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S バンド熱陰極高周波電子銃の現状 都大学・ S 京都大学・ バンド熱陰極高周波電子銃の現状 京 FEL 発振のための入射電力 ～ FEL 発振のための入射電力振幅 振幅・ ・位相 位相制御 制御～ ～ ～ Toshiteru Kii Kii Toshiteru Institute of Advanced Energy, Kyoto University Institute of Advanced Energy, Kyoto University Hideaki Ohgaki Ohgaki Hideaki Kai Masuda Kai Masuda Heisyun Heisyun Zen Zen Satoshi Sasaki Satoshi Sasaki Takumi Shiiyama Shiiyama Takumi 5 回 第 5 回高周波電子銃研究会 高周波電子銃研究会 第 Dec. 4, 2007 Dec. 4, 2007

1. introduction Purpose of KU- -FEL : FEL : Purpose of KU Purpose of KU-FEL : “Compact and Economical Compact and Economical “ “Compact and Economical MIR- -FEL Facility for Energy Science FEL Facility for Energy Science” ” MIR MIR-FEL Facility for Energy Science” bio / chemical / material research with advanced photon bio / chemical / material research with advanced photon bio / chemical / material research with advanced photon Example of applications using FEL Example of applications using FEL Example of applications using FEL Generation of sustainable energy source generation of clean energy of alcohol and/or H 2 from polluted gas source from H 2 O and CO 2 clean fuel クリーン燃料 Basic study of high-efficiency solar cells clean fuel H 2 C O 2 H 2 CO 2 CO 2 ( ( 水素) 二酸化炭素) H 2 ②自由電子レーザ ①自由電子レーザ clean fuel FEL FEL FEL FEL FEL クリーン燃料 CH 3 OH H 2 O Separation of DNA and/or RNA C H 3 O H H 2 C O H 2 O (水) ( メタノール) … Recycling accelerant 脱酸素触媒 酸素付加触媒 （安価な金属／金属酸化物触媒） … Fingerprint region of molecular Fingerprint region of molecular Fingerprint region of molecular … = MIR ( 2.5 ~ 10 = MIR ( 2.5 ~ 10 µ µ m ) m ) FEL = MIR ( 2.5 ~ 10 µ m ) FEL ③自由電子レーザ

Undulator Radiation vs. Electron Energy Undulator Radiation vs. Electron Energy Undulator Radiation vs. Electron Energy 19.0 µ m 20 ⎛ + ⎞ λ 2 K 18 ⎜ ⎟ λ ≈ u 1 ⎜ ⎟ γ r 2 16 ⎝ ⎠ Wavelength ( µ m) 2 2 13.2 µ m 14 K = 0.95 12 ⋅ ⋅ λ e B 10 = ≈ ⋅ λ 0 u K 93 . 36 B π ⋅ 0 u 2 m c 8 0 K = 0.17 4.7 µ m 6 4 3.3 µ m 2 20 25 30 35 40 Beam Energy (M eV) λ R : FEL radiation e : charge of the electron λ u : undulator period [m] m : mass of electron B 0 : undulator field [T] c : velocity of light γ : Lorenz factor

Arrangement of the KU- -FEL FEL Arrangement of the KU Arrangement of the KU-FEL Frequency S- -band band Frequency S Structure 4.5 cells Structure 4.5 cells µ sec ~5 µ Macropulse Macropulse sec ~5 Cathode LaB 6 ~1900 ºC (since Sep. 2007) Type Halbach Type Halbach Length Length 1.6 m 1.6 m Period Number 40 Period Number 40 Period 40 mm Period 40 mm Gap 25.5- -45 mm 45 mm Gap 25.5 Peak Magnetic Field 0.26- -0.045 T 0.045 T Peak Magnetic Field 0.26 K- -value value 0.99- -0.17 0.17 K 0.99

2. Thermionic RF gun Why therminonic RF gun? Compact, Easy to operate, inexpensive….. What is the demerits? Back-Bombardment problem cathode cathode RF RF power power

Problem in thermionic RF gun (1) Problem in thermionic RF gun (1) Back- Back -streaming electrons streaming electrons hit cathode. hit cathode. Cathode temperature increases. temperature increases. Cathode Current density on cathode surface Current density on cathode surface increases. increases. thermionic thermionic cathode cathode Time evolution of electron Time evolution of electron Time evolution of electron beam and input/reflected beam and input/reflected beam and input/reflected RF power RF power RF power Beam loading increases and then Beam loading increases and then resonant frequency of cavity changes. resonant frequency of cavity changes. Beam current becomes unstable. Beam current becomes unstable. Maximum pulse duration is limited to Maximum pulse duration is limited to at most several µ µ sec. (at the gun exit) sec. (at the gun exit) at most several

Problem in thermionic RF gun (2) Problem in thermionic RF gun (2) Cathode φ 6 mm T surface = 1000 ℃ Beam current after the bending magnet 0.08 0.06 CT3における電流量 (A) 0.04 ) A 0.02 ( t n 0.00 e r r u -0.02 c m -0.04 a e -0.06 B -0.08 -0.10 -6 -4 -2 0 2 4 6 Time ( µ sec) Sw eep (A T) Macro pulse duration after the bending Macro pulse duration after the bending magnet was less than 500 ns. magnet was less than 500 ns.

