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Linear Collider IR Options

Linear Collider IR Options. Tom Markiewicz / SLAC LC Workshop 2002, U. Chicago 07 January 2002. Bunch Structure Crossing Angle Time Packaging of Detector Backgrounds Beam-Beam Feedback Schemes (RB). IP Beam Parameters Luminosity (RB) Luminosity Sensitivity (RB) IP Backgrounds. Outline.

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Linear Collider IR Options

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  1. Linear Collider IR Options Tom Markiewicz / SLAC LC Workshop 2002, U. Chicago 07 January 2002

  2. Bunch Structure Crossing Angle Time Packaging of Detector Backgrounds Beam-Beam Feedback Schemes (RB) IP Beam Parameters Luminosity (RB) Luminosity Sensitivity (RB) IP Backgrounds Outline Beam Delivery & IR Choices ~Accelerator Technology Independent IR Options IR Layout Choices Site Layout Choices Detector Occupancies & Acceptances

  3. Bunch Structure vs. X-Angle • Crab Cavities • Beam Steering • “r<20cm” Hardware • Lum Monitor • Magnet Technology • L* (IP to 1st Quad = QD0) • Beam Extraction • Beam Diagnostics • Beam Dumps • “Maximum” Ecm • Minimize bends • Compatibility with other designs

  4. Beam Separation Required Before 1st Parasitic Collision at ctB/2 IP Luminosity Loss vs. Crossing Angle for CLIC, tB=0.67 ns D. Schulte, LCWS 2000

  5. NLC Detector MaskingPlan View w/ 20mrad X-angle Large Det.- 3 T Silicon Det.- 5 T 30 mrad 32 mrad

  6. JLC IR8 mrad Design Elevation View • Iron magnet in a SC Compensating magnet • 8 mrad crossing angle • Extract beam through coil pocket • Vibration suppression through support tube

  7. TESLA IRInstrumented W Mask & Pair-LumMon w/ Low Z Mask

  8. Maximum Crossing AngleCrab Cavity • Transverse RF cavities on each side of IP rotate the bunches so they collide head on • Cavity power req. and relative voltage & phase stability limit maximum crossing angle: • 2% DL/L when bunch overlap error Dx ~ 0.4 sx • Since Dx = (qC/2)Dz , at qC=20mrad phase error Dz corresponds to ~10mm • ~ 0.2 degree of X-Band phase Dx qC< 40 mrad

  9. Crossing Angle ConsiderationsInteraction with Detector’s Solenoid • Beam Steering before IP: • Transverse component of solenoid changes position and angle of beams at the IP • 1.7 mm , 34.4 mrad at 1 TeV, L*=2m, Bs=6 T, qC=20mrad • Dispersion and SR cause spot size blow up • Dispersion adds 3.1 mm to vertical spot size • SR contribution tiny; goes as (L*BsqC)5/2 • Beam steering and QD position adjustment make this a NON-PROBLEM • Beam Steering after IP: • Energy dependence of angle of extraction line • Steering: position (410 mm) & angle (69 mrad) different from B=0 case at 1 TeV • Only run with solenoid ON and Realign extraction line when necessary

  10. Luminosity Monitor DetailNon cylindrically symmetric geometry for inner detectors

  11. Baseline Magnet Technology Choices Extraction outside QD0 • Permanent Magnets (NLC) • Compact, stiff, few external connections, no flowing fluids • Adjustment more difficult Extraction in QD0 Coil Pocket • Conventional Iron in SC Tube (JLC) • Adjustable, familiar • Massive, SC tube shields magnet from solenoid Extraction through QD0 Bore • Superconducting (TESLA) • Adjustable, large aperture bore • Massive and not stiff

  12. TESLA SC Final Doublet QuadsMature LHC based Design • QD0: • L=2.7m • G=250 T/m • Aperture=24mm • QF1: • L=1.0m

  13. NLC Final Doublet Quad Options Permanent Magnet Option: compact, stiff, connection free 5.7cm BNL Compact SC

  14. NLC Extraction Line150 m long with chicane and common g and e- dump X-Angle allows separate beam line to cleanly bring disrupted beam to dump and allows for post-IP Diagnostics 0.2% of beam ~ 4kW lost @ 1 TeV 0-0.002% beam ~ 0-20W lost @ 500 GeV

  15. TESLA Vertical Extraction at 0º Electrostatic separators at 20m Shielded septum at 50m (ctB/2) Dipoles to e-/+ dump at z=240m Calculated losses OK Challenging problem No space for diagnostic equipment Photons to separate dump at 240m with hole for incoming beam

  16. TESLA Pre-IP Polarimeter and Energy Spectrometer No TESLA plans for post IP diagnostics NLC plans pre-IP diagnostics but no work yet begun No detailed work on post-IP diagnostics done yet

