CEPC RF Power Sources System Zusheng Zhou(周祖圣) On behalf of RF Power Source System Institute of High Energy Physics Nov. 7, 2017

Contents ■Design proposal ■R&D High Efficiency klystron development Collider RF Source Booster RF Source Linac RF Source ■R&D High Efficiency klystron development ■Summary

Collider SRF Parameters: CEPC-Collider Cavity Type 650MHz 2-cell Cavity number 336 Coupler input power 300 (kW) (Higgs mode) The CEPC collider SRF system consists of 336 2-cell cavities. A minimum transmitter power of 300 kW to cavity coupler is required to meet the sum of the radiated, HOM and reflected power demands .

Collider RF Source Parameters: CEPC-Collider Klystron Type 650MHz CW Klystron number 168 Klystron output power 800 kW Considering the klystron operation lifetime, power redundancy, transmission losses and linear operation region, a single 800 kW klystron amplifier will drive two of collider cavities through a magic tee and related circulators, phase shift and loads.

Collider RF Unit: (Collider RF Unit 1 of 168) Schematic of the RF Power source system A Magic Tee is needed to split the power to the two 2-cell cavities. One of the cavity feed line consists of a phase shifter. A CW 800 kW circulator and load is installed to protect klystron.

Collider Klystron: The acquisition of high efficiency of RF power source for CEPC project is a key issue. As of now, a CW/long pulsed tubes which are relatively low perveance has a range up to 60-65%. Considering the recent high efficiency approach, our goal is set to be the efficiency of around 80% and tried to manufacture a klystron prototype in China.

Collider Klystron: Because of klystron efficiency is more than 80%, in order to fulfill this program, there may have following problems: 1) No experience and no related infrastructure on this kind of klystron; 2) Design and simulation are not enough and matured; 3) Let’s start from classical design to higher efficiency design.

Collider Merits Saving the money Saving the time Possible to try 2 or 3 designs Klystron: Classic RF cavity section (1) #1 prototype (2) #2 prototype High Efficiency RF cavity section

Module switch frequency Collider PSM Power supply: Schematic diagram Specification Parameters Unit Value High voltage kV 120 Current A 15 Module quantity   168 Module voltage V 800 Module switch frequency Hz 1k Voltage stability % < 0.2 Efficiency >95 Turn-off time us <5 Stored energy J <15 Because klystron parameters are not final determined, the design of high voltage and current of PSM are only preliminary.

Amplitude stabilization Collider Lower Lever RF system: Schematic diagram Specification Parameters Value/Unit Phase stabilization 0.1deg (rms) Amplitude stabilization 0.1% (rms) Tuner range >200kHz Piezo range >500Hz Signal number 20 channel

Booster SRF Parameters: H W Z 1300 14.1 4.4 3.4 15% 9% 3% 96 64 32 RF frequency [MHz] 1300 Input power (peak) / cavity [kW] 14.1 4.4 3.4 RF power duty factor 15% 9% 3% Cavity number 96 64 32 The CEPC Booster RF system consists of 1300 MHz superconducting RF cavities. There are 12 cryo-modules, each containing eight 9-cell superconducting cavities. These cavities need 96 sets of 1300 MHz power sources on Higgs mode.

Booster RF Power source choice: Different possible alternatives, klystron, solid state amplifier(SSA) and IOT et al. Compared with vacuum tube, SSA is much high reliability for redundancy design, high flexibility for module design, low maintenance requirements, absence of warm-up time and low voltage operation. Compared with IOT, SSA is much stable and less costly. The efficiency of SSA is also reasonable. So the SSA is priority selection for CEPC booster RF power system.

Booster SSA Parameters: Value Frequency 1.3 GHz Power >25 kW (pulsed and CW) Gain ≥65 dB Bandwidth (1 dB) ≥ 1 MHz Amplitude stability ≤0.1% RMS Phase stability ≤0.1°RMS Efficiency ≥45% The mean time between failures (MTBF) should be larger than 30,000 hours, and less than 5% of the power modules fail per year.

Booster RF Transmission and LLRF:

Linac The CEPC Linac is a 500 m long S-band Linac with maximum electron and positron beam energy of 10 GeV. The main high power RF components of the CEPC Linac are composed of 74 units of 80 MW S-band klystrons and conventional solid state modulators.

Linac RF Unit: 74 klystrons are used to provide power for 287 accelerating structures 1 klystron for 2 accelerating structures (3 sets) 1 klystron for 4 accelerating structures (others)

Linac S Band 80MW Klystron: Parameters Value Frequency 2856 MHz Output power 80MW Pulse width 4μs Voltage 350 kV Current 416 A Efficiency 55% Based on existed S band 65MW klystron applied in BEPCII Linac, the BAC method will be adopt to increase the klystron efficiency from 40% to 55%.

Schematic of the solid state modulator Linac Parameters Value Peak voltage 400kV Peak current 420A Pulse length ~6µs Voltage stability ±0.1% Peak power 160MW Pulse flatness ±0.25% Solid State Modulator: Schematic of the solid state modulator

R&D 1: 650MHz/800kW CW klystron development for CEPC Collider demands.

R&D 1: 650MHz/800kW CW klystron development for CEPC Collider demands. The design of the electron gun and collector has been completed; RF Section for classical design klystron is completed; Mechanical design for classical design klystron is about to begin. RF Section for high efficiency design klystron is almost completed. Fabrication for high efficiency klystron will be discussed.

R&D 1: 650MHz/800kW CW klystron development for CEPC Collider demands. We also form a joint institute with local government and Company: GLVAC Industrial Technology Research Institute of High Power Devices.

R&D 1: 650MHz/800kW CW klystron development for CEPC Collider demands. High efficiency klystron collaboration team will be established including IHEP, IE, THU and GLVAC et al. We have got more than 10M RMB budget to push this kind of high efficiency klystron development.

R&D 2: 2856MHz/80MW Pulsed Klystron Development for CEPC Linac demands. The 80MW klystron will be development from existed 65MW klystron made in China. The operation time of 1st 65MW domestic klystron is more than 45,000h. The 3 new domestic klystrons are installed in BEPCII Linac in this Summer.

R&D 2: 2856MHz/80MW Pulsed Klystron Development for CEPC Linac demands. The design of high efficiency RF cavity section is almost completed. We are planning to apply IHEP Innovation & Development Funding to support it in near future. We hope it will be fabricated based on 65MW klystron in Chinese company.

Summary The RF Power sources system of CEPC Collider, Booster and Linac are described; RF distribution system will be discussed with Division of Facilities Operation and Maintenance; 650MHz/800kW klystron development are key mission in near future; We are also pushing 2856MHz/80MW klystron fabrication base on 65MW klystron in Chinese company.

Thanks for your attention!