# Presentation: 881533

## Linear Collider IR Options

**Tom Markiewicz / SLAC**
**LC Workshop 2002, U. Chicago**
**07 January 2002**

## Outline

**Bunch Structure**
**Crossing Angle**
**Time Packaging of  Detector Backgrounds**
- Beam-Beam Feedback Schemes (RB)

**IP Beam Parameters**
- Luminosity (RB)
- Luminosity Sensitivity (RB)
**IP Backgrounds**

**IR Options**
- IR Layout Choices
- Site Layout Choices
- Detector Occupancies & Acceptances

**Beam Delivery & IR Choices **
**~Accelerator Technology Independent**

## Bunch Structure vs. X-Angle

|  | TESLA-500 | JLC/NLC-500 | CLIC-3TeV |
| --- | --- | --- | --- |
| B | 337 ns | 1.4ns | 0.67 ns |
| c B | 100 m |  4.2m | 2.0 m |
| NB | 2820 | 192 | 154 |
| Train  | 950 s | 269 ns | 103 ns |
| f | 5 Hz | 120/150 Hz | 100 Hz |
| 1/f | 200 msec | 8.3/6.6 msec | 10 msec |
| MIN C | 0 mrad | ~4 mrad | ~12mrad |
| Chosen C | 0 mrad
Could be anything | JLC=8 mrad
NLC=20 mrad | 20 mrad |

- Crab Cavities
- Beam Steering
- “r<20cm” Hardware
- Lum Monitor
- Magnet Technology
- L* (IP to 1st Quad = QD0)
- Beam Extraction
- Beam Diagnostics
- Beam Dumps
- “Maximum” Ecm
- Minimize bends
- Compatibility with other designs

## Beam Separation Required Before 1st Parasitic Collision at cB/2

**Beam Separation Required Before 1****st**** Parasitic Collision at c********B****/2**

- IP

- Luminosity Loss vs. Crossing Angle for CLIC, B=0.67 ns
- D. Schulte, LCWS 2000

## NLC Detector MaskingPlan View w/ 20mrad X-angle

**NLC Detector Masking****Plan View w/ 20mrad X-angle**

- 32 mrad

- 30 mrad

- Large Det.- 3 T

- Silicon Det.- 5 T

## JLC IR8 mrad Design 

- Elevation View

- Iron magnet in a SC Compensating magnet
- 8 mrad crossing angle
- Extract beam through coil pocket
- Vibration suppression through support tube

**JLC IR****8 mrad Design**** **

## TESLA IRInstrumented W Mask & Pair-LumMon w/ Low Z Mask

## Maximum Crossing AngleCrab Cavity

- Transverse RF cavities on each side of IP rotate the bunches so they collide head on
- Cavity power req. and relative voltage & phase stability limit maximum crossing angle:
- 2% *L*/*L* when bunch overlap error       x ~ 0.4 x
- Since x = (C/2)z , at C=20mrad phase error z corresponds to ~10m
- ~ 0.2 degree of X-Band phase

******C**** ****< 40 mrad**

- x

## Crossing Angle Considerations Interaction with Detector’s Solenoid

**Beam Steering before IP:**
- Transverse component of solenoid changes position and angle of beams at the IP
- 1.7 m , 34.4 rad at 1 TeV, L*=2m, Bs=6 T, C=20mrad
- Dispersion and SR cause spot size blow up
-  Dispersion adds 3.1 m to vertical spot size
- SR contribution tiny; goes as (L*BsC)5/2
**Beam steering and QD position adjustment make this a NON-PROBLEM**
**Beam Steering after IP:**
- Energy dependence of angle of extraction line
- Steering: position (410 m) & angle (69 rad) different from B=0 case at 1 TeV
**Only run with solenoid ON and Realign extraction line when necessary**

