the nlc design

NLC - The Next Linear Collider Project

Tor Raubenheimer

The NLC Design

Linear Collider Workshop 2000

FNAL

October 24th, 2000


NLC Design Changes

• Focused on cost reduction over last year – expect 30% reduction

• Many RF system improvements

• Facility length reduced by 20%

• Hi/Lo energy IR scheme and BDS redesign to optimize L and open future expansion possibilities

• Investigating 180 Hz operation

• Technology based on results from test facilities: FFTB, NLCTA, ASSET, KEK ATF and knowledge gained from SLC operation

26 km


NLC Project Scope

• Injector Systems

• Main Linac– Housing with all internal services– Half filled for initial 500 GeV cms– Upgrade by adding rf, water, power to the

2nd half of the tunnels

• Beam Delivery (high energy IR)– Two BDS tunnels and IR halls with

services– some components must be upgraded to get

from 1 TeV to 1.5 TeV

1.5 TeV

0.5 - 1.0 TeV

(1.5 TeV withincreased gradientor length)

1.5 TeV

(length will support a 5 TeV FFS)


NLC Energy Evolution

Stage 1: Initial operation

500 GeV cms

L = 5x1033 20x1033 500 fb1

Stage 2: Add additional X-band rf components

1 TeV cms

L = 20x1033 30x1033 1000 fb1

Higher Energy Upgrades:– 1.5 TeV with upgrade of linac rf system or length increase

• injector and beam delivery built for 1.5 TeV– 3 TeV+ with advanced rf system and upgraded injector

• see CLIC parameters: “A 3-TeV e+e- Linear Collider Based on CLIC Technology,” CERN-2000-008

• beam delivery sized for 3 to 5 TeV collisions


NLC Progress

• Established collaborations with KEK, LBNL, LLNL, and Fermilab

• Optimized parameters and established common rf design with KEK

• Performed bottoms-up cost estimate for Lehman review

• Successful Lehman review—questionable project cost!

• Have demonstrated most necessary rf hardware however the cost optimized hardware is still in development and rf power handling is still a question

• Improving rf designs for reduced cost and improved efficiency

• Working on cost reduction throughout design!


NLC Collaboration

• MOU signed with KEK to pursue common R&D towards LC– Focused on rf development and ATF at KEK– ISG progress report: SLAC-R-559 or KEK-Report-2000-7

• MOUs signed with LBNL, LLNL, and FNAL– Berkeley concentrating on magnet design and damping ring issues– Livermore focusing on solid-state modulators

• Fermilab taking responsibility for main linac beamline: • Emittance preservation, structure design, optics layout• Structure manufacture, magnet design, vacuum systems

• 1st US collaboration meeting at SLAC last January

• 1st MAC meeting last June at Fermilab; 2nd MAC meeting in October at SLAC; 3rd MAC meeting in May ‘01 at LBNL


NLC RF System

• RF system consists of 4 primary components:

– Modulators: line ac pulsed dc for klystrons (500 kV, 250 A)

– Klystrons: dc pulse 75MW at 11.424 GHz

– RF Pulse Compression (DLDS): compresses rf pulse temporally, increasing the peak power, and delivers the power to the structures

– Accelerator Structures (DDS & RDDS): designed to transfer power to the beam while preventing dipole mode driven instabilities

• Each linac has 100 modules consisting of 1 modulator, 8 klystrons, 1 DLDS system, and 24 accelerator structures

• Need good efficiency, reliability, and low cost!


Solid-State Modulator

• Conventional modulators are expensive and inefficientwith short pulses: ~ 60%

• Program at LLNL todevelop ‘Induction Modulator’based on solid-state IGBTs: efficiency ~ 80%

• IGBTs developed for e-trains with 2 to 3 kV and 3kA

• Drive 8 klystrons at once

• Full modulator finished thiswinter

10 Core Test Stack


Solid State Modulator 8-pac

15' 2"

8' 6"

24"

22"

38"

8"

4' 2"

4' 5"

30"

4' 4"

50"

21"

6' 5"


PPM Klystrons


XP-1 75 MW Klystron

• XP-1 based on very successful 50 MW Periodic-Permanent Magnet (PPM) klystron but included many ‘simplifications’

• XP-1 testing results:– 71 MW @ 300 ns @ 10 Hz

• Limited by gun oscillation– 75 MW @ 1.5 µs @ 5 Hz

• After installation of load in gun region • Limited by 20 GHz oscillation in collector region!

