1. SuperB Injector (2)
R. Boni, INFN-LNF - on behalf of the “Injector Study Group”
SuperB Mini-MAC, Frascati July, 2008
D. Alesini, R. Boni, F. Marcellini, M. Preger, P. Raimondi, C. Vaccarezza, INFN-LNF.
J. Seeman, SLAC
SuperB

2. Preliminary conclusions of the Biodola-Meeting (31/05-04/06, 2008)
for the SB Injector…
S-band, 100 Hz, room-temperature linac, recycling (a.m.a.p.)
PEP2 hardware (i.e. damping rings, dipoles, TL, etc …)
2) Use of Polarized Gun
Use of Damping Rings for both e- and e+ beams
The SB-Linac is a quasi-continuous injection machine:
topping-up filling time: ≈ 12 sec per ring per min. ≈ 24 sec per min.
SuperB Mini-MAC, Frascati July, 2008

3. GOAL Talk Summary To reduce the topping-up injection time ,..
… that is … to increase the average luminosity
Talk Summary
1. Injector layout
e+/e- injection process (damping rings & by-pass line)
Electron gun
Laser system
5. Kickers
6. Parameters
SuperB Mini-MAC, Frascati July, 2008

4. 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.
SuperB Mini-MAC, Frascati July, 2008

5. e+/e- INJECTION PROCESS
1 μsec
SLED RF PULSE
✦ 2 bunches, ≈ 50 nsec apart, are emitted by a SLC-type polarized electron gun, illuminated by laser pulses at the rep. rate of 100 Hz.
✦ the bunches have different charge (1 nC and 0.1 nC), 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 GeV Linac
[three bunches are accelerated simultaneously down the SLC injector ….]
SuperB Mini-MAC, Frascati July, 2008

6. …… 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 GeV 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.
SuperB Mini-MAC, Frascati July, 2008

7. ✦ Spin Rotator is needed to avoid depolarization in the electron DR
…… 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
SuperB Mini-MAC, Frascati July, 2008

8. Kickers timing t < ΔT ≈ …… e+/e- INJECTION PROCESS ……cont.d
20 ÷ 30 nsec
t < ΔT
Kickers timing t ≈
SuperB Mini-MAC, Frascati July, 2008

9. 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
SuperB Mini-MAC, Frascati July, 2008

10. … example of by-pass configuration
…. 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.
SuperB Mini-MAC, Frascati July, 2008

11. … alternative by-pass configuration:
…. BY-PASS LINE [ e+/e- INJECTION PROCESS ……] …cont.d
… alternative by-pass configuration:
✦ to avoid depolarization if the by-pass introduces a degradation. ≈
SuperB Mini-MAC, Frascati July, 2008

12. … alternative by-pass configuration:
…. 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
capture section ≈
SuperB Mini-MAC, Frascati July, 2008

13. …… 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 GeV linac, up to 7 and 4 GeV respectively.
SuperB Mini-MAC, Frascati July, 2008

14. PEP2 Damping Rings SuperB Mini-MAC, Frascati 16-17 July, 2008
A 1.2 CeV 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
SuperB Mini-MAC, Frascati July, 2008

15. 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
(± 5mm, i.e. 30 psec)
175 psec e- e+
SuperB Mini-MAC, Frascati July, 2008

16. ELECTRON GUN laser light input 7 x 1010 electrons in 1 nsec q ≈ 11 nC
Based on the SLC polarized electron source:
✦ DC gun,
✦ GaAs derivative photocathode,
✦ 800 nm laser,
✦ SHB bunching,
laser light input
GaAs photocathode
SLC polarized Gun
- 120 kV
7 x 1010 electrons in 1 nsec
q ≈ 11 nC
I ≈ 11 A
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
SuperB Mini-MAC, Frascati July, 2008

17. … 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 GaAs photocathode can be also considered; no SHB needed;
[J.Clendenin et al., SLAC-PUB-11526, Oct. 2005]
SuperB Mini-MAC, Frascati July, 2008

18. LASER SYSTEM Feasible … !!
✦ the bunches have different charge (1 nC and 0.1 nC), due to different laser beam energies.
Feasible … !!
Laser
oscillator
Transport
PBS
PBS
Laser
amplifier
P-pol
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 )
SuperB Mini-MAC, Frascati July, 2008