## Luminosity Monitor DetailNon cylindrically symmetric geometry for inner detectors

**Luminosity Monitor Detail****Non cylindrically symmetric geometry for inner detectors**

## Baseline Magnet Technology Choices

- Extraction outside QD0
- Permanent Magnets (NLC)
- Compact, stiff, few external connections, no flowing fluids
- Adjustment more difficult
- Extraction in QD0 Coil Pocket
- Conventional Iron in SC Tube (JLC)
- Adjustable, familiar
- Massive, SC tube shields magnet from solenoid
- Extraction through QD0 Bore
- Superconducting (TESLA)
- Adjustable, large aperture bore
- Massive and not stiff

## TESLA SC Final Doublet QuadsMature LHC based Design

- QD0:
- L=2.7m
- G=250 T/m
- Aperture=24mm
- QF1:
- L=1.0m

## NLC Final Doublet Quad Options

- Permanent Magnet Option: compact, stiff, connection free

- 5.7cm BNL Compact SC

| Magnet | Aperture | Gradient | Rmax | Z_ip | Length |
| --- | --- | --- | --- | --- | --- |
| QD0 | 1.0 cm | 144 T/m | 5.6cm | 3.81 m | 2.0m |
| QF1 | 1.0 cm | 36.4 T/m | 2.2cm | 7.76 m | 4.0 m |

## NLC Extraction Line150 m long with chicane and common  and e- dump

**X-Angle allows separate beam line to cleanly bring disrupted beam to dump and allows for post-IP Diagnostics**

**0.2% of beam ~ 4kW lost @ 1 TeV**
**0-0.002% beam ~ 0-20W lost @ 500 GeV**

## TESLA Vertical Extraction at 0o

- Electrostatic separators at 20m
- Shielded septum at 50m (cB/2)
- Dipoles to e-/+ dump at z=240m
**Calculated losses OK**
**Challenging problem**
**No space for diagnostic equipment**

- Photons to separate dump at 240m with hole for incoming beam

## TESLA Pre-IP Polarimeter and Energy Spectrometer

- No TESLA plans for post IP diagnostics
- NLC plans pre-IP diagnostics but no work yet begun
- No detailed work on post-IP diagnostics done yet

## Energy FlexibilityEnergy Dependence of Luminosity 

- Final Focus magnet apertures set by lowest energy
- Highest energy operation limited by magnet strength, synchrotron radiation and system length

- For fixed geometry

## Luminosity Scaling with Energy

- Luminosity increases linearly with energy at High and Low E IRs
- Above maximum design energy, L drops quadratically due to synchrotron radiation emittance growth
- Range can be extended by changing geometry to soften bend angle

- This LEIR design done when there was 80mrad of bending to get to IR2
- Now at ~25mrad curves essentially identical

## NLC & TESLA both have Minimal Angles to Primary IR & ~20mrad to IR2

- 30 km

**Bypass Lines**
**50, 175, 250 GeV**

**IR1**
** ****(250 GeV to multi-TeV)**

**Length for**
**500 GeV/beam**

**Injector Systems for 1.5 TeV**

**IR2**
** ****(90 GeV to ~TeV)**

## TESLA Post-Linac Layout

## e+

- Skew Correction / Emittance Diagnostics

- Skew Correction / Emittance Diagnostics

- e-

- Interaction Region Transport (High Energy)

- Interaction Region Transport (High Energy)

- Collimation / Final Focus
- (High Energy)

- Collimation / Final Focus
- (High Energy)

- IR Hall (High Energy)

- IR Hall (Low Energy)

- IP1

- IP2

- Interaction Region Transport (Low Energy)

- Interaction Region Transport (Low Energy)

- Collimation / Final Focus
- (Low Energy)

- Collimation / Final Focus
- (Low Energy)

## Pros & Cons of a Crossing Angle

- Cons:
- Beam Steering Correction		**Easy**
- Crab cavity Required		**OK as long as ********C****<~40 mrad**
- LUM not cylindrically
- symmetric				**Who cares?**
- Net pT to interaction
- Pros
- Separate Extraction Line
- Post IP Diagnostics			**Pre-IP Diagnostics**
- Single ,e beam dump		**Higher P e-dump anywhere**
- Allows for future reduction 	**Who cares?**
-      in beam spacing                             **Dig later if really needed**

