FFAG Accelerators for Radio-Isotopes Production

FFAG Accelerators for Radio-Isotopes Production

Alessandro G. Ruggiero

Brookhaven National Laboratory

FFAG 2007, Grenoble, France

April 12-17, 2007

4/16/2007 FFAG 2007 -- Alessandro G. Ruggiero 2/18

FFAG for Hadron (proton and HI) Applications

Non-Relativistic Velocity < 1 (forget µ and e !)High Power Mode 1 - 10 MwattMedium Energy range 1 - 10 GeV/uHigh Repetition Rate 50 Hz

1 - 10 kHzCW

Narrow Width 10-30 cmLong Drifts > 1 mStrong Focusing (d) FDF (d)

Non Isochronous << T

RI and EN productionEnergy ProductionPulsed and Continuous Neutron ProductionNuclear Waste TransmutationTritium ProductionNuclear Physics (K, π, … mesons)Proton Drivers for Neutrino Factory, -SuperBeams, µ-CollidersNo Medical or Lower Energy or Lower Intensity Applications

RCS

SCL expensive

Cyclotron

FFAG


Previous Studies

AGS-based Facility for RIP following FAIR (T. Roser, Februray 2006)

too complicate RCS

needed accumulator ring(s) and e-cooling

A.G. Ruggiero “AGS-less RIA with FFAG Accelerators”, BNL Internal Report, C-A/AP 238, May 2006Abstract

We have studied the use of Non-Scaling Fixed-Field Alternating-Gradient (FFAG) accelerators for the acceleration of heavy ions to produce radioisotopes and exotic nuclear fragments. We have taken as reference a beam of nuclei of Uranium 238 partially stripped to +28 charge state.

A.G. Ruggiero, T. Roser, D. Trbjevic, “A Non-Scaling FFAG for Rare Isotopes Production”, Proceedings of EPAC, Edinburgh, Scotland TUPLS027Abstract

This is a report to demonstrate the use of Non-Scaling Fixed-Field Alternating-Gradient (FFAG) accelerators [1] in acceleration of partially stripped ions of Uranium-238 for Rare Isotopes Production. The following example assumes a beam final energy of 500 MeV/u with an average beam output current of 1 µA-particle and a beam average power of 120 kWatt.

P.N. Ostroumov, Phys. Rev. Spec. Topics Acc. and Beams, 5(2002) 030101


Goals of RIA (SCL) Uranium 238

ECR 12 keV/u Charge State 30RFQ 168 keV/uLow- SCL 9.3 MeV/u 57.5 and 115 MHz

Stripper 1 (Lithium Film) Charge State 69-73Medium- SCL 80.3 MeV/u 172.5 and 345 MHz

Stripper 2 (Carbon Wheel) Charge State 87-90High- SCL 400 MeV/u 805 MHz

CW Mode of Operation 4.2µA-particle 400 kWatt

Reliable but Expensive Project 360 SC Cavities

ECR RFQ

Low- Medium-

High- Section

G = 0.81 G = 0.61 G = 0.49

Stripper 2Stripper 1


FFAG-Scenarios

Three possible modes of operation;

A. Acceleration with Broadband RF Cavity frep = 1 kHz

B. Pulsed Mode with Harmonic Number Jump frep = 10 kHz

C. CW Mode with Harmonic Number Jump frep = CW

Final Energy 400 MeV/uAverage Power 400 kWattAverage Current 4.2 µA-particle

I.S. Inj. Linac

RFQ

15 MeV/u 80 MeV/u 400 MeV/u

FFAG-1 FFAG-2

4.2 µA-particle

Charge State 30+

Charge State 90+

Charge State 70+

±40.3% ±41.4%


A. Acceleration with Broadband RF Cavity

FFAG-1 (+70) FFAG-2 (+90)

