B Injector 2 Super R Boni INFNLNF on
B Injector (2) Super R. Boni, INFN-LNF - on behalf of the “Injector Study Group” Super. B Mini-MAC, Frascati 16 -17 July, 2008 D. Alesini, R. Boni, F. Marcellini, M. Preger, P. Raimondi, C. Vaccarezza, INFN-LNF. J. Seeman, SLAC Super. B
Preliminary conclusions of the Biodola-Meeting (31/05 -04/06, 2008) for the SB Injector… 1) S-band, 100 Hz, room-temperature linac, recycling (a. m. a. p. ) PEP 2 hardware (i. e. damping rings, dipoles, TL, etc …) 2) Use of Polarized Gun 3) Use of Damping Rings for both e- and e+ beams 4) The SB-Linac is a quasi-continuous injection machine: topping-up filling time: ≈ 12 sec per ring per min. ≈ 24 sec per min. Super. B Mini-MAC, Frascati 16 -17 July, 2008
GOAL 1. To reduce the topping-up injection time , . . … that is … to increase the average luminosity Talk Summary 1. Injector layout 2. e+/e- injection process (damping rings & by-pass line) 3. Electron gun 4. Laser system 5. Kickers 6. Parameters Super. B Mini-MAC, Frascati 16 -17 July, 2008
INJECTOR SCHEMATIC LAYOUT e+ 4 Gev e- 7 Gev It is proposed to contemporary inject electrons and positrons in the respective rings. This can be carried out by means of simultaneous acceleration of both e- and e+ along the linac. A reduction of the rings filling time can be therefore achieved. Super. B Mini-MAC, Frascati 16 -17 July, 2008
e+/e- INJECTION PROCESS ✦ 2 bunches, ≈ 50 nsec apart, are emitted by a SLC-type polarized electron gun, illuminated by laser pulses at the rep. SLED rate of RF 100 PULSE Hz. ✦ the bunches have different charge (1 n. C and 0. 1 n. C), due to different laser beam energies. ✦ the lower charge bunch induces weaker wake-fields in the accelerating sections, therefore it travels ahead. ✦ leading and trailing bunches are accelerated down the 1. 2 Ge. V Linac 1 μsec [three bunches are accelerated simultaneously down the SLC injector …. ] Super. B Mini-MAC, Frascati 16 -17 July, 2008
…… e+/e- INJECTION PROCESS ……cont. d ✦ the leading low-charge bunch is injected, by a stripline kicker, into the e- DR; ✦ meanwhile, an electron bunch is extracted from the DR and injected into the linac by a kicker, 50 nsec before the arrival of the high-charge bunch; ✦ the trailing high-charge bunch goes straight into the 2 Ge. V linac and is sent to the positron target. ✦ the previous bunch, in turn, will be extracted after 10 msec (3 damping times) and injected into the linac, 50 nsec before the arrival of the next high-charge bunch. Super. B Mini-MAC, Frascati 16 -17 July, 2008
…… e+/e- INJECTION PROCESS ……cont. d ✦ Spin Rotator is needed to avoid depolarization in the electron DR K K ✦ Spin direction is longitudinal when exits the Gun ✦ Spin direction must be perpendicular to the horizontal plane when the bunch enters the DR Super. B Mini-MAC, Frascati 16 -17 July, 2008
…… e+/e- INJECTION PROCESS ……cont. d 20 ÷ 30 nsec t < ΔT Kickers timing t ≈ Super. B Mini-MAC, Frascati 16 -17 July, 2008
BY-PASS LINE [ e+/e- INJECTION PROCESS ……] ✦ the low-charge bunch is deflected, with a stripline kicker, into the by-pass line and re-injected into the linac with a delay Δ; ✦ meanwhile, a positron bunch, generated by the PS, travels through a S-band section up to rejoin with the by-passed e- bunch. L by-pass BY-PASS length = L + Δ 50 nsec - Δ Super. B Mini-MAC, Frascati 16 -17 July, 2008
…. BY-PASS LINE [ e+/e- INJECTION PROCESS ……] …cont. d … example of by-pass configuration ≈ L ≈ 23÷ 24 mt. with Δ ≈ 10 nsec BPL ≈ L + 3 mt. Super. B Mini-MAC, Frascati 16 -17 July, 2008