– 72 MW @ 3.1 µs @ 1 Hz• After installation of tailpipe rf load in collector• Repetition rate limited by heating• Pulse length limited by modulator

• Designing a second 75 MW tube with better field profile and features to improve manufacturing—to be tested this fall


DLDS Pulse Compression

4 Delay Lines, 2 Modes/LineEffective Compression Ratio=8 Klystron Pulse Width=3.05 s Accelerator Pulse Width=0.381 sTotal Waveguide Length=174 km (for a 500 GeV Collider)

Klystron 8-Pack

Combiner/Launcher System

Delay Lines120.65 mm diameter waveguide

ExtractorExtracts the TE12 mode and passes the TE01mode

56.3 m Beam direction


DLDS Pulse Compression Test

• All components have been designed

• Multi-mode transmission properties have been verified

• High power testswill start in 2001

• Full system test in2003

NLCTA Setup


Accelerator Structures


DDS3 Structure BPM Test


RDDS1 Structure Construction

• RDDS1 cells were designed at SLAC and machined at KEK – final machining performed on diamond-turning lathe

• Attained excellent results:frequency errors less than 1 MHz, i.e. <1m errors

• Tolerances for dipole modefrequencies are 5 times looser!

• Bonding process still needsto be understood!


High Power Damage

• Have had difficulty processing 1.8m long structures to 70 MV/m (NLC design gradient)– Observed significant damage to structure irises at 50 MV/m

• 1.8m structures consist of 206 cells– Single cells can operate at 150 200 MV/m without damage

– A 26 cm structure has been run to 140 MV/m (some damage)

– A 75 cm structure has been run at 90 MV/m (some damage)

• Theoretical model predicts the damage is related to the group velocity of the rf power in the structure

• Building 12 structures with KEK to study length and group velocity dependence – will be tested in 2001


NLC RF System Highlights

• Developing solid-state modulator with LLNL– Much less expensive, more reliable, smaller package

• Demonstrated (periodic permanent magnet) PPM 75 MW klystron operation for NLC with 3s rf pulse (2x expected!)– Half as many klystron/modulator systems required!

• Tested mode propagation needed for multi-moded DLDS– Less expensive rf pulse compression system

• Built DDS3 structure and RDDS1 structure with KEK– DDS3 exceeded alignment requirements and demonstrated rf BPM– RDDS will shorten linac length by 6%—sub-micron errors in cell

fabrication– Observed structure damage at high gradients!

• High power component tests finished in 2001 and full system test in 2003


NLC Cost Reduction Strategy

• Costs distributed throughout system attack all• Primary changes:

– Solid state modulator (powers 8 klystrons for 40% of the cost)– Longer linac rf pulses (half as many klystrons/modulators)– Permanent magnets (eliminate cable plant/PS, improved reliability)– Cut & cover tunnels (lower cost but may need terrain following)– Moving electronics to tunnel (eliminate cable plant)

– Redesign bunch compressors (lower final energy, shorter system)

– Redesign collimation system (reduce length of by factor of two)– New final focus (reduce length and components in BDS)

• Expect reduction in cost by 30% with another 10 to 15% in scope reduction if desired

• Additional gains from further R&D and layout changes


Steel

SteelPM

PM

PM

PM

PM

FNAL Prototype PM Quad

Mechanical Adjuster Concerns

– Calibration

– 1 m Magnetic Axis Stability

– Response Time

– Reliability

Rotatable PM (Nd-Fe-B) Blockto Adjust Field (+/ 10%)

Steel Pole Pieces (Flux Return Steel Not Shown)

