cat-kek-sokendai school on spallation neutron sources 1 rapid cycling synchrotron (i)...

CAT-KEK-Sokendai School on Spallation Neutron Sources

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Rapid Cycling Synchrotron (I)


K. Endo (KEK)Feb. 2-7, 2004


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Contents

1) Rapid Cycling Synchrotron2) Accelerator-Based Pulsed Neutron Sour

ces – Existing Facilities3) Next Generation Spallation Neutron Sou

rces4) Advantage/Disadvantage of RCS5) Combined or Separated function RCS6) Proton Driver for Neutrino Factory


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Rapid Cycling Synchrotron (RCS) (1)

Increasing the repetition rate to 10~60Hz, it is possible to obtain much higher proton intensity. This type is called as a “rapid cycling synchrotron,” but it requires special design consideration including its power supply.

Magnet: AC magnet made of laminated steel plates and requires design study using 2D or 3D field simulation code.

Power supply: Resonant circuit to provide with sinusoidal current under the operation of the basing DC power supply.

Operation: Combined function is easy. Separated function requires a precise tracking between Bending and Focusing fields.


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Rapid Cycling Synchrotron (2)

• Resonance Condition: Loads including magnets, capacitor and choke transformer are in resonance condition.

• Energy exchanged between magnets and capacitors, while the pulse power supply provides the losses.

• Utilize Full AC Field Swing: superpose DC field to AC field to have Injection at bottom AC field.

Choke Transformer is introduced to decouple the pulse power supply.• Reduce magnet voltage: adopt multi-mesh circuit.


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Rapid Cycling Synchrotron (3) – White circuit

Princeton 3GeV proton synchrotron in 1956.


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Example of magnet, coil and pole end profile for rapid cycling synchrotron.

Effect of magnet end pole profile(a) Rogowsky profile, and (b) Distribution of flux lines.


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SCR Firingcircuit

DI O BOARD-1

DI O BOARD-2

Motorcontrol l er

Motor

NEC-9801

PCDAC

DC b

ias

PS

strobe

16 bi ts

16 bi ts BdcBac16 16

VFC VFC

F-coi l

S-coi l

backl eg wi ndi ng

counter counter

RS-232C

Bac reference

I NT

FC

setti ngs off l i p number& i nterval

Experi mental setup for the control of pul se and dc power suppl i es

Rch Rm

LmCLchVs/ n

I

I 2

Choke trans.

Vs/ n

T

Pri mary windi ng vol tage

t=0

MagnetCapaci tor

1:n

Vs/ n

(a)

(b)

Lch/ n2

I p

I 1

Ti

t=[0.0, 0.2] sec t=[3. 0, 3. 2] sec

Numeri cal resul ts of the si ngl e mesh magnet current f or the i nterval of t=0. 0 ~ 0. 2 sec and t=0. 3 ~ 3. 0 sec assumi ng Lm=0. 044 H, Rm=0. 152W and T=0. 020 sec. Ampl i tude i s arbi trary.


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Multi-mesh circuitNINA electron synchrotroncombined function magnet Max. energy = 4GeV Mean orbit rad. = 35.1m Bending rad. = 20.8m Injection energy = 40MeV Field @4GeV = 0.64T Repetition = 50Hz


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Accelerator-Based Pulsed Neutron SourcesExisting Facilities

Acc. type Beam Energy (MeV)

Rep. Rate (Hz)

Av. Beam Current (A)

Pulse Width (ms)

Beam Power (kW)

IPNS (ANL) Linac/RCS (CF, 13.6m dia.)

50450

30

15

0.1

7

KENS (KEK) Linac/RCS (CF, 12m dia.)

40500

20

6

0.1

3

ISIS (RAL) Linac/RCS (SF, 52m dia.)

70800

50

200

0.1

160

LANSCE_PSR (LANL) Linac/AR (SF, 30m dia.)

800

20

125

7500.25

100

SINQ (PSI) Cyclotron 72590

continuous

1500 900


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Layout of Proton Sources

Layout of Spallation Neutron Source

AR

RCS

Cyclotron

TargetLANL

RAL, ANL, KEK

PSI

Linac

Cyclotron-driven

Synchrotron-driven

Linac-driven


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Next Generation Spallation Neutron Sources

Scheme Max. beam power

(MW)

Bunch compression

(sec)

Magnet system

NSNS

(USA)

1GeV Linac +60Hz-AR

1

2 (upgrade)

1000 to 0.5 SF

(FODO)

ESS

(EU)

1.334GeV Linac + 50Hz-AR

x 2

5 600 to 0.4 SF

(Triplet)

J-PARC

(Japan)

0.4GeV Linac +25Hz-3GeV

RCS

1 500 to 0.1 SF

(FODO)


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NSNS (1) – ORNL1,2,3,4)

H- ion source+2.5MeV RFQ: LBNL 50mA-H-

Linac

NC-DTL+CCL: LANL (2.5200MeV).

SC-Linac: JLab. (2001000MeV).

Accumulation Ring: BNL

Charge exchange injection (H-p)

1200 turn injection, Short (1sec) and intense proton pulses are extracted at 60Hz.

Mercury target: ORNL

Exp. Facilities: ANL+ORNL

Extraction is a single turn with full aperture at a pulse repetition rate of 60Hz. Extraction system consists of a full-aperture kicker and a Lambertson magnet septum. Vertically kicked and horizontally extracted.


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NSNS (2)


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NSNS (3)


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ESS (European Spallation Source) (1)

Main parameters of ESS

Linac

Beam energy = 1.334 GeV

Beam power = 5.1 MW(av.)

