Crystal Collimation at the Tevatron

1. Crystal Channeling Fermilab Crystal Collimation at the Tevatron Nikolai Mokhov and Dean Still Fermilab Accelerator Division Seminar FNAL January 12, 2006

2. OUTLINE • Introduction • Crystal Extraction and Collimation: a Little History • Towards Crystal Collimation at the Tevatron • Crystal Collaboration: Optimal Crystals and Expts • Implementation and Commissioning at the Tevatron • 980-GeV Beam Crystal Channeling and Collimation • Encouraging Results, Problems and Future Plans • Summary Crystal Collimation at Tevatron - Mokhov & Still

3. INRODUCTION • Bent-crystal technique is well established for extraction and handling of high energy hadron and heavy-ion beams from accelerators. Such an extraction was successfully demonstrated for up to 900 GeV beams at JINR, IHEP, CERN and Fermilab, and measurements confirmed its high efficiency predicted in simulations. • It was shown (SSC, 1991) that it is promising to apply this technique to a beam halo collimation at high energy colliders. A bent crystal, serving as a primary element, should coherently bend halo particles onto a secondary collimator. First successful measurements were performed at IHEP in 1998 for 1 to 70 GeV protons. Based on realistic modeling (1999, 2003), it was proposed to implement a bent crystal into the Tevatron collimation system. It was done, and first results are presented here. Crystal Collimation at Tevatron - Mokhov & Still

4. CRYSTAL CHANNELING • Channeling/Dechanneling • Critical angle c = (2U/pv)1/2 • Bending: Ueff = U(x) – pvkx, k=1/R • Dechanneling due to MCS & bending --> LD= 0.9m x p (TeV/c) --> LB = LD (1-F/3)2, F=3k/kc, kc~Z2/pv (well ‘disappears’) Channeling probability Extremely high interplanar electric fields from screened nuclei (a few GV/cm) allow to bend and focus (cylindrically-shaped crystal exit) high-energy beams with very short crystals. Interplanar spacing ~ 2Å. It was shown at CERN and IHEP that crystals are heat- and radiation-resistant. Deflection efficiency deteriorates at about 6%/1020 p/cm2 rate Crystal Collimation at Tevatron - Mokhov & Still

5. CHANNELING: EARLY DAYS (E. Tsyganov et al, 1976-1984) “What will happen with the trajectory of the channeled particles if we bend the crystal? Up to some critical value of the bending radius a particle trajectory will repeat the shape of a bent crystal. This unexpected phenomenon caused by the fact that the particle in this case gradually goes to high electric field of the atoms. It then starts to be bent in the direction of the crystal bending. A stable trajectory in this case goes away from the potential minimum, in the region where electrical fields are strong enough to create the necessary transverse acceleration”. First successful JINR experiments in 1979. 7.5-GeV proton bent crystal extraction was demonstrated at JINR in 1984 Crystal Collimation at Tevatron - Mokhov & Still

6. Crystal Extraction at SPS: RD22 (W. Scandale et al) • Multiple scattering and dechanneling determine the energy dependence of the extraction efficiency. • For a given beam energy and crystal bending angle there is an optimal crystal length. • Channelling efficiency consistently of the order of 10 % (more than an order on magnitude larger than in previous experiments) • Experimental evidence of multiturn effect in extraction mode • Robust method to evaluate the extraction efficiency • Experimental validation of simulation code at high energy • Extraction of Lead ions G. Arduini et al., CERN SL 97-031 and SL 97-055 1991-1997 Crystal Collimation at Tevatron - Mokhov & Still

7. Crystal Extraction at Tevatron: E853 (R. Carrigan, T. Murphy et al) • Bad: • Interaction counters very sensitive to beam motion • Beams in the 108 - 109 regime need special • instrumentation • Beam halo behavior is often non-linear • Lattice location important (RHIC – difficult, Tevatron • better but imperfect) • Good: • First parasitic TeV MHz beam extraction from collider • Measured channeling and extraction efficiencies 33% • and 23%, respectively • Crystal extraction works well, robust (900 GeV) • Extraction in diffusion modes means crystal • collimation can work • Multiple pass works 900-GeV crystal extraction 6/6/95 Crystal Collimation at Tevatron - Mokhov & Still

