nlc - the next linear collider project andy ringwall 3/28/00 permanent magnets for the nlc a....

NLC - The Next Linear Collider Project

Andy Ringwall

3/28/00

Permanent Magnets for the NLC

A. Ringwall, C. Spencer, C. Rago(SLAC)

V. Kashikhin, V. Tsvetkov, J. Volk, B. Fowler, A. Makarov(FNAL)

S. Marks, R. Schlueter, K. Robinson(LBL)

A. Johnson, D. Milestone, B. Lynch(Stanford, DFM)

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NLC Background

• Next Linear Collider(NLC): electron-positron collider presently in the conceptual design phase.

• Collaborators: SLAC, FNAL, KEK, LBL, LLNL

• Energy: 500 GeV - 1 TeV CM, upgradeable to 1.5 TeV

• Target luminosity: >5 x 1033(500 GeV); >1034(1 TeV)

• Four primary beamline areas:– Injector(Inj)

– Damping Rings(DR)

– Main Linac(ML)

– Beam Delivery(BD)

• Test facilities:– NLC Test Accelerator(NLCTA)

– Accelerator Test Facility(ATF)

– Final Focus Test Beam(FFTB)

– Accelerator Structure SET-up(ASSET)

• Completed first DOE review(CD-1) in 5/99; several more reviews planned CD-0.4, CD-0.8, CDR.

• FNAL collaboration began in Fall of ‘99.

30 km

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NLC Magnet Summary

Magnet Type Styles Quantity• Quadrupole 38 3681

• Dipole 20 1592

• Corrector 3 492

• Trims 13 777

• Sextupole 6 402

• Solenoid 4 ~10

• Pulsed Magnets 6 23• Others 7 48

• Total 97 6967

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Magnet Requirements Overview

• Beam based alignment for quadrupoles:– Beam centered on quad to < 1 m.

– All quadrupoles have dedicated beam position monitors(BPM’s).

• Vibration:– Nanometer level jitter(f > 10 Hz) tolerances.

– FFTB quad ‘water on’ vibration excessive.

• Strength stability(B/Bn):

– Jitter tolerance: < 10-4 to < 5 x 10-6

– Short term(minutes) tolerances: < 10-3

• Multipoles(still defining):– Looser in Inj., ML and BD(single pass).

– Tighter in DR’s.

• NLC availability goal of 85 % for a 9 month run.

• Radiation dose rate(still defining):– High in DR’s (50 W/m, avg.)

– Lower in ML(1.4 W/m, avg.)

• Movers:– All quads and sextupoles on movers.

– Achieve < 200 nm step size

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Beam Based Alignment

• Beam centered on quadrupole to < 1 m.

• Use BPM feedback and mover steering to center quad on the beam. But where is the BPM with respect to the quad(mechanical offset and BPM readout error)?

• First step is to find the offset of each individual BPM to its quad: – Vary an individual quad’s strength by 20 % in several steps.

– Measure the beam kick due to quad/beam offset using downstream BPM’s.

– Reconstruct the orbit and determine offset of that quad to its BPM; proceed to next quad magnet.

– Repeat procedure weekly, monthly as needed.

• Implement automated steering procedure using movers.

• During 20% quad strength variation, quad center must not move by more than 1 m; the lower the better.

• Magnet design must minimize change in relative pole strengths during this strength variation.

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Baseline Electromagnet Design

CD-1 Review(Dipoles, Quad, Sextupoles)• Assume resistive electromagnets(EM)

– Solid core preferred

– Round conductors(improve reliability)

• Power supplies– Individual supplies for each magnet.

– Limited stringing (BD bends).

– Cables sized over NEC minimums to reduce power dissipation in the tunnel.

– Redundant supplies in ‘n out of k’ configuration.

• Movers(FFTB design)– Cam-style mover design for X,Y, and roll.

– Sub-micron step size.

Post CD-1 Review• Maximize stringing of quads

– Use inexpensive shunt supplies for BBA variation and steering trim(5%).

– Redundancy on strung supplies.

– Cut cost of supplies and cableplant.

