CEPC RF Power Source System Zusheng Zhou zhouzs@ihep.ac.cn Institute of High Energy Physics, Chinese Academy of Sciences CEPC international workshop November 12-14, 2018

Outline Design consideration R&D Progress Summary Collider Booster Linac injector R&D Progress Design goal 1st prototype fabrication High efficiency design Summary

Introduction Injector 10GeV Energy Ramp 10-45/120GeV Electron High power RF sources are required to provide the energy needed to accelerate particles or keep particles energy stable. Positron Booster C=100km CEPC Booster SppC Three rings in the same tunnel： Collider & Booster SppC Collider Ring C=100km CEPC Collider 45/120 GeV

Collider The Collider beam power is more than 60 MW. The increase in efficiency of RF power sources is considered a high priority issue. RF power sources - efficiencies Tetrodes IOTs Klystrons SSA Magnetrons DC–400MHz (200–1500)MHz 300 MHz – 1 GHz DC – 20 GHz GHz range 1 MW 1.2 MW 1.5 MW < 1MW 85% - 90% (class C) 70% 65% 60% 90% Remark Broadcast technology, widely discontinued Oscillator, not amplifier! High power klystrons are the more attractive choice because of their high efficiency, low cost and more stable than IOT and SSA for CEPC collider.

Much higher efficiency, less energy consumption. Collider System overall efficiency CEPC Collider SRF Wall Plug Efficiency Wall to PSM power supply/modulator 95% Modulator to klystron 96% Klystron to waveguide 70% Waveguide to coupler Coupler to cavity ~100% Cavity to beam Overall efficiency ~60.6% The critical factor is klystron efficiency Much higher efficiency, less energy consumption.

CEPC at 800 RMB/MWh and 6000 hours/year Collider Efficiency impact on operation cost (Only considering operation efficiency of klystrons) CEPC at 800 RMB/MWh and 6000 hours/year Save Money 130M RMB 1 year 90 M RMB Excessive electricity bill, M RMB NOW Efficiency, % COMING FUTURE

Coupler input power(kW) Collider Transmission system Superconducting Cavity power demands Parameters Value Freq.(MHz) 650+/-0.5 Cavity No. 240 Coupler input power(kW) 300 Considering klystron lifetime, power redundancy and cost, the 2 cavities will be powered with one CW klystron capable to deliver more than 800 kW. Distribution of RF power (800kW) to the cavities (300kW), including waveguide, power divider, phase shifter, circulator and load. Other Auxiliary PS, Interlock and Controls, LLRF, Pre-amplifier.

Collider Transmission system Schematic of the RF Transmission System (RFTS)

Collider High efficiency klystron The vast majority of the existing commercial klystrons in the electronic efficiency range between 40% and 55 %. Only a few klystron available on the market are capable of operating with about 65 % efficiency or above. In a recent theoretical calculation，more than 80% RF power conversion efficiency is achieved in CW klystron. Considering this recent high efficiency approach, our design goal is to achieve around 80% on saturation point. CEPC Klystron Key Design Parameters Parameters Units Values Centre frequency MHz 650±0.5 Output power kW 800 Efficiency(Goal) % 80(70 linear)

Collider PSM Power supply PSM Design Parameters Parameters Units Values High voltage kV 130 Current A 16 Module quantity   168 Module voltage V 800 Module switch frequency Hz 1k Module number of redundancy 9 Voltage stability % < 0.2 Efficiency >95 Turn-off time us <5 Stored energy J <20

Collider Infrastructure Collider Power Source Gallery Klystron and transmission system are placed underground. PSM high voltage power supply and related auxiliary power supply are on the ground.

Collider Infrastructure For space savings, transmission system in part are placed in RF tunnel.

Booster Introduction The Booster RF system consists of 1.3 GHz superconducting RF cavities. There are 12 cryo-modules for Higgs operation, each containing eight 9-cell superconducting cavities. These cavities need 96 set 1300 MHz power sources.

Booster Power source choice-SSA Their capabilities extend from a few kW to several hundred kW, and from less than 100 MHz to above 1 GHz. Reasonable efficiency (~50%), high gain, and modular design provide high reliability. High reliability for redundancy design, high flexibility for module design, high stability, low maintenance requirements, absence of warm-up time and low voltage operation and reasonable efficiency. So the SSA has been chosen for the Booster RF power source system.

Booster Solid state amplifier 1.3 GHz/25kW SSA Specifications Parameters Values Frequency 1.3 GHz Power 25 kW Gain ≥65 dB Bandwidth (1dB) ≥ 1 MHz Amplitude stability ≤0.1% RMS Phase stability ≤0.1°RMS Phase Variation ≤10° Harmonic < -30 dBc Spurious < -60 dBc Efficiency at 25kW ≥45% MTBF ≥30000 h Redundancy 1 power module failure

Booster RF Transmission system

Linac injector Introduction The main high power RF components are 75 units of 80 MW S-band klystrons and conventional solid state modulators. A waveguide system is used for power transmission from the klystrons to the accelerating structures, 75 klystrons are used to provide power for 288 accelerating structures.