19. POSITRON SOURCE beam power = E . N . e- . fHz NLC PS FRASCATI PS 20.2
Int.l Conf. on High Energy Particle Accelerators, 1995
FRASCATI PS
beam power = E . N . e- . fHz
Parameter
SLC-94
NLC-II
SuperB
E (GeV) 30
6.22 3
N of particles
3.5 x 1010
113 x 1010
6 x 1010
Rep.rate (Hz)
120
100
Beam power (kW)
20.2
134
2.9
SuperB Mini-MAC, Frascati July, 2008

20. CONVENTIONAL DEVICE … POSITRON SOURCE … cont.d
High Gradient (25-27 MV/m)
S-band Capture Section with
focusing solenoids
Adiabatic matching device +
flux concentrator of ~ 6÷7 T peak field
CONVENTIONAL DEVICE
SuperB Mini-MAC, Frascati July, 2008

21. 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 kV
5 ns
SuperB Mini-MAC, Frascati July, 2008

22. … injection-Extraction Kickers …cont.d
30 nsec
✦ The SuperB-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.
Kickers parameters: scaling from DAFNE (at constant deflection)
DAFNE MeV
Deflection Θ mrad 1 m)
HV kV
Kicker length L mt.
Plates distance d cm
Pulse width nsec Θ
Lm·VkV
EGeV·dcm
DEFLECTION
10 Hz
SuperB Injector GeV 3 GeV
Deflection Θ mrad 5 mrad
HV kV kV
Kicker length L mt 6 mt.
Plates distance d cm 5 cm
Pulse witdh ≈ 30 nsec ≈ 30 nsec
100 Hz
SuperB Mini-MAC, Frascati July, 2008

23. … injection-Extraction Kickers …cont.d
Input ports
Output
ports
(LOAD)
Strip ceramic supports
BEAM
Tapered stripline
Elliptical cross section
HV feedthrough
DAFNE KICKERS
SuperB Mini-MAC, Frascati July, 2008

24. RF Linacs Layout e- > 7 GeV e+ > 4 GeV 16 RF Stations
SuperB Mini-MAC, Frascati July, 2008

25. RF Linac Main Specs. N° of RF power stations 36
N° of accelerating sections
108
Klystron output peak 100pps
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 kW
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.
SuperB Mini-MAC, Frascati July, 2008

26. e-/e+ Production Capability
Main rings particles/bunch
nb =
Particles injected for topping-up at
90% of peak luminosity
ni =
Efficiency of e+ transport from PS
η+ ≈ 0.9
N. of positrons after PS
N+ =
N. of electrons at the PS
(e-/e+ conversion 3 GeV ≈ 10%)
N-PS =
q-PS = 10 nC
Electron transport efficiency
η- ≈ 0.9
N. of e-/bunch from the Gun for
e+ production
N-G =
q-G = 11 nC
Gun current/bunch
11 A (1 nsec)
“LER + HER” re-filling time
(1251 bunches per ring)
≈ 12 sec
Time between ≈ 90% of Lpeak
≈ 42 sec
SuperB Mini-MAC, Frascati July, 2008

27. ! t t … about the topping-up time …. ≈ 12 sec Linac RF Rings RF = 6
DR’s RF
= 4
main rings filling
4.2 nsec
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.
DR’s filling t
≈ 6 sec
≈ 4.2 sec
The LASER system is
more tricky but still feasible !
SuperB Mini-MAC, Frascati July, 2008

28. e-/e+ production with injection of “ twin bunches”
50 nsec
Main rings particles/bunch
nb =
Particles injected for topping-up at
95% of peak luminosity
ni =
Electron Gun current/shot
5.5 A (1 nsec)
“LER + HER” re-filling time
(1251 bunches per ring)
≈ 6 sec
Time between ≈ 95% of Lpeak
≈ 21 sec
SuperB Mini-MAC, Frascati July, 2008

29. Established and firm points ……
✦ Room-temperature linac
✦ GHz – 100 Hz, with SLAC-type acc. structures
✦ 60 MWpeak RF power sources
✦ Damping Rings for both electrons and positrons
✦ e+ 3 GeV
✦ Use of a SLC-like polarized gun
SuperB Mini-MAC, Frascati July, 2008

30. 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
SuperB Mini-MAC, Frascati July, 2008