K. Moffeit 6 Jan 2005 WORKSHOP Machine-Detector Interface at the International Linear Collider SLAC January 6-8, 2005 Polarimetry at the ILC Design issues

K. Moffeit 6 Jan 2005

WORKSHOP Machine-Detector Interface

at the International Linear ColliderSLAC January 6-8, 2005

Polarimetry at the ILCDesign issues and measurement

strategy

Ken Moffeit SLAC

http://www.slac.stanford.edu/

http://www-project.slac.stanford.edu/ilc/


Layout of the ILCTESLA US Option


Spin Precession

bendbendspin

GeVEg

44065.0

)(

2

2

Change in spin direction for various bend angles and the projection of the longitudinal polarization. Electron beam energy is 250 GeV.

Change in Bend Angle Change in Spin Direction

Longitudinal Polarization Projection

1 mrad 32.5 o 84.3%

275 rad 8.9 o 98.8%

100 rad 3.25 o 99.8%


Extraction Line Beam Properties

Angular divergences of the incoming and outgoing disrupted beams for ILC collision parameters. BMT depolarization due to the angular divergences.

Parameter e+e-

(x)in 35 rad

(y)in 10 rad

(x)out 275 rad

(y)out 55 rad

(PBMT)IP 1.2 %


Summary of Expected Depolarization Effects for the ILC Design

Note: 1. In the NLC design, there was an additional 1% depolarization from the

180o turn around at 8 GeV (not present in the current ILC design).2. Need to revisit spin-flip calculation.

Region Luminosity-weighted Depolarization

Injector <0.1%

Damping Ring <0.1%

Compressor and Pre-Linac -------

Linac <0.1%

Beam Delivery <0.1%

Beam orbit jitter <0.1%

IP incoming Beam divergence <0.1%

IP disrupted beam divergence 0.3%

Spin-flips from collisions ~0.1%

TOTAL ~0.4%


Important Design Considerations

• Common for upstream and downstream polarimeters• Beam size at Compton IP (<100m)• Direction of beam at Compton IP is the same as at the Detector IP (<50rad)• Dedicated Chicanes for both upstream and downstream polarimeters (~50 meters in length)

• Upstream Polarimeter• Compton IP before energy slit (to avoid backgrounds in the Physics Detector from low energy Compton electrons)

• Downstream polarimeter • Compatible with the energy spectrometer• Design exist for 20 mrad crossing angle at e+e- IP• Create design for 2 mrad crossing angle?• Backgrounds from beam-beam collisions (0.75 to 1 mrad beam stay clear)

• Positron polarization or e-e- option• Plan for polarimeters in both beam lines


Crossing Angle

•Direction of beam at Compton IP is the same as at the Detector IP (<50rad)

•Simultaneous running of 2 IRs and spin orientation selected for each IR •Not possible to change spin orientation train to train with the spin rotation solenoids•Use spin precession to find energies for spin rotation with 11 mrad between beam direction at two IRs

For =11mrad spin direction changes by every 125.85 GeV

Both IR 1 and IR 2 will have longitudinal polarization at energies: 251.7 GeV and 503.4 GeV

At these energies you can switch beams train to train between the two IRs and have longitudinal polarization at both.


Layout of the Beam Delivery System to two Interaction

Regions with Crossing Angles

IR-1 and IR-2 Requires locations for upstream Compton Polarimeters with beam direction within 50 rad of that at the IP.

Upstream Polarimeter before energy slit

Mark Woodley ref talk

IR2

IR1

Energy SlitPolarimeter Chicane


Upstream Polarimeter Design Issues

• Direction of beam at Compton IP is the same as at the Detector IP (<50rad)• Laser beam access to Compton IP

Measure laser polarization near Compton IP• Measure Compton Scattered electrons (Energy ~25 GeV)

Momentum analyzedDetected with a segmented gas Cerenkov Counter

Tesla design vs Chicane design?


Tesla Design

• Minimal space and no special magnets required• Need to change laser wavelength for z-pole running


Dedicated Upstream Polarimeter Chicane

BD1z=0 m

BD219.1 m

BD326.5 m

BD4z=50.6 m

45.59 GeV

K Moffeit 24 Nov 04

UpstreamPolarimeter Chicane

10 cm

10 meters

CerenkovDetector

17 GeV

25 GeV

250 GeV

35 GeV2.5 cmWide

Plan View

• Requires ~50 meters length• Same B-field at Z-pole, 250 GeV and 500 GeV running• Same magnet design as for upstream energy chicane• Good acceptance of Compton Spectrum at all energies without changing laser wavelength


Extraction Beam Line OpticsYuri Nosochkov: Extraction Line for 20mrad Crossing Angle IR

