interaction region transport system: optics and issues

NLC - The Next Linear Collider Project

Interaction Region Transport System: Optics and Issues

25-May-1999

Lehmann Review

P. Tenenbaum

Author NameDate

Slide #

Next Linear ColliderNext Linear Collider

0

100

200

300

400

500

0 500 1000 1500 2000 2500 3000

HorizontalVertical

Ho

rizo

nta

l

z, meters

sqrt(bx,y

),

m1/2

IPSwitch

10 mradarc

Coupling/Emittance

DiagnosticsBeta

Matching

ChromaticCorrection(Horizontal)

Chromatic Correction(Vertical)

Final Transform/Final Doublet

IP

Interaction Region Transport Schematic:Betatron Functions

Author NameDate

Slide #


IRT Issues

• Operating range (CM energies)

• Energy Bandwidth

• SR in bends, quads– power deposition

– emittance dilution

• Backgrounds and Beam Stayclears

• IR Layout and Technology

• Crab Cavity

• Tight Tolerances– Position jitter and drift

– Magnet Field jitter and drift

– Magnet Roll

– Magnet Harmonics

• Machine Protection

• Extraction of Disrupted Beam

• Diagnostics and Operations

Author NameDate

Slide #


Center-of-Mass Operating Range

• All magnets OK from 350 GeV to 1 TeV CM except last quad

• Last quad: needs to be changed at ~750 GeV CM

• Tunnel length set for 1.5 TeV CM

• Above 1 TeV CM: Weaker CCX/CCY bends, move magnets 13 cm (x), new doublet, new sextupoles

Title:(8047A063doc)Creator:Adobe Illustrator(TM) 5.5Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

Author NameDate

Slide #


Energy Bandwidth

• Limited by higher-order chromatic effects

• Some improvement possible with sextupoles at IP images (“Brinkmann” sextupoles)

• Limited at low energy by larger emittances (chromogeometrics)

• Another optimization pass needed

0.7

0.8

0.9

1

1.1

1.2

1.3

300 400 500 600 700 800 900 1000 1100

Low-Energy Doublet

High-Energy Doublet

Low-

Ener

gy D

oubl

et

Center-of-Mass Energy (GeV)

Band

wid

th (%

)

Author NameDate

Slide #


Synchrotron Radiation

• SR in CCX/CCY bends breaks chromatic correction

• SR in FD limits spot size (“Oide Effect”)

• Conflict:– Bandwidth likes strong bends,

short quads

– SR likes weak bends, long quads

• SR power in 10 mrad arc: 6.3 kW (1 TeV CM), 22 kW (1.5 TeV CM)

3

4

5

6

7

8

9

300 400 500 600 700 800 900 1000 1100

Low-Energy Doublet

High-Energy Doublet

Low

-Ene

rgy

Dou

blet

Center-of-Mass Energy (GeV)

Geo

met

ric L

umin

osity

, 10

33cm

-2se

c-1

Author NameDate

Slide #


Backgrounds and Beam Stayclears

• Collimate at ~ 5 x, ~ 35 y, 4% energy (collimation), 7 x, 42 y (CCX/CCY)

• Stay-clears: 14 x, 60 y or better: vacuum system has 1.2 cm OD (IP Switch Beta Match), 3.0 cm OD (CCX FD), 2 cm 1.28 cm OD (FD)

• Soft bend (11 gauss @ 1 TeV CM) separates bend SR from detector

• Still an area which needs considerable study!

Author NameDate

Slide #


IR Layout and Technology

• Need to focus beam down to nanometer sizes

• Accommodate extraction line for disrupted beam

• Cope with collision debris

• Final Doublet has exciting mix of technologies (PM, SC, Fe), mechanical conflicts

• Support of doublet (in detector) a problem (optical anchor?)