PM (Strontium Ferrite) Section


Post-Linac Collimation System

Tighter Looser

Optics Tolerances

Never

Seldom

Single Pulse Collimator Damage

ZDR

‘Consumable’ collimators damaged 1000x per year

‘Renewable’ collimators

damaged each pulse

Conventional collimators not damaged

• High power beams will damage collimators unless beam sizes are increased

• Studying ‘consumable’ and ‘renewable’ collimator systems

AlwaysConsumable Collimators

Beam damage

• Experimental study of collimator wakefields


Post Linac Collimation

• Most main linac faults will be energy errors design for passive energy collimation

• Infrequent betatron errors ‘consumable’ betatron collimation

• Reduce collimator system length from 2.5 km to roughly 1.2 km—still working on optimal design

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Collimator Muon Production

1000

104

105

106

107

108

109

1010

1011

-2500 -2000 -1500 -1000 -500 0

No Spoilers, 500 GeV CMTwo Spoilers, 500 GeV CMNo Spoilers, 1 TeV CMTwo Spoilers, 1 TeV CM

Elec

trons

Los

t / M

uon

Rea

chin

g IP

Distance from IP (m)

Muon Secondaries into LCD Large EndcapSeptember 2000 Beam Delivery System Design


Final Focus and Interaction Region

• Old final focus was a scaled up model of the SLAC Final Focus Test Beam (FFTB) beamline

• Modular design with orthogonal control using symmetry

• Chromatic correction is performed with pairs of sextupoles at large dispersion points separated by to cancel geometric aberrations—requires lots of bending to generate

• Length of system: was roughly 1.8 km—driven by synchrotron radiation at 1.5 TeV

• New design: chromatic correction is performed at final doublet so synchrotron radiation has little effect

Length is roughly 700m and will operate at 5 TeV!


New Final Focus

• One third the length - many fewer components!• Can operate with 2.5 TeV beams (for 3 5 TeV cms)• 4.3 meter L* (twice 1999 design without tighter tolerances)• Optical functions are not separated and dispersion in the FD

0 200 400 600 800 1000 1200 1400 1600 18000

100

200

300

400

500

b1 / 2

(

m1

/ 2 )

s (m)

-0.15

-0.10

-0.05

0.00

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x

by

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(

m)

0 100 200 300 4000

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m1

/ 2 )

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xb

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1999 Design 2000 Design


Hi/Lo IR Layout

• Final focus aperture is set by low energy beams 1/ but highest energy operation is limited by magnet strength, synchrotron radiation and system length Final focus has limited energy range without rebuilding magnets and

vacuum system

• Simplify design by dedicating one IR to ‘low’ energy operation and one to ‘high’ energy operation– ‘Low’ energy range of 90–350? GeV (build arcs for 500 GeV)

– ‘High’ energy range of 250–1000 GeV (with upgrade to 1.5 TeV)

• High energy beamline would have minimal bending to allow for upgrades to very high collision energies – ‘High’ energy BDS could be upgraded to multi-TeV operation!


Hi/Lo IR Layout

High energy IP0.25-5.0 TeV

upgraded in stages

Low energy IP92-350 (500??) GeV

Low energy (50 - 175 GeV) beamlines

Return lines: production and possibly drive beam -share main linac tunnel

Centralized injector systempossibly for TBA drive beamgeneration also

e+ e-

Site roughly 26 km in lengthwith two 10 km linacs

Possible staged commissioning


Luminosity Scaling with Energy

• Assuming same injector, the luminosity scales as:

limited) (SR :EnergyHigh

limited)function (beta :Energy Mid

limited) (aperture :Energy Low

5.2

2

L

L

L


Route to High Luminosity in NLC

• NLC design has built-in margins to cover nominal operating plane including 50% charge overhead and 300% emittance dilution– NLC damping rings spec. to produce 0.02 mm-mrad although design

requires 0.03 mm-mrad– SLC used ‘emittance bumps’ to reduce emittance dilution from 1000% to

100%—technique not included in NLC emittance budgets– Use margins to achieve higher luminosity

• Present prototypes and R&D results are better than initial specs (see RDDS cell frequencies and DDS3 alignment & S-BPM) y < 25% in linac if production components are similar to prototypes

Both will lead to increased luminosity (341033 at 880 GeV)


Luminosity

• Intrinsic luminosity:– this is the luminosity the

machine could support limited by physical effects

• Design luminosity:– this includes some

operational limitations

• Initial luminosity:– this includes large

margins to ensure easy startup at lower lum.

