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Some future accelerator scenarios at RAL.
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FELIX QVI POTVIT RERVM COGNOSCERE CAVSAS
Some future accelerator scenarios at RAL
David FindlayAccelerator DivisionISIS DepartmentRutherford Appleton Laboratory
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ISIS accelerator upgrades:
½ MW upgrade
1 MW upgrade
2½ MW upgrade
5 MW upgrade
Other accelerator projects:
Neutrino factory
[MICE]
RF considerations
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People involved:
Dean AdamsMike Clarke-GaytherPaul DrummIan GardnerFrank GerigkChris PriorGrahame ReesKevin TilleyChris Warsop…
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ISIS upgrades not necessarily accelerator upgrades
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Source strength×
Reliability×
Instrumentation×
Innovation×
Investment×
Support facilities×
Support staff×
Cost effectiveness×
User community
10×1×1×1×1×1×1×1×1
2×1×
1.26×
1.26×
1.26×
1.26×
1.26×
1.26×
1.26
1×1×
1.39×
1.39×
1.39×
1.39×
1.39×
1.39×
1.39
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Source strength
Actually neutrons per electron-volt per steradian per second
— not protons (although powers usually in terms
of protons)
Reflector
Moderators
Primary targetProtons
Moderator
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Accelerator beam power:
Beam energy (electron-volts) × beam current (amps) = beam power (watts)
Or ( MeV × µA ) ÷ 1000 = kW
ISIS at present: 800 MeV, 200 µA 160 kW~2×1016 primary neutrons per second
ISIS after RFQ and second harmonic RF upgrades:
800 MeV, 300 µA 240 kW (¼ MW)~3×1016 primary neutrons per second
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ISIS at present
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Second Target Station upgrade
No power upgrade, but 18 more instruments (7 on Day 1)
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ISIS at present
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New ~180 MeV linac
½ MW upgrade
— extra power by increasing current
Present 70 MeV linac
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Higher injection energy space charge forces less of a problem
Should be able to inject and accelerate higher currents
~300 µA at 70 MeV (with 2RF upgrade)~600 µA at 180 MeV?
800 MeV × 600 µA = 480 kW ≈ 0.5 MW
Need detailed beam dynamics calculations to confirm
— ASTeC Intense Beams Group
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Proton beam
Individual proton in beam
Space charge forces
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What physical modifications to ring necessary?
Increased fields in injection dipoles (~65%)(70 MeV 369 MeV/c, 180 MeV 608
MeV/c)
Increased activation from trapping losses— increased incomplete stripping losses— but opportunity for beam chopper
Decreased adiabatic damping— beam may be harder to extract— new extract septum?
More power from RF cavity drivers (Ia: 10 13 A)
Target?
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Beam loss
Why chopper?
Ion source Linac Ring
Bunching
Also to minimise RF transients and control beam intensity
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No beam loss
Ion source Linac Ring
Bunching
With chopper — gaps in beam
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Chopper performance required
DC accelerator
RF accelerator
ns – µs spacing
ESS: 280 MHz, bunch spacing 3.57 ns
Switch between bunches
Partially chopped bunches a problem! Tune shifts!
Good
Bad
On
Off
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RAL beam chopper design
Robust design with explicit provision for high power beam collection
Switching time: between 280 MHz beam bunchesSlow transmission line
Lumped line — thermally hardened
0
1
0
12 ns 8
ns
Up to 100 µs
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Close-coupled chopper module
1145 mm
Slow switch
Fast switch
Beam
Buncher cavity
Buncher cavity
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1 MW upgrade
Extra power by increasing energy
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Protons in tungsten
0
25
50
75
100
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0 500 1000 1500 2000 2500 3000
Proton energy (MeV)
Pro
ton
ran
ge
(cm
)
Transmutation and energy production with high power accelerators, G. P. Lawrence, Los Alamos National Laboratory, http://epaper.kek.jp/p95/ARTICLES/FPD/FPD03.PDF
Proton range in tungsten target from integrating stopping power
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1 MW upgrade800 MeV synch.TS
1
TS2
3 GeV synch.
TS3
(+ 8 GeV)
µ
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Circumference of 3 GeV synchrotron= 3 × circumference of 800 MeV
synchrotron
800 MeV26 m
radius 2 – 3 µC per bunch
3 GeV78 m radius
Can “fit in” three times as much charge
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800 MeV, 300 µA 240 kW
3 GeV, 300 µA 900 kW
— ~4 × beam power, so 4 × RF power
Use same RF drivers as on present ISIS synchrotron
~30 RF cavities ~30 RF drivers (HPDs)
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Synchrotrons are swept frequency devices(resonant frequency of RF accelerating
cavities has to change throughout acceleration cycle)
Linacs are fixed frequency devices
On ISIS
linac, 202.5 MHz
synchrotron, 1.3 - 3.1 MHz
1 MW synchrotron, 3.1 - 3.6 MHz
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Synergy with neutrino factory
Same synchrotron
if design magnets to go up to 8 GeV
if run at (say) 50/3 pps to avoid more RF power
could be used for neutrino factory(e.g. target tests)
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2½ & 5 MW upgrades
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2½ and/or 5 MW upgrades
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2½ MW upgrade
TS3
µ
180 MeV linac2 × 1.2 GeV
synchrotrons39 m radius
1 × 3 GeV synchrotron78 m radius50 pps
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Circumference of 3 GeV synchrotron= 2 × circumference of 1.2 GeV
synchrotron
3 GeV78 m radius
1.2 GeV39 m radius
1.2 GeV39 m radius
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5 MW upgrade
TS3
µ
180 MeV linac2 × 1.2 GeV
synchrotrons39 m radius
2 × 6 GeV synchrotron78 m radius2 × 25 pps
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Neutrino factory
To produce ~1021 neutrinos per year
To facilitate measurements of mass of neutrino through long base line experiments
Neutrino physics: very hot topic; neutrinos not mass-less; neutrino masses are “something new”; physics “beyond the standard model”; implications for cosmology; possibly helps explains matter/antimatter asymmetry of the universe; why is there a physical universe at all
Running ~2020?
