration details NEG heaters off NEG heaters on St707 Ion pumps on 10-2 Ion pumps off 600° C 500° C 10-4 400° C Hydrogen Equilibrium Pressure (Torr) Embrittlement Limit (20 Torr l/g) 10-6 300° C 10-8 200° C 10-10 10-2 10-1 100 101 Hydrogen Concentration Torr l/g 100 Heat NEGs for 1 hr 400-450 degC Time 11:45-12:45 Tubro cart pump: 220 L/s Pressure at pump about 10-5 Torr

9. LER NEG Test chamber

10. Recent test NEG data We held the test NEG at our regen temperature for a month

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).

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

13. One of the NEGs that was removed last summer

14. One of the collimators that was removed The NEG in this chamber was one of the hottest

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

16. Chamber Model Layout 3 69.33 m HER downstream LER downstream 4 plot plot Q5 NEG ST plot 2 1 Support chamber Q5 NEG plot plot 5 6 LER upstream HER upstream 66.114 m

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.

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.

19. Upstream LER Ideal LER beam line from Q2 septum to about 63 m upstream

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.

21. HER scrubbing

22. HER Upstream Q5 chamber • We plan to replace this chamber NEG temp in Q5 chamber Diamond BW (HER) BaBar Deadtime

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

24. HER upstream NEG screen This is a post at the center of the chamber

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