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

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

Previous studies: The Pre-Injector Linac CLIC beam physics meeting Previous studies: The Pre-Injector Linac The total yield: 8.0 e+/e- 2.8 e+/e- 1.09 e+/e- 0.98 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

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

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

Previous studies: Injector Linac CLIC beam physics meeting Previous studies: Injector Linac CDR Positron yield, 0.97 𝑒 + / 𝑒 − , is increased by a factor of 2.5. Energy acceptance → 1%: → yield: 0.39 𝑒 + / 𝑒 − All positrons are within 1% acceptance window of the pre-damping ring. C. Bayar Cafer Bayar 19 November 2014

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

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

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

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: http://dx.doi.org/10.1016/j.nima.2017.07.010 C. Bayar Cafer Bayar 19 November 2014

Cost evaluation update Main assumptions New Parameters: E= 380 GeV, N= 5.2 109 (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

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

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

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 1300-1700 64 18 3 2.3-2.5 8.0 30 81 7920 e+ pre-injector 20 82 15 2 5 9.0 40 45 11663 injector linac 2660 11 3600-4000 50 14 1 127.0 300 42 136480 positron drive linac 5000 112 223.0 400 261240 booster linac 6140 7.3 1700-2000 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

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

Cost summary Injector linac savings: 288 MCHF 314 instead of 624 klystrons  12-15 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

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

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

LEETCHI

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

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

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 !

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

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

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

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

End

Cathode and connector

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

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 0.0145 c Filling time 389 ns Average aperture a 17 mm Taper amax – amin 20 – 14 mm Cell size b 64.3-62.9 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