• Magnetic distortions of solenoid (6 T) solved problem -0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 2 4 6 8 10 12

Author NameDate

Slide #


Crab Cavity

• Large Crossing Angle + Small Beams = Crab Cavity needed

• Crab cavity relative phase tol = 0.2° (X-Band) or 0.05° (S-Band)

• X-Band cavity has lower power, fewer cells

• S-Band cavity has larger aperture

Author NameDate

Slide #


Tolerances• Position jitter and bend field jitter

– deflect beams at IP -- they do not collide

• Quad field errors– shift waist at IP

• Sextupole position errors– introduce waist, dispersion, coupling errors at IP

• Quad position drift– deflects beam between sextupoles, or

– introduces dispersion

• Quad rolls produce xy coupling (unflattens beam)

• High-order multipole content dilutes emittance

• Made much worse in CCX/CCY/FTrans (large b’s)

Author NameDate

Slide #


Typical Tolerances By Region(Most challenging tolerances highlighted)

Tolerance IPSW/BB/BM CCX->FTrans F. Doublet

Bend Angle 2 x 10-5 3 x 10-6 ---

Quad y jitter 45 nm 4 nm 0.7 nm

Quad y drift 57 m 25 nm 100 nm

Quad dK 1% 1.7 x 10-5 4 x 10-6

Quad Roll 1 mrad 5 rad 2 rad

Quad sext. 100 % 0.1% 0.01%

Sext y drift --- 50 nm ---

Above tolerances are for 2% Spot Size growth / aberration

Still need to develop more detailed tolerance budget...

Author NameDate

Slide #


Machine Protection

• Similar to linac system: only slow steering devices permitted, orbit and magnet strengths monitored

• Generally less severe than in linac– no irises, so beam hits at glancing angle

– beam is very large in many spots

• Commissioning requires:– pilot beams

– high-powered pulsed dump (end of linac)

– low-powered pulsed dump (entrance to beta match)

– very-low-powered insertable stopper (entrance to doublet)

• Not yet a solved problem

Author NameDate

Slide #


Extraction of Disrupted Beam

• Post-collision beam has large emittance and energy spread

• 1 MW of power beamstrahlung photons

• Ideal solution: 1 high-power dump for photons and electrons

• Need to minimize losses in dumpline (backgrounds)

• Possible backgrounds from dump backshine

• Need to measure polarization, energy spectrum of post-collision beam

• For NLC beam, 0.25% of power = whole SLC beam!

Author NameDate

Slide #


Proposed Extraction Line LayoutTitle:

Creator:Unified Graphics SystemPreview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

Author NameDate

Slide #


Diagnostics and Operations

• 1 BPM/quad, 1 m resolution; several RF cavity BPMs, resolution ~ 30 nm

• 10 wire scanners for incoming , beta matching, extracted beam measurements

• 5 skew quads, 4 small sexts for static aberration tuning

• All quads and All sexts on movers, No power supply stringing for quads/sexts

• Many feedbacks which can in principle ease our tolerances

• More study of this area is needed...

Author NameDate

Slide #


Final Focus Feedbacks (proposed)

Name Type Location Actuator

BB Launch Standard Big Bend x/ycor

Wire Launch Standard/Subtrain Big Bend x/ycor

BM Launch Standard Beta Match x/ycor

Lumm Fbck 1 Standard CCY + FTrans x/ycor

Lumm Fbck 2 Dither CCX + CCY Sext Movers

Crab Cavity Standard FTrans Phase Shifter

Timing Standard FTrans/Sitewide Master Phase

IP Collide Superfast Final Doublet x/ycor striplines

Author NameDate

Slide #


Work Still to be Done

• Re-optimize bandwidth of FF

• Detailed background studies/ collimation (inc. vacuum)

• Complete IR design, eliminate conflicts, IP anchor

• Crab cavity design/feedback

• Better, more optimal tolerance budget, specs for optical correction magnets

• Complete study of MPS issues: are sacrificial collimators needed?

• Additional work on extraction line:– 2 high-power dumps?

– Handle lost beam power

– Instrumentation

• Much more detailed study of feedback and tuning– “cradle to grave” simulation of

tuning strategy

– Quantitative understanding of feedbacks

– study full linac-to-IP transport with feedbacks

interaction region transport system: optics and issues

Documents