1. Loss Limitations and Collimation Angelika Drees, R. Fliller, W. Fu The RHIC Collimation Sytem: history and overview RHIC Loss Limitations Operational limits Beam Dumps/Quench Limits Soil Activation Exp. Background Summary

2. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 RHIC Collimator Configuration  RHIC was originally built with a 1-stage collimation system only: 1 dual plane h/v scraper with 45 cm copper jaws, linear motion in both planes, skew motion only in horizontal 1 bent crystal collimator for studies in 1 ring (yellow) only  The system was upgraded after the 2003 run because of high experimental backgrounds and gap cleaning demands. Crystal approach proved non sufficient.

3. RHIC overview: collimation system 2004 and upgrade (capped area) New blue 2ndary vertical collimator (v2) New yellow 2ndary vert. Collimator (v2) 2000-2003: 1-stage system including bent crystal in 1 ring 2004: Traditional 2-stage system with 2 horizontal and 1 vertical secondary collimators 2005: Traditional 2-stage system with 2 horizontal and 2 vertical secondary collimators

4. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimator Section Layout In the shutdown 2003-2004 the collimation system was upgraded to a conventional 2- stage system including new individual secondary collimators for both planes. The new system was first used in the run 2004 for both, Au and protons.

5. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimator Design cross-section of the primary collimator (dual plane) H V H 45 cm copper jaws One side only Rotatable, positioning: few  m

6. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Crystal Collimation Attempt during Fill 3061 (Au) STAR “Yellow Halo” signal during Crystal Collimation attempt scraper is closer to the beam toward the bottom of graph crystal is at 13.6 mm from beam center and channeling Scraper alone is more effective than the crystal and scraper together … If you want to know why we pulled out the crystal and installed traditional secondaries …

7. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Loss Limitations  Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour  Quench limit: magnet quenches due to accidental local losses during ramp/store => BLMs magnet quenches at beam dump due to debunched beam => gap cleaning  Soil activation (not under radiation protection), depends on integrated yearly losses  Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time)

8. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Operational Limits: Monitoring of Beam Loss/hour dirty dump alarm level is reset alarm level max. 1 hour After every dump (operational or accidental) all RHIC loss monitors are analyzed. If dump appears to be “dirty”, i.e. unmasked loss monitors register losses above a certain level, injection into RHIC will be blocked for 1 hour (see figure).

9. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Loss Limitations  Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour  Quench limit: magnet quenches due to accidental local losses during ramp/store => BLMs magnet quenches at beam dump due to debunched beam => gap cleaning  Soil activation (not under radiation protection), depends on integrated yearly losses  Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time)

10. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 fill 4118 Accidental Local Losses: BLM thresholds Magnet quenches can be caused by fast (ms) type losses. => BLM trip levels (thresholds) fill 4198 Continuous scraping/losses cause magnet quenches as well. Trip levels don’t help.  software integration  or collimators

11. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimators as limiting Aperture during Store It is difficult to maintain limiting aperture position at all times – especially during ramp!

12. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimator use during the Ramp Losses around RHIC on 2 ramps during FY01 top: beam scraping at abort kickers center: scrapers inserted bottom: lattice Using the collimators reduced losses at abort kickers by x100

13. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Loss Limitations  Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour  Quench limit: magnet quenches due to accidental local losses during ramp/store => BLMs magnet quenches at beam dump due to debunched beam => gap cleaning  Soil activation (not under radiation protection), depends on integrated yearly losses  Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ration in experiments and keep false trigger rate small (dead time)

14. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Gap Cleaning: Motivation and Method  gap cleaning is necessary due to the extensive debunching of HI beams (quenching risk)  method: debunched beam is excited transversely (continuously during the store: 1Hz) using damping kickers the collimation system absorbs the large amplitude particles (in addition to halo)  debunched beam should be lost in collimator area, efficiency relies on collimator performance to avoid increase of exp. backgrounds

15. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Excitation frequency for Cleaning default procedure: excite around betatron tune of bunched beam (measured automatically at the end of ramp) optional procedure: perform automated tune scan to find resonant tune of debunched beam and excite with this frequency

16. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 fill 4471, Feb. 06 2004 start of cleaning ~5 10 9 56 x 56 Cleaning ON vs. cleaning OFF: yellow: cleaning off, started around 3:30 to allow clean beam dump blue: cleaning on, debunched beam is continuously excited and absorbed by collimators

17. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 1 Hz excitation on standard BLMs: Normal cleaning levels are < 1% of trip Level => acceptable

18. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Debunching rate clearly correlated with bunch current at the beginning of the store. For 4h store length, an upper limit of 1.4*10 9 ions per bunch results to maintain less than 5*10 9 debunched beam at the end of store (for safe beam dump). Remaining debunching with Cleaning ON:

19. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Loss Limitations  Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour  Quench limit: magnet quenches due to accidental local losses during ramp/store => BLMs magnet quenches at beam dump due to debunched beam => gap cleaning  Soil activation (not under radiation protection), depends on integrated yearly losses RHIC has to operate such that leachate (from activated soil) cannot contain concentrations of 3 H or 22 Na that exceed 5% of the drinking water standard Method: either cap the collimator area (prevent leaching) or use removable soil samples inside tunnel near collimators/dumps to monitor activation level. 22 Na is easily measured.