Energy Chicane

Compton IP


Extraction Line Polarimeter Elements

Energy Chicane and Polarimeter Chicane Separate

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

250 GeV

25 GeV

45.59 GeV

K Moffeit 24 Nov 04

2 mradenergystripe

2 mradenergystripe

BDE1Az=3172cm

BDE2A3972cm

BDE3A5172cm

3 mradenergystripe

3 mradenergystripe

Shielding

Energy Chicane

Polarimeter Chicane

10 cm

10 meters

Synchrotronstripe

Detector

Synchrotronstripe Detector

CerenkovDetector

Wiggler

Low Field

Wiggler

Low Field

17 GeV

25 GeV

1 mrad1 mrad

BPM BPM

Quad

BPM

35 GeV


Polarimeter Chicane Plan View

BDE1Az=3172cm

BDE2A3972cm

BDE3A5172cm

Energy Chicane

Polarimeter Chicane

10 cm

10 meters

Wiggler

1 mrad

Wiggler

Mirror BoxLaser Exit

Mirror BoxLaser

Entrance

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

1 mrad

e- laser angle 10 mrad

Compton IP


Measurement of Polarization with Compton Gammas

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

250 GeV

Ken Moffeit 13 Dec 04

PolarimeterChicane

10 cm

10 meters

CerenkovDetector

25 GeV

Quad

35 GeV

Thin Radiatorfor GammaConversion

PositronDetector

ElectronDetector

125 GeV

1 mrad

125 GeV

1 mrad

100 GeV

100 GeV

170 meters

Requires: • Quadrupole after Chicane off • Single beam running

1 mrad beam stay clear

½ mrad beam stay clear

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

250 GeV

Ken Moffeit 13 Dec 04

Polarimeter Chicane

10 cm

10 meters

CerenkovDetector

25 GeV

Quad

35 GeV

Thin Radiatorfor GammaConversion

ElectronDetector

PositronDetector

0.5 mrad

0.5 mrad

65 Meters

125 GeV

125 GeV

100 GeV

100 GeV


Running at different beam energies

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

250 GeV

25 GeV

45.59 GeV

K Moffeit 24 Nov 04

2 mradenergystripe

2 mradenergystripe

BDE1Az=3172cm

BDE2A3972cm

BDE3A5172cm

3 mradenergystripe

3 mradenergystripe

Shielding

Energy Chicane

Polarimeter Chicane

10 cm

10 meters

Synchrotronstripe

Detector


CerenkovDetector

Wiggler

Low Field

Wiggler

Low Field

17 GeV

25 GeV

1 mrad

1 mrad

BPM BPM

Quad

BPM

35 GeV

Z-pole Running

250 GeV


Detector Options

Segmented Gas Cherenkov Detector• Propane Gas or C4F10 Gas (nonflammable)• Threshold ~10 MeV (good for reducing backgrounds from synchrotron radiation and low energy electrons

Other Detector Schemes•Quartz detector

•Threshold ~200keV•Greater flexibility for small channel width (may be useful for upstream polarimeter)• Simple detector

•Other


Laser System Options• Collide every bunch (for possible upstream choice) (complex) • Low Rate high power Laser similar to SLC (probably required downstream); 5Hz laser can have timing varied to scan thru all bunches in train (simple)• Resonate cavity—HERA (very complex)

e+/e- beam Upstream

Laser beam

Downstream

Laser Beam

Energy 250 GeV 2.3 eV 2.3 eV

Charge or energy/bunch

2.1010 35 J 100 mJ

Bunches/sec 14100 14100 5

Bunch length t 1.3 ps 10 ps 1 ns

Average current (power)

45 A 0.5 W 0.5 W

x . y (m) 10 . 1 upstream

30 . 60 downstream

50 . 50 100 . 100


Compton Polarimeter Parameters at 250 GeV (cont.)

Upstream Polarimeter Downstream Polarimeter

Beam crossing angle 10 mrad 11.5 mrad

Luminosity 1.5 . 1032 cm-2s-1 5 . 1030 cm-2s-1

Event rate at 25 GeV endpoint

300,000/GeV/sec 10,000/GeV/sec

P/P stat. error <1% / sec < 1% / min

P/P syst. error <0.5% <0.5%

Requirements on measurement times for 0.25% stat error?• for sqrt(s)=500 GeV, 0.25% per week/month?• for Z-pole, 0.25% per day/week?• for systematic studies, 0.25%/hour useful?


Fabry-Perot Cavity at HERA


Backgrounds and Collimation

Need to study•Synchrotron radiation backgrounds from bends and quads•Low energy disrupted electrons•Beam gas•Beam dump backsplash

BD1Az=8296 cm

BD2A10326 cm

BD3A11556 cm

BD4Az=13586 cm

250 GeV

25 GeV

45.59 GeV

K Moffeit 24 Nov 04

2 mradenergystripe

2 mradenergystripe

BDE1Az=3172cm

BDE2A3972cm

BDE3A5172cm

3 mradenergystripe

3 mradenergystripe

Shielding

Energy Chicane

Polarimeter Chicane

10 cm

10 meters

Synchrotronstripe

Detector


CerenkovDetector

Wiggler

Low Field

Wiggler

Low Field

17 GeV

25 GeV

1 mrad

1 mrad

BPM BPM

Quad

BPM

35 GeV


Summary

• Accelerator design issues– Location of polarimeters– Downstream polarimeter may be difficult for e+e- 2 deg crossing

angle– No net bend angle in e- beam direction at Compton IP and e-

direction at e+e- IP– Positron polarization or e- e- needs polarimeters in both beam lines

• Polarimeter design issues– Laser + optics (5 to 10 hz high power al la SLC, every bunch-TESLA design,

resonate cavity--HERA)

– Detectors: Gas Cherenkov, Quartz Cherenkov

• Beam test needs before TDR– Nothing stands out

Documents

K. Moffeit 6 Jan 2005 WORKSHOP Machine-Detector Interface at the International Linear Collider SLAC January 6-8, 2005 Polarimetry at the ILC Design issues