The RAL Front End Test Stand

David FindlayISIS Accelerator Division

Rutherford Appleton LaboratoryOxfordshire, UK

STVLTVS EST QVI ACCELERATORIBVS CVRANDIS VICTVM QVAERIT

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CCLRC

Council for the Central Laboratory of theResearch Councils

Member of RCUK (Research Councils UK)BBSRC, CCLRC, EPSRC, ESRC, MRC, NERC, PPARC

Provides large facilities for UK scienceLasers, neutrons, synchrotron radiation

BBSRC Biotechnology & Biological Sciences Research CouncilCCLRC Council for the Central Laboratory of the Research CouncilsEPSRC Engineering & Physical Sciences Research CouncilESRC Economic & Social Research CouncilMRC Medical Research CouncilNERC Natural Environment Research CouncilPPARC Particle Physics & Astronomy Research Council

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Rutherford Appleton Laboratory

ISIS

Diamond

Daresbury Laboratory

SRS

4GLS

CCLRC

44

ISIS~270 people total

Accelerator Division (~95)Diffraction & Muons DivisionInstrumentation DivisionSpectroscopy & Support DivisionTarget Division

David Findlay Photonuclear physics / light nucleiPhotofissionRadioactive wasteAccelerator servicesGemstones (in private sector)Medical sterilisation (in private

sector)ISIS

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Why a [proton driver] front end test stand?

Prove key elements of high power proton accelerators

Applications of a RAL test standGeneric Spallation neutron sources Neutrino factories Transmutation machines Tritium generators Energy amplifiers Training / Young people / Real

hardwareSpecific ISIS upgrades UKNF UK academic accelerator community

66

ISISWorld’s leading spallation neutron sourceNatural wish to stay at or near frontUpgrade strategies / CCLRC funding / ASTeC

(ASTeC = CCLRC’s Accelerator Science & Technology Centre)

UK Neutrino FactoryStrong drive from UKNF communityPPARC support for proton driver R&DSynergies with possible ISIS upgrades

UK academic communityImperial College - CCLRC joint appointment

Lecturer / Senior Lecturer in Accelerator Science

Extend university accelerator centres to protons

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What’s in a front end?Ion source, LEBT, RFQ and beam chopper

Why does it matter?Where beam quality set for entire machine

What has to be tested?New, high performance ion sources, RFQs,beam choppers

ISIS 0.16/0.24 MW NowPSI 0.75 MW [not pulsed]SNS 1 MW Near futureJPARC 1 MW Near futureNF 4 MW — a big step! Further away[ISIS 1, 2, 5 MW Plans]

1010

So, planning to build front end test stand at RAL

But already had one!

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ISIS RFQ Test Stand

RFQ to replace ISIS Cockcroft-Walton

202.5 MHz, 4-rod, 35 keV i/p, 665 keV o/p50 mA / 10% DF design, 30 mA / 2% DF use

Test stand built to characterise and soak test

Met specifications

Soak tested successfully for >2000 hours

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Proton driver front end test stand at RAL

ISIS Accelerator Division CCLRC/ASTeCImperial College PPARCWarwick University PPARC

+ ?

+ 1½ × ½ SY/year EU (HPRI-CT-2001-50021)+ 5 × ½ SY/year EU (HIPPI/CARE/ESGARD)

Mike Clarke-Gayther, Dan Faircloth, Frank Gerigk, Paul Harrison, Alan Letchford, Ken Long, ...

2020

Relationship with CERN test stand

Formal cooperation through HIPPI

Two approaches to beam chopper

But differentCERN test stand for Linac4 then SPLProton / H– ion sourcesRAL test stand more genericDifferences reflect organisation’s missions

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RFQ234 MHz

Bunch +

accel-erate

Chopper

Switch in 2 ns

for~0.1 ms

LEBT

Match ion

source to RFQ

H– ion sourc

e

60 mA

2 ms

Beam

stop

Dia

gn

osti

cs

Transverse emittances,energy & energy spectra,bunch widths, halo, ...

Block diagram of RAL front end test stand

75 keV 2½ – 3 MeV

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H– ion source — Development to ~60 mA required Based on ISIS H– ion source (35 mA)

LEBT — Revision of ISIS RFQ LEBT probably sufficient

RFQ — Base on ISIS & ESS 4-rod RFQs ISIS RFQ designed for 10% RF duty factor cf.