Only one likely in world, but not yet one design
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Want intense beam of neutrinos — but can’t accelerate neutrinos (no charge)
Can get neutrinos from muons
If muons decay in flight, neutrinos tend to go in direction of muons
So get intense beams of neutrinos by accelerating intense beam of muons — but no natural source of muons
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p + AZ n, , … (pion production)
+ (pion muon + neutrino)
e + + (muon electron + 2 × neutrinos)
Particle masses and lifetimes
neutrino ~0
electron 0.5 MeVstable
muon 106 MeV 2.2 µs
pion 140 MeV 26 ns
proton 938 MeV stable
neutron 940 MeV 15 mins.
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Key elements of neutrino factory
Few MW protons
Target to produce pions and let them out
Decay & capture channel where pions decay to muons
Muon cooling
Muon acceleration (~100 kW muons)
Muon storage ring where muons decay into neutrinos
[Detectors several 1000 miles away looking at storage ring]
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p + AZ n, , … (pion production)
+ (pion muon + neutrino)
e + + (muon electron + 2 × neutrinos)
KARMEN experiment at ISIS
Electron anti-neutrinos not produced by ISIS, so their appearance would be evidence for neutrino oscillations and thus evidence for neutrino mass’s in all directions — KARMEN close to target
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Muon
Storage
Ring
High current H– sourceProton
DriverTarget Capture
Co
olin
g
Muon Acceleration
‘near’ detector (1000–3000km)
‘far’ detector (5000–8000km)
‘local’ detector
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UK Neutrino Factory
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FNALBNL
CERNGSICEAINFN
JHF
DUBNA
RAL?
Neutrino experiment
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Neutrino factory: proton driver options
2.2 GeV SC linac (CERN)15 GeV synchrotron (RAL)8 & 16 GeV synchrotron (FNAL)15 GeV synchrotron (CERN)24 GeV synchrotron (BNL)50 GeV synchrotron (JHF)
Typically 4 MW of protons required
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Protons pions muons
http://puhep1.princeton.edu/mumu/target/targettrans15.pdf
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Muons produced with large energy and angular spreads
— pretty ghastly source for an accelerator
“Phase rotation” in energy-time phase space to selectively speed up slow muons
— several different schemes, all need RF
“Cooling” to reduce transverse motion but not longitudinal motion
— reduce longitud. and transv. energy in absorber
— put back longitud. only— MICE experiment at RAL
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Particle with transverse momentum
After losing energy in absorber
After acceleration in RF cavity
Muon Ionisation Cooling Experiment
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Muon acceleration
Muon mass 106 MeV, mean life 2 µs — must be quick!
Synchrotrons not possible — must use linacsRecirculating linacs to minimise cost
Superconducting linacs to minimise overall length by maximising acceleration gradient
Few microamps of muons cf. ~1 mA in proton driver
— ~100 kW beam power
Muon beam emittances large“Large" aperture linacs“Low” frequencies, e.g. ~200 MHz
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50 GeV muon recirculating
superconducting linac
ISIS synchrotron
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RF engineering considerations
Valves & klystrons
Transmission lines
Acceleration cavities
Amplitude & phase control
Beam compensation
— and people
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Valves & klystrons
~100 in proton driver, ~100 in muon accelerator
20000 h lifetime, 4 h to change 4% time lost
Test stands to test on receipt(valves for ISIS linac not always
acceptable)Cosset in operation (e.g. closed loop heater power control)
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Transmission lines and acceleration cavities
Arc protection (e.g. for klystrons)
Quality of engineering in highly radioactive areas (e.g. muon phase rotation)
Design for remote manipulation?
“Bussed” RF over ~500 mWaveguide, ~10 kW, –40 dB couplersTemperature stability important
5°C, 500 m, 500 MHz, 10–5 coeff. therm. expans. 15° phase shift
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Amplitude and phase control
Usual requirements: control good to 1% and 1°
Superconducting pulsed cavities — more difficult control problem than with normal conducting since greater fraction of RF power goes to beam
Expect to benefit from SNS experience
Beam compensation
In synchrotron, beam pulse induces signal in resonant RF cavity — have to “subtract” off — feed-forward systems
“Cathode follower” driver — low impedance— RAL/KEK/ANL collaboration
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Servo loops for RF for ISIS proton synchrotron
VFO matched to time-varying magnetic field— 0.17 – 0.71 tesla in 10 ms— 1.3 – 3.1 MHz
Loops to control amplitude of cavity voltages
Loops to control phases of cavities around ring
Loops to hold each cavity on tune
Loops to vary RF frequency to hold beam on orbit
Same for upgrade synchrotrons
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People
Accelerator RF work both routine and highly scientific/technical at same time
Need to draw young people in — recognised within CCLRC-PPARC’s initiative for university accelerator centres
But need hardware to train people on — important element of current bid to set up proton driver front end test stand at RAL — CCLRC – university (Imperial College) collaboration
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Summary
Described some ISIS accelerator upgrades
Described other accelerator possibilities at RAL
Likelihood of these projects difficult to quantify, but we did get the £100M Second Target Station