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Backgrounds Update Tom Markiewicz SLAC

Backgrounds Update Tom Markiewicz SLAC. LCWS Cornell 15 July 2003. Outline. Pair Background Energy Conservation What is getting hit? Backgrounds at Machine Startup John Jaros asks: What if the machine is 1000x worse than you expect? A first look…. Muon Background Update

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Backgrounds Update Tom Markiewicz SLAC

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  1. Backgrounds UpdateTom MarkiewiczSLAC LCWS Cornell 15 July 2003

  2. Outline • Pair Background Energy Conservation • What is getting hit? • Backgrounds at Machine Startup • John Jaros asks: What if the machine is 1000x worse than you expect? • A first look…. • Muon Background Update • Study by TRC Collimation Task Force sets apertures and calculates source terms • Lew Keller makes & transports muons to the detector wit & without tunnel-filling toroids

  3. Pair Refresher Course • At 500 Gev w/ NLC beam parameters: • 49.2K e- per bunch @ <E>=4.05 GeV • 200 TeV Total • 0.37mWatts per side

  4. Pairs Lost on Lum and QDF1

  5. Pair Energy Flow Remaining 81.7% of pairs convert into photons and are absorbed by masks & calorimeters

  6. Collimation System Designed to Make Detector Free of Machine Backgrounds E=250 GeV N=1.4E12 0.1% Halo distributed as 1/X and 1/Y for 6<Ax<16sx and 24<Ay<73sy with Dp/p=0.01 gaussian distributed

  7. SR at IP due to Halo Quad Ng=7.3 Ne- Quad <Eg>=4.8 MeV Bend Log10(E) (GeV) Y Bend X (cm) X (cm)

  8. X-Y at Spoiler #3 30mm x 25mm 6sx<Ax<16sx 24sy<Ay<73sy 60mm x 50mm 12sx<Ax<32sx 48sy<Ay<146sy

  9. Loss Distribution in “Worst Case” Scenario E=250 GeV N=1.4E12 0.1% Halo distributed as 1/X and 1/Y for 2*6<Ax<2*16sx and 2*24<Ay<2*73sy with Dp/p=0.01 gaussian distributed AND SP/AB/DP x2-x3

  10. Worst Case Ray Distribution at Spoiler#1

  11. SR at IP in “1000x worse case” SR distribution ~2x wider in y at IP with direct hits unless BP >1.25cm

  12. NLC Beam Delivery thru 1999 Protect via distance and “Big Bend” Currently 3x shorter & No Bend

  13. Layout of Spoilers, Absorbers & Protection Collimators Energy Betatron FF Betatron Cleanup

  14. Calculated Beam Loss:Input to MuCarlo

  15. 9 & 18m Toroid Spoiler Walls 0.6m 0.6m 2cm 4.5m B B 170 Tons/m Design Constraints: Minimize gap & minimize stray field in beampipe

  16. First 100 Muons from PC1 of HEIR beamline that reach z=0 IR1 line has 9m & 18m magnetized walls Somewhat arbitrary Goal: 10 muons / detector / train (from both e-,e+ systems) IR2 line has 18m wall NO 18m wall in IR2 line

  17. Muon Yield For 250 GeV pm>1 GeV/c m/e = 5 x 10-4 Yield scales with beam energy

  18. Muon rate in detector ~1000x design goal before adding spoiler walls 4.4E-6 Muons/Scraped e- ** Assumed Halo 1E-3

  19. Distributions with No Spoilers at 250 Gev/ Beam Muon Tunnel HCAL ECAL

  20. 18m Wall Downbeam of all sources reduces rate by x30 25% from E coll (recall pessimistic 1% spread!) 75% from Betatron coll

  21. Donut Toroid Muon Attenuators • Well defined source locations followed by at least 5m of free space (at 250 GeV/beam) may be serviced by devoted attenuators • Nice if there is a dipole between the source and the donut • Lattice does not always permit this • NLC betatron collimation system has space for 6 5m-long attenuators (SP2/AB2,PC1,SP3/AB3/PC2,PC3,SP4/AB4/PC4,PC5/SP5/AB5) • NLC energy collimation region has no space • NLC MuCarlo study uses 120cm diameter donut toroids JLC advocates double donut TESLA uses single donut

  22. Donuts reduce Muon rate from Betatron Region rate by x8

  23. Additional 9m Wall reduces Betatron m rate by x50 and E Coll m rate by x100

  24. Distributions with 2 Spoilers at 250 Gev/ Beam Muon Tunnel HCAL ECAL

  25. Radiation Safety Aspect of Collimator System Muons • Can you occupy IR2 when IR1 is running? • Can you occupy IR1 when IR2 is running? Last studied for 2001 BD model with shared collimation An issue whenever IR2 “sees” IR1 collimators IR2 line has 18m wall NO 18m wall in IR2 line

  26. Muon Dose Rates in IR1 and IR2 when other IR has beam Simultaneous Occupation OK if Magnetized Wall Is Present • SLAC Rad Safety Rules: • 0.5 mrem/hr for normal operation • 25 rem/hr (3 rem max dose) for max credible accident • Run MUCARLO and find maximum dose rate in any 80cmx80cm area • If do nothing and halo=10-3, dose is 10-20x SLAC 0.5 mrem limit • 18m mag spoiler buys you x20 to 40; IR2 looks OK in any event • Max credible accident only dumps 103 more beam, limit is 50E3 higher

  27. Conclusions on Muons • Unless the beam halo loss rate is ~10-6, all collimator designs will need some combination of magnetized spoilers to reduce the muon flux • For the case of the NLC design it appears that two magnetized walls serve the purpose. • At least one wall per IR per side may be required for personnel protection • Current plan is to leave space for the caverns that would enclose these walls but to not install until measurements of halo and muon production sources indicate it is necessary. • Judicious use of point muon attenuators may be useful

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