…. BY-PASS LINE [ e+/e- INJECTION PROCESS ……] …cont. d … alternative by-pass configuration: ✦ to avoid depolarization if the by-pass introduces a degradation. ≈ Super. B Mini-MAC, Frascati 16 -17 July, 2008
…. BY-PASS LINE [ e+/e- INJECTION PROCESS ……] …cont. d … alternative by-pass configuration: ✦ low charge bunches go straigth through a 5 mm hole of the positron target ✦ high-charge bunches move transversely ≈ 1 cm with a pulsed bump and hit the target ✦ the produced e+ move back to the center line before the capture section ≈ Super. B Mini-MAC, Frascati 16 -17 July, 2008
…… e+/e- INJECTION PROCESS ……cont. d ✦ the trailing positron bunch is kicked into the e+ DR and damps for 10 msec; ✦ meanwhile, a damped positron bunch is kicked-out the DR and injected into the linac, 40 nsec behind the electron bunch; ✦ both e- and e+ bunches are accelerated down the 3 Ge. V linac, up to 7 and 4 Ge. V respectively. Super. B Mini-MAC, Frascati 16 -17 July, 2008
PEP 2 Damping Rings A 1. 2 Ce. V DAMPING RING COMPLEX FOR THE STANFORD LINEAR COLLIDER, G. E. FISCHER, W. DAVIES-WHITE, T. FIEGUTH, H. WIEDEMANN Stanford Linear Accelerator Center SLAC-PUB 3170, July 1983 Super. B Mini-MAC, Frascati 16 -17 July, 2008
IMPORTANT REQUIREMENT for By-Pass and DR TL’s To position the bunches at the correct accelerating phase, the length of BP and DR TL’s must be finely tuned (± 5 mm, i. e. 30 psec) 175 psec e+ e- Super. B Mini-MAC, Frascati 16 -17 July, 2008
ELECTRON GUN Based on the SLC polarized electron source: ✦ ✦ DC gun, Ga. As derivative photocathode, 800 nm laser, SHB bunching, The Polarized Electron Gun for the SLC D. C Schultz, J. Clendenin, J. Frisch, E. Hoyt, L. Klaisner, M. Woods, D. Wright, M. Zolotorev Stanford Linear Accelerator Center, SLAC-PUB-5768, March 1992 laser light input 7 x 1010 electrons in 1 nsec q ≈ 11 n. C I ≈ 11 A Ga. As photocathode - 120 k. V SLC polarized Gun Super. B Mini-MAC, Frascati 16 -17 July, 2008
… ELECTRON GUN. . cont. d ✦ 2 bunches, 50 nsec apart, are emitted by a SLC-type polarized electron gun, illuminated by laser pulses, followed by SHB systems; ✦ RF guns with Ga. As photocathode can be also considered; no SHB needed; [J. Clendenin et al. , SLAC-PUB-11526, Oct. 2005] Super. B Mini-MAC, Frascati 16 -17 July, 2008
LASER SYSTEM ✦ the bunches have different charge (1 n. C and 0. 1 n. C), due to different laser beam energies. Feasible … !! Laser oscillator PBS Laser amplifier P-pol Transport PBS 50 ns ell-pol QWP 50 ns delay S-pol PBS = polarizer beam splitter (reflects s-polarization and transmits p-polarization) QWP = quarter wave plate (produces an elliptical pol. to control the two pulses intensity) ( courtesy C. Vicario ) Super. B Mini-MAC, Frascati 16 -17 July, 2008
POSITRON SOURCE NLC PS Int. l Conf. on High Energy Particle Accelerators, 1995 beam power = E. N. e-. f. Hz Parameter SLC-94 NLC-II Super. B E (Ge. V) 30 6. 22 3 N of particles 3. 5 x 1010 113 x 1010 6 x 1010 Rep. rate (Hz) 120 100 Beam power (k. W) 20. 2 134 2. 9 FRASCATI PS Super. B Mini-MAC, Frascati 16 -17 July, 2008
… POSITRON SOURCE … cont. d High Gradient (25 -27 MV/m) S-band Capture Section with focusing solenoids CONVENTIONAL DEVICE Adiabatic matching device + flux concentrator of ~ 6÷ 7 T peak field Super. B Mini-MAC, Frascati 16 -17 July, 2008
Injection-Extraction Kickers ✦ The process of the injection/extraction of e-/e+ bunches into/from the DR’s/BP requires the use of stripline kickers. ✦ High performance fast kickers have been already developed (DAFNE) or designed (ILC). ✦ In DAFNE, fast stripline kickers allow to inject the bunches without perturbing the adjacent ones. 45 k. V 5 ns Super. B Mini-MAC, Frascati 16 -17 July, 2008
