nlc - the next linear collider project interaction region issues jeff gronberg / llnl santa cruz...

NLC - The Next Linear Collider Project

Interaction Region Issues

Jeff Gronberg / LLNL

Santa Cruz Linear Collider Retreat

June 26-29 2002

This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.


Outline

• Backgrounds which drive the detector design– Good: Luminosity related

– Bad: Machine backgrounds

• SVX is closest to the IP and least shielded from machine backgrounds, it is the primary driver of the design

• Photon Collider design– Basic principles

– TESLA and NLC/JLC differences

• Opportunities at SLC– Final quad stabilization

– Beam Halo reduction through non-linear optics

– Photon Collider test bed


The NLC beam delivery group has been actively studying the IR for many years

IR Design and BackgroundsTakashi Maruyama, Lew Keller, Rainer Pitthan

Tor Raubenheimer, Andrei Seryi, Peter Tenenbaum, Nan Phinney, Pantaleo Raimondi, Mark Woodley, Yuri Nosochkov

Stan Hertzbach (U. Mass)

Jeff Gronberg, Tony Hill (LLNL)

R&D EffortsJoe Frisch, Linda Hendrickson, Tom Himel

Eric Doyle, Leif Eriksson, Knut Skarpaas, Steve Smith

Tom Mattison & Students (UBC)

Phil Burrows, Simon Jolly, Gavin Nesom, Glen White, Colin Perry (Oxford)

Brett Parker (BNL)

University groups are already involved in the IR design


Beams attracted to each other reduce effective spot size and increase luminosity

•HD ~ 1.4-2.1

Pinch makes beamstrahlung photons: •1.2-1.6 /e- with E~3-5% E_beam•Photons themselves go straight to dump

•Not a background problem, but angular dist. (1 mrad) limits extraction line length

Particles that lose a photon are off-energy

Beam-Beam InteractionSR photons from individual particles in one bunch when in the E field of

the opposing bunch

NLC-1 TeV

Slide of T. Markiewicz


Pair ProductionPhotons interact with opposing e, to produce e+,e- pairs and

hadrons

Pair PT:• SMALL Pt from individual pair creation process• LARGE Pt from collective field of opposing

bunch – limited by finite size of the bunch

e+e- (Coherent Production)

e ee+e-

e+e-

ee eee+e-

500 GeV designs



Pair Stay-Clear from Guinea-Pig Generator and Geant



e,,n secondaries made when pairs hit high Z surface of LUM or Q1

High momentum pairs mostly in exit beampipe

Low momentum pairs trapped by detector solenoid field

N.B. Major TESLA / NLC difference

TESLA has zero crossing angle, low energy particles travel farther down the beam pipe before hitting anything


The basic design drivers are the same for TESLA and NLC

# pairs scales w/ Luminosity

1-2x109/sec

The solenoidal field is the primary defense against the pair backgrounds

Low energy particles will shower in the material of

the beam line

The detector must be protected by masks against secondary particles


Neutron Backgrounds at the SVXThe closer to the IP a particle is lost, the worse

Off-energy e+/e- pairs hit material near the IP; Pair-LumMon,

beam-pipe and Ext.-line magnets

Radiative Bhabhas & Lost beam <x10

Showering particles produce neutrons which can damage

the SVX

Solutions:• Move L* away from IP• Open extraction line aperture• Low Z (Carbon, etc.) absorber

where space permits


Design IR to Control e+e- Pairs

Direct Hits•Increase detector solenoid field

•Increase minimum beam pipe radius at VXD

•Move beampipe away from pairs ASAP

Secondaries (e+,e-, ,n)•Point of first contact as far from IP/VXD as possible

•Increase L* if possible•Largest exit aperture possible to accept off-energy particles •Keep extraneous instrumentation out of pair region

Masks•Instrumented conical M1 protrudes at least ~60cm from face of PAIR-LumMon

•Longer= more protection but eats into EndCap CAL acceptance•M1,M2 at least 8-10cm thick to protect against backscattered photons leaking into CAL

•Low Z (Graphite, Be) 10-50cm wide disks covering area where pairs hit the low angle W/Si Pair Luminosity monitor



HALO Synchrotron Radiation Fans with Nominal 240 rad x 1000 rad Collimation

Stan Hertzbach



Neutrons from the Beam Dump

Limiting Aperture

Radius (cm)z(m)

# Neutrons per Year

Neutrons from Beam Dump(s)

Solutions: Geometry & Shielding

• Shield dump, move it as far away as possible, and use smallest window– Constrained by angular

distribution of beamstrahlung photons

• Minimize extraction line aperture

• Keep sensitive stuff beyond limiting aperture– If VXD Rmin down x2 Fluence

UP x40


Muon Backgrounds from Halo CollimatorsNo Big Bend, Latest Collimation & Short FF

If Halo = 10-6, no need to do anything

If Halo = 10-3 and experiment requires <1 muon per 1012 e- add magnetized tunnel filling shielding

Reality probably in between

18m & 9m Magnetized

steel spoilers

Betatron

BetatronCleanup

EnergyFF



Background Projects

• Iterate all results for consistent set of results– Beam parameters, detectors, solenoid design, beamlines not

consistent

• Detector response to known backgrounds– TPC, Cal, Lum, Pol, etc.

• Dose calculations on SC or REC QD0• Collimator scattering study:

– Locations, apertures, beam loss, …

• GEANT4 beamline model• -Hadron production• …• …


Realistic IR Layout

500 GeV TRC Optics w/ Large Detector

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 2 4 6 8 10 12 14

Masking Support

VXD support & alignment

Instrumented Masks

Lum_Pair Mon

Vacuum req.