Average / peak current = 3.8 / 107 mA

Repetition rate = 50 Hz

Beam pulse duration = 2 x 0.6 msec

Be

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am duty cycle = 6.0 %

Two Accumulator rings

Frequency = 50 Hz (parallel operation)

Proton beam / ring = 2.34 x 10 ppp

Bunch length = 0.4 sec at ejection

Mean radius = 26.0 m


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ESS (2) 5) - Options for 5MW proton beam @50Hz in pulse of time duration 1s or less

1. 0.8GeV H- linac + 3 ARs2. 1.334GeV H- linac + 2 ARs3. 0.8GeV H- linac + 2 RCSs of 3GeV and 25Hz4. 2.4GeV H- linac + 1 AR5. 0.8GeV H- linac + 1.6 or 3GeV superconducting FFAG, 30GeV KAON Factory type accelerator, or 1GeV proton induction linac

Expensive2nd option: highest operational reliability3rd option: secondary consideration for a long pulse (2ms) facilityLow energy injection: severe space charge limit but less severe heat problem for H- stripping foil


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ESS (3) – AR option

Two 50Hz, 1.334GeV AR (Accumulation Ring). AR’s act to compress the time duration of the LinacPulse by a multi-turn (1000 turns/ring) charge exchange injec

tion.


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ESS (4) – RCS option

Two 25Hz RCS operate out of phase at 3GeV, 50Hz.

Very high power RF system occupies more straight sections than 1.334GeV AR, leading to 4 superperiods.

Mean radius: 45.9mInjection: 0.8GeVSpace charge tune shift: 0.2, twic

e of AR.Injection flat bottom: 2.5msDual harmonics: 20Hz sinusoidal

rise and 40Hz fall.


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J-PARC (1)6)


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J-PARC (2)


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J-PARC (3) - Future upgrade


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Advantage/Disadvantage of RCS7)

1) Neutron yield is proportional to beam power (Eb x Ib). Trade off between repetition rate, beam current and beam energy. RCS achieves high power at low repetition rate at reasonable cost compared to linac/compressor scenario.

2) RCS requires high power RF cavity

3) Care for Eddy current due to rapid change of Magnetic field

4) Space charge limit at low energy injection, so the peak current in RCS is several times smaller

5) Longer beam-in-ring time (10 to 20ms) compared to linac/compressor ring (1 to 2s) will have a greater risk of instabilities associated with large number of cavities.


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Comparison of Linac- and RCS-based concepts

Linac-based RCS-based

Beam energy low high

Beam current high low

Beam loss control severe mitigated

H- ion source high current

high duty

moderate

Construction cost expensive less costly

Required RF power for AR or RCS

low high


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Reducing RCS-RF power by Dual-frequency mode Excitation

For the case of IPNS upgrade study to 1 MW at ANL,

Single mode;

2 GeV, 0.5 mA, 30 Hz RCS requires 180 kV RF voltage.

Dual mode;

2 GeV, 0.5 mA, 20 / 60 Hz dual mode: 120 kV RF voltage.


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Combined or Separated function RCSTracking between dipole and quadrupole fields

• Combined

• Separated

• Tracking maintained but limited tunability. NINA, Fermilab, KEK-PS

• Dipoles and quads are serially connected, but requires trim quad windings or dependent correction quad. SSC, SSRL

• Serial resonance circuit for quad. J-PARC• Independent excitation of B, QF and QD, e

ach phase adjusted within ±1sec. No magnet saturation. BESSY II Booster (10Hz)


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Tuning of QF and QD for Separated-function RCS

Bucking choke is used to cancel the induced voltage

in the trim coil caused by the main coil circuit.


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Proton Driver for Neutrino Factory (1)8) - RCS based

• Proton driver for neutrino factory,

fitting into CERN-ISR beam power: 4MW final bunch duration: 1ns

RAL: Synchrotron-based two RCS options 1) 1.2GeV @50Hz + 5GeV @25Hz 2) 3GeV @25Hz + 15GeV @12.5HzCERN: Linac-based proton driver 2.2GeV @75Hz linac + Accumulator and Compressor rings


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Proton Driver for Neutrino Factory (2) - Linac-based


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References

1) W.T. Weng et al, “Accumulator Ring Design for the NSNS Project,” PAC97, pp.970.

2) D. Raparia et al, “The NSNS Ring to Target Beam Transport Line,” BNL/NSNS Technical Note No.006.

3) J. Wei et al, “Low-Loss Design for the High-Intensity Accumulator Ring of the Spallation Neutron Source,” PRST-AB, 3, 080101 (2000)

4) “Final Design Review: SNS Super Conducting Linac RF Control System,” 2000.

5) G. Bauer et al (ed.), “The ESS Feasibility Study Vol. III Technical Study,” ESS-96-53-M, 1996.

6) Draft of “Accelerator Technical Report for High-Intensity Proton Accelerator Facility Project,” JEARI/KEK Joint Team, http://hadron.kek.jp/member/onishi/tdr/index.html

7) Y. Cho, “Synchrotron-Based Spallation N eutron Source Concept,” APAC98, Tsukuba, 1998.

8) C,.R. Prior et al, “Synchrotron-Based Proton Drivers for a Neutrino Factory,” EPAC2000, Vienna, 2000, pp.963-965.

http://hadron.kek.jp/member/onishi/tdr/index.html

cat-kek-sokendai school on spallation neutron sources 1 rapid cycling synchrotron (i)...

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