## Backgrounds and IR Layouts

- Most important background is the incoherent production of e+e- pairs.
- # pairs scales with luminosity and is ~equal for both designs.
- Detector occupancies depend on machine bunch structure and relevant readout time
- GEANT and FLUKA based simulations indicated that in both cases occupancies are acceptable and the CCD-based vertex detector lifetime is some number of years.
- IR Designs are similar in the use of tungsten shielding, instrumented masks, and low Z material to absorb low energy charged and neutral secondary backgrounds

|  | TESLA-500 | JLC/NLC-500 |
| --- | --- | --- |
| N | 2.0 x 1010 | 0.75 x 1010 |
| x | 550 nm | 243 nm |
| y | 5 nm | 3 nm |
| z | 300 m | 110 m |

## Beam-Beam InteractionSR photons from individual particles in one bunch when in the E field of the opposing bunch

- 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 Interaction**SR photons from individual particles in one bunch when in the E field of the opposing bunch

## Pair ProductionPhotons 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**

- 500 GeV designs

## e+,e- pairs from beams.  interactions

- # pairs scales w/ Luminosity
- 1-2x109/sec

- BSOL, L*,& Masks

## NLC/TESLA Beam-Beam Comparison

|  | NLC500 | TESLA500 |
| --- | --- | --- |
| Dy | 14 | 25 |
|  | 0.11 | 0.06 |
| n | 1.17 | 1.6 |
| b | 4.6% | 3.2% |
| HD | 1.4 | 2.1 |
| # pairs/bunch | 49,000 | 130,000 |
| <E>_pair e | 5.5 GeV | 2.8 GeV |
| #pairs/ sec | 1.1E9 | 1.8E9 |

- Larger ******z** for TESLA
- More time for disruption
- larger luminosity enhancement
- more sensitivity to jitter
- Lower charge density
- lower energy photons
- Real results come from beam-beam sim. (Guinea-Pig/CAIN) and GEANT3/FLUKA

## Pairs as a Fast Luminosity Monitor

- Also, Pair angular distribution carries information of beam transverse aspect ratio (Tauchi/KEK)

- TESLA

##  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

## 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

## Detector Occupancies are Acceptable fcn(bunch structure, integration time)

**Detector Occupancies are Acceptable**** ****fcn(bunch structure, integration time)**

**LCD=L2 Hit Density/Train in VXD &TPC vs. Radius**

**TESLA VXD Hits/BX vs. Radius**

## Photons 

**TESLA #********/BX in TPC vs. z**

- Beampipe @ r=1.0cm, B=3T

- Extraction Line (6m) “shines” thru shield here, but not here

- Beampipe @ r=2.2cm, B=4T

## Neutron BackgroundsThe closer to the IP a particle is lost, the worse

**Neutron Backgrounds****The closer to the IP a particle is lost, the worse**

- Off-energy e+/e- pairs hit the Pair-LumMon, beam-pipe and Ext.-line magnets
- Radiative Bhabhas & Lost beam <x10
- Solutions:
- Move L* away from IP
- Open extraction line aperture
- Low Z (Carbon, etc.) absorber where space permits

- 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

## Neutrons from the Beam Dump

- Geometric fall off of neutron flux passing 1 mrad aperture

- Limiting Aperture

- Radius (cm)

- z(m)

- # Neutrons per Year

- 1.0

- 0.5

- Integral

## Neutron BackgroundsSummary

- 			 **NLC-LD-500 GeV      NLC-SD-500 GeV        Tesla-500 GeV**
- Beam-Beam pairs		1.8   x 109 hits/cm2/yr	        0.5   x 109 hits/cm2/yr        O(109 hits/cm2/yr)
- Radiative Bhabhas		1.5   x 107 hits/cm2/yr		no hits                   <0.5x108 hits/cm2/yr
- Beam loss in extraction line	0.1   x 108 hits/cm2/year     0.1   x 108 hits/cm2/year
- Backshine from dump		1.0   x 108 hits/cm2/yr	        1.0   x 108 hits/cm2/yr               negligible
**TOTAL****	****	****	****1.9   x 10****9**** hits/cm****2****/yr   0.6   x 10****9**** hits/cm****2****/yr**