•REC QD0

•SC QD0

•Beampipe support

Apertures

Optical lines of sight

Detector access


A Photon Collider requires additional hardware in the IP


NLC/JLC Photon Collider Hardware

MERCURY Laser

1 pulse = 100 Joules = 1 train

Laser Plant

12 Lasers x 10Hz = 120Hz

Beam Splitter

1, 100 Joule pulse -> 100, 1 Joule pulses

Beam Pipe Optics AssemblyInterferometric Alignment System


MERCURY commissioning has begunOne amplifier head with 4 of 7 crystals installed

beam

diode package on split backplanes

gas-cooledamplifier head

vacuumenclosure

pump duct and homogenizer

Status

• Producing 10 Joule pulses at 0.1 Hz•Theoretical max 14 Joules w/ 4 crystals

• Operation of two heads with 14 crystals within the next year

• Installation of new front end for 10Hz operation


NLC solution might be adapted to TESLA, but TESLA bunch spacing opens new options

• A single light pulse can travel around the ring and hit every bunch in the TESLA train– DESY and Max Born Institute will prototype a scale model

• Tolerances are tight, but enormous savings in laser power


All detector elements are affected by the photon collider environment

• Outgoing beam: Compton backscattering leaves a large energy spread

• On-energy peak (30% of particles)• Low-energy tail (Multiple backscatters)• Hard cutoff at 5 GeV

• Solution: – Zero field extraction line to the dump, no diagnostics– Increase extraction line aperture, SVX sees the beam dump!

• hadrons: resolved photon events– Every bunch crossing has tracks

– ~ 730 GeV / train into the calorimeter with cos() < 0.9

– Events look more like those from a hadron machine than a lepton machine

TESLA bunch spacing makes it easier to isolate a single bunch crossing


System Integration – Optics/Beampipe

• Essentially identical to e+e- IR

• All masking preserved

• 30 mRad x-angle

• Extraction line ± 10 mRadian

• New mirror design 6 cm thick, with central hole 7 cm radius.– Remove all material

from the flight path of the backgrounds

LCD - Large with new mirror placement


Photon Collider projects

• Detector studies– Rad-hard SVX design

– Resolved photon backgrounds

• SVX b-tagging

• Jet resolution

• Timing requirements

– Complete background and reconstruction simulation

• Machine studies– Optics / beampipe integration

– Crossing angle minimization

– Realistic IR layout

– Radiation damage to the optics

• Coupon tests

The photon collider has all of the issues of the regular e+e- IR and then some


Engineering Test Facility at SLC

• Beam Energy:• DR emittances: x,y (m-rad)

• FF emittances: x,y (m-rad)

• IP Betas: x / y

• Bunch length: z

• IP spot sizes: x,y

• Beam currents: N

NLC

250 GeV

300 / 2

same

0.11 mm

245/2.7nm

7.5E9

SLC

30 GeV

1100 / 50

8 / 0.1 mm

0.1 – 1.0 mm

1500/55nm

6.0E9

• An e+e- linear collider exists and could be resurrected as a test facility for <$2M– Test of final quad stabilization

– Beam halo reduction

– Photon collider demo


IP Girder Testbed


Nanometer Stability of Colliding Beams

Colliding beams provide a Direct Model-Independent Test of any engineering solution to the final doublet stability problem

Not possible in FFTB

50 100 10000.1

1

10

Beam offset in BPM for 1 nm beam offset at IP

Design beam parameters

z=1000 m

z=100 m

Bea

m o

ffs

et in

BP

M ,

m

(*y )

1/2 , nm

Beam-Beam Deflection gives 1nm stability resolution

BPMres

400nm


Controlling Beam Backgrounds with Non-Linear Optical Elements

Tail Folding via Octupole Pairs has the promise of relaxing collimation depths

Confidence that comes from an Actual Demonstration may permit a great savings in collimator design, radiation shielding, and muon shielding

-30 -20 -10 0 10 20 30-30

-20

-10

0

10

20

30

X-Y at QD0

Octupoles ON

Octupoles OFF

Y (

mm

)

X (mm)

-40 -20 0 20 40-40

-20

0

20

40

X-Y at QF1

Octupoles ON

Octupoles OFF

Y (

mm

)

X (mm)


SLC Photon Collider testbed hardware

MERCURY Laser Laser Plant Beam Splitter

Beam Pipe Optics AssemblyInterferometric Alignment System

Pulses at 30 Hz at SLC, 11,000 Hz at NLCThe laser is easy for a SLC testbed

A small 30Hz, 15W average power laser is sufficient for this experiment

½ size to fit in SLC


Particle spectra in SLC photon collider

• A 0.1 Joule laser pulse converts 25% of the incoming electrons.

• Maximum energy transfer is 1/3 of the beam energy– First direct production of

luminosity– Look for 2 2 processes in

the SLD calorimeter to measure luminosity

• e+e- e+e-

• e e• e+e-

GeV/c

e

Par

ticl

es


Summary

• The optimization of the IR is not complete– Understanding and mitigation of backgrounds

– Realistic engineering of the machine / detector interface

• A photon collider presents new challenges– Detector backgrounds are worse

– The impact on physics reconstruction must be studied

– Additional detector constraints must be understood

• SLC has great potential as a test facility– Proof-of-principle for colliding nm beams

– Beam halo reduction through non-linear optics

– Photon collider demonstration

nlc - the next linear collider project interaction region issues jeff gronberg / llnl santa cruz...

Documents

linear collider project

e pairs

opposing e

linear collider project

markiewicz slide

ir design slide

opposing bunch nlc

geant slide