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 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

Pulsed Beam Option intermediate extraction energy p,d rfq chopper 2-gap SC linac 1 GeV Fast deflector <3 MeV/A 88-176-352 MHz 176-352 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

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

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

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 EURISOL Town Meeting

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 EURISOL Town Meeting

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

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 EURISOL Town Meeting

EURISOL Splitter* Layout H- 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) EURISOL Town Meeting

Stripper 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 Promising candidate for such a thick foil: Carbon Nano-Tube (CNT) foil EURISOL Town Meeting

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 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

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 EURISOL Town Meeting

H- - H0 Phase Spaces H- AT THE CHICANE OUTPUT H0 AT THE CHICANE OUTPUT H0 AT THE FOIL INPUT EURISOL Town Meeting

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 EURISOL Town Meeting

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

H- Transport Along 3 Splitters 1st chicane output 2nd chicane output 3rd chicane output EURISOL Town Meeting

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