NLC - The Next Linear Collider Project NLC Backgrounds What’s New? Tom Markiewicz LC’99, Frascati, Italy October 1999

Tom Markiewicz NLC - The Next Linear Collider Project Background Calculations Summary Overall status presented by Takashi Maruyama/SLAC at LCWS 4/99 at Sitges, Spain New Developments by Jeff Gronberg/LLNL New Be ring mask effectively eliminates backscattered hits in VXD-L1 Allows 1.2 cm VXD Layer 1 for fields down to 3 Tesla Study potential problem with scattering angle approx. used by FLUKA Synchrotron Radiation: Stan Hertzbach updates analysis from 1996: OK for 8  x x 40  y Takashi Maruyama adds 200m of incoming beamline to GEANT Study SR, off-energy beam striking apertures, beam-gas scattering SR from disrupted beam in extraction line not a problem Muon Background: Lew Keller/SLAC 9m long tunnel filling spoilers are the best insurance against muons. Current plan is to build ONLY ONE cavern downstream of last collimator, but to leave it empty until needed.

Tom Markiewicz NLC - The Next Linear Collider Project Background Simulations Machine Parameters: 1 TeV c.o.m. NLC “B” 1.0E10 e-/bunch; 95 b/train; 120 Hz Generators: “Guinea-Pig” Program Simulators: GEANT3: e+/e- & photons FLUKA98: neutrons Geometry: LCD Small Detector w/ real field Important that layout is as realistic as possible Complete Extraction Line and Dump  200 m of INCOMING beam line

Tom Markiewicz NLC - The Next Linear Collider Project Radiative Bhabhas 125K per =370 GeV IP Backgrounds e+,e- pairs from beams.  interactions 44K per =10.5 GeV (0.85 W)

Tom Markiewicz NLC - The Next Linear Collider Project Maximum Radius of Pair e-,e+ vs. z ( 1 TeV, Constant B z, 20 mrad  c ) Small Detector w/ 6 Tesla Solenoid 1.2 cm

Tom Markiewicz NLC - The Next Linear Collider Project IR Layout Details X (cm) Y(cm) Q1 Extraction Beampipe Maximum Radius of Pair Background x-y Distribution of Pair e-,e+ at z = 2 m 1 TeV, 6 Tesla Field Map Pairs deposit ~ ½ Watt DC  10 9 rad/year Plan View - 6 Tesla Detector Low Z absorber Pair Energy Monitor Collar

Tom Markiewicz NLC - The Next Linear Collider Project Detector Backgrounds (LCD Small Detector) Hit Density a very rapid function of r = 2 cm, goal is met Work in Progress: Addition of low Z absorbers in TESLA & JLC designs have eliminated backscatters

Tom Markiewicz NLC - The Next Linear Collider Project Be Ring Mask placed along field lines that reach VXD-L1 Reduces backscattered component of VXD-L1 hits to 16% of total Direct hits now dominate VXD-L1 whereas before were only 11% of total VXD-L1 Hit Density = 2.0 hits/mm 2 /train Under study: why did # VXD hits/primary e- increase to make density go from expected 1.2 to observed 2.0?

Tom Markiewicz NLC - The Next Linear Collider Project 1.2 cm VXD L1 in BOTH L & S Detectors Black:Layer 1 Turquoise:Layer 2 Green:Layer 3 Blue:Layer 4 Red:Layer 5 B (Tesla) Hits / bunch ~3.5 x more Layer 1hits at 3 Tesla With few backscattered hits, LCD group currently feels aggressive 1.2 cm VXD is also possible for Large Detector (3-4 T) detector 2.0 hits/mm 2 /train 84% from multiple hits by primary pair electrons

Tom Markiewicz NLC - The Next Linear Collider Project Neutron Backgrounds e+/e- pairs and radiative Bhabhas hitting beam-pipe and magnets in the extraction line. Disrupted beam lost in the extraction line % beam loss in recent redesign Disrupted beam and beamstrahlung photons in the dump Neutron hit density in VXD Beam-Beam pairs1.7 x 10 9 hits/cm 2 /yr Radiative Bhabhas0.02 x 10 9 hits/cm 2 /yr Beam loss in extraction line0.01 x 10 9 hits/cm 2 /year Backshine from dump0.25 x 10 9 hits/cm 2 /yr TOTAL2.0 x 10 9 hits/cm 2 /yr

Tom Markiewicz NLC - The Next Linear Collider Project Neutrons from the Beam Dump

Tom Markiewicz NLC - The Next Linear Collider Project Possible Problem with FLUKA may UNDERESTIMATE Beam Dump Contribution to Neutron Background More detailed study of source of VXD neutron hits indicated that NOTHING is coming down the beampipe Leads to study of scattering angles in FLUKA Learn of polar scattering angle approximation: OK for transport through bulk material (shielding) Not so good for small angle scattering down beam pipe Severity of problem unknown at this time Investigation under way with COG (a LLNL neutron transport code) May also try MARS code

Tom Markiewicz NLC - The Next Linear Collider Project Quadrupole Synchrotron Radiation Update (Stan Hertzbach) Apertures: Q1: 5.9 mm and 5.4 mm radius SR “stay-clear” considered (6.4 mm spec. in DIMAD) Extraction line: 10 mm radius beam pipe for z < 6 m, then 9 mm in quad magnets Criteria: No SR hits inner bore of Q1 or Be Ring Mask protecting VXD-L1 This is stricter than used in the past, where hits were allowed and we studied rescattering. It may be too strict, but # photons rises quickly! Assumptions: Flat beam halo assumed to fill collimation aperture Consider 8  x x 40  y and greater collimation depth Geometry: Horizontal beamline with detector rotated 10 mrad

Tom Markiewicz NLC - The Next Linear Collider Project QSR Masking Conclusions SR masks at 11m (y) and 12m (x) satisfy goal of NO Q1 / NO BeRM hits for 8  x x 40  y collimation and current Q1 aperture Increasing y collimation depth not possible Additional masks at 4m (y) and 8m (x) required to maintain goals if want to increase x collimation depth to 12  x Q1 SR stay-clear needs to be smaller (magnet engineering) Current feeling is that this is too close to the detector (50 mW of SR with an average photon energy of 49 GeV) Try to design Q1 so that aperture is increased for last 25% of its length closest to IP Maintain full diameter aperture of extraction beam pipe: Implications for Q1 support structure near L*=2m

Tom Markiewicz NLC - The Next Linear Collider Project Maruyama’s Conclusions on QSR from GEANT Extraction line generates 63.1  /e of = 31.1 MeV 36 kW per beam 160 W per beam strikes extraction line, mostly 90 < z < 130 m Incoming beam analysis in progress Misunderstanding in feeding beam parameters to GEANT. Need to check against Hertzbach’s work and include masks at 11 and 12m. Ignoring this: QSR generates 17.2  /e of = 28.5 MeV 8.9 kW per beam 6 W per beam strikes extraction line, mostly 6 < z < 9 m