8. Two-Stage Collimation with Target and Crystal Courtesy R. Assmann Crystal Collimation at Tevatron - Mokhov & Still

9. FIRST PROPOSAL FOR CRYSTAL COLLIMATION (SSC, 1991) Fraction of outscattered protons (%) per one 20 TeV proton: Calculated beam loss in SSC lattice was drastically down withW target and especially with bent crystal (Maslov, Mokhov, Yazynin). Crystal Collimation at Tevatron - Mokhov & Still

10. 1 to 70 GeV Crystal Collimation at IHEP: V. Biryukov et al (1998) Also crystal extraction, focusing, characterization, radiation damage and heating Crystal Collimation at Tevatron - Mokhov & Still

11. Crystal Collimation at RHIC (2003) • Measured bent crystal channeling • for gold ions was 26% • Crystal channeling worked as • expected once lattice functions and • halo distribution were understood • Collimation was unsuccessful because lattice was not optimal in • area of collimator and IP (high • angular spread at crystal, phase • advances): crystal caused • background Crystal Collimation at Tevatron - Mokhov & Still

12. 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: 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 proposed for Run-II with primary and secondary collimators at appropriate locations optimized in STRUCT/MARS runs (Church, Drozhdin, Mokhov, 1999). • Current system with a tertiary collimator (Drozhdin, Mokhov,Still). • Crystal collimation (Carrigan, Drozhdin, Mokhov, Still). Crystal Collimation at Tevatron - Mokhov & Still

13. BENT CRYSTAL FOR TEVATRON COLLIMATION • Biryukov, Drozhdin, Mokhov (PAC99) have shown – and later calculations (2003) confirmed - that implementation of a silicon bent crystal instead of amorphous primary collimators (targets), can improve the Tevatron collimation system efficiency by a factor of: • 2 with one (horizontal) target replaced, and with contribution from beam-gas scattering unsuppressed • 3 with one (horizontal) target replaced, and with contribution from beam-gas scattering suppressed • up to a factor of 10 for the horizontal scraping itself. Crystal Collimation at Tevatron - Mokhov & Still

14. TEV BEAM LOSS REDUCTION WITH CRYSTAL (1999) 10-fold hit rate reduction at DØ and BØ (horizontal component). 4-fold reduction of radiation loads to downstream SC magnets. Crystal Collimation at Tevatron - Mokhov & Still

15. TEVATRON: CRYSTAL ALIGNEMENT (1999) The crystal critical angle is ±5 µrad, therefore the efficiency depends strongly on the crystal alignment. With the alignment of -(104 - 111) µrad the large amplitude protons are captured by the crystal over the next 32 turns after the first scattering. For poorer alignment it takes longer time for the scattered protons to get into the critical region, which increases background in the detectors. Crystal Collimation at Tevatron - Mokhov & Still

16. PROPOSAL FOR CRYSTAL COLLIMATION (2003) Current collimation system in Tevatron is somewhat different compared to the one planned before Run-II. Based on detailed modeling, Carrigan, Drozhdin, Mokhov and Still, proposed to implement a bent crystal in the EØ straight section. It was done in 2005, Dean Still will describe the implementation and show first results. Crystal Collimation at Tevatron - Mokhov & Still

17. Crystal Channeling Workshop at CERN, Dec. 05 • A theoretical interpretation of the Tevatron results was given at the Crystal Channeling workshop at CERN on December 8-9, 2005. Yuri Ivanov (PNPI) has shown that the pure channeling, calculated from the crystal properties, is consistent with 2 to 3 passages of the proton beam through the crystal with a channeling efficiency of about 92%. • Confirmed by IHEP modeling. • The observed plateau is explained by • reflections from atomic planes and • corresponds to 6 to 9 beam passages. • The volume capture is estimated to be • negligible in the considered case. • The consensus was reached that the TeV crystal needs to be replaced with the optimal one with a bending angle of about 0.15 mrad, that the beam diagnostics must be implemented to see the deflected beam (phosphorous screen, BPM, flying wires, secondary emission monitor etc), and that the characterization and knowledge of the additional crystal parameters (miscut angle, surface perfection) are vital for success of the studies. Crystal Collimation at Tevatron - Mokhov & Still

