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
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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
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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]
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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, ...
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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