NLC - The Next Linear Collider Project NLC Backgrounds What’s New? Tom Markiewicz LC’99,...

NLC - The Next Linear Collider Project

NLC BackgroundsWhat’s New?

Tom Markiewicz

LC’99, Frascati, Italy

October 1999

Tom Markiewicz


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


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


Radiative Bhabhas125K per bunch @ <E>=370 GeV

IP Backgrounds

e+,e- pairs from beams. interactions44K per bunch @ <E>=10.5 GeV (0.85 W)

Tom Markiewicz


Maximum Radius of Pair e-,e+ vs. z( 1 TeV, Constant Bz, 20 mrad c )

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 0.5 1 1.5 2 2.5

Small Detector w/ 6 Tesla Solenoid

1.2 cm

Tom Markiewicz


IR Layout Details

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 0.5 1 1.5 2 2.5

X (cm)

Y(cm)

Q1

Extraction Beampipe

Maximum Radius of Pair Background

x-y Distribution of Pair e-,e+ at z = 2 m1 TeV, 6 Tesla Field Map

Pairs deposit ~ ½ Watt DC 109 rad/year

Plan View - 6 Tesla Detector

Low Z absorber

Pair Energy Monitor

Collar

Tom Markiewicz


Detector Backgrounds(LCD Small Detector)

Detector Issue Current Results

VXD hit density Goal: < 1 hit/mm2/trainFind: < 10 hits/mm2/train at r=1.2 cmMain source: Charged secondaries from e+,e- pairs hitting Q1 face

Tracking Chamber Hits Goal: < 104 /trainFind: ~105 /train at r = 30 cm secondaries from e+e- pairs hitting beam pipe and VXD

VXD Lifetime Goal: 3 x 109 neutrons/cm2

Find: 2 x 109 neutrons/cm2/year (1.5 year lifetime)Main Source: Neutron secondaries from e+e- pairs

hitting 2m < z < 6m

Hit Density a very rapid function of radius: @ r = 2 cm, goal is met

Work in Progress: Addition of low Z absorbers in TESLA & JLC designs have eliminated backscatters

Tom Markiewicz


Be Ring Maskplaced along field lines that reach VXD-L1

Reduces backscattered component of VXD-L1 hits to 16% of total

Direct hits now dominateVXD-L1 whereas before were only 11% of total

VXD-L1 Hit Density = 2.0 hits/mm2/train

Under study: why did # VXD hits/primary e- increase to make density go from expected 1.2 to observed 2.0?

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0 0.5 1 1.5 2 2.5

Tom Markiewicz


1.2 cm VXD L1 in BOTH L & S Detectors

Black: Layer 1Turquoise: Layer 2 Green: Layer 3 Blue: Layer 4 Red: Layer 5

B (Tesla)

Hit

s / b

unch

~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/mm2/train

84% from multiple hits by primary pair electrons

Tom Markiewicz


Neutron Backgrounds

•e+/e- pairs and radiative Bhabhas hitting beam-pipe and magnets in the extraction line.•Disrupted beam lost in the extraction line.

•0.25 % beam loss in recent redesign•Disrupted beam and beamstrahlung photons in the dump

Neutron hit density in VXD

Beam-Beam pairs 1.7 x 109 hits/cm2/yr

Radiative Bhabhas 0.02 x 109 hits/cm2/yr

Beam loss in extraction line 0.01 x 109 hits/cm2/year

Backshine from dump 0.25 x 109 hits/cm2/yr

TOTAL 2.0 x 109 hits/cm2/yr

Tom Markiewicz


Neutrons from the Beam Dump

Tom Markiewicz


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


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


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 12x

•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


Maruyama’s Conclusions on QSR from GEANT

Extraction line generates 63.1 /e of <E> = 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 <E> = 28.5 MeV

•8.9 kW per beam

•6 W per beam strikes extraction line, mostly 6 < z < 9 m

NLC - The Next Linear Collider Project NLC Backgrounds What’s New? Tom Markiewicz LC’99,...

Documents

Transcript of NLC - The Next Linear Collider Project NLC Backgrounds What’s New? Tom Markiewicz LC’99,...