**Neutron Backgrounds****Summary**

- Figure of merit is 3 x 109 for CCD VXD

## Detector Occupanciesfrom e+e- Pairs @ 500 GeV

| Detector | Per bunch | R. O.  | Eff.#B | Occupancy | Comment |
| --- | --- | --- | --- | --- | --- |
| VXD-L1 | 36E-3/mm2 | 50 s | 148 | 5.3/ mm2 | 1.5cm, 4T |
| VXD-L2 | 3.1E-3/mm2 | 250 s | 742 | 2.3/ mm2 | 2.6cm, 4T |
| TPC | 1336, 5trks | 55 s | 160 | Few per mil |  |
| Barrel ECAL | 1176, 0.63GeV | 150 ns | 1 | 0.63 GeV | 101>3MeV |
| Endcap ECAL | 1176, 1.92GeV | 150 ns | 1 | 1.92 GeV | 91>3MeV |
| VXD-L1 | 38E-3/mm2 | 8 ms | 190 | 7.2/ mm2 | 1.2cm, 3T |
| VXD-L2 | 3.1E-3/mm2 | 8 ms | 190 | 0.6/ mm2 | 1.4cm, 3T |
| TPC | 1377, ?trks | 8 ms | 190 | “Few per mil” | Needs Study |
| Barrel ECAL | 547 , 0.73 GeV | 8 ms | 190 | 139 GeV | Needs Study |
| Endcap ECAL | 597,  0.9 GeV | 8 ms | 190 | 171 GeV | Needs Study |

- TESLA

- NLC

## Synchrotron Radiationfrom Beam Halo in Final Doublet

**At SLD/SLC SR WAS a (THE) PROBLEM**
- SR from triplet WOULD have directly hit beam-pipe and VXD
- Conical masks shadowed the beam pipe inner radius
- geometry set so that photons needed a minimum of TWO bounces to hit a detector
- Background rates consistent with “flat halo” model:
-  0.1%  - 1% of the beam filled the phase space allowed by the collimator setting.
**At NLC/TESLA**
- Allow NO direct SR hits ANYWHERE near IP
- Collimate halo before the linac AND after the linac
**VXD MINIMUM RADIUS sets collimation depth as well as B_s**
- Pain level goes at least as square of VXD min radius:
- Muon production, collimator wakefields, collimator damage, radiation, .......

- X=450 rad
- Y=270 rad

- X=32 rad
- Y=28 rad

**BE SURE YOU NEED IT!**

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

- (Similar plots for TESLA)

## Muon Backgrounds from Halo CollimatorsNo Big Bend, Latest Collimation & Short FF

**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 1012 e- add magnetized tunnel filling shielding
- Reality probably in between

- 18m & 9m Magnetized steel spoilers

- Betatron

- BetatronCleanup

- Energy

- FF

## LD Muon Endcap Background #e- Scraped to Make 1Muon

- Calculated Halo is 10-6

- Efficiency of Collimator System is 105

- Bunch Train =1012

- Engineer for 10-3 Halo

##  IR

**Differences w.r.to **
**e+e- IR**
- Annular Mirror system
- 10 mrad exit aperture instead of 1 mrad
-  30mrad C to accommodate exit aperture
- Larger inner radius of VXD as first 2 layers of LD/SD VXD look in direct line of sight w/dump

## Independent Systems Model for e- Injection on e+ Arm

**RED**=**New Stuff**

## Fixed Target Options

## Your IR Options ARE Open!

**Beam Delivery and IR Choices are ~**
**Independent of RF Technology**
- And while each regional machine design group has a
**CONCEPTUAL DESIGN**
- (in my view at least)
- We are far from needing to freeze any parameter which can impact either the
**PHYSICS PROGRAM**
- Or the
**DETECTOR DESIGN**
- There is a wealth of work to be done, particularly in the areas of diagnostic detector development and performance simulation
-  (at SLC experimental physicists did this)
- Groups from U-Mass, UBC, Oxford, Brunel, NW,U.Hawaii.... are participating
- “Machine-Teach IN” tomorrow 4:15-6:00 Room 208