Injection Extraction Injection Extraction

Circumference m 204 204

Kinetic Energy MeV/u 15 80 80 400

0.1767 0.3885 0.3885 0.7131

Revol. Freq. MHz 0.2597 0.5689 0.5710 1.0438

Revol.Period µs 3.851 1.758 1.751 0.958

h 6 6

RF Frequency MHz 1.558 3.423 3.423 6.273

RF Peak Voltage MVolt 0.8 1.6

RF Phase degrees 60 60

Bunch Area eV/u-s 0.02 0.02

Emittance, norm. π mm-mrad

110 110

sp. ch. 0.018 0.0077 0.016 0.0063

Nions / pulse x 1010 2.63 2.63

Accel. Period ms 0.758 0.726

No. of Revol. 319 611

Rep. Rate kHz 1 1

Ave. Current µA-particle 1093 2397 2403 4400

RF Beam Power kWatt 53.0 116.3 300.0 548.6

60 turns

18 µA-p IonSource


A. Acceleration with Broadband RF Cavity

Revol. Freq. 3.851 µsI.S. 4 µA-particleStored Current 1093 µA-particleInjected Turns 275Filling Period 1 ms

Long Drift 1.089 mShort Drift 0.130 mF-Length 0.301 mD-Length 0.602 m

No. of Periods 80

I.S. Inj. Linac

RFQ

15 MeV/u 80 MeV/u 400 MeV/u

FFAG-1 FFAG-2Accumulator

F F D

Extraction Trajectory

Injection Trajectory


Lattice Function along one period

Injection

Ejection


FFAG heavy ion driver

400 MeV/u, 400 kW, 1 kHz 6.3 x 1012 nucleon/pulse = 2.6 x 1010 U/pulse = 4.2 pA (OK for ECR)

Use EBIS as space charge neutralized accumulator. Extract pulses for single turn injection. Accelerate multiple charge states.

Energy choices: Kinetic E Momentum Beta Rev. Frequency (C=153m)

Injection Ring 1 10 MeV/u 137 MeV/c/u 0.145 0.28 MHz

Injection Ring 2 67 MeV/u 381 MeV/c/u 0.359 0.70 MHz

Extraction 400 MeV/u 954 MeV/c/u 0.713 1.39 MHz

Ring 1: U28+; Bmax = 9.2 Tm B ~ 0.8 T for 50% filling factor; 1ms acc. time 500 turn acceleration 2 MeV/turn 40 keV/m for 50 m rf broadband Finemet cavities?

Ring 2: U56+; Bmax = 12.2 Tm B ~ 1.0 T for 50% filling factor; 1ms acc. time 1000 turn acceleration 3 MeV/turn 60 keV/m for 50 m rf broadband Finemet cavities?

10 MeV/n

To target station and fast fragment spectrometer

67 MeV/n 400 MeV/nECR EBIS RFQ Linac StripperU28+ U56+

Ring 1 Ring 2

Thomas Roser


B. Acceleration with Harmonic Number Jump

FFAG-1 (+70) FFAG-2 (+90)




0.1767 0.3885 0.3885 0.7131

Revol. Freq. MHz 0.2597 0.5689 0.5710 1.0438

Revol.Period µs 3.851 1.758 1.751 0.958

h 388 x 8 176 x 8 352 x 4 192 x 4

RF Frequency MHz 806.0 803.9

RF Peak Voltage MVolt 2 x (8 x 4) cavities 1 x (4 x 8) cavities


Bunch Area eV/u-µs 10 10


100 100

sp. ch. 0.017 0.011 0.010 0.005

Nions / pulse x 109 2.63 2.63

Accel. Period µs 74.0 54.0

No. of Revol. 26 +4/8 40

Rep. Rate kHz 10 10

Ave. Current µA-particle 437 964 961 1762

RF Beam Power kWatt 8.3 238 119 3036

6 turns

75 µA-p Ion Src


Constant-RF Voltage Profile (805 MHz)

Using these RF Voltage Profiles it is possible to operate in CW mode provided that the Ion Source delivers continuously 4.2 µA-particles.

