CEPC 650MHz High Efficiency Klystron R&D Zusheng ZHOU(周祖圣) Beihang Uniersity Sep. 2, 2016

Contents ■Design proposal ■R&D Progress ■Summary

Design proposal

(top parameters of D. Wang 20160329) CEPC Main Ring SRF parameters Parameters (top parameters of D. Wang 20160329) H (Pre-CDR) W Z 650 MHz cavity (bulk Nb) 5-cell 2-cell Cavity number 384 480 160 32 VRF (GeV) 7 3.65 0.82 0.13 Eacc (MV/m) 15.9 16.5 11.1 8.6 Q0 @ 2 K 4E10 2E10 Cryomodule number 96 80 16 Max. phase shift of 4+4 trains (deg) / 3.9 7.4 12.9 RF power c.w. / cavity (kW) 276 215 224* 254* Cavity number per klystron 2 2 / 4 Total klystron number 192 HOM power / cav. (kW) 3.6 0.8 0.4 Total RF power (MW) 106 104 36* 8* Total cav. wall loss @ 4.5 K eq. (kW) 22.2 24

(top parameters of D. Wang 20160329) CEPC Main Ring SRF parameters Parameters (top parameters of D. Wang 20160329) H (Pre-CDR) W Z 650 MHz cavity (bulk Nb) 5-cell 2-cell Cavity number 384 480 160 32 VRF (GeV) 7 3.65 0.82 0.13 Eacc (MV/m) 15.9 16.5 11.1 8.6 Q0 @ 2 K 4E10 2E10 Cryomodule number 96 80 16 Max. phase shift of 4+4 trains (deg) / 3.9 7.4 12.9 RF power c.w. / cavity (kW) 276 215 224* 254* Cavity number per klystron 2 2 / 4 Total klystron number 192 HOM power / cav. (kW) 3.6 0.8 0.4 Total RF power (MW) 106 104 36* 8* Total cav. wall loss @ 4.5 K eq. (kW) 22.2 24

Klystron output power (kW) 1 klystron power 2 cavities CEPC Main Ring RF Power source Baseline Considering klystron lifetime and power redundancy, 2 cavities will be powered with a CW klystron capable to deliver more than 800 kW. Parameters Value Operation frequency 650MHz+/-0.5MHz RF input power (kW) 280 CW（250） RF source number 160 Klystron output power (kW) 800 CW 1 klystron power 2 cavities

Klystron key design parameters Centre frequency (MHz) CEPC Main Ring RF Power source Klystron key design parameters Parameters Now Future Centre frequency (MHz) 650+/-0.5 Output power (kW) 800 Beam voltage (kV) 80 70 Beam current (A) 16 15 Efficiency (%) 65

Klystron key design parameters Centre frequency (MHz) CEPC Main Ring RF Power source Klystron key design parameters Parameters Now Future Centre frequency (MHz) 650+/-0.5 Output power (kW) 800 Beam voltage (kV) 80 70 Beam current (A) 16 15 Efficiency (%) 65 How to do?

Klystron key design parameters Centre frequency (MHz) CEPC Main Ring RF Power source Klystron key design parameters Parameters Now Future Centre frequency (MHz) 650+/-0.5 Output power (kW) 800 Beam voltage (kV) 80 70 Beam current (A) 16 15 Efficiency (%) 65 How to do? There are some R&D work supported by IHEP innovation funds.

R&D Progress

Klystron Schedule and strategy 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 beam tester, classical design and currently progressed design(higher efficiency design).

Short term Schedule

Klystron Schedule and strategy(2) Merits Saving the money Saving the time Possible to try 2 or 3 designs (1) Beam tester (2) #1 prototype (3) #2 prototype

Simulation Results using DGUN Triode gun（anode modulated）with f10 hole DGUN simulation result : Beam Diameter=17.8mm Current=15.12 A Perveance= 1.43 μA/V3/2 Vc =-81.5kV VMA=-48.0kV 1.77 kV/mm on Anode 3.94 kV/mm on BFE 2.51 kV/mm on M.Anode 54 mm 35.6 mm ０ 4 2 6 5 10 15 25 30 35 Cathode R(mm) Current Density (mA/mm2) 20

Simulation Results using EGUN Triode gun （anode modulated）with f10 hole EGUN simulation result : Beam Diameter=17.7mm Current=14.88 A Perveance= 1.41 μA/V3/2

Simulation Results using CST CST simulation result : Beam Diameter=17.7mm Current=14.88 A Perveance= 1.41 μA/V3/2

Simulation Results Comparison Electron Gun Vc =-81.5kV, VMA=-48.0kV Type DGUN EGUN CST Current(A) 15.12 14.88 Beam DIA(mm) 17.8 17.7 Perveance(μA/V3/2) 1.43 1.41

Simulation Results Comparison Magnet field Amplitude of magnetic field Bz on axis

Ripple rate = 8.0%

Beam Optics for Collector

Gun assembly with Drift Tube and Collector 500 1000 1500 2000 2500 4000 3500 3000 Z (mm) Solenoid

HV Gun Envelop for Electron Gun

Collector Design and Simulation Collector shape and beam dissipation optimization J collector optimization using universal beam spread curve collector optimization using EGUN code Analytic design Numerical design Collector Length 2147mm 1912mm Collector radius 210mm Total Beam power 1231kW 1230kW Capability of power density in collector 150W/cm2 Max power density in collector 197W/cm2 207W/cm2 Crosscheck of beam trajectory with EGUN and MAGIC

Collector Design and Simulation(2) Groove dimensions optimization Groove number Groove dimensions(a:b) Total water flow rate Water pressure loss for ideal smooth surface 180 1:2 1400kg/min 2.34E+4 Pa Contour of temperature and water pressure loss

Collector Design and Simulation(3) Collector Thermal analysis Groove structure for 2 meter tapered collector in Ansys-CFX contour of temperature on inner surface of copper domain contour of temperature of water domain

Collector Design and Simulation(4) Collector geometry of tapered part 2030mm A B C D E Geometry of collector tapered part Section A B C D E groove number 180 150 120 60 40

RF Section Design and Simulation The results of 1D code AJDISK indicate that the efficiency is 73% and the 1dB bandwidth is more than 2 MHz .

RF Section Design and Simulation(2) All six cavities have been designed and optimized using CST and HFSS. Input and output cavities electromagnetic field

RF Section Design and Simulation(3) The simulation results of two-cavity klystron in 1D-code AJDISK and 3D-code CST are in good agreement, which indicate that 3D simulation in CST is feasible. The results of two cavity klystron in CST

Current Status -Beam tester Concept Simulation Gun HV Seal Collector Drawing Gun HV Seal Drawing

Current Status -Beam tester The drawing has almost completed! It’s ready for manufacturing!!

Summary The design of the electron gun and collector has been completed; RF Section for classical design klystron is almost completed; Mechanical design for beam tester is also completed; Pushing procurement and manufacture for beam tester as soon as possible; Mechanical design for classical design klystron is about to begin. RF Section for high efficiency design klystron is about to begin.

Thanks for your attention!