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NLC IP Layout Issues

NLC IP Layout Issues. Jeff Gronberg/LLNL MAC Collaboration Meeting June 1, 2000. CCX,CCY. L*. L*. Today’s report is on Yesterday’s FF Design. Old FF : Remotely correct chromaticity of final doublet Long and length depends on Energy 2m L*, inside detector, Length scales with L*

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NLC IP Layout Issues

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  1. NLC IP Layout Issues Jeff Gronberg/LLNL MAC Collaboration Meeting June 1, 2000

  2. CCX,CCY L* L* Today’s report is on Yesterday’s FF Design • Old FF : Remotely correct chromaticity of final doublet • Long and length depends on Energy • 2m L*, inside detector, Length scales with L* • Adequate but limited energy bandwidth • “classical” telescope design, tested at FFTB • Studied since <1995 • Magnets engineered • New FF : Locally correct chromaticity of final doublet • Short and length roughly independent of Energy • Length roughly independent of L* • Larger energy bandwidth and dynamic aperture (easier collimation) • Transverse separation of 2 IPs more difficult • Collimation system closer to the IP • No magnets engineering yet

  3. 1995-99 Beam Delivery Layout

  4. 2000 Beam Delivery Layout

  5. Basic Issues • Bunch Spacing: 2.8 ns / 84 cm (or 1.4 ns / 42 cm) • Need some crossing angle to avoid unwanted collisions before bunch gets to the IP, 4-30 mrad • Beam-beam effects: e+e- pair production, disrupted beam energy, beamstrahlung photons, gg hadron production and machine backgrounds • Masks, L*, collimation depth, halo assumptions, spoilers,... • Small spot sizes: sx /sy = 235 nm / 3.9 nm • Need to control position & motion of final quads and/or position of the beam

  6. Basic Issue #1Bunch Structure • TESLA: 337 ns, 2820 bunches • 0 degree crossing angle • Detectors clear after 1 bunch worth of backgrounds (except maybe VXD) • “Slow” feedback system (80 pulses <=> 100 sigma offset) on beam-beam deflection signal corrects beam position for all drifts and jitters • NLC: 2.8 ns (or 1.4 ns), 95 bunches • Crossing angle to avoid unwanted collisions before bunch gets to the IP • Integrate 95 bunches of background before clear • 120 Hz “slow” feedback system for drifts; other means for high frequency jitter

  7. Crossing Angle Considerations~ 4-30 mrad • Crab Cavity: • Transverse RF cavity on each side of IP rotates bunches so they collide head on • relative timing accuracy determines maximum crossing angle • Beam Steering: • Transverse component of detector solenoid steers beams and causes spot size blow up • Handle with clever upstream beam steering gymnastics • Transverse Space for (easier) extraction line • Non cylindrically symmetric geometry for inner detectors • If crossing angle comes from “Big Bend” • get extra protection from muons • pay for extra optics to deal with dispersion Current design choice = 20 mrad

  8. Luminosity Monitor Detail

  9. LCD Small Detector with L* =2m CD1 Optics Plan View Tunnel Wall M2 Q1 Q1-SC Q2 M1 Beam Pipe 10 mrad Lum -10 mrad RF Shield Q1-EXT Support Tube

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

  11. Basic Issue#2: BackgroundsWell Studied by ALL GROUPS: Not a Problem • Machine Backgrounds: • Synchrotron Radiation • Muons Production at collimators • Direct Beam Loss • Beam-Gas • Collimator edge scattering • Neutron back-shine from Dump • Extraction Line Losses “Bad”, get nothing in exchange 1) Don’t make them 2) Keep them from IP if you do “Good”, scale with luminosity 1) Transport them away from IP 2) Shield sensitive detectors 3) Timing • IP Backgrounds: • Beam-Beam Interaction • Disrupted primary beam • Beamstrahlung photons • e+,e- pairs from beams. gg interactions • Hadrons from beams. gg interactions • Radiative Bhabhas

  12. Energy Distributions Radiative Bhabhas 125K per bunch @ <E>=370 GeV

  13. Extraction Line150 m long with common g and e- dump

  14. Neutrons from the Beam Dump

  15. Muon Backgrounds(Lew Keller) • Beam Halo: • 10-6 (calculated) • 10-3(current NLC assumption) • 10-2(worst SLC, ZDR assumption) • Pre-linac (8 GeV) Collimation: Damping ring extraction root of all evil at SLC • Collimation system “depth”: 8 sx 40 sy • Loosen it and get less muons and an easier optical lattice • Increase it and get more synchrotron radiation (for the same halo) • Big Bend:buys ~ x5 in muon protection • Distance from IP: more is better for muons: 30x more muons in new, shorter FF • Spoilers: 9m long tunnel-filling toroids bend muons away from IP, endcaps see <1/train • spoilers buy x2000 @ 250 GeV/beam and x500 @ 500 GeV/beam • Let the detector eat more: • Design goal of 1 muon in detector/train is achievable, with some pain • What is real detector limit? No spoilers leave <6 muons per square m of endcap

  16. Synchrotron Radiation(Stan Hertzbach) • Goal: No SR hits inner bore of Q1 or Be Ring Mask protecting VXD-L1 • Assumptions: Flat beam halo assumed to fill collimation aperture 8 sx 40 sy • At IP, SR due only to halo particles spraying g in the final doublet • Tighter/looser collimation limits what is hit • Assumed halo (0.1%) tells you power deposited • Incoming Aperture: 5.9mm radial stay-clear on Q1 (5.4 drawn on plots) • Exit Apertures: 10mm radius beam-pipe, then increasing • Results • SR masks at 11m (y) and 12m (x) keep upstream SR away from Q1 and Q2 • Q1 aperture just big enough so that 8 sx 40 sy collimation works • Looser collimation or smaller apertures would require masks closer to the IP

  17. Luminosity Loss vs. Jitter

  18. Basic Issues #3Vibration • Control position & motion of final quads and/or position of the beam to achieve sx /sy = 235 nm / 3.9 nm • Get a seismically quiet site • Don’t screw it up: Pumps, compressors, fluids • Good magnet and detector engineering: Light, stiff Q1 • Tie to “bedrock”: get lenses outside detector as soon as possible • Slow feedback: based on 120 Hz, controls frequencies < ~ 3-5 Hz • Fast (10-20 ns) feedback on front of bunch train corrects the (guaranteed correlated) train offset • “Actively” tie lenses inside detector to bedrock: • Optical Interferometer + piezo-mover or Inertial sensor + piezo-mover • The less cantilevering and the best lines-of-sight through the detector the better

  19. Conclusions Each potential problem in the beam delivery/IR/detector area has a variety of possible solutions that we have only begun to investigate Many of these are independent of the machine technology Working groups have been actively collaborating to resolve issues through meetings (next: FF/IR workshop, Daresbury, June 2000) and personnel exchange

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