  17. Energy FlexibilityEnergy Dependence of Luminosity • Final Focus magnet apertures set by lowest energy • Highest energy operation limited by magnet strength, synchrotron radiation and system length For fixed geometry

  18. Luminosity Scaling with Energy Luminosity increases linearly with energy at High and Low E IRs Above maximum design energy, L drops quadratically due to synchrotron radiation emittance growth Range can be extended by changing geometry to soften bend angle This LEIR design done when there was 80mrad of bending to get to IR2 Now at ~25mrad curves essentially identical

  19. NLC & TESLA both have Minimal Angles to Primary IR & ~20mrad to IR2 Bypass Lines 50, 175, 250 GeV Length for 500 GeV/beam IR2 (90 GeV to ~TeV) 30 km IR1 (250 GeV to multi-TeV) Injector Systems for 1.5 TeV

  20. TESLA Post-Linac Layout

  21. e+ Skew Correction / Emittance Diagnostics Interaction Region Transport (High Energy) Interaction Region Transport (Low Energy) Collimation / Final Focus (High Energy) Collimation / Final Focus (Low Energy) IR Hall (High Energy) IR Hall (Low Energy) IP2 IP1 Collimation / Final Focus (Low Energy) Collimation / Final Focus (High Energy) Interaction Region Transport (Low Energy) Interaction Region Transport (High Energy) Skew Correction / Emittance Diagnostics e-

  22. Pros & Cons of a Crossing Angle Cons: • Beam Steering Correction Easy • Crab cavity Required OK as long as qC<~40 mrad • LUM not cylindrically symmetric Who cares? • Net pT to interaction Pros • Separate Extraction Line • Post IP Diagnostics Pre-IP Diagnostics • Single g,e beam dump Higher P e-dump anywhere • Allows for future reduction Who cares? in beam spacing Dig later if really needed

  23. Backgrounds and IR Layouts Most important background is the incoherent production of e+e- pairs. • # pairs scales with luminosity and is ~equal for both designs. • Detector occupancies depend on machine bunch structure and relevant readout time • GEANT and FLUKA based simulations indicated that in both cases occupancies are acceptable and the CCD-based vertex detector lifetime is some number of years. • IR Designs are similar in the use of tungsten shielding, instrumented masks, and low Z material to absorb low energy charged and neutral secondary backgrounds

  24. Beam-Beam InteractionSR photons from individual particles in one bunch when in the E field of the opposing bunch • Beams attracted to each other reduce effective spot size and increase luminosity • HD ~ 1.4-2.1 • Pinch makes beamstrahlung photons: • 1.2-1.6 g/e- with E~3-5% E_beam • Photons themselves go straight to dump • Not a background problem, but angular dist. (1 mrad) limits extraction line length • Particles that lose a photon are off-energy

  25. gg e+e- eg ee+e- ee eee+e- ge+e- (Coherent Production) Pair ProductionPhotons interact with opposing e,g to produce e+,e- pairs and hadrons Pair PT: • SMALL Pt from individual pair creation process • LARGE Pt from collective field of opposing bunch • limited by finite size of the bunch 500 GeV designs

  26. e+,e- pairs from beams. g interactions # pairs scales w/ Luminosity 1-2x109/sec BSOL, L*,& Masks

  27. NLC/TESLA Beam-Beam Comparison • Larger sz for TESLA • More time for disruption • larger luminosity enhancement • more sensitivity to jitter • Lower charge density • lower energy photons • Real results come from beam-beam sim. (Guinea-Pig/CAIN) and GEANT3/FLUKA

  28. Pairs as a Fast Luminosity Monitor TESLA Also, Pair angular distribution carries information of beam transverse aspect ratio (Tauchi/KEK)

  29. Pair Stay-Clear from Guinea-Pig Generator and Geant

  30. e,g,n secondaries made when pairs hit high Z surface of LUM or Q1 High momentum pairs mostly in exit beampipe Low momentum pairs trapped by detector solenoid field

  31. Design IR to Control e+e- Pairs • Direct Hits • Increase detector solenoid field • Increase minimum beam pipe radius at VXD • Move beampipe away from pairs ASAP • Secondaries (e+,e-, g,n) • Point of first contact as far from IP/VXD as possible • Increase L* if possible • Largest exit aperture possible to accept off-energy particles • Keep extraneous instrumentation out of pair region • Masks • Instrumented conical M1 protrudes at least ~60cm from face of PAIR-LumMon • Longer= more protection but eats into EndCap CAL acceptance • M1,M2 at least 8-10cm thick to protect against backscattered photons leaking into CAL • Low Z (Graphite, Be) 10-50cm wide disks covering area where pairs hit the low angle W/Si Pair Luminosity monitor