… injection-Extraction Kickers …cont. d ✦ The Super. B-Injector does not need very fast kickers. Kicker pulses with 10÷ 15 nsec rise/fall time and 10 nsec flat-top should be OK for the purpose. 30 nsec Kickers parameters: scaling from DAFNE (at constant deflection) DAFNE Deflection Θ HV Kicker length L Plates distance d Pulse width Super. B Injector Deflection Θ HV Kicker length L Plates distance d Pulse witdh 510 Me. V 5 mrad (5 mm @ 1 m) 45 k. V 1 mt. 10 Hz 5 cm 5 nsec 1. 2 Ge. V 5 mrad 45 k. V 2. 4 mt 5 cm ≈ 30 nsec DEFLECTION Θ 3 Ge. V 5 mrad 45 k. V 6 mt. 5 cm ≈ 30 nsec Lm·Vk. V EGe. V·dcm 100 Hz Super. B Mini-MAC, Frascati 16 -17 July, 2008
… injection-Extraction Kickers …cont. d Input ports Strip ceramic supports Elliptical cross section DAFNE KICKERS HV feedthrough BEAM Output ports (LOAD) Tapered stripline Super. B Mini-MAC, Frascati 16 -17 July, 2008
RF Linacs Layout 16 RF Stations 20 RF Stations e- > 7 Ge. V e+ > 4 Ge. V Super. B Mini-MAC, Frascati 16 -17 July, 2008
RF Linac Main Specs. N° of RF power stations 36 N° of accelerating sections 108 Klystron output peak power @ 100 pps 60 MW (4 μsec) Input RF power per acc. section 50 MW (1 μsec) Average accelerating gradient [unloaded] 23. 5 MV/m Total average kly RF power 800 k. W Total wall-plug modulator power ≈ 3 MW Total wall-plug Injector power (incl. DR’s) ≈ 6 MW Total injector length ≈ 400 m. Total RF active length 324 m. Super. B Mini-MAC, Frascati 16 -17 July, 2008
e-/e+ Production Capability Main rings particles/bunch nb = 5. 5. 1010 Particles injected for topping-up at 90% of peak luminosity ni = 5. 5. 109 Efficiency of e+ transport from PS η+ ≈ 0. 9 N. of positrons after PS N+ = 6. 1. 109 N. of electrons at the PS N-PS = 6. 1. 1010 q-PS = 10 n. C (e-/e+ conversion efficiency @ 3 Ge. V ≈ 10%) Electron transport efficiency η- ≈ 0. 9 N. of e-/bunch from the Gun for e+ production N-G = 6. 8. 1010 q-G = 11 n. C Gun current/bunch 11 A (1 nsec) “LER + HER” re-filling time (1251 bunches per ring) Time between injections @ ≈ 90% of Lpeak ≈ 12 sec ≈ 42 sec Super. B Mini-MAC, Frascati 16 -17 July, 2008
… about the topping-up time …. t ≈ 12 sec main rings filling The simultaneous injection of more than 2 bunches at a time … can be studied. It would allow to reduce even more the re-filling time. 4. 2 nsec DR’s filling 4. 2 nsec t ≈ 6 sec t ≈ 4. 2 sec Linac RF Rings RF =6 Linac RF DR’s RF =4 The LASER system is more tricky but still feasible ! Super. B Mini-MAC, Frascati 16 -17 July, 2008
e-/e+ production with injection of “ twin bunches” 50 nsec Main rings particles/bunch nb = 5. 5. 1010 Particles injected for topping-up at 95% of peak luminosity ni = 2. 7. 109 Electron Gun current/shot “LER + HER” re-filling time (1251 bunches per ring) Time between injections @ ≈ 95% of Lpeak 5. 5 A (1 nsec) ≈ 6 sec ≈ 21 sec Super. B Mini-MAC, Frascati 16 -17 July, 2008
Established and firm points …… ✦ Room-temperature linac ✦ S-band @ 2. 856 GHz – 100 Hz, with SLAC-type acc. structures ✦ 60 MWpeak RF power sources ✦ Damping Rings for both electrons and positrons ✦ e+ production @ 3 Ge. V ✦ Use of a SLC-like polarized gun Super. B Mini-MAC, Frascati 16 -17 July, 2008
Matters requiring R&D and/or “Study-Groups” ✦ DR’s injection-extraction : kickers, spin-rotators, TL length tuning, … ✦ By-pass line : kickers, length tuning ✦ Electron Gun : use a copy of the SLC gun or develope a new one ? ✦ Laser system ✦ TIMING & BEAM DIAGNOSTICS Super. B Mini-MAC, Frascati 16 -17 July, 2008
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