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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

125

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

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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