R&D Progress Strategy and plan Progress of 1st prototype fabrication 650MHz/800kW meets CEPC project demands >80% efficiency Progress of 1st prototype fabrication Beam dynamic, beam optics and cooling system Mechanical design, infrastructure preparation Design progress on high efficiency klystron Optimization using different methods Multi-Beam Klystron consideration

Strategy and plan (2016 to 2021) 3 or more klystron prototypes 2016 2017 2018 2019 2020 2021 Prototypes Step1 1st 4th Step2 2nd 5th Step3 3rd 6th more

Progress of 1st prototype development Conventional method based on 2nd harmonic cavity in order to investigate the design and manufacture technologies for high power CW klystron Design Parameters Main parameters Goal Freq. (MHz) 650 Vk (kV) -81.5 Ik (A) 15.1 Perveance (µP) 0.65 Efficiency (%) >60 Output power (kW) 800 1dB bandwidth (MHz) ±0.5

Dynamics for 1st tube 1D optimization on the dynamics and cross checked by 2D &3D 1D AJDISK 73% efficiency 2D EMSYS 68% efficiency 3D CST 65% efficiency

Electron beam trajectory without RF drive Gun design Results for beam optics using different codes and thermal-structure analysis using ANSYS Main parameters DGUN EGUN MAGIC2D CST Design goal Beam waist radius (mm) 17.8 17.48 17.64 17.5 Perveance (µPerv) 0.64 0.65 Current density <0.45 0.39~0.43 <0.5 Current uniformity 9.8% <10% Beam optics Thermal deformation Electron beam trajectory without RF drive Beam profile shows laminar flow Ripple rate < 5%

On-axis magnetic field Focusing coils Designed by 2D and cross checked by 3D, very good consistency obtained 15 regular coils with 1 bucking coil near the gun 2D solenoid model 3D solenoid model On-axis magnetic field

Cavity chain and it’s cooling system RF design and cooling analysis conducted Grooved nose cone for each cavity to suppress the multipacting effect Grooved nose cone Cavity chain Cooling pipes distribution Temperature distribution cavity chain cooling scheme

Collector and window ~2m long collector to sustain 1.23MW full beam power Thermal load distribution Temperature distribution Mechanical design >800 kW sustainable CW RF power and <1.05 VSWR @ 650±0.5MHz Temperature distribution Mechanical design

Mechanical design progress 3D model and 2D drawings are ready for manufacturing 3D model 2D drawings

165 pages Klystron body

Collector Oil tank Coils

Infrastructure preparation The contract of new big furnace has been signed last month and construction period is less than 8 month. All the procedures for the construction of the plant have been completed. Construction period is less than 4 month. Dimension of main building

High efficiency design Schemes of 3 designs Scheme 1：Optimize cavity chain by using the same gun as 1st tube Scheme 2: With high voltage gun (110 kV/9.1 A), low perveance Scheme 3：MBK, 54 kV/20 A electron gun Parameter Scheme1 Scheme2 Scheme3 Freq. (MHz) 650 Voltage (kV) 81.5 110 54 Current (A) 15.1 9.1 20(2.5×8) Beam No. 1 8 Perveance (µP) 0.65 0.25 1.6(0.2×8) Efficency (%) >70 ~80 >80 Power(kW) 800 800(100×8)

Tentative Scheme 1 Same gun with the 1st tube Optimization 8 CAV/1 2nd harmonic CAV/80%/3.1m 10 CAV/2 2nd harmonic CAV/80%/2.9m 8 CAV/2 2nd harmonic CAV and 1 3rd harmonic CAV/80%/2.2m

Tentative Scheme 2 Based on CSM，with 2nd and 3rd harmonic cavities Better bunching with shorter length AJDISK/EMSYS/CST 86%/81%/77% Reduce beam aperture and beam size KLYC 1D/ KLYC 2D/ EMSYS 82.6%/80.8%/81%

Tentative Scheme 3 Based on CSM, with 2nd and 3rd harmonic cavities Perveance is 0.2 µPerv CSM: 8 CAV / 2.4m / 88.5% CSM: 7 CAV / 1.8m / 87.6% 650MHz 1300MHz 1950MHz

Summary Design of RF power sources for collider, booster and linac is showed; The increase in efficiency of RF power sources is considered a high priority issue; All drawings of the 1st prototype has finished and it is being processed and manufactured in the machine shop; The three different schemes for the high efficiency klystron design are ongoing simultaneously and more prototypes will be manufactured in the near future.

Thanks for your attention!