Evaluation of the back streaming electrons (1) Evaluation of the back streaming electrons (1) 1999~2001 1999~2001 Evaluating Method Evaluating Method 0-dimensional model modeling modeling Cathode surface temperature, T cathode cathode • cathode cathode • RF RF • heater heater • power power • 1st cavity • 1st cavity • electrons • electrons Heater P ｂ power, P h AT 4 BT Measure the Measure the surface temp. surface temp. by using IR by using IR thermometer thermometer

P heater P heater P heater P heater + +P P beam beam P heater P heater with beam without without beam beam Δ T av ~ 20 ° C 45sec

Comparison with PIC simulation KUBLAI 2.0 experimental evaluation (i) experimental evaluation (ii) 1.6 simulation 1 pps pps operation operation 1 Heater power : about 10 W Heater power : about 10 W 1.2 <P b > [W] 0.8 0.4 0.0 0 1 2 3 4 5 6 7 8 RF input [MW] Back- -streaming beam power was not negligible. streaming beam power was not negligible. Back

Evaluation of the back streaming electrons (2) Evaluation of the back streaming electrons (2) To estimate the time evolution of the cathode surface including the effect the effect To estimate the time evolution of the cathode surface including of the thermal conduction in the cathde cathde, 1 dimensional model was developed. , 1 dimensional model was developed. of the thermal conduction in the 2002 ~ present 2002 ~ present 1 dimensional model 1 dimensional model Cathode Cathode Q b (x, x,t t) ) Q b ( heater heater Back- Back -streaming streaming Q h Q electros electros h x x [ ] ⎛ = × − 8 ∂ ∂ C 5 . 67 10 J / sec/ m 2 ⎜ T T [ ] ρ = λ + τ ⎜ ρ = 3 C V Q ( x , ) 19000 kg / m ⎜ ∂ τ ∂ b [ ] 2 ⎜ λ = x 155 J / kg / K ⎝

2. energy compensation by controlling input rf amplitude Why therminonic RF gun? Compact, Easy to operate, inexpensive….. What is the demerits? Back-Bombardment problem Back-streaming electrons hit the cathode Surface temperature rises Beam current increases Input modulated RF power Beam loading increases Beam energy decreases Beam energy is kept constant Macropulse duration decreases Macropulse duration increases

RF amplitude modulation for beam energy compensation 10 9 14 % modulation 8 7 Power [MW] 6 5 Flat RF Modulated RF 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 Time [ µ sec]

Results 100 9.0 Flat RF Modulated RF 8.5 80 8.0 Energy [MeV] Current [mA] 60 7.5 40 7.0 Flat RF Modulated RF 20 6.5 6.0 0 3 4 5 6 7 0 1 2 3 4 5 6 7 8 9 10 Time [ µ sec] Time [ µ sec] Beam energy was Macropulse duration kept constant. was improved But phase advance was observed.

3. Phase compensation Origin of the phase advance Amplitude modulation Input rf Output rf Klystron voltage increases Electron velocity changes V k =148 kV V k =158 kV Schematic view of Klystron

600 Kly. Vol. 8 Klystron Voltage / 20 [kV] Beam Power [MW] Current [mA] 400 6 P in Phase advance I gun 4 in the macro pulse 200 2 P ref 0 0 420 0 5 10 15 Time [ µ s] 400 Phase [deg.] 380 V k =148 kV 330 degree 360 ~40 deg. 340 V k =158 kV 370 degree 320 300 280 -2 0 2 4 Time [ µ s]

Block diagram of the Phase Compensation Phase Compensation PS Kly#1 ~100dBm Gun S.G. 29dB -60dB ch.1 PC Phase Detector FG ch.2 -60dB ~103dBm Acc Kly#2 PS SG : Signal Generator PS : Phase Shifter FG : Function Generator PC : (Computer) ADC & DAC

Results (Amplitude & Phase modulation) Phase stability : < 2 deg. 420 144 400 Phase [deg.] 380 Phase [deg.] 142 360 140 ~40 deg. 340 ~2 deg. 138 320 300 136 280 -2 0 2 4 -2 0 2 4 Time [ µ s] Time [ µ s] Without Phase compensation With Phase compensation

Results (Amplitude & Phase modulation) Macro pulse duration@ FC2 830ns >>> 4.0 µ s 0.06 AM on, PM on AM off, PM off Current [A] 0.04 4.0 µ s 0.02 830 ns 0 0 2 4 Time [ µ s]

Results (Amplitude & Phase modulation) Energy distribution @FC2 AM = off, PM = off AM = on, PM = on

Results (Amplitude & Phase modulation) Energy distribution @ACC out 27 160 27 160 26 26 120 120 Energy [MeV] Energy [MeV] Current [mA] Current [mA] 25 25 80 80 24 24 23 40 23 40 22 22 0 0 21 21 -3 -2 -1 0 1 2 3 4 5 -3 -2 -1 0 1 2 3 4 5 Time [ µ s] Time [ µ s] Acc AM = off, Acc PM = off Acc AM = on, Acc PM = on

Results (Amplitude & Phase modulation) Energy distribution @ACC out 200 with Acc BL comp. Charge [a.u.] 150 w/o Acc 100 BL comp. 50 0 23 24 25 26 Energy [MeV]