1 / 37

Progress on Ion Beam Focusing with Bent Crystals at the H8-RD22 Experiment at CERN

This seminar by Walter Scandale discusses the progress made in ion beam focusing using bent crystals at the H8-RD22 experiment at CERN. The seminar covers the experimental layout, tracking detectors, and results of the 2006 run, as well as the potential benefits of crystal collimation in primary collimation.

rpeoples
Download Presentation

Progress on Ion Beam Focusing with Bent Crystals at the H8-RD22 Experiment at CERN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Walter Scandale CERN For the H8-RD22 collaboration (CERN, FNAL, INFN, IHEP, JINR, PNPI) ALICE seminar 30 April 2007 H8-RD22 Experiment:progress on ion beam focusing with bent crystals We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT-2003-506395). Walter Scandale

  2. Outlook • Reminder of the concept of collimation • Why using crystals • The H8-RD22 experiment at CERN • Silicon crystals • Experimental layout • High precision goniometric system • Tracking detectors • The results of the 2006 run • Crystal Angular Scans (Strip and Quasi-Mosaic Crystals) • Double Reflection Effect • Concluding remarks and future plans Walter Scandale

  3. Walter Scandale Two stage collimation Beam propagation Beam Core Primary halo (p) Secondary halo p p p Tertiary halo Impact parameter ≤ 1 mm p e Secondary collimator (massive absorber) Primary collimator (scatterer) p Shower e Sensitive equipment Shower

  4. Walter Scandale Two stage collimation phase space x’ Capture condition: Secondary collimator (conversion in hadr. shower ) Primary collimator (scatterer) x’ x x’ mainly due to multiple Coulomb scattering, with <x’2>~ L   N N 2 1 • short primary scatterer • longer secondary collimator downstream with larger gap aperture • halo particles captured through amplitude increase via multiple scattering and multi-turn effect. Curtesy of Bellodi

  5. Walter Scandale Requirements for LHC Courtesy of R. Assmann

  6. Walter Scandale Collimation aperture Courtesy of R. Assmann Open problems: • Resistive impedance (up to 100 times the whole LHC) • Electron cloud (local concentration) IR3 and IR7 insertions are equipped with 54 collimators made of carbon-carbon

  7. Walter Scandale LHC stability diagram All the machinewith Cu coated (5 mm)collimators All the machine Without collimators (TCDQ+RW+BB) Courtesy of E. Metral

  8. Walter Scandale Ion collimation: why an issue? Nominal ion beam has 100 times less beam power than proton beam, but particle-collimator physics very different: ~20 times higher probability of nuclear interactions respect to p A new disturbance respect to p High probability to undergo nuclear interactions in the scatterer before 2-stage collimation condition is satisfied Large variety of daughter nuclei, Monte Carlo calculated specific x-sections loss 1 n (59%) 207Pb or 2 n (11%) 206Pb Curtesy of Bellodi

  9. Walter Scandale Ion collimation: what can fail? Typical transverse momentum transferred in NF ~ 1 A∙MeV/c, even smaller for ED processes (compared to ~10 A∙MeV/c due to beam emittance). After first impact/grazing with scatterer: • high probability of nuclear interactions • production of isotopes with different Z/A ratio and momentum and direction almost unchanged • secondary ions not intercepted by the secondary and lost downstream in SC magnets because of different Br LHC energy acceptance: - arcs: ~ ±1% - IR3: ~ ±0.2% Curtesy of Bellodi

  10. Walter Scandale Loss map from computer simulations ~50% current limiton nominal 208Pb ion beam (due to collimation inefficiency) not to be taken at face value: • X-sections for nuclear processes have estimated errors of ~±50% • 8.5 W/m heat load limit is only an average from early studies (Jeanneret et al.1996). Should really be considered on a magnet-to-magnet basis • hcoll~4% depends on impact parameter distribution on the scatterer (input assumption, difficult to predict..) • 12 min lifetime is another arbitrary number. Nominal ion beam with collision optics and standard collimator settings: Curtesy of Bellodi