Main Linac Quad

• Aperture: .5 in

• Length: 12.5 in

• Bpole tip: 8 kG

• Power: 1 kW

Damping Ring C-Quad

• Aperture: 4 cm

• Length: 25 cm

• Bpole tip: 8 kG

• Power: 4 kW

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Baseline Magnet Costs

• Magnet systems were 9 %(450 M) of the NLC CD-1 cost.

• Typical ML quad CD-1 cost estimate:– Magnet: $ 8,700– Power Supply: $ 24,500– Cables: $ 16,000– Power bill/yr: $ 315

• Facilities infrastructure– Power supply buildings and alcoves– Water cooling

• Value graph– Power supplies and cables has high worth

but a higher relative cost.– Prefer that cost be in line with worth.

• What about permanent magnets?

Power Supply

Field Windings Poles

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40%

Relative Worth

Rel

ativ

e C

ost

Cost Worth, EM Quad

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Permanent Magnet Option

• Permanent magnet(PM) idea originated during a reliability exercise for the main linac magnets and was shelved at that time due to BBA and energy flexibility concerns (90 % strength variation required for ML magnets).

• PM idea resurrected fall of ‘99:– N. Phinney reassessment of BBA requirements, ML strength variation reduced to 20 %.

– J. Cornuelle’s visit to Fermi lab, discussions about recycler ring PM’s.

• Preliminary meeting at FNAL in November of ‘99(SLAC, FNAL)– Design options discussed; J. Volk’s initial PANDIRA runs.

– BBA requirement is difficult; need to develop a proof of principle prototype.

• Second meeting at SLAC January of ‘00(SLAC, FNAL, LBL)– Build one or more ML quad prototypes.

– Clearly define magnet requirements across machine and develop rough designs.

• Rough costing exercise completed; all NLC magnets assumed to be PM– Ballpark savings of $282 M over CD-1 estimates.

– Save $187 M over post CD-1 cost reductions.

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Permanent Magnet Pro’s and Con’s

PM Pro’s• Eliminate power supplies:

– Supplies and temperature controlled racks.

– No alcoves or support buildings.

• Substantial reduction in cableplant:– Eliminate power cables and trays.

– No cable heat dissipation.

• Eliminate EM power and cooling:– No flow induced vibration.

– Reduced cooling capacity:

• LCW load, pumps, headers

• HVAC(air cooled magnets, cables)

– Operate at lower LCW pressure.

– Lower operating costs.

• Improved availability:– Power supply trips

– Water leaks

• Enhanced machine protection:– No coil shorts, mis-steered beam

PM Con’s• Difficulty in meeting BBA requirements.

• PM long term stability:– Radiation resistance

– Temperature coefficients

– Long term demagnetization effects

• Limits on energy flexibility.

• Cost of PM material.

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NLC PM Candidates

• Original list of NLC PM candidates(from N. Phinney’s):– If injector is centralized, then transport line quads could be PM.

– Bunch compressor bends and quads.

– Damping ring bends and sextupoles.

– Main linac quads up to 150 GeV(use EM’s from 150 to 250 GeV for energy flexibility).

– Main linac quads past 250 GeV(drift lattice for an initial 500 GeV CM machine).

– Only soft bends, final doublet, and extraction lines in beam delivery area.

– Trims, correctors, pulsed magnets, solenoids, septums, spin rotators are not candidates for PM technology.

• Presently assuming 50%(about 3321) of NLC magnets would be viable for PM’s.

• Prototype results will help define limits of applying PM technology to NLC.

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PM Material, Basics

• Net dipole moment, m (A-m2), from aligned domains.

• Dipole moment per unit volume defines magnetization, M(A/m), along the magnetization or ‘easy’ axis.

• M related to surface currents, Js(A/m). • MMF(A) is product of surface currents

and easy dimension.

