1. Status of the CLIC Injector studies
CLIC beam physics meeting
Status of the CLIC Injector studies
Positron chain optimization, Cafer Bayar’s work
Cost reduction for 380 GeV stage
Drive beam electron source news
LCWS 2017, Strasbourg, France, Steffen Doebert, CERN, BE-RF
Cafer Bayar 19 November 2014

2. The CLIC Injector Complex
CLIC beam physics meeting
The CLIC Injector Complex
We have designed and optimised the beam transport and acceleration from the target to the pre-damping ring.
The goal of the study is to maximize the positron yield accepted by the pre-damping ring.
C. Bayar
Cafer Bayar 19 November 2014

3. Previous studies: The Pre-Injector Linac
CLIC beam physics meeting
Previous studies: The Pre-Injector Linac
The total yield: e+/e e+/e e+/e e+/e- (effective) e+
Target
AMD
Solenoid
TW Structures
The effective yield : (-20,20) degrees in phase and (150,250) MeV in energy
Total yield: 0.93 e+/e-
Effective yield: 0.48 e+/e-
Total yield: 0.89 e+/e-
Effective yield: 0.50 e+/e-
Parameters of the accelerating structures in the Pre-Injector linac
Acceleration
Deceleration
Parameters
Unit
Value
Cell length cm 5
Frequency
GHz 2
Phase advance per cell π
2/3
Average axial electric field
MV/m 15
C. Bayar
Cafer Bayar 19 November 2014

4. CLIC beam physics meeting
PREVIOUS STUDIES: OPTIMIZATION IN THE PRE-INJECTOR LINAC
The decelerating mode creates a second peak in the phase spectrum.
For the optimization, a phase of 40 degrees after maximum deceleration is optimum.
Optimized Decelerating mode
Accelerating mode
Decelerating mode
C. Bayar
Cafer Bayar 19 November 2014

5. CLIC beam physics meeting
PREVIOUS RESULTS: PRE-INECTOR LINAC
The effective yield : (-20,20) degrees in phase and (150,250) MeV in energy
The optimised decelerating mode result in almost a factor two higher yield compared to the accelerating mode which has a yield of 0.5 e+/e.
C. Bayar
Cafer Bayar 19 November 2014

6. Previous studies: Injector Linac
CLIC beam physics meeting
Previous studies: Injector Linac
CDR
Positron yield, 𝑒 + / 𝑒 − , is increased by a factor of 2.5.
Energy acceptance → 1%: → yield: 𝑒 + / 𝑒 −
All positrons are within 1% acceptance window of the pre-damping ring.
C. Bayar
Cafer Bayar 19 November 2014

7. OLD positron source in CDR
CLIC beam physics meeting
OLD positron source in CDR
We have removed parallel stations and bunch compressor due to the optimization of the pre-injector linac
C. Bayar
Cafer Bayar 19 November 2014

8. CLIC beam physics meeting
Preliminary new Pre-Injector Linac results at 5 GEV OPTION
CLIC beam physics meeting
5 GeV option (previous)
5 GeV option (new)
The effective yield : (-20,20) degrees in phase and (150,250) MeV in energy
Energy (GeV)
Target exit
(e+/e-)
AMD exit
Total yield (e+/e-)
Effective yield (e+/e-)
5 (new)
7.14
3.06
1.36
1.21
5 (previous)
8.00
2.80
1.09
0.98
5 (CDR)
2.10
0.95
0.38
*Positrons at the target exit are generated for 3 GeV and 5 GeV options by Yanliang Han
C. Bayar
Cafer Bayar 19 November 2014

9. CLIC beam physics meeting
Preliminary new Pre-Injector Linac results at 3 gev OPTION
3 GeV option
In 3 GeV option, the effective yield is around 0.44 e+/e-.
The effective yield : (-20,20) degrees in phase and (150,250) MeV in energy
Energy (GeV)
Target exit
(e+/e-)
AMD exit (e+/e-)
Total yield (e+/e-)
Effective yield (e+/e-)
3 (new)
4.18
1.38
0.50
0.44
5 (new)
7.14
3.06
1.36
1.21
5 (previous)
8.00
2.80
1.09
0.98
5 (CDR)
2.10
0.95
0.39
Work in progress !
C. Bayar
Cafer Bayar 19 November 2014

10. CLIC beam physics meeting
Conclusions
Positron yield at the entrance of the pre-damping ring within acceptance window: 0.97 e+/e-
Positron yield at the entrance of the pre-damping ring is increased by a factor 2.5 compared to the CLIC CDR
This result allows to reduce the beam current or energy of the electron driver linac.
It provides significant cost savings for electron driver linac, need to cost the different options
A single target station can be used for the first stage of CLIC at 380 GeV
C. Bayar, A. K. Ciftci, S. Doebert and A. Latina, “Design and Optimisation of the Positron Production Chain for CLIC from target to the Damping Ring”, Nuclear Inst. and Methods in Physics Research, A. Reference: NIMA 59959, 7 July 2017.
DOI:
C. Bayar
Cafer Bayar 19 November 2014