18. Two identical characterized crystals for SPS and TeV • It was proposed that PNPI will expressly fabricate a pair of identical crystals optimized for the Tevatron (about 1-mm thick, 0.12-mrad bending angle, minimal miscut angle), and ship them to INFN (Ferrara) for chemical etching and characterization. • Then by mid-spring 2006, one crystal goes to Fermilab for installation in the Tevatron in the spring shutdown, and another one goes to CERN for beam characterization in the extracted beamline in June-July to use these data for optimal crystal use in the Tevatron starting about mid-summer. • The crystal preparation, etching, characterization and beam tests will be done for INFN and INTAS money. Crystal Collimation at Tevatron - Mokhov & Still

19. SPSH8 Beam Line Beam line parameters taken from C.Biino et al., PL B403(1997)163 105 protons/s 400 GeV/c 3μrad 5mmx5mm Vacuum pipe Crystal Scintillators S2, S3 20 m 20 m Scintillator S1 0.5 mm (1 μrad) AMS type detector Silicon with X- and Y-strips X-position resolution 30 μm 0.3 mm (1.5 μrad) θcritical ≈ 10 μrad θbending ≈ 100 μrad √2x30μm/20m ≈ 2 μrad Crystal Collimation at Tevatron - Mokhov & Still

20. CRYSTAL COLLABORATION: EXPERIMENTS • Beam-crystal experiments at CERN: • Characterize “TeV” crystal to guarantee success at Tevatron: extracted beam at H8 or P0, summer 2006, approved, supported by INFN (400 keuro) and INTAS/CERN (130 keuro) • Crystal collimation efficiency in SPS (a’la Tevatron): 2007, based on success at Tevatron and extracted beamlines • Responsibility split between CERN, INFN, Fermilab, PNPI, JINR and IHEP in 7 areas: Tank (crystal, goniometer, integration), pipe, scintillators, silicon, calculations, analysis, and DAQ. • Fermilab contribution to these experiments: calculations (crystal, track reconstruction and beam loss, Drozhdin & Mokhov), detectors (scintillating fibers, Alan Bross), data taking (Dean Still). • In the spring shutdown: replace Tevatron crystal with an optimal characterized one, and perform measurements to come to a reliable conclusion about crystal collimation efficiency. • We have a proposal from KEK to collaborate (Tevatron, J-PARC, ILC). Crystal Collimation at Tevatron - Mokhov & Still

21. INTAS-2006 Project: Crystal Channeling Just Approved • ”Experimental study of crystal channeling at CERN SPS for use at the LHC in diffractive physics and halo cleaning” Extraction of ~450-GeV proton beam from SPS with a bent crystal: a’la RD22 at CERN and 900-GeV E853 at Tevatron First station: deflection at large angles (some mrad) Crystal Collimation at Tevatron - Mokhov & Still

22. Second station: deflection at small angles (0.2 mrad) Crystal Collimation at Tevatron - Mokhov & Still

23. OTHER CRYSTAL CHANNELING APPLICATIONS • Since early ’80s, many successful applications at FNAL, CERN & IHEP • Crystal-based beam lines • Beam splitting (recent success at KEK with 12 GeV protons) • Beam focusing • Beam diagnostics • Very recent proposals for LHC, ILC & J-PARC • Calibration of CMS calorimeters with LHC beam • TOTEM: larger acceptance for diffractive Higgs, reaching Coulomb region • Beam splitting at J-PARC • Collimation at ILC with tests at ATF Crystal Collimation at Tevatron - Mokhov & Still