• B-H curve:– Remanent induction, Br

– Intrinsic induction curve, J

– Coercivity, Hc

– Intrinsic coercivity, Hci

– Flux density at op. point, Bd

– Field at op. point, Hd

– Permeance coefficient, Pc = -Bd/Hd

– Recoil permeability, ur

– Field at 90% Br, Hk

m

M

Jms

Jms

Jms = M X n

B-H Curve

B = uo (H + M(H)) [inside brick]

MMF = Jms • deasy

deasy

Init

ial c

urve

Intrinsic Curve, J

B Curv

e, B

Br

Bd

HdHk HcHci

+ B (T, kG)

-B

-H+H(kA/m, kOe)

Pc

PM Brick

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PM Material Choices

CERAMIC

• Strontium or barium ferrite

• Inexpensive

• Radiation resistant

• Low Br, .38 T

• High temp coefficient, -.2 % / C (Br increases, Hc decreases w/ incrrease in temp)

• Brittle

RARE EARTH COBALT (REC)

• Sm-Co 1:5, 2:17

• Expensive

• Small industrial base

• Radiation resistant(2:17 good, 1:5 is worse)

• High Br, 1.05 T

• Low temp coefficient, -.03% / C(Br and Hc decrease w/ increase in temp)

• Brittle

Nd-Fe-B

• Ceramic < $ < REC

• Large industrial base

• Poor radiation resistance

• Highest Br, 1.2 T

• High temp coefficient, .1% / C(Br and Hc decrease w/ increase in temp)

• Plated to prevent corrosion

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PM Material Processing and Properties

Rare Earth PM Processing

• Receive cast material

• Crush, hydrogen decrepitate(brittles Nd-Fe-B)

• Jet mill to a fine powder, separate to desired particle size(single domain or other)

• Chromatographic inspection, micro-alloy

• Die press; at around 50 % compaction, apply domain orienting field(develops anisotropy)

• Sinter, quench, and age(defines Hci)

• Saw and grind bricks to shape

• Pulse magnetize

• Thermally stabilize(age) in the open circuit condition

• Helmholtz inspect

• Plate(Nd-Fe-B), package, and ship

Properties

• Property variations:– Can only hold B-H curve properties(Br,

Hc, ur, Hk) to a few %.

– Variations in composition and heat treatment vary microstructure even within same batch.

• Magnetization angle tolerance:– Easy axis defined during die or hydrosatic

pressing.

– Can only define axis to a ground datum to within a few degrees.

• Recoil permeability– Non unity, 1.02-1.10

– Orthotropic, u/u// 1.1

• Brick size can be limited due to cracking during quench(Sm-Co 2:17).

• Thermally stabilizing magnet in final permeance configuration can help limit long term demagnetization.

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Hybrid PM Design Variants

PM Options

Fixed StrengthPM only

Variable Strength

Fe Pole

Variable Strength

Fixed Strength

Hybrid + rotating PM elements

Hybrid + integral trim coil

Hybrid

Hybrid + stand-alone trim coil

Hybrid w/ counter-rotating sections

Hybrid + rotating outer PM ring

PM segments(Halbach magnet)

PM w/ counter-rotating sections

Hybrid + moving shunts

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Prototype Main Linac Quad

• Prototype requirements:– Aperture: .5 in

– Nominal length: 12.75 in

– Pole tip field: 8 kG max

– Range: -20 %

– Center shift: < 1 m

– Absolutie field accuracy: < .5 %

– Multipoles: b3/b2 < 2 %

– Good field aperture: 10 mm

– Op. temp. variation: +/- 1 C• Electromagnet version in fabrication:

– Solid core: C1008 plate

– Round Cu conductor: .25” X .063” W

– Power: 1 kW

– Voltage: 6 V

– Current: 167 A

– Total flow: 1 gpm

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PM Prototype: Corner Tuner Design

• Preliminary design:– Sm-Co 2:17 bricks outboard of poles.

– Rotating Sm-Co 2:17 tuners in corners.

– Pole supports between poles.

– Temperature compensator(if needed); applies to all hybrid PM designs.

• Advantages:– Similar to recycler ring quads.

– Large space available for pole supports.

• Disadvantages/issues:– PM material is not used most efficiently.

– High demag field in some areas.

– Non-symmetric demag fields across element, could affect center shift tolerance.

PM Quad Prototype: FCS217

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PM Prototype: Wedge Design

• Preliminary design:– Sm-Co 2:17 bricks outboard and

between poles.

– Rotating tuners(Nd-Fe-B) outboard of poles.

– Tuning washers outboard of lateral bricks(optional).

– Flux return rotated 90°.

• Advantages:– PM material is used efficiently.

– Symmetric demag. field across elements.

• Disadvantages/issues:– More complicated assembly.

– Diamond flux return does not integrate well with cam-style mover.