  11. Walter Scandale Crystal collimation Beam propagation Beam Core Crystal channeling Primary halo (p) Crystal Shower p p Sensitive equipment Absorber • Primary halo directly extracted! • Much less secondary and tertiary halos!? e ..but no enough data available to substantiate the idea…

  12. Walter Scandale amorphous scatterer Crystal collimation: a smart approach for primary collimation • A bent crystal deflects halo particles toward a downstream absorber: • the selective and coherent scattering on atomic planes of an aligned Si-crystal may replace more efficiently • the random scattering process on single atoms of an amorphous scatterer. The hope is to get • Larger collimation efficiency • Larger gap of the secondary collimator --> reduced impedance

  13. Walter Scandale RD 22: extraction of 120 GeV protons (SPS: 1990-95) The RD22 Collaboration, CERN DRDC 94-11 • Large channeling efficiency measured for the first time • Consistent with simulation expectation extended to high energy beams • Experimental proof of multi-turn effect (channeling after multi-traversals) • Definition of a reliable procedure to measure the channeling efficiency

  14. Walter Scandale RD 22: extraction of ion (SPS: 1996-97) • Extraction experiments on bent crystals channelling were conducted at the SPS with ion beams in 1996-1997 (G.Arduini, W.Herr, J.Klem, L.Gatignon et al.) • Direct-type experiment on fully stripped Pb82+ ions at 400 GeV/c/u (external beamline) and 270 GeV/c/u (stored beam in ring with different excitation levels) • 60×18 mm crystal, bent over 50mm, 4mrad deflection, 3-points bend Theory: • Critical angle, dechannelling length and MS expected to depend on p/Z ratio ions should behave like p of equivalent momentum per charge • Nuclear interaction rate expected to be strongly decreased for channelled vs non-channelled ions • EMD should also decrease by a factor 10-100 • ….. however not confirmed by measurements ….

  15. Walter Scandale RD 22: extraction of ions (SPS: 1996-97) • Single pass experiment– external beamline • Very good agreement with theoretical model, corroborates expectations • Ion channelling demonstrated for the first time, with efficiency ~10-14% • Multi-pass experiment – SPS ring • More complex problem with not so clear outcome • lack of knowledge on physics of nuclear interactions involved in multipass extraction • Narrower angular scan (suppressed contribution of multipass extraction?) • Lower deflection efficiencies (up to 10%) and bigger spread in values for different configurations • Open issues • EMD suppression not proved experimentally (neutron loss?) • Radiation damage to crystal not investigated(much lower limit expected than for p) • Multi-pass ion interactions not clear (Si~amorphous material if channelling conditions are not satisfied.. )

  16. Walter Scandale At crystal Lambertson, crystal E853: extraction of 900 GeV protons (Tevatron: 1993-98) • Extracted significant beams from the Tevatron parasitic, kicked and RF stimulated • First ever luminosity-driven extraction • Highest energy channeling ever • Useful collimation studies • Extensive information on time-dependent behavior • Very robust

  17. Walter Scandale Crystal collimation at RHIC STAR Background during crystal collimation • Indirect experiment (measure particles disappearance) with Au and p runs • Si crystal 5×1 mm with B=465 mrad located in interaction region matching section • Positioning not optimal (large beam divergence and  ≠ 0) • Crystal bends in the same plane where it scrapes  sensitivity to horiz. halo No clear interpretation of the results! • Measured ch. efficiency (~25%) doesn’t match theoretical predictions ( 56% with nominal machine optics). Better agreement and consistency when using measured beam divergence  need accurate knowledge of lattice functions. • Multipass physics and halo distribution models too simplistic? • Low channelling efficiency  collimation not successful & increased backgrounds !! Not conclusive & abandoned ! R.Fliller III, A.Drees, 2005 4 crystal scans with different scraper positions - xs

  18. Walter Scandale Crystal collimation at FNAL Crystal Collimator in E0 replacing a Tungsten Target (2005) Crystal Tungsten scatterer 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!

