Simultaneous Delivery of Parallel Proton Beams with the EURISOL

Driver

Rita Paparella, INFN-LNL, Italy

With the kind advice of D. Berkovits, J-L. Biarotte, M. Comunian, R. Duperrier, A. Facco, A. Ponton, D. Uriot, I. Yamane, D. Zenere.

EURISOL Town Meeting Helsinki, 17-09-20072

R.Paparella

EURISOL PROTON DRIVER Requirements

• Simultaneously delivering high power, cw proton beams• 3 x 100 kW H+ beam branches• 1 x 4MW H- beam • Low rate beam losses (below 1W/m)• Beam current of secondary lines finely adjustable without

perturbing main H- beam

Splitter 3 X

EURISOL Town Meeting Helsinki, 17-09-20073

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Pulsed Beam Option

– Long pulses to 4 MW target

– Short pulses to 200 kW targets

• Fast deflector at 1 GeV

– Deflector risetime O(s) beam losses

– Beam chopper (duty cycle ~100 %)

• Secondary beam intensity not adjustable

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88-176-352 MHz 176-352 MHz 704 MHz To RIB sources

• RIB sources require beam pulses at 50 Hz and 1 ms

EURISOL Town Meeting Helsinki, 17-09-20074

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• Stripping methods: Carbon Foil Stripping

– stripping efficiency depends on the foil thickness

– 3 beams: H-, H+, H0

– No foil supporting 4 MW beams

– Intolerably short foil lifetime

– Beam losses

– No possibility of fine adjustment of beam current

Beam Separation by Changing its A/qNegative ions advantage:

possibility of partially strip the ion beam at the accelerator exit two different beam type: 1 negative & 1 positive

EURISOL Town Meeting Helsinki, 17-09-20075

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Stripping Method: Laser Photo-Detachment

• Bunched Beam all the laser power should intercept the bunches – Laser pulse should be shorter than 1 ns; otherwise:– Pulsed beam, chopper and kickers

• Only a small fraction of the ions is photo detached/neutralized

• Not enough high power and/or repetition rate

EURISOL Town Meeting Helsinki, 17-09-20076

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Stripping Method: Lorentz Stripping • Transverse magnetic field in the laboratory frame electric field

in the rest frame of the H- ions according to the Lorentz transformation of the fields:

• This electric field can remove the extra electron of H- ion

• H- beam partially stripped into H0 inside the magnet

• 1 GeV H- ions few kilo-gauss sufficient to strip the first electron (binding energy = 0.755 eV)

• Fraction of the original number of ions stripped per unit path length traveled is a function of the magnetic field (L. R. Scherk, Can. J. Phys. 57, 588 (1979) )

• H0 production rate finely adjusted by varying B

BcE

EURISOL Town Meeting Helsinki, 17-09-20077

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Lorentz Stripping

• Only 2 states of charge after magnetic stripping: H- and H0

(with adjustable beam intensity)

• Impossible to remove the second electron (binding energy 13.6 eV)

– Transitions to higher H0 atomic states with laser and magnetic stripping

– H0 stripping by Carbon foil

Ions travel a finite distance beforebeing stripped angular spread Emittance growth

B

H-

H0

H-

2

EURISOL Town Meeting Helsinki, 17-09-20078

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EURISOL Magnetic Neutralizer• Chicane Outgoing H- beam line not changed

Only two beams Magnetic field changed to adjust the beam current of the generated H0 beam

• B transverse to beam trajectory alternates in direction

Magnetic length 30 mm

Separation for house coils 40 mm

Magnetic fields [T] 0.33; 0.66; 0.33

, deflection angle ~ 0.1 °

d0, H0 displacement 0.11 mm

Neutralization fraction, by Lorentz stripping, of 2.5%, totally in the second magnet finely adjustable

EURISOL Town Meeting Helsinki, 17-09-20079

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Fringe Fields

Very weak focusing in both horizontal and vertical planes Chicane beam optics insensitive to dipoles fringe field shape

Short rectangular magnets, small bending angle

EURISOL Town Meeting Helsinki, 17-09-200710

R.Paparella

EURISOL Splitter* Layout

• 3-step splitting scheme developed

– Magnetic neutralizer to extract H0 beam

– 1 bending magnet to separate H0 from H-

– 1 stripper foil on the H0 line to strip H0 in H+

– 1 bending magnet to send H+ to target and residual H0 to beam dump (~50 W)

* A. Facco, R. Paparella D. Berkovits, I. Yamane, “Splitting of high power, cw proton beams”, PRST-AB 10, 091001 (2007)

H-

H-

EURISOL Town Meeting Helsinki, 17-09-200711

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Stripper Foil

• Promising candidate for such a thick foil: Carbon Nano-Tube (CNT) foil

• Necessary thickness to reduce unconverted H0 beam to a safe level (~50 W) estimated to be >=500 g/cm2

• 1 GeV - 100 A H0 the heat load is estimated 0.1 W not serious heat load

• Expected foil lifetime of several weeks

EURISOL Town Meeting Helsinki, 17-09-200712

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H- Beam Transport

εx, εy (norm. rms) 0,3 ·mm·mrad

εz (norm. rms) 0,4 ·mm·mrad

Current 4 mA

Macro particles 100.000

Bunch Frequency 176 MHz

• 3x2D Gaussian distribution simulated

• Chicane aperture necessarily narrow H- beam has a waist in both horizontal and vertical planes

EURISOL Town Meeting Helsinki, 17-09-200713

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H0 Beam Emittance• H0 phase space distribution calculated starting from trajectories of H- particles,

assumed with Gaussian distribution

d0 0,1 mm

Horizontal half angular spread 3,3 mrad

εx (norm. rms.) ~ 0,8 ·mm·mrad

εy (norm. rms.) 0,3 ·mm·mrad

εz (norm. rms.) 0,4 ·mm·mrad

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H- - H0 Phase Spaces

H0 AT THE FOIL INPUT

H0 AT THE CHICANE OUTPUTH- AT THE CHICANE OUTPUT

EURISOL Town Meeting Helsinki, 17-09-200715

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H+ Beam Transport

• 3 x RMS envelope from the carbon foil to the target• Phase space at the foil output

H+ AT THE FOIL OUTPUT

EURISOL Town Meeting Helsinki, 17-09-200716

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3 Splitters Layout• Unperturbed H- beam

• Nearly unchanged H- emittance

same system repeated three times

Beam transport between two chicanes will transfer the same profile from the entrance to the exit

same quality proton beams to three 100kW targets

EURISOL Town Meeting Helsinki, 17-09-200717

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H- Transport Along 3 Splitters

1st chicane output

2nd chicane output 3rd chicane output

EURISOL Town Meeting Helsinki, 17-09-200718

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Summary and Conclusions• A newly designed beam splitter, composed of a 3 magnets chicane

and a foil has been developed and confirmed to be feasible

• Extracted beam current of secondary lines finely adjustable without perturbing main beam

• Expected foil lifetime of several weeks

• Emittance growth of primary H- beam negligible

• Emittance of secondary H0 beam suitable for lossless transport to the 100 KW targets

• EURISOL scheme might be used in different configurations and for pulsed beam allowing elimination of choppers and kickers

• The 3-step proposed splitter fulfils the EURISOL requirements