  32. Detector Occupancies are Acceptablefcn(bunch structure, integration time) LCD=L2 Hit Density/Train in VXD &TPC vs. Radius TESLA VXD Hits/BX vs. Radius

  33. g in LD TPC 1 TeV g in LD Endcap CAL 1 TeV g in SD Endcap CAL 1 TeV Photons Beampipe @ r=2.2cm, B=4T Beampipe @ r=1.0cm, B=3T TESLA #g/BX in TPC vs. z Extraction Line (6m) “shines” thru shield here, but not here

  34. Off-energy e+/e- pairs hit the Pair-LumMon, beam-pipe and Ext.-line magnets Radiative Bhabhas & Lost beam <x10 Solutions: Move L* away from IP Open extraction line aperture Low Z (Carbon, etc.) absorber where space permits Neutrons from Beam Dump(s) Solutions: Geometry & Shielding Shield dump, move it as far away as possible, and use smallest window Constrained by angular distribution of beamstrahlung photons Minimize extraction line aperture Keep sensitive stuff beyond limiting aperture If VXD Rmin down x2 Fluence UP x40 Neutron BackgroundsThe closer to the IP a particle is lost, the worse

  35. Neutrons from the Beam Dump # Neutrons per Year Limiting Aperture Integral Geometric fall off of neutron flux passing 1 mrad aperture 0.5 1.0 Radius (cm) z(m)

  36. Neutron BackgroundsSummary Neutron hit density in VXD NLC-LD-500 GeV NLC-SD-500 GeV Tesla-500 GeV Beam-Beam pairs 1.8 x 109 hits/cm2/yr 0.5 x 109 hits/cm2/yr O(109 hits/cm2/yr) Radiative Bhabhas 1.5 x 107 hits/cm2/yr no hits <0.5x108 hits/cm2/yr Beam loss in extraction line 0.1 x 108 hits/cm2/year 0.1 x 108 hits/cm2/year Backshine from dump 1.0 x 108 hits/cm2/yr 1.0 x 108 hits/cm2/yr negligible TOTAL 1.9 x 109 hits/cm2/yr 0.6 x 109 hits/cm2/yr Figure of merit is 3 x 109 for CCD VXD

  37. Detector Occupanciesfrom e+e- Pairs @ 500 GeV TESLA NLC

  38. Synchrotron Radiationfrom Beam Halo in Final Doublet • At SLD/SLC SR WAS a (THE) PROBLEM • SR from triplet WOULD have directly hit beam-pipe and VXD • Conical masks shadowed the beam pipe inner radius • geometry set so that photons needed a minimum of TWO bounces to hit a detector • Background rates consistent with “flat halo” model: • 0.1% - 1% of the beam filled the phase space allowed by the collimator setting. • At NLC/TESLA • Allow NO direct SR hits ANYWHERE near IP • Collimate halo before the linac AND after the linac • VXD MINIMUM RADIUS sets collimation depth as well as B_s • Pain level goes at least as square of VXD min radius: • Muon production, collimator wakefields, collimator damage, radiation, ……. qX=450 mrad qY=270 mrad qX=32 mrad qY=28 mrad BE SURE YOU NEED IT!

  39. HALO Synchrotron Radiation Fans with Nominal 240 mrad x 1000 mrad Collimation (Similar plots for TESLA)

  40. Muon Backgrounds from Halo CollimatorsNo Big Bend, Latest Collimation & Short FF FF Energy 18m & 9m Magnetized steel spoilers Betatron BetatronCleanup If Halo = 10-6, no need to do anything If Halo = 10-3 and experiment requires <1 muon per 1012 e- add magnetized tunnel filling shielding Reality probably in between

  41. LD Muon Endcap Background#e- Scraped to Make 1Muon Bunch Train =1012 Engineer for 10-3 Halo Efficiency of Collimator System is 105 Calculated Halo is 10-6

  42. gg IR • Differences w.r.to • e+e- IR • Annular Mirror system • 10 mrad exit aperture instead of 1 mrad • 30mrad qC to accommodate exit aperture • Larger inner radius of VXD as first 2 layers of LD/SD VXD look in direct line of sight w/dump

  43. Independent Systems Model for e- Injection on e+ Arm RED=New Stuff

  44. Fixed Target Options

  45. Your IR Options ARE Open! Beam Delivery and IR Choices are ~ Independent of RF Technology And while each regional machine design group has a CONCEPTUAL DESIGN (in my view at least) We are far from needing to freeze any parameter which can impact either the PHYSICS PROGRAM Or the DETECTOR DESIGN There is a wealth of work to be done, particularly in the areas of diagnostic detector development and performance simulation (at SLC experimental physicists did this) Groups from U-Mass, UBC, Oxford, Brunel, NW,U.Hawaii…. are participating “Machine-Teach IN” tomorrow 4:15-6:00 Room 208

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