Intrinsic Design Initial

Dampingrings

300 / 2 300 / 2 300 / 3

MainLinac

315 / 2 330 / 3 400 / 7.2

Beamdelivery

330 / 2 360 / 3.5 450 / 8.5

Lum. 30x1033 22x1033 5x1033

Example: at 500 GeV cms


Parameters for 500 GeV and 1 TeV

A B C H A B C HCMS Energy (GeV) 510 500 482 490 1022 1000 964 888

Luminosity (1033) 5.3 5.4 5.5 22 10.6 10.8 11 34Repetition Rate (Hz) 120 120 120 120 120 120 120 120

Bunch Charge (1010) 0.7 0.82 1 0.75 0.7 0.82 1 0.75Bunches/RF Pulse 95 95 95 190 95 95 95 190Bunch Separation (ns) 2.8 2.8 2.8 1.4 2.8 2.8 2.8 1.4Eff. Gradient (MV/m) 58.7 57.3 55.2 50.2 58.7 57.3 55.2 50.2

Injected x / y (10-8) 300 / 3 300 / 3 300 / 3 300 / 2 300 / 3 300 / 3 300 / 3 300 / 2

x at IP (10-8 m-rad) 400 450 500 360 400 450 500 360

y at IP (10-8 m-rad) 6.5 8.5 12 3.5 6.5 8.5 12 3.5b

x / by at IP (mm) 12 / 0.12 12 / 0.12 13 / 0.15 8 / 0.10 12 / 0.12 12 / 0.15 13 / 0.15 10 / 0.12

x / y at IP (nm) 310 / 4.0 330 / 4.6 365 / 6.2 245 / 2.7 220 / 2.8 235 / 3.2 260 / 4.4 200 / 2.2

z at IP (um) 90 120 140 110 90 120 140 110Uave 0.11 0.09 0.08 0.11 0.32 0.25 0.23 0.26Pinch Enhancement 1.46 1.35 1.39 1.43 1.46 1.35 1.39 1.49

Beamstrahlung dB (%) 3.2 3 3 4.6 8.3 8.1 8.4 8.8Photons per e+/e- 0.86 0.96 1.05 1.17 1.12 1.25 1.38 1.33Two Linac Length (km) 5 5 5 5.4 9.9 9.9 9.9 9.9

IP Parameters for the JLC / NLC (2/24/00)500 GeV 1 TeV


Low Energy IR Luminosity

1.4 ns Low d B 1.4 ns Low d B 1.4 ns Low d B

Luminosity (1033) 4.1 2 10.4 5.1 14.1 7Pinch Enhancement 1.4 1.3 1.4 1.3 1.4 1.3Repetition Rate (Hz) 180 180 180 180 180 180

Bunch Charge (1010) 0.75 0.75 0.75 0.75 0.75 0.75Bunches/RF Pulse 190 190 190 190 190 190Bunch Separation (ns) 1.4 1.4 1.4 1.4 1.4 1.4

Injected x / y (10-8) 300 / 3 300 / 3 300 / 3 300 / 3 300 / 3 300 / 3

x at IP (10-8 m-rad) 400 400 400 400 400 400

y at IP (10-8 m-rad) 4.6 4.6 5.2 5.2 5.5 5.5

Tolerances 10 10 10 10 10 10b

x / by at IP (mm) 10 / 0.12 35 / 0.12 10 / 0.12 35 / 0.12 10 / 0.12 35 / 0.12

x / y at IP (nm) 670 / 7.8 1250 / 7.8 404 / 5.1 760 / 5.1 340 / 4.4 640 / 4.4

z at IP (um) 125 125 125 125 125 125

L0 / Ltotal (%) 62 78 49 67 44 63Uave 0.007 0.004 0.033 0.017 0.081 0.043

Beamstrahlung dB (%) 0.16 0.05 1 0.31 1.8 0.57Photons per e+/e- 0.47 0.25 0.75 0.41 0.88 0.48Polarization loss (%) ?? 0.07 0.02 0.2 0.06 0.31 0.09

