backgrounds update tom markiewicz slac

NLC - The Next Linear Collider Project

Backgrounds UpdateTom Markiewicz

SLAC

LCWS Cornell15 July 2003

Tom Markiewicz


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

Tom Markiewicz


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

Tom Markiewicz


Pairs Lost on Lum and QDF1

Tom Markiewicz


Pair Energy Flow

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0 2 4 6 8 10 12

QD0SD0

M1

Pair LumMon

M2

Low Z shield

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0 2 4 6 8 10 12

QD0SD0

M1

Pair LumMon

M2

Low Z shield

Remaining 81.7% of pairs convert into photons and are absorbed by masks & calorimeters

E dep per bunch (GeV)

Power (mW)

% Total E_dep

% Total Pair

Energy

Peak E dep per

bunch per cc

Power (Watts)

Rads/10^7 sec

LowZ (Be) 1187.87 4.38 3.26% 0.60% 19.22 7.09E-05 3838.808Lum (W) 23585.62 87.05 64.72% 11.83% 138.75 5.12E-04 2653.51QD0 (Fe) 915.22 3.38 2.51% 0.46% 1.72 6.35E-06 80.66752QDF1 (Fe) 10755.11 39.70 29.51% 5.39% 156.19 5.76E-04 7325.267Total 36443.82 134.51 100.00% 18.28%

Tom Markiewicz

NLC - The Next Linear Collider ProjectCollimation System Designed to Make

Detector Free of Machine Backgrounds

E=250 GeVN=1.4E120.1% Halo distributed as 1/X and 1/Y for 6<Ax<16x and 24<Ay<73y with p/p=0.01 gaussian distributed

Tom Markiewicz


SR at IP due to Halo

X (cm)

Y

X (cm)

Log10(E) (GeV)

Quad

Bend

.3 Ne-<E>=4.8 MeVQuad

Bend

Tom Markiewicz


X-Y at Spoiler #3

30m x 25m

6x<Ax<16x

24y<Ay<73y

60m x 50m

12x<Ax<32x

48y<Ay<146y

Tom Markiewicz


Loss Distribution in “Worst Case” Scenario

E=250 GeVN=1.4E120.1% Halo distributed as 1/X and 1/Y for 2*6<Ax<2*16x and 2*24<Ay<2*73y with p/p=0.01 gaussian distributed AND SP/AB/DP x2-x3

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 500 1000 1500

z

N 1000x

Tom Markiewicz


Worst Case Ray Distribution at Spoiler#1

Tom Markiewicz


SR at IP in “1000x worse case”

SR distribution ~2x wider in y at IP with direct hits unless BP >1.25cm

Tom Markiewicz


NLC Beam Delivery thru 1999

-30

-20

-10

0

10

20

30

-6000 -4000 -2000 0 2000 4000 6000

e- e+

Collimation Collimation

Interaction Region 1

IR2

IR Transport = Final Focus

Extraction

Big Bend=10 mrad

Interaction Point 2Protect via distance and “Big Bend”

-5

0

5

10

15

20

25

30

35

40

-2000 -1500 -1000 -500 0 500 1000 1500 2000

e- e+Low E IP

Angle =10 mrad

Hi E IP

Currently 3x shorter & No Bend

Tom Markiewicz


Layout of Spoilers, Absorbers & Protection

Collimators

Betatron

Betatron Cleanup

Energy

FF

Tom Markiewicz


Calculated Beam Loss:Input to MuCarlo

Tom Markiewicz


9 & 18m Toroid Spoiler Walls

4.5m

0.6m0.6m 2cm

BB

170 Tons/m

Design Constraints: Minimize gap & minimize stray field in beampipe

Tom Markiewicz


First 100 Muons from PC1 of HEIR beamline that reach z=0 IR1 line has 9m & 18m magnetized walls

NO 18m wall in IR2 line

IR2 line has 18m wall

Somewhat arbitrary Goal: 10 muons / detector / train (from both e-,e+ systems)

Tom Markiewicz


Muon Yield

For 250 GeV p>1 GeV/c/e = 5 x 10-4

Yield scales with beam energy

Tom Markiewicz


Muon rate in detector ~1000x design goal before adding

spoiler walls4.4E-6 Muons/Scraped e-

** Assumed Halo 1E-3

Tom Markiewicz


Distributions with No Spoilers at 250 Gev/ Beam

Muon

HCAL

ECAL

Tunnel

Tom Markiewicz


18m Wall Downbeam of all sources reduces rate by x30

25% from E coll (recall pessimistic 1%

spread!)75% from Betatron

coll

Tom Markiewicz


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

Tom Markiewicz


Donuts reduce Muon rate from Betatron Region rate

by x8

Tom Markiewicz


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

rate by x100

Tom Markiewicz


Distributions with 2 Spoilers at 250 Gev/ Beam

Muon

HCAL

ECAL

Tunnel

Tom Markiewicz


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

NO 18m wall in IR2 line

IR2 line has 18m wall

Tom Markiewicz


Muon Dose Rates in IR1 and IR2 when other IR has beam

1.0 TeV CM

No Spoiler 18m Mag Spoiler @ z=321m

Source Halo IR1 (mr/hr)

IR2 (mr/hr)

IR1 (mr/hr)

IR2 (mr/hr)

Total for 2 beams 10.9 0.29 0.61 0.15

Total for 2 beams @500 GeV

4.5 0.13 0.12 0.01

•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

•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

Simultaneous Occupation OK if Magnetized Wall Is Present

Tom Markiewicz


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

backgrounds update tom markiewicz slac

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