PM Quad Prototype: FWS217

PM bricks, 12X

Poles, 4X

PM tuner elements, 4X

Flux return

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PM Prototype: Shunt Design

• Preliminary design:– Bricks located between the poles.

– Steel shunts outboard of bricks.

– Shunts translate on the horizontal and vertical axes.

• Advantages:– Shunt material properties have less

variation than a PM element.

– Shunt tuner less expensive than PM.

• Disadvantages/issues:– Modulating the permeance of each

circuit might change relative strength of poles leading to a center shift.

– Large forces in shunts.

– Unison translation scheme required.

PM Quad Prototype: FRS217PM bricks, 4X

Poles, 4XShunts, 4X

Flux return

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Rotating Tuner Forces and Torques

Tuner element forces and torques(single element)FNAL version: fcn38a(Nd-Fe-B)

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-4.00

-2.00

0.00

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0 20 40 60 80 90 100 120 140 160 180

' (degrees)

Un

it f

orc

e (l

b/i

n);

U

nit

to

rqu

e(lb

-in

/in

)

unit force, Ansysunit torque, Ansysunit force, Pandiraunit torque, Pandira

x

y

M

'

Z, out of page

Tuning element, first quadrant

45 deg

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Prototype: Rotating Tuner Concept

• Cylindrical PM elements magnetized to their cylindrical axis.

• Align and epoxy in housing.

• Measure strength and orientation then balance:

– Add or rotate additional PM element material.

– Counter rotate two end elements; set strength and orientation.

– Use rotating element(s) to correct center shift.

• Supported tuner by bearings in endwall, max radial load 200 lb

– Limit deflections

– Limit bearing play

• Attach gears to one end; element access at opposite end

Rotating tuner: Single adjustable element

Rotating tuner: Counter-rotating elements

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Prototype: Rotating Tuner Actuation

• Allow tuner elements to self align with field; lock tuner housing with set screw.

• Connect elements using sprockets, chain or timing belt; remove backlash.

• Rotate using single worm gear and stepper motor:

– Torque 200 in-lb(four elements).

– Gears always loaded by magnetic torque; no backlash.

– Non back-driveable; no brake required.

– Second worm drive for perturbation studies.

• Transduction: encoder for stepper motor; potentiometer or RVDT on elements; limit switches and hardstops.

Endwall

Sprocket, lg

Sprocket, sm, 3X

Worm gear, aux

Worm, auxWorm

Base plate

Worm gear

Element assy, 4X

A

A

Section A-A

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Prototype Measurements

• Measuring center shift:– Use rotating coil with two offset windings in the same

plane; buck quad and measure change in dipole.

– Using an FFTB EM quad, T. Slaton was able to resolve center shift to 2 m using a rotating coil.

– Difficulty with set-up: thermal variations, vibration, cable loads, etc.

• New measurement set-up for SPEAR 3:– Granite table, lower working height off table.

– Use integrator, slower rotation speeds and low vibration.

– Add thermal enclosure, temp control as needed.

– EM prototype will precede PM prototype; piggyback off of this work.

• Taut wire systems available– Taut wire on precision translation stages(SPEAR 3)

– Pulsed taut wire system also available.

• Brick and tuning element measurements– Helmholtz coil measurements of brick and tuner

moments; sort to help balance poles and tuners.

– Magnetic knockdown to uniform strength(optional).Small Bucking Coil

Taut Wire Setup

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Summary and Future Work

• Summary– Permanent magnet technology for the NLC holds promise for cost reduction, facilities

simplification, improved reliability, and meeting magnet vibration tolerances.

– Initial assessment and design development is underway(FNAL, SLAC, LBL)

– The center shift tolerance required for BBA will be the most difficult requirement to meet. High radiation areas may not be suitable for PM.

• Future work– Prototype development:

• Choose magnetic designs for prototyping early April ‘00.

• Continue magnetic analysis and perturbation studies.

• Final design review in mid-May ‘00.

• Prototype built and tested by mid-September ‘00.

– Other NLC PM candidates:

• Complete first pass at requirements by early April.

• Develop parametric sizing and costing models for bends, quads, and sextupoles.

• Refine PM machine configuration and costs.

nlc - the next linear collider project andy ringwall 3/28/00 permanent magnets for the nlc a....

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