1. Positron Source and Injector
Variola – LAL, Orsay
Elba Meeting 2011

2. Actual status with open points
Positron source
Scheme
Linac
To do List

3. Injector : 1) Positron source 2) Polarimetry 3) Linac lattice
4) Scheme
We lost the only researcher at (quasi) full time on SuperB. We are replacing him but needs time…

4. Preger – Guiducci Scheme
“new” scheme
THERMIONIC
GUN
SHB
0.6 GeV PC
0.7 GeV
BUNCH
COMPRESSOR
5.7 GeV e+
4.0 GeV e-
POLARIZED
SLAC GUN
B graded
S band
Sections
50 MeV e+ e-
combiner
DC dipole
0.2 GeV
300 MeV
CAPTURE
SECTION
Diag lina
Polarization, en spread
Emittance bunch length
0.6 GeV (safety)
Diag line
Energy, spread, beam size
current
monitor
Separator e+-e-
Bunch length
Emittance
250 MeV
matching
Moller polarimeter
4 GeV (straight line)
HE diag
Emittance,,En spread
Monitor
Size and position
En spread
Proposal for
Vacuum regions
We propose to stay with the SLAC gun in the positron line and to have a custom
Polarised, low charge electron sources in the electron line

5. Positrons (thanks to Freddy)
- 1) Target production and optimization
2) AMD vs QWT, Parmela, Geant4 and Astra ok
3) Polarization studies (Geant4) – not needed
4) Capture in 4 different scenarios :
S band acceleration + S band
S band deceleration + S band
L band deceleration + L band
L band TM020 deceleration + L band
5) Transport (FODO design) up to 1 GeV in the 4 cases
6) Coupling studies
7) GHz cavity design
8) TM020 cavity design : 4 cells will be prototyped in Aluminium
9) Comparison with Dafne source (~ok). Experiment soon?

6. RF in tanks
P.Lepercq (LAL) has calculated the Travelling Wave Fields in SuperFish and adapted them for ASTRA’s simulation:
Field line in a 6 cells TW cavity
2π/3 mode
Longitudinal field in a single tank (2.856 GHz):
Seen by ref. particle
25 MV/m
Adaptation and normalisation
P.Lepercq
1 tank = ~3.054 m

7. Realisations: Design Study of Travelling wave Section (1)
Design of RF structure (using Superfish)
Structure with 6 cylindrical cavities
Using TM020-2/3
Operating at 3 GHz
Design Parameters:
Cell dimensions: Rcell ~ 9 cm Lcell ~ 3.331cm
Irises dimensions: Riris=1.5 cm Liris= 0.8 cm
E-field TM020-2/3
Ez along z-axis
P.Lepercq

8. Design Study of Travelling wave Section (2)
3D Structure (Under study)
Structure will include reduced height waveguides for matching
The goal is to realize a low power demonstrator in aluminum material (and if it is ok a copper one)
S11 (dB)
Mode 
Mode 0
Mode 2/3
HFSS Simulation
Simulations show the good separation of the TM020 -2/3
E.Mandag

9. Target Yields Studies Target Geant 4 simulation (O. Dadoun – LAL): 1.7
If we increase the energy of the drive beam, the positron yield goes up.
For a 600 MeV e- beam, the optimum yield is 1.7 e+/e- with a W-target thickness of 1.04 cm
O.Dadoun

10. Stress and thermal effects
PEDD
@200 MeV Pedd J/g/e-
@ 300 MeV Pedd J/g/e-
@ 500MeV Pedd J/g/e-
6.6e10*5 = e- (10nc 5 bunch)
So (max limit 35 J/g)
200 MeV on a PEDD= 0.55J/g
300 MeV on 0.85 J/g
500MeV 1 J/g
AVERAGE deposited energy:
@200 MeV 52.5 MeV/e- 300 MeV MeV/e- 500MeV 120 MeV/e-
Tungsten density g/cm3
So for the different cases in a cubic cm target we have to multiply for 25 (Hz) and ~20 (density)
So in the worst case (500 MeV) we have 160W (70 and Not so hard to cool
O.Dadoun

11. The ACS Accelerating / Deceleration
depending on the type of RF cavities within the ACS
1st scenario = GHz full acceleration
2nd scenario = GHz deceleration + acceleration
3rd scenario = GHz deceleration + acceleration
4rd scenario = combination of RF types (using 3 GHz TM020 mode for deceleration and GHz TM010 for downstream acceleration).