20. Fill 4581: Au ions (100 GeV), blue gap cleaning was off The debunched beam is lost at the collimators: deb.rate = 2*10^7 ions/min loss rate (total beam) is: loss rate = 3*10^7 ions/min (lost anywhere: triplets, dump...) total: 2-5*10^7 ions/min

21. Fill 4471, Feb. 06 2004, Au ions, 100 GeV T he debunched beam is lost at the collimators: deb.rate = 2.3*10^7 ions/min loss rate (total beam) is: loss rate = 3*10^7 ions/min total (at collimators): 2.5-5*10^7 ions/min

22. Fill 4870, Mar 24 2004, Au ions, 100 GeV T he debunched beam is lost at the collimators: deb.rate = 2.4*10^7 ions/min loss rate (total blue beam) is: 3*10^7 ions/min loss rate (total yellow beam) is: 8*10^7 ions/min total (at blue collimators): 2.5-5*10^7 ions/min total (at yellow collimators): 2.5-10*10^7 ions/min

23. Beam losses with proton beams Typical “bad” store: Loss rate: 10 10^11 = 5 10^9 p/min

24. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Assumptions for Soil Activation Calculation  Au Operation: total loss/min (from gap cleaning): 2*10 7 ions/min assume all is lost at collimators, 10% at new V2 -> 2*10 6 ions/min during the store assume average of 100 h/week at store (best week last run) add 0-3 10 6 ions/min @ v2 => 2-5*10 6 ions/min  proton Operation: total loss/min (from bad lifetime store during high intensity run): 5*10 9 p/min assume all is lost at collimators, 10% at new v2 -> 5*10 8 p/min during the store assume average of 80 h/week at store (best avg. last run)

25. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Calculate Soil Activation (Na-22) from Loss Data Calculate for v2: given the assumptions and using an estimation with the bare collimator/no shielding (there is some concrete shielding @ v2), for Na-22, assuming 15 weeks for each of the Au and proton ions (ie. 30 weeks in total) we get: 8.7 (18) pCi/l and 11.0 pCi/l for the case of Au-ions and protons respectively. This adds up to 19.7 (29) pCi/l (after 1year), which is just the same (or x1.5 of) the 5% drinking water limit (20 pCi/l) for Na-22. Compare with Measurement (from soil sample): activation level at primary collimator calculated: 200 pCi/l. measured: 13 pCi/l assuming 100% of all losses at primary collimator is conservative the 15+15 weeks of running is conservative the operating efficiency is overestimated distance collimator-soil is underestimated

26. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Loss Limitations  Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time).  Collimator positioning should be reliable and efficient for background reduction  Time at the beginning of the store is precious because this has the highest luminosity -> Collimation and positioning of collimators should be FAST (and precise!)

27. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimation during Fill 1759 (Au) FY01 run has low beam current intensities 1-stage system only PHENIX benefits (some) from collimation there is generally no/little need for collimation during the FY01 run

28. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimation during Fill 3094 in FY03 (d-Au) All experiments but PHOBOS benefit from collimation vertical scraper retraction (vert. lines) clearly raises background reduction rates are between 2 and 5

29. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Automatic Steering Algorithm RHIC has 5 jaws per ring, most allow both, linear motion and angular motion (to parallelize with beam). Potentially time consuming! => 18 degrees of freedom (+ 4 more next run) Requires automation (3 steps): 1.Move to STDBY position (based on BPM readings) 2.Move Closer to beam (based on loss monitor feedback, serial) 3.Remove Halo/Store (based on lattice functions, parallel)

30. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimation during Fill 4854 (Au) in the blue ring Serial collimator steering (mode: Move Closer), following parallel mode does not improve backgrounds. Vertical lines denote when each collimator moves. Background improvement approx. x6. Note: secondary vertical collimator quite efficient.

31. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Collimation during Fill 4436 (Au) Parallel collimator steering (mode: “Store”), using lattice fct. and assumed emittances. Vertical lines denote when collimators start and stop moving simultaneously. Background improvement approx. x10. Note: procedure stops automatically when desired background levels are reached.

32. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Fill 3254 1-stage Fill 4854 2-stage Compare RHIC data from 1-stage and 2-stage collimation system

33. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Comparison of Background Reduction Rates Background signal d-Au 2003  * = 3m Au-Au 2004  *=3m STAR Blue511 STAR Yellow13 PHENIX Blue411 PHENIX Yellow14 Average ratio of uncollimated to collimated background for the STAR and PHENIX detectors (sensitive to beam direction) over 6 stores in 2003 and 2004. In both cases PHOBOS had a  * of 3m.

34. Angelika Drees ICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004 Summary  Operational Limit about 1 normal ‘fill’ /hour in uncontrolled areas  Magnet Quenches store/ramps: BLM thresholds pull permit (fast and slow modes) beam dump: continuous gap cleaning  Soil activation maintain 5% of DWS (i.e. 20 pCi/l 22 Na) by caps or soil sample monitoring in uncapped areas  Exp. Background traditional 2-stage collimation system achieves average background reduction of x10