  19. Walter Scandale The H8 line 4 m upstream Si det goniometer in 2006 bending magnets goniometer in 2007

  20. Walter Scandale Goniometer with crystal holders S3 GC S5 vacuum vacuum B5 B6 vacuum p H S6 S2 S4 S1 Si microstrips (AMS) Si microstrips (AGILE) 70 m S2 B 6 Q 14 vacuum vacuum p 50 m 3-4 m The H8-RD22 apparatus 2006 Variant for 2007 Angular resolution

  21. Walter Scandale beam Strip silicon crystals Crystals sizes: 0.9 x 70 x 3 mm3 and 0.5 x 70 x 3 mm3 Anticlastic bending Main bending • Strip Crystals have been fabricated in theSensors and Semiconductor Laboratory (U. of Ferrara) • Mechanical bending exploits anticlastic forces

  22. Walter Scandale Quasi-mosaic silicon crystals Quasi-Mosaic Crystals fabricated in PNPI (Gatchina, Russia) • the mechanical bending of the crystal induces the bending of the atomic planes (initially flat and normal to large faces of plate) due to anisotropy •  depends on the choice of crystallographic plane and on the angle of n111 respect to the crystal face Quasi-mosaic bending Crystal plate sizes: ~ 1 x 30 x 55 mm3 O.I.Sumbaev (1957) critical angle for 400 GeV/c protons:qc ≈ 10 mrad Anticlastic bending R Main bending

  23. Walter Scandale Crystals High precision goniometer Silicon detector Scintillator Goniometer Granite Block

  24. Walter Scandale Detector upstream of the crystal (on the granite block): 1 double-sided silicon microstrip detector: Resolution ~ 10 mmin bending direction (X coordinate) Resolution ~ 30 mmin non-bending direction (Y coordinate) Active area ~ 7.0 x 2.8 cm2 Detector downstream of the crystal (on the granite block) : 1 BABY double-sided microstrip detectors (IRST): Resolution better than 10 mmin bending direction Resolution better than 20 mmin non-bending direction Active area ~ 1.9 x 1.9 cm2 DOWNSTREAM TELESCOPE (at 65 m from crystal location): 4 AMS LADDERS: Resolution ~ 10 mmin bending direction Resolution ~ 30 mmin non-bending direction Active area ~ 4 x 7 cm2 AMS Silicon Detectors Silicon thickness: 300 mm

  25. Walter Scandale AGILE Silicon Detectors • Single-sided silicon strip detectors • Built by Agile (INFN/TC-01/006) • active area 9.5 x 9.5 cm2 • Spatial resolution: ~ 40 m at normal incidence (~ 30 m for tracks at 11°) • Silicon thickness: 410 mm • Upstream detector (before goniometer) • 2 silicon detectors at 90° (corresponds to 1 X-Y plane) • Downstream detector 1 (at 65 m from crystal location): • 4 X-Y silicon planes • Downstream detector 2 (at 65 m from crystal location): • 6 X-Y silicon planes interleaved with 300 m tungsten planes

  26. Walter Scandale Gas Chamber and Scintillators • Gas Chamber • Parallel plate chamber • 0.6  12.8 mm2 active area • filled with Ar 70% + CO2 30% • 64 strips (pitch equal to 200 mm) • mounted on X-Y table • able to withstand rates up to 108 ppp • Scintillating detectors • Finger scintillators: 0.1  1  10 mm3 • Scintillating hodoscope: 16 strips with 2  4  30 mm3 read-out by MAPMT (fast beam monitoring) • Scintillator plates 100  100  4 mm3 used for triggering silicon detectors

  27. Walter Scandale U  d Angular scan of a crystal (1) Predictions in 1985-’87 by A.M.Taratin and S.A.Vorobiev, and O.I. Sumbaev Theoretical explanation of channeling and volume reflection phenomena Channeled Reflected • Involved processes: • channeling • volume capture • de-channeling • volume reflection