12. Recap 4 Scenarios under investigation Scenario 1 2 3 4
25MV/m for acceleration
Scenario 1 2 3 4
RF (MHz) – strategy
acc
2856 – dec
(S-band)
1428 – dec
(L-band)
3000 dec acc
Mean Energy (MeV)
302
287
295
333
Erms (MeV)
21.4
32.3 (12)
16.83 (9.09)
5.2 (3.2)
Zrms (mm)
2.7
6.4
8.89
3.5
Xrms (mm)
3.8
4.4
8.0
8.1
X’rms (mrad)
1.02
1.11
1.69
1.4
Ex =X’X (mm.mrad)
4.6
13.0
11.4
Total Yield (%)
2.8
7.53
32.3
31.9
Yield ±10MeV (%)
1.3
3.9
19.6
29.3
With a positron injection of 10 nC and a yield of 3.9%, we will have positrons at 300 MeV ±10MeV (scenario 2 – 2.8 GHz)

13. End of 1st Tank – 3000 MHz Length of 1st tank = ~2.93 m
Scenario 4
Length of 1st tank = ~2.93 m
Cell length= 3.331cm
Tank Phase f1= 280o
Tank Gradient G1=10MV/m
Gaussian Fit sz = m
Energy (MeV)
Energy (MeV)
Z (m)
Z (m)

14. Layout Example Up to ~1050 MeV
Acc. Cavity GHz, Peak gradient= 13MV/m
3 GHz 10 MV/m
Fodo cells
38  ~160 m
Solenoid 0.5 T
0.534.1 m
Matching section
34.3 ~38 m

15. At end of the fodo accelerating section
3.0 GHz tank (deceleration), ~1050 MeV
At ~160 m, after the target.
At exit of last cavity, Particles within a cut radius:
Energy (MeV)
Yield (e+/e-)
Total yield
Yield ± 10 MeV
1050 ±10 MeV
Radius (m)
Z (m)
240 pC
F.Poirier

16. Further studies at 1 GeV Example from 1.428 GHz (scenario 3)
Emittance matching
En Spread matching
Coupling correction
Linearization
Matching with the transfer line
Injection in DR
Y (m)
X (m)
Cross-plane Coupling !!!
use cross plane correction

17. Use of SW 4.284GHz cavities for longitudinal beam shaping
New idea - Linearization in `TM 012/030 L Band (but can work also in S…)
Use of SW 4.284GHz cavities for longitudinal beam shaping
At the exit of 1st cavity
Eavr = 954.7MeV
dE = 22.4MeV
At the exit of 3rd cavity
Eavr = 927.3MeV
dE = 14.9MeV
At the exit of the Conventional Linac
Eavr = MeV
dE = 26.4 MeV
At the exit of 5th cavity
Eavr = 898.1MeV
dE = 8.4MeV
At the exit of 7th cavity
Eavr = 868.8MeV
dE = 5.6MeV
Feasible, but $
and cavities.
Can be interesting for S band, but see before…
Thalia.Xenophontos

18. LINAC

19. First order linear design for the main linac, considerations.
Exit from the damping ring :
H plane => e =
a = 0.47
b = 11.81
V plane => e =
a = 0.52
b =16.14
Use of commercial Qpoles

20. Tested:
Both quadrupoles
1 / 2 / 3 SLAC cavity period 3,5 / 7 / 10,5 m
Doublet lattice
Best solution found => 2 cavity period FODO, ~ 4.5 T/m
Matching line simple (3 quads)

21. Period, 2 Slac S Band cavities / EMQO-01-200-340
Beam envelope. Final energy 5 GeV
H Pascal

22. Non exhaustive to do list

23. SIMULATIONS :
6) Main Linac
1) L Band Scheme, positron capture
- C band solution?
- Coupling compensation
- Validation of the geometry (distance between cavities, integration of Qpoles, diagnostics and pumps)
- Emittance matching in the damping ring
- L Band solution with 1.5 cm aperture cavities (to increase the gradient)
- Full tracking simulation
- Hybrid Linac (starting from the end change the L Band with S Band)
- Alignment errors
- Matching section after the Transfer line
2) S Band Scheme, positron capture
- Check that the actual FODO can provide transport for 0.2 and 1 GeV (new Preger and Guiducci scheme)
- Capture with 1.5 and 2 cm aperture
- Final linearization with 0.9, 1.5 and 2 cm aperture. Cavities in TM 012 or 030 modes
7) Electron source
- Deceleration with large aperture
- Gun (recover the SLAC results)
3) Possible experiment on DAFNE Linac with deceleration
- 200 MeV Linac simulation
- Matching and deflector for 0.2 and 1 GeV beams
4) GeV drive beam Linac for positron production (based on DAFNE Linac design?)
- Diagnostics and polarimetry
8) Damping ring
5) Positron target
- Injection and injection losses
- PEDD from 10 to 16 nC
- Thermal budget from 10 to 16 nC
- Neutrons

24.  TECHNICAL DESIGN
RF design and prototyping
L Band cavity with 1.5 cm aperture (grad maximization)
S Band cavity with 1.5 and 2 cm aperture
TM 012,030 cavities for linearization (s band and L?)
Prototyping: TM020 L band, High gradient L band, Large aperture S band, Linearization S Band.
QWT Engineering
Design and pulsed magnet engineering
Vacuum chamber and permanent magnet
Vacuum
Vacuum design for all the linacs systems, integration
RF system
Rf klystrons for S and L band
Sled (L band design)
Network
Integration of everything!!!

25. Conclusions 1) Scheme ready (guns?...)
2) A lot of work has been done to find a cheap solution
3) Technical constraints must be solved by prototyping. $?
4) We miss manpower (end of the year +1). Other French labs? Frascati or Italy? Who else?
5) Also at the Lab support level we need a project.
We are ready to pursue our effort but in a well defined scheme and with the necessary manpower
Thanks to everybody providing me slides