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Crystal Collimation at SSC and Tevatron

CARE CC-2005. Fermilab. Crystal Collimation at SSC and Tevatron. Nikolai Mokhov, Fermilab. CARE Workshop on Crystal Collimation in Hadron Storage Rings CERN March 7-8, 2005. OUTLINE. Introduction Beam Collimation at Hadron Colliders First Look at Crystal Collimation for SSC

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Crystal Collimation at SSC and Tevatron

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  1. CARE CC-2005 Fermilab Crystal Collimation at SSC and Tevatron Nikolai Mokhov, Fermilab CARE Workshop on Crystal Collimation in Hadron Storage RingsCERNMarch 7-8, 2005

  2. OUTLINE • Introduction • Beam Collimation at Hadron Colliders • First Look at Crystal Collimation for SSC • Full-scale Modeling for Tevatron • Proposal for Crystal Collimation at Tevatron • Implementation and Commissioning at Tevatron Crystal Collimation - N.V. Mokhov

  3. INRODUCTION • Bent-crystal technique is well established for extracting high energy beams from accelerators. It was successfully applied at up to 900 GeV in E-853 at Fermilab, and simulations were able to predict the results correctly. Experiments at IHEP Protvino have demonstrated that 50-70% of the beam can be extracted using a thin (3-5 mm) Si channeling crystal with bending of 0.5-1.5 mrad. • It was shown (SSC, 1991) that it is promising to apply this technique to a beam halo scraping at high energy colliders. A bent crystal, serving as a primary element, should coherently bend halo particles onto a secondary collimator. Based on realistic modeling (1999, 2003), it was proposed to implement a bent crystal into the Tevatron collimation system. It was done, and commissioning is planned in March 2005. Crystal Collimation - N.V. Mokhov

  4. BEAM COLLIMATION AT COLLIDERS • Beam collimation is mandatory at any superconducting hadron collider to sustain favorable background conditions in experiments, maintain operational reliability in stores and over the life of the machine, protect components against excessive irradiation and possible catastrophic damage, and reduce the impact of radiation on the environment. • Only with a very efficient beam collimation system can one reduce uncontrolled beam losses in the machine and detectors to allowable levels. • Bent crystal provides a possibility to substantially improve collimation efficiency. Crystal Collimation - N.V. Mokhov

  5. SSC BEAM SCRAPER SYSTEM (1991) Primary H/V scrapers with/without target followed by a set of secondary collimators at appropriate phase advances Crystal Collimation - N.V. Mokhov

  6. SSC SCRAPERS: 3 CASES STUDIED FOR 2 AND 20 TeV • No target; copper (1.2-2 m), tungsten (0.8-1m), and graphite (4m) scrapers. • 0.5-1 mm tungsten target at the front of copper scraper. • 5-mm silicon bent crystal at the front of copper scraper. Multi-turn STRUCT/MARS calculations of beam loss distributions and heat loads to SSC components. Crystal Collimation - N.V. Mokhov

  7. IMPACT PARAMETER ON SCRAPER AT 20 TEV • No target: 1-2 mm. • With 1 mm tungsten target: 100-150 mm. • With 5-mm silicon bent crystal: up to 500 mm. Crystal Collimation - N.V. Mokhov

  8. COLLIMATION INEFFICIENCY AT SSC Fraction of outscattered protons (%) per one 20 TeV proton: Calculated beam losses in SSC lattice were drastically down withW target and especially with bent crystal. Crystal Collimation - N.V. Mokhov

  9. ENERGY DEPOSITION IN CU SCRAPER AT 20 TEV Crystal Collimation - N.V. Mokhov

  10. ABSORPTION EFFICIENCY OF COPPER SCRAPER AT 20 TEV Crystal Collimation - N.V. Mokhov

  11. 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 optimal locations optimized in STRUCT/MARS runs (Church, Drozhdin, Mokhov, 1999). • Current system with tertiary collimators (Drozhdin, Mokhov,Still). • Crystal primary collimator to be commissioned in March 2005. Crystal Collimation - N.V. Mokhov

  12. TEVATRON RUN-II COLLIMATION Currently for proton beam, we have additionally D17(3) H/V, A11 (V) and A48 (V). Last two are for abort kicker prefire. Crystal Collimation - N.V. Mokhov

  13. PROTON/ANTIPROTON BEAMS ON TEVATRON COLLIMATORS Crystal Collimation - N.V. Mokhov

  14. BENT CRYSTAL FOR TEVATRON COLLIMATION (‘99) • Biryukov, Drozhdin, Mokhov (PAC99) have shown how a silicon bent crystal can improve the Tevatron collimation system efficiency. Two cases were compared for a 900 GeV proton beam: • • the Run II collimation system with only one of three primary collimators—(D17h) horizontal—used. It intercepts large-amplitude protons and protons with positive Dp; • • the same collimation scheme, but a silicon bent crystal is used instead of D17h. • In reality, two additional primary collimators (bent crystals) should be used at D17v and D49h locations for vertical amplitude and off-momentum scraping. Therefore, results presented here represent about 30% of total losses in the machine. Crystal Collimation - N.V. Mokhov

