1. 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.

2. NLC - The Next Linear Collider Project 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

3. NLC - The Next Linear Collider Project The NLC beam delivery group has been actively studying the IR for many years IR Design and Backgrounds Takashi 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 Efforts Joe 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

4. NLC - The Next Linear Collider Project Beams attracted to each other reduce effective spot size and increase luminosity H D ~ 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 Interaction SR photons from individual particles in one bunch when in the E field of the opposing bunch NLC-1 TeV Slide of T. Markiewicz

5. NLC - The Next Linear Collider Project Pair Production Photons interact with opposing e,  to produce e+,e- pairs and hadrons Pair P T : 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 Slide of T. Markiewicz

6. NLC - The Next Linear Collider Project Pair Stay-Clear from Guinea-Pig Generator and Geant Slide of T. Markiewicz

7. NLC - The Next Linear Collider Project 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

8. NLC - The Next Linear Collider Project The basic design drivers are the same for TESLA and NLC # pairs scales w/ Luminosity 1-2x10 9 /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

9. NLC - The Next Linear Collider Project Neutron Backgrounds at the SVX The 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

10. NLC - The Next Linear Collider Project 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 Slide of T. Markiewicz

11. NLC - The Next Linear Collider Project HALO Synchrotron Radiation Fans with Nominal 240  rad x 1000  rad Collimation Stan Hertzbach Slide of T. Markiewicz

12. NLC - The Next Linear Collider Project 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 R min down x2 Fluence UP x40

13. NLC - The Next Linear Collider Project Muon Backgrounds from Halo Collimators No 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 10 12 e- add magnetized tunnel filling shielding Reality probably in between 18m & 9m Magnetized steel spoilers Betatron Betatron Cleanup Energy FF Slide of T. Markiewicz

14. NLC - The Next Linear Collider Project 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 …

15. NLC - The Next Linear Collider Project Realistic IR Layout 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

16. NLC - The Next Linear Collider Project A Photon Collider requires additional hardware in the IP

17. NLC - The Next Linear Collider Project 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

18. NLC - The Next Linear Collider Project MERCURY commissioning has begun One amplifier head with 4 of 7 crystals installed beam diode package on split backplanes gas-cooled amplifier head vacuum enclosure 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

19. NLC - The Next Linear Collider Project 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

20. NLC - The Next Linear Collider Project 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

21. NLC - The Next Linear Collider Project 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

22. NLC - The Next Linear Collider Project 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

23. NLC - The Next Linear Collider Project 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

24. NLC - The Next Linear Collider Project IP Girder Testbed

25. NLC - The Next Linear Collider Project 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 Beam-Beam Deflection gives 1nm stability resolution BPM res 400nm

26. NLC - The Next Linear Collider Project 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

27. NLC - The Next Linear Collider Project SLC Photon Collider testbed hardware MERCURY Laser Laser PlantBeam Splitter Beam Pipe Optics AssemblyInterferometric Alignment System Pulses at 30 Hz at SLC, 11,000 Hz at NLC The 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

28. NLC - The Next Linear Collider Project 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 Particles

29. NLC - The Next Linear Collider Project 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