1. TEVATRON COLLIDER COLLIMATORS AND ABSORBERS Fermilab Materials for Collimators and Absorbers Nikolai Mokhov, Fermilab Workshop on Materials for Collimators and Beam Absorbers CERN, Switzerland September 3-5, 2007

2. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 2 OUTLINE Introduction Tevatron Parameters Quench Levels and Collimation Constraints Collimation System Evolution 1979 to 2007 Newest System in Main Injector External Beam Abort Dump Collider Internal Beam Dump Summary

3. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 3 INTRODUCTION At hadron colliders, as at any other accelerator, the creation of beam halo is unavoidable. This happens because of beam-gas interactions, intra-beam scattering, proton-proton (antiproton) collisions in the interaction regions (IP), and particle diffusion due to RF noise, ground motion and resonances excited by the accelerator magnet nonlinearities and power supplies ripple. As a result of halo interactions with limiting apertures, hadronic and electromagnetic showers are induced in accelerator and detector components causing numerous deleterious effects ranging from minor to severe. An accidental beam loss induced by an unsynchronized abort launched at abort system malfunction, can cause catastrophic damage to the collider equipment. Only with a very efficient beam collimation system can one reduce uncontrolled beam losses in the machine to an allowable level. Design of such a system for high-energy high-intensity beams is very challenging. Beam absorbers in straight sections or at the end of an extraction line is another subject of serious concern: -> Tevatron.

4. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 4 TEVATRON MACHINE PARAMETERS Injection Energy150 Gev Flattop Energy980 Gev (800 GeV Fixed Target) Number of bunches36 proton & 36 antiproton (996 Fixed Target) Particles per bunch300 E9 protons & 40-100 E9 pbars Total Beam Intensities at 150, 980 GevProtons 1E13 Antiprotons 1.4 E12, 3E12 (2.5 E13 Fixed Target) Orbits TypesBoth beams in 1 vacuum pipe ; Beams separated by electrostatic separators Lowbeta steps15 different lattice in 25 steps Beta *1.7m and transition to 28cm Number of IP’s2 : CDF & D0 Shot setup (Fill) time2 hours (57 second cycle time Fixed Target) Store lengths~ 24 hours

5. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 5 SLOW AND FAST QUENCH LEVELS IN TEVATRON 0.975

6. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 6 BEAM COLLIMATION CONSTRAINTS AT COLLIDERS Sustain favorable background conditions in experiments. Maintain operational reliability in stores: quench stability and dynamic heat loads on cryogenics. Prevent quenching SC magnets and damage of machine and detector components at unsynchronized beam aborts. Minimize radiation damage to components, maximize their lifetime. Minimize impact of radiation on personnel and environment: prompt and residual radiation (hands-on maintenance).

7. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 7 TEVATRON COLLIMATION SYSTEM EVOLUTION Design report, commissioning, initial operation: a few single 0.9 to 1.8- m long SS collimators in front of SC magnets (Edwards, Pruss, Van Ginneken, 1979-1984). A set of two-unit collimators at optimal locations based on STRUCT/MARS modeling allowed 5-fold increase of 800-GeV proton beam intensity at fast resonant extraction (Drozhdin, Harrison, Mokhov, 1985). First two-stage system, two 2.5-mm thick L-shape tungsten targets with 0.3-mm offset relative to A0 scrapers: 5-fold reduction of beam loss rates upstream D0 and CDF detectors (Drozhdin, Mokhov et al., 1995). Genuine two-stage system designed for Run-II with primary and secondary collimators at appropriate locations optimized in STRUCT/MARS runs (Church, Drozhdin, Mokhov, 1999) -> clean TeV Current system with a tertiary collimator (Drozhdin, Mokhov,Still). Crystal collimation (Carrigan, Drozhdin, Mokhov, Still).

8. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 8 TEVATRON COLLIMATION SET (1985) - 1

9. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 9 TEVATRON COLLIMATION SET (1985) - 2

10. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 10 EXCERPTS FROM FN-418 REPORT (1985) 1. 2. 3. 4. 5.

11. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 11 TOWARDS TWO-STAGE COLLIMATION (1995) Adding two 2.5-mm L-shape tungsten “primary collimators” on A0 scraper resulted in 2.5 to 5 times lower beam losses in D0 and B0 regions

12. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 12 TEVATRON RUN-II COLLIMATION SYSTEM (1999)

13. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 13 CURRENT TEVATRON COLLIMATION SYSTEM Primary: L-shaped 2.5-mm thick tungsten blades at 5 to 6  from the beam axis in a high-  (betatron cleaning) and non-zero dispersion (momentum cleaning) regions; three targets (H, V and off-momentum). Secondary: 1.5-m long stainless steel adjustable H&V collimators (L-shape jaws) located at the appropriate phase advances (30 & 150 deg) 1  farther from the beam axis, alligned parallel to the envelope of the circulating beam. Tertiary: 1-m long stainless steel adjustable units upstream of the low-beta region – to catch remedies from secondary collimators and beam-gas products, and to protect inner triplet and detector at abort kicker prefires (mandatory!) <- since 2003. Longitudinal beam loss, beam-gas scattering and elastic part of collision loss are the main mechanisms of the slow beam halo growth. The system intercepts 99.9% of this halo, with 3×10 7 p/s scraping rate.

14. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 14 COLLIMATION SYSTEM PERFORMANCE IN RUN II Halo Rates at Collider Detectors: D0 alignment and Vacuum improvements

15. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 15 2003 BEAM ACCIDENT IN TEVATRON December 5, 2003 A 2/3 ring beam-induced fast quench, caused by a Roman Pot moved into beam due to a control error, with beam loss damaging 2 collimators and 2 spool pieces (3 correction elements); two-week shutdown.

16. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 16 CRYSTAL COLLIMATION IN TEVATRON (2006) Using the crystal, the secondary collimator E03 can remain further (1 mm or so) from the beam and achieve almost a factor of 2 better result in reduction of CDF losses a half a ring (2 miles) downstream! A 2-year plan for crystal collimation collaborative study (FNAL, CERN, INFN, IHEP et al) in Tevatron has just been approved by AAC & LARP Crystal aligned at peak (118  rad) E03 BLM CDF PIN

17. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 17 Beam Cleaning in MI-8 Injection Line (2006) The 4-unit collimation system was designed and installed to cut 10 12 p/s of 8-GeV proton beam. Residual dose rate on collimator shielding outer surface was the driver, therefore a 12-cm marble shell was implemented. Towars a MW beam in the Main Injector

18. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 18 MAIN INJECTOR RING COLLIMATION (2007) System designed for >1-MW beam in MI ring Multi-component system of primary & secondary collimators and masks, most with marble shells. Spreads over 200 m. It is installed these days.

19. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 19 TEVATRON EXTERNAL C0 BEAM DUMP (1980-1997) Two cores, 15x15x2.5 cm3 x 350 graphite plates, contained in Al boxes with grooves for cooling water, surrounded with steel/concrete shield; well instrumen- ted: ion chamber, 5 PRT, downstream calorimeter and radiation monitors.  T~1000 degC in graphite

20. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 20 TEVATRON COLLIDER INTERNAL DUMP AT A0

21. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 21 TEVATRON COLLIDER INTERNAL BEAM DUMP (2)  T max ~800 deg C in graphite

22. Materials Workshop, CERN, Sept 3-5, 2007Tevatron Collimators and Absorbers - N.V. Mokhov 22 SUMMARY Beam collimation is mandatory at any superconducting collider to protect components against excessive irradiation, minimize backgrounds in the experiments, maintain operational reliability over the life of the machine, and reduce the impact of radiation on environment, both at normal operation and accidental situations. Highly-efficient two-stage collimation system at Tevatron reliably serves these purposes. Recent developments include marble shells and crystal collimation. The later, gives a possibility to test channeling techniques in a collider as an interesting option for LHC. External and internal Tevatron collider graphite-based beam absorbers also exhibit high performance.