  15. CDF AND DØ DETECTORS AND ROMAN POTS • Our studies have shown that the accelerator related background in the DØ and CDF collider detectors is originated from beam halo loss predominantly in the inner triplet region. In addition to the optically small aperture at bmaxlocation, the aperture restrictions in this area are the DØ forward detector’s Roman pots placed at 8s and the BØ Roman pots placed at 10s at the entrance and exit of the beam separators. Crystal Collimation - N.V. Mokhov

  16. USING BENT CRYSTAL IN TEVATRON • A silicon (110) crystal bent at an angle of 0.1-0.3 mrad is placed upstream of the D17 secondary collimator instead of the original thin scattering tungsten target in the same position. • Crystal channeling is simulated with the CATCH code. Particle tracking in the lattice is done with the STRUCT code with updated MARS physics. A non-channeling amorphous layer on the crystal surface due to its irregularity at a micron level is taken into account as a silicon target upstream of the crystal. Crystal Collimation - N.V. Mokhov

  17. BENT CRYSTAL MODEL (1999) Crystal Collimation - N.V. Mokhov

  18. BEAM LOSS REDUCTION WITH CRYSTAL 10-fold hit rate (beam loss) reduction in DØ and BØ. 4-fold reduction of radiation loads on downstream SC magnets. Crystal Collimation - N.V. Mokhov

  19. PROTON DISTRIBUTIONS ON CRYSTAL Crystal Collimation - N.V. Mokhov

  20. CRYSTAL ALIGNEMENT 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 - N.V. Mokhov

  21. CRYSTAL LENGTH Angular distribution of protons after scattering on the amorphous layer depends on the crystal length. Shorter crystal would give smaller particle divergence, which should improve the system efficiency. In reality, a combined effect of scattering, channeling and tracking in the lattice could smear such a simple dependence. A shorter crystal indeed is better for the CDF Roman pots if its length <5 mm, but for longer crystals and for the DØ detectors the results obtained are almost independent of length. Crystal Collimation - N.V. Mokhov

  22. BEAM LOSS DISTRIBUTIONS • Overall beam loss distributions along the Tevatron lattice are shown on next page for the two studied cases with a 5 mm thick tungsten target and a 5 mm thick silicon bent crystal as the D17 primary scatterer at 5s. The secondary collimators are installed at 6s. Beam loss on the primary element itself is not shown. One sees that not only beam loss is lower at the collider detectors at BØ and DØ , but the entire machine becomes cleaner if the bent crystal is used. Crystal Collimation - N.V. Mokhov

  23. BEAM LOSS with W (top) and Si (bottom) Crystal Collimation - N.V. Mokhov

  24. CONCLUSIONS FROM 1999 STUDY • The studies performed have shown that a replacement of the amorphous tungsten target as a primary collimator in the Tevatron beam collimation system with a 5 mm thick silicon bent crystal would reduce by about one order of magnitude the accelerator-related backgrounds in the CDF and DØ detectors and decrease beam losses in the supercondcting magnets of the D sector by a factor of four. Crystal Collimation - N.V. Mokhov

  25. MOTIVATION FOR CRYSTAL COLLIMATION Tevatron: Growing concern that with the increase of beam intensities, proton losses due to beam-beam effects during a store, would hinder detectors from taking data for a portion of a store CDF halo loss limit Further increase of collimation efficiency is needed ! Goal Courtesy D. Still Crystal Collimation - N.V. Mokhov

  26. Courtesy D. Still Crystal Collimation - N.V. Mokhov

  27. 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. Crystal Collimation - N.V. Mokhov

  28. BENT CRYSTAL IN EØ 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. Crystal Collimation - N.V. Mokhov

  29. CHANNELED AND SCATTERED PROTONS ON EØ SECONDARY COLLIMATOR Crystal Collimation - N.V. Mokhov

  30. BEAM LOSS: CRYSTAL vs TARGET Substantial improvement for DØ and modest effect for BØ (CDF) Crystal Collimation - N.V. Mokhov

  31. Courtesy D. Still 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 - N.V. Mokhov

  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. • With the proposed single crystal implementation at Tevatron, a scraping efficiency is expected to be increased by about an order of magnitude, and machine-related backgrounds in CDF and DØ be reduced by at least a factor of two (a second crystal is needed and beam gas scattering upstream the detectors is unaffected by crystal). Commissioning at 150 and 980 GeV is planned in March 2005. • 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 - N.V. Mokhov

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