24. MOTIVATION FOR CRYSTAL COLLIMATION Over 2004 shutdown improved Tevatron Vacuum and alignment. Also installed Crystal collimator. Proton Halo Loss Limit Crystal Collimation at Tevatron - Mokhov & Still

25. Collimator Scattered trajectories Target @ ~5s Collimator @~6s WHERE TO INSTALL CRYSTAL Install Crystal Collimator at E0 to replace a Tungsten Target and utilize the rest of the collimator 2 stage System. Proton Set 1 D49 Tar, E03 & F172 2nd Proton Set 2 D171Tar, D173 & A0 Pbar Set 1 F49 Tar, F48 & D172 Pbar Set 2 F173 Tar, F171 & E02 Crystal Collimation at Tevatron - Mokhov & Still

26. Beam Direction 5mm REPLACING PRIMARY COLLIMATOR WITH CRYSTAL Current primary H-collimator (D49 tungsten L-shaped target) is before the dog-leg at bH=96 m, D=2.3 m. The crystal is in the dog-leg at bH=73 m, D=2.5 m, about the same phase advance wrt secondary collimators. Channeled and scattered protons on E0 secondary collimator as of 1999 1. Installed modified BNL assembly and crystal during Fall 2004 shutdown 2. Vertical assembly was found to have “fallen” during exercising horizontal motion: repaired in place in February 2005 3. Beam studies at 150 and 980 GeV in summer and fall of 2005 O-shaped 110 Si-crystal 5-mm long, 5 mm H, 1mm V bending angle 0.439 mrad miscut angle 0.465 mrad Crystal Collimation at Tevatron - Mokhov & Still

27. CRYSTAL COLLIMATOR SYSTEM Laser – angular measurement PIN Diode BLM E0 Scintillator Paddles BLM 31.542 m 14 mm crystal channeled beam Pin Diode E03H 2nd Collimator E03 Secondary Collimator E0 Crystal Collimator Assembly Crystal Collimation at Tevatron - Mokhov & Still

28. 980-GEV BEAM CHANNELING Independent simulations by V. Biryukov and Y. Ivanov show channeling efficiencies of 90% to 95% possible. Crystal Collimation at Tevatron - Mokhov & Still

29. RESULTS OF E03 COLLIMATOR SCAN FOR DIFFERENT CRYSTAL ANGLES • Channeled beam produces a shoulder 7mm from the core. • The channeled beam should have been ~12mm from the core. • First data set suggested the channeled beam was hitting an aperture. • But on 1/10/2006, after moving the crystal 10mm, new data proved there was no aperture limit. Scatter Channel V capture Crystal Collimation at Tevatron - Mokhov & Still

30. COMPARING EFFECTS OF PROTON HALO LOSSES FOR BENT CRYSTAL AND TUNGSTEN TARGET 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! Crystal Collimation at Tevatron - Mokhov & Still

31. FUTURE PLANS • Finished data collection and analysis using current BNL crystal and have some answers as to “Does and how much CC reduce CDF and D0 proton halo losses?” • Next long shutdown (> March 2006) - install 1-TeV custom crystal from Protvino/Ferrara (0.15-mrad bend, 3-mm length) and gather data, analyze and prepare conclusions. Crystal Collimation at Tevatron - Mokhov & Still

32. SUMMARY • Detailed simulations show that it is promising to use a bent crystal as a primary collimator (target) to increase efficiency of beam collimation at hadron colliders. • We have demonstrated high-efficiency channeling for 1-TeV proton beam. • It seems that there is a two-fold reduction in CDF loss rates, but we are careful with a final conclusion about reduction of beam losses at the Tevatron critical locations due to limited aperture effects of current crystal setup. • Hopeful with new crystal that we can come to a reliable conclusion about amount of a halo reduction. • With optimized crystal-based collimation system at LHC, one can expect substantial reduction of beam loss rates and accelerator-related backgrounds in detectors. Crystal Collimation at Tevatron - Mokhov & Still