Ratio of Initial to Final Harmonic Number = f / i = 4.04

FFAG-2FFAG-1


CW Mode of Operation ( < 1)

Uranium Mass Number, A = 238Charge State, Q = +90

Rest Energy, E0 = 931.?? MeV/uKinetic Energy, E = 400 keV/uAverage Power, P = 400 kWattAverage Current, I = P/AE = 4.2 µA-ion

M equally-spaced cavities around ring at constant frequency fRF and phase RF

Energy Gain En = (Q/A) eVn sin RF

fRF = constant = n hn f∞ --> n+1 hn+1 = n hn

f∞ = C / c T / T = C / C – / C / C << / = 0, Isochronous

Tn

Tn + 1

Tn - 1

Vn

Vn + 1

Vn - 1ECR

Cyclotron, Muons Protons, < 1


Harmonic Number Jump (HNJ)

The variation of h with can be calculated precisely on a computer, but here we use a linear approximation ( a very good one indeed!)

En+1 = E0 n2 n

3 h / (1 – p n2) hn h = hn+1 – hn

= (Q/A) eVn sin RF

hn is local value between cavity crossings h is harmonic number jump between cavity crossings = –1

p n2 << 1

By integration

Max. energy gain per crossing Emax = Ef f f2 h M c / fRF Ctot

Number of Crossings nf = fRF Ctot (1 – i / f) / M i c h

Acceleration Period tf = fRF Ctot2 (1 – i

2 / f2) / 2 M2 i

2 c2 h

Vn = g n TTF (0 / n) Cavity gap g = RF 0 / 2

Physical Review ST A&B 9, 100101 (2006)


Consequences of Harmonic-Number Jump

To avoid beam losses, the number of bunches ought to be less than the harmonic number at all time. On the other end, because of the change of the revolution period, the number of RF buckets will vary. There is a difference between the case of acceleration below and above transition energy. Below transition energy the beam extension at injection ought to be shorter than the revolution period. That is, the number of injected bunches cannot be larger than the RF harmonic number at extraction. The situation is different when the beam is injected above the transition energy. In this case the revolution period decreases and the harmonic number increases during acceleration. Below Transition Above Transition

hf / hi = f / i


Beam-Bunch Time Structure

FFAG-1 FFAG-2

Cavity Groups 8 4Cavities per Group 4 8

0 0.22 0.50Cavity Gap, cm 4.1 9.3RF Phase 30o 60o

RF Voltage / Cavity 2 MVolt 1 MVoltOrbit Separation, mm 2 - 20 2 - 11Beam rms Width, mm 5 - 4 3 - 2.5Beam rms Height, mm 7.5 5.0

ECR Ion Source 4.2 µA-ion Tfinal

Tinitial Bunching Freq. = 57 MHz

(1 bunch / 14 rf buckets)


C. CW Mode of Acceleration by HNJ

FFAG-1 (+70) FFAG-2 (+90)




0.1767 0.3885 0.3885 0.7131

Revol. Freq. MHz 0.2597 0.5689 0.5710 1.0438

Revol.Period µs 3.851 1.758 1.751 0.958

h 388 x 8 176 x 8 352 x 4 192 x 4

h -1 -1

RF Frequency MHz 806.0 803.9

RF Peak Voltage MVolt 2 x (8 x 4) cavities 1 x (4 x 8) cavities


Bunch Area eV/u-µs 10 10


10 10

Nions / turn x 107 2.51 2.51

Accel. Period µs 74.0 54.0

No. of Revol. 26 +4/8 40

Rep. Rate CW CW


Energy Gain Profile

FFAG-1 FFAG-2


RF Voltage Cavity Profile for HNJ

cm cm

TM11 TM01 TM11

805 MHz

Gap =4-9 cm

8 MV/m ± 3 MV/m

20 cm

1 m

Documents

FFAG Accelerators for Radio-Isotopes Production