ISIS 2% 75 keV in, 2½ – 3 MeV out, 234.8 MHz Most expensive item: ~1 – 2 MW RF driver

Beam chopper — Development required Based on ESS concept

But need ion source, LEBT and RFQ to test beam chopper

Ion source development rig (ISDR) at RAL

H– ion source R&D programme — for future high power proton accelerators (e.g. for future spallation neutron sources) — × ~10 output required

1 inch

Important milestone passed

Successful thermal modelling of world leading ISIS ion source — extraction of surface temperatures

Excellent agreement between calculated and measured thermocouple temperatures

Anode

200°C

Ab initio calc. Meas.°C °C

Anode t/c 456 400 – 600Cathode t/c 501 440 - 530Body t/c 416 390 - 460

600°C Cathod

e

Close-coupled chopper module

1145 mm

Slow switch

Fast switch

Beam

Buncher cavity

Buncher cavity

Beam chopper R&D programme — specialised hardware — fast, high voltage pulser specified and procured

1½ kV rise in <2 ns

90 100 110 120 130 140 150

t (ns)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

norm

alis

ed p

ulse

am

plitu

de (

%) 4.2% droop in 10.1 ns1.88 ns (10-90%) 1.14 ns (90-10%)

10.1 ns

KF10NS01.AXG

100% = -1480 V

Vpsu = 62 V

first pulse in burst

delay = t - 10.1 ns = 92.9 ns

102.2%

102.2% = -1512 V

A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M

Overall philosophyRF frequency? One RFQ or two? Interactions with ISIS?

Ion sourceFix Bruker Extract Power SupplyExperiments: separate Penning field, neutralisation, electrode geometryTest new geometry, higher extract potential and separate Penning fieldFurther mods. + testsDesign, build & test ×2 larger ion sourceDesign "operational" sourceBuild "operational" source

LEBT[Pretty well blanked out by RFQ installation & commissioning work]Review performance of existing test stand LEBTMagnetic or electrostatic?Design new LEBT (MAFIA, magnet design, particle tracking, vacuum)Build new LEBT

RFQ[Pretty well blanked out by RFQ installation & commissioning work]Re-visit physics designRe-visit mechanical/thermal/vacuum designAssessment of RF driverSpecification of RF driver

Beam chopperMeasurements with Kentech pulsers — to check computer codesHigh voltage, high current MOSFET switch developmentThermal calcs. for beam dumpsRepresentative prototype meander line testRepresentative prototype lumped line testPre-production meander line testPre-production lumped line testRF cavities and quadrupoles, low level RF systems

DiagnosticsReview ISIS RFQ test stand diagnosticsDesign beam current measurement apparatusRe-use magn. spectr., gas scatt. spectr., coax. target?Specify suite of diagnostics (incl. halo m's'ment) (also beam dump)

Beam dynamicsBeam dynamics for LEBT, RFQ, chopper lineError limits for RF phase and gradient, quadrupole gradient, etc.

Infrastructure / Overall practicalitiesEstimate footprint for 2–3 MeV test stand / Clash with synch. RF area?Estimate radiation shielding incl. beam losses in RFQ, chopper)Estimate services requirements and ancillary apparatus requirementsProduce outline specification and drawing of test standExtend lead shedBuild and install stands and supports

20072004 2005 2006

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RAL front end test stand for:

ISIS upgradeFront end of 180 MeV linac

234.8 MHz DTL to ~80 MeV704.4 MHz SCL to 180 MeV (like Linac4 at CERN)

UK neutrino factory

High power proton accelerators in general

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New ~180 MeV linac

Present 70 MeV linac

ISIS half-megawatt upgrade

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UK Neutrino Factory

New ~180 MeV linac

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With existing funding, at end of three years, i.e. by March 2007, expect to have

Dedicated area (in R8 (probably))Lead shed (shield against RFQ X-rays)Support structure / StandsOperational ~60 mA H– ion source availableLEBT assembledDesign for RFQSpecification for RF driverProven electrical design for beam chopperDesign for quadrupoles and cavities for chopperSpecification of diagnostics

R8

R8, area easily available 290 m²

More space available

5 m 1

2

27½

7

12

1½

4½

7

6

10

5½

7

RFQ Chopper

DiagnosticsLEBTIon source

RF driver area

Mag. spectr.

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Opportunities to take advantage of:

Area in R8 already well provided — space, electricity, water, air, crane, loading bay, on main ISIS controls circuit, …

Significant existing hardware — high power arc driver and high power extraction pulser for H– ion source, TMPs, gas scattering spectrometer, magnetic spectrometer, emittance scanners, data acquisition systems, 200 kW RF driver, ...

3737

2004–2007

Overall scheme, design, infrastructure, specifications, some hardware

2007

Complete scheme

Hope to demonstrate high quality chopping of ~60 mA H– beams at ~2½ MeV

[End]

Novel gas scattering energy spectrometer at RAL

Surface barrier detector + Cs137 conversion source

Experimental ion source and assembly

RAL beam chopper design

Robust design with explicit provision for high power beam collection

Slow transmission line

Lumped line — thermally hardened

0

1

0

12 ns 8

ns

Up to 100 µs