11. Cost evaluation update Main assumptions
New Parameters: E= 380 GeV, N= (at IP?), Nb= 352
PDR for electrons not needed
Use 2 GHz bunch spacing through out the complex, shorter rf pulses in linac’s and no need for delay loop
No lower energy running. One rf pulse length and charge only
Optimise timing of the beams to gain efficiency (Pulse Compressor optimisation) Consequence will be ~ 4 us offset between electrons and positrons
Investigate to use booster linac as positron driver (saves positron driver) Not investigated yet
Factor of 2 improvement in positron capture and transport

12. Igor’s PC study
Have to be optimized for new pulse length, see following

13. Rf-module cost model
Typical 2 GHz rf module including accelerators and beam line
Acc 1
Acc 2
Acc 3
Acc 4
Quad
BPM
Mod
Pulse compressor
Kly 1
Kly 2
50 MW, 8 ms
Power depends on pulse length needed

14. Cost per linac 500 GeV Total 716 MCHF
Energy Gain (MeV)
Bunch charge (10^9)
rf pulse length (ns)
Power per structure (MW)
Loaded gradient (MV/m)
Configuration (structure/2 klystrons)
No of rf modules
pulse compressor gain
No of structures
Length (m)
Energy gain per module
Cost
e- pre-injector
200
7.8 64 18 3
8.0 30 81
7920
e+ pre-injector 20 82 15 2 5
9.0 40 45
11663
injector linac
2660 11 50 14 1
127.0
300 42
136480
positron drive linac
5000
112
223.0
400
261240
booster linac
6140
7.3 72 16
128
2-2.3
256.0
473 48
298560
Total 716 MCHF
Keep gradient constant, reconfigure structure plumbing and add klystrons
Almost factor 2 more rf power
Not optimized for the 500 GeV machine

15. Cost per linac 380 GeV 428 MCHF Positron capture linac 1 m structure
Energy Gain (MeV)
Bunch charge (10^9)
rf pulse length (ns)
Power per structure (MW)
Loaded gradient (MV/m)
Configuration (structure/2 klystrons)
No of rf modules
pulse compressor gain
No of structures
Length (m)
Energy gain per module
Cost
e- pre-injector
200 6
600 90 20 4 2
4.4 7 14
120
5830
e+ pre-injector
20-40
102 15 19 60
11660
injector linac
2660
2x600 83 18 3 33
2.7 99
194 81
87120
positron drive linac
5000 42
167
326
122430
booster linac
6140
5.6 75 76
228
445
200640
428 MCHF
Positron capture linac 1 m structure
~ 300 klystrons

16. Cost summary Injector linac savings: 288 MCHF
314 instead of 624 klystrons  MW power savings
Could consider only one positron target and pre-injector linac.
Electron PDR + delay loop: ~ 150 MCHF ? Consequence: need excellent emittance from polarised electron source likely possible but would need some R&D

17. Drive beam source parameters
Baseline
Beam energy
140 keV
Beam current
5 to 7 A
Pulse length
140 µs
Emittance (RMS)
< 20 mm mrad
Repetition rate
50 Hz
Beam power
4,9 to 6,9 kW
Shot to shot charge variation
0.1 %
Flat top charge variation
0.1 % after correction
Studied in collaboration with CEA/CESTA

18. LEETCHI Low Energy Electrons from a Thermionic Cathode at High Intensity
HVPS
Capacitor
Voltage
divider
HV deck
OTR window
Dump
Current transformer
Gun
Solenoid
Implemented at CERN

19. LEETCHI

20. Simulations Solenoid Current transformer Diode OTR 45 mm 412 mm 119 mm

21. Comparison between experimental results and simulations
Excellent agreement between experiment and simulations !

22. Comparison between experimental results and simulations
CST Tracking
simulations
Is = 5.4 A
Is = 5.6 A
Is = 5.8 A
Spectacular agreement between experiment and simulations !

23. Picture of the cathode CPI YU156
Pierce electrodes
Picture of the cathode CPI YU156
Small grid
Mesh size 160 x 160 µm
20 mm
Large grid
Mesh size 1.5 x 3.0 mm
45-degree-angle view

24. Cathode grid effects Small grid Electron beam Cathode Anode Large grid
Equipotential
lines
Cathode
Anode
Large grid

25. Cathode grid effects 4.5 A, Is = 6.4 A 0.5 A, Is = 5.6 A
Serious emittance degradation due to the cathode grid. According to simulation this can be mitigated by changing the grid thickness and the cathode – anode distance

26. Conclusions
Excellent and very successful collaboration between CEA and CERN on drive beam electron source !
Significant cost savings could be achieved for the 380 GeV machine
Improvements in the positron chain studied and still ongoing
Injector continue to be a low priority for CLIC studies

27. End

28. Cathode and connector

29. Injector timing Injector linac e+ e- 1100 ns (CDR)  4000 ns e- e+ e-
Booster linac
Positron production pulse
3300 ns
1100 ns ?

30. 2 GHz accelerating structure
Parameter
Value
Frequency
1998 MHz
Structure length (30 cells)
1.5 m
Shunt impedance
54.3 – 43.3 MW/m
Average group velocity c
Filling time
389 ns
Average aperture a
17 mm
Taper amax – amin
20 – 14 mm
Cell size b mm
Group velocity vg/c
2.54 – 0.7 %
Cell Length and iris thickness
50 mm, 8 mm
2p/ 3 traveling wave, should be damped eventually