  28. Walter Scandale Angular scan of a crystal (2) Results of the angular scan with Strip Crystal measured volume reflection angle: ~ 10 mrad

  29. Walter Scandale Angular scan of a crystal (3) measured volume reflection angle: ~ 10 mrad

  30. Walter Scandale Scan of Quasi-Mosaic Crystal • Orientation (111) • Bending angle: ~ 80 rad • Crystal sizes: 30 x 58 x 0.84 mm3 measured volume reflection angle: ~ 10 mrad

  31. Walter Scandale Double Reflection on Quasi-Mosaic Crystals (1) • Experimental setup: • exploited rotational stage for off-axis alignment of the first crystal (preliminary scan) • used upper linear stage for alignment of second crystal • many steps for finding perfect alignment conditions

  32. Walter Scandale Double Reflection on Quasi-Mosaic Crystals (2) double reflection angle: ~ 20 mrad

  33. Walter Scandale Refl2 Chan2 Refl1 Chan1 unperturbed Double Reflection on Quasi-Mosaic Crystals (3) Misaligned crystals -> two reflections angle: ~ 10 mrad

  34. Walter Scandale Conclusive remarks • First observation of Volume Reflection Effect in bent silicon crystals with 400 GeV/c protons with efficiency close to unity • Measurement of volume reflection angle: ~ 10 mrad • First observation of Double Reflection using two crystals in series: combined reflection angle is ~ 20 mrad and efficiency close to 1 • Channeling and Volume Reflection phenomena studied with Strip and Quasi-Mosaic Silicon Crystals (different fabrication techniques) • Measurement of crystals with different crystalline planes orientations: (111) and (110) • Many thanks to • Efthymiopoulos, • L. Gatignon, • C. Rembser, • R. Maccaferri • SPS-OP team Many thanks for the financial support to • CARE-HHH • INTAS-CERN • INFN-CSN1 and INFN-NTA • CERN AB & AT departments

  35. Walter Scandale Open issues • Crystal efficiency for channeling and volume reflection at both LHC injection (450 GeV) and top (7 TeV) energies. • Probability spectrum of proton deflections at 0.45 to 7 TeV for all physics processes down to a 10-5 level. • Damage limit of crystals for instantaneous shock beam impact at ~15 MJ/mm2. • Damage limit of crystals for integrated dose at ~5×1016 p/year at 7 TeV. • Handling of crystals during normal operation at high-power impact. • Requirements for alignment and operational set-up (goniometer conceptual design, tolerances, time, etc.). • ……. Ion specific concerns: • Si/ion interactions fairly understood for single pass channelling experiments.. what about multi-pass case? Crystal behaves like amorphous material for small impact parameters (surface effects) what happens to isotopes produced by nuclear interactions with the wrong rigidity? • What is the role played by nuclear/EM interactions in the case of volume reflection?

  36. Walter Scandale Future plans • 7 weeks beam time requested in 2007 at the SPS • protons (H8 beam-line) at 400 GeV • electrons and/or positrons at 300 GeV • ions during dedicated MDs • Investigate edge-effect • Test of multi-strip crystals (Ferrara Sensor and Semiconductor Laboratory) to increase the angle of volume reflection • Test of germanium strip crystals and possibly zeolites • Upgrade of goniometric system with cradle for investigation of axial channeling • Upgrade and refurbishment of existing silicon microstrip detectors in order to increase spatial resolution • 0.1  1  10 mm3 • CARE-HHH workshop CC 07 22-23 March 2007 • Proposal of LARP to create a working group aiming at a crystal experiment in the Tevatron

  37. Walter Scandale ALICE contribution • ALICE is supporting the effort of H8-RD22 in 2007, especially for the ion run • Crucial help expected in detecting fragmentation and EM dissociation down stream of the crystals in the next October run with ions

More Related