IP Parameters for low energy IR90 GeV 250 GeV 350 GeV


Possible 1.5 TeV Parameters

• Two cases considered initially:– doubled rf power– 50% increased length

• Both cases ac power limited to 200 MW

• Higher energy parameter sets are based on the CLIC parameter sets and require lower emittance beams and smaller IP spot sizes

IP Parameters for the JLC / NLC

A BCMS Energy (GeV) 1406 1478

Luminosity (1033) 14 12.4Repetition Rate (Hz) 60 90

Bunch Charge (1010) 1.4 0.95Bunches/RF Pulse 95 95Bunch Separation (ns) 2.8 2.8Eff. Gradient (MV/m) 77 55

Injected x / y (10-8) 300/3 300/3

x at IP (10-8 m-rad) 450 450

y at IP (10-8 m-rad) 14 10b

x / by at IP (mm) 15/0.2 13/0.20

x / y at IP (nm) 220/4.5 200/3.7

z at IP (um) 130 150Uave 0.6 0.42Pinch Enhancement 1.58 1.52

Beamstrahlung dB (%) 21.7 14.1Photons per e+/e- 2.06 1.61

1.5 TeV


Route to High Luminosity in NLC

• NLC design has built-in margins to cover nominal operating plane including 50% charge overhead and 300% emittance dilution– NLC damping rings spec. to produce 0.02 mm-mrad although design

requires 0.03 mm-mrad– SLC used ‘emittance bumps’ to reduce emittance dilution from 1000% to

100%—technique not included in NLC emittance budgets– Use margins to achieve higher luminosity

• Present prototypes and R&D results are better than initial specs (see RDDS cell frequencies and structure alignment & S-BPM) y < 25% in linac if production rf components are similar to prototypes

Both will lead to increased luminosity (341033 at 880 GeV)


High Luminosity Issues

• High luminosity operation was first described at Snowmass ‘96 but as something to be attained well after initial operation, i.e. long learning curve

• Presently there is pressure to verify high luminosity operation is possible from the beginning

• Need to perform study on beam bumps to verify effectiveness (no question in simple simulation!) and rebalance emittance budgets

• Need to verify that all requirements are being treated consistently for high luminosity operation although without the conservatism that is presently used


180 Hz Operation Possibility

• 180 Hz operation is decoupled from low/high energy IR– two options: 180 Hz at 500 GeV or 120-60 Hz at 500 GeV and 60-

120 Hz at lower (250 GeV) energy

– Choice depends on AC power

• Primary issues are:– power consumption, average heating and radiation

– machine protection (60 Hz minimum operation for any low beam)

– emittance generation / damping rings must be redesigned

– duplicate BDS beam lines for dual energy operation

• Might start low energy IR before before completion of high energy IR and full facility


Outstanding Issues (a few of many!)

• Sources– Current limit in e- source and target limits in e+ source

• Damping rings– Require excellent stability

– In addition to conventional instabilities, new effects may be important

• RF breakdown– Difficulty processing up to 70 MV/m and damage at 5060 MV/m

– 450 Joules in DLDS rf pulse compression system

• Collimation and IR– Have to collimate ‘all’ particles outside 8x and 40 y without destroying

collimators or beam emittance

– Need high field magnets in IR with nm-level stability

• Reliability


Summary

• Lots of progress on NLC design in last year!• Lehman review positive but cost was too high!!

• Continual improvement in rf components cost reductions• More aggressive approach to design cost reductions• New concepts cost reductions• Lots of ideas for further improvements

• Expect 30% cost reduction with further reduction possible from additional R&D and/or scope reduction

• NLC is designed for high luminosity (similar to TESLA) however neither design has much margin at these parameters

• NLC facility will be designed to support a future multi-TeV LC

the nlc design

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