1. 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.

2. EURISOL PROTON DRIVER Requirements
Splitter
3 X
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
EURISOL Town Meeting

3. Pulsed Beam Option
intermediate
extraction
energy
p,d rfq
chopper
2-gap SC linac
1 GeV
Fast
deflector
<3 MeV/A
MHz
MHz
704 MHz
To RIB sources
RIB sources require beam pulses at  50 Hz and 1 ms 
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
In the past, a first option was considered, the pulsed beam option, using a fast deflector, but the RIB restrictions gave some difficulties, and moreover fast deflectors are expensive technologies, with a risetime that means beam losses and the necessity of beam chopping with duty cycle of 100% required. And moreover with this system, the secondary beam intensity was not adjustable has instead required by Eurisol.
For these reasons another option have been studied, using negative ions:
EURISOL Town Meeting

4. Beam Separation by Changing its A/q
Negative ions advantage:
possibility of partially strip the ion beam at the accelerator exit  two different beam type: 1 negative & 1 positive
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
EURISOL Town Meeting

5. 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
Another method is the laser photo-detachment, where a photon beam interact with the main beam, detaching the external electron, but at the moment doesn’t exist any cw laser with enough power
EURISOL Town Meeting

6. 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 = 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
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7. 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  B H- H0 2
Ions travel a finite distance before being stripped  angular spread 
Emittance growth
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8. 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

9. Fringe Fields Short rectangular magnets, small bending angle
Very weak focusing in both horizontal and vertical planes 
Chicane beam optics insensitive to dipoles fringe field shape
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10. EURISOL Splitter* LayoutH-
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, (2007)
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11. Stripper Foil
Necessary thickness to reduce unconverted H0 beam to a safe level (~50 W) estimated to be >=500 g/cm2
1 GeV A H0  the heat load is estimated 0.1 W  not serious heat load
Expected foil lifetime of several weeks
Promising candidate for such a thick foil: Carbon Nano-Tube (CNT) foil
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12. H- Beam Transport 3x2D Gaussian distribution simulated
εx, εy (norm. rms)
0,3 ·mm·mrad
εz (norm. rms)
0,4 ·mm·mrad
Current
4 mA
Macro particles
Bunch Frequency
176 MHz
3x2D Gaussian distribution simulated
Chicane aperture necessarily narrow  H- beam has a waist in both horizontal and vertical planes
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13. 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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14. H- - H0 Phase Spaces H- AT THE CHICANE OUTPUT H0 AT THE CHICANE OUTPUT
H0 AT THE FOIL INPUT
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15. H+ Beam Transport 3 x RMS envelope from the carbon foil to the target
H+ AT THE FOIL OUTPUT
3 x RMS envelope from the carbon foil to the target
Phase space at the foil output
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16. 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
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17. H- Transport Along 3 Splitters
1st chicane output
2nd chicane output
3rd chicane output
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18. 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
EURISOL Town Meeting