Activities on FEL Development and Application at Kyoto University

Transcription

1 Activities on FEL Development and Application at Kyoto University China-Korea-Japan Joint Workshop on Electron / Photon Sources and Applications Dec. 2-3, SINAP, Shanghai Kai Masuda Inst. Advanced Energy, Kyoto Univ.

2 KU-FEL Development History 1998: KU-FEL development started. CUP K-J exchange program started. 2002: 40 MeV acceleration. 2004: FEL facility re-built. 2006: Undulator installation. 2008: (Mar.) FEL lasing. 2008: (May) FEL saturation. Asian Core exchange program started. 2010: A user station constructed User stations under construction.

3 Kyoto Univ. Free Electron Laser (KU-FEL) MIR-FEL & e-beam for applications in energy sciences Wavelength range: achieved μm target μm thermionic rf gun slit energy filter bunch compression 9 MeV accelerator tube MeV beam dump mirror undulator mirror

4 Thermionic RF Gun employs a thermionic cathode in rf accelerating structure, produces electron bunches bright enough for MIR-FEL, drive rf power <10 MW GHz <10 μsec <10 Hz thermionic cathode rf resonant cavities thermionic cathode mount

5 Thermionic RF Gun employs a thermionic cathode in rf accelerating structure, produces electron bunches bright enough for MIR-FEL, with such advantages as: much higher E-field than DC gun bunched beams without buncher photocathode & laser not required moderate vacuum requirement micropulse rate as high as 2.9 GHz with a disadvantage of: electron back-bombardment onto the thermionic cathode thermionic cathode rf resonant cavities micropulses ~psec time a macropulse ~μsec, ~Hz

6 Back-Bombardment in the Thermionic RF Gun is seen to result rapid increase of beam current which induces energy drop. We need modulation of drive rf power P in (both amp. and phase) to compensate it. Macropulse Current [ma] experimental B.-B. effect x2 micropulses ~psec a macropulse ~μsec time phase modulation of P in 10% P in amp. modulation of P in e-beam rf gun

7 Feedforward Control of RF Amp. & Phase M.O. 2856MHz Phase Shifter Phase Shifter 200W amplifier 500W amplifier TV2019B6 Klystron No.1 PV-3030A1 Klystron No.2 Δφ depends on Gain RF Gun Accelerator Tube rf-gun bunch phase detection acc. Function Generator Out Phase Detector Ref. Test PC Oscillo -scope Out Phase Detector Test Ref. bunch phase depends on increasing beam current

8 Electron Beam & FEL Properties at Present Electron Beam Properties energy 24 MeV rms emittance 3.5πmm mrad rms energy spread 0.8 % macropulse length 5.5 μsec macropulse current 115 ma peak current ~40 A FEL Properties wavelength μm spectral width (FWHM) 1% macropulse energy 5 mj macropulse length 1 μsec macropulse power 5 kw coherent length (FWHM) 200 μm coherent time (FWHM) 350 fsec peak power ~5 MW long-term stability (FWHM) 15% Further R&Ds are needed for: improved FEL stability, and extended wavelength range

9 Back-Bombardment in the Thermionic RF Gun is seen to result rapid increase of beam current which induces energy drop. We need modulation of drive rf power P in (both amp. and phase) to compensate it. The modulation, ΔP in and/or dp in /dt, gives the macropulse length limitation. Macropulse Current [ma] x2 ΔP in, dp in /dt micropulses ~psec a macropulse ~μsec time phase modulation of P in amp. modulation of P in 10% P in rf gun e-beam have been developed to keep energy and micropulse spacing constant.

10 Choice of Thermionic Cathode Material may mitigate the problem, because power deposition by electrons depends, temperature rise depends, and increase of extraction current depends on cathode material. ΔT ΔJ Calculated ΔT & ΔJ by Electron Bombardment CaB 6 LaB 6 CeB 6 PrB 6 GdB 6 Energy kev ΔT K ΔJ Acm -2 ΔT K ΔJ Acm -2 ΔT K ΔJ Acm -2 ΔT K ΔJ Acm -2 ΔT K ΔJ Acm We plan experimental evaluation of CeB 6

11 Triode RF Gun Upgrade of the Existing Gun Addition of a short-gap rf cavity provides a novel RF gun structure, what we call Triode RF gun, without need of modification of existing gun body. Simulation suggests >80 % reduction of electron back-bombardment, by optimal choice of phase & amplitude to the short-gap rf cavity, with minimal modification of drive rf power circuit. A prototype has been developed, and rf coupler design is under way. klystron WG/COAX converter phase shifter 0-20dB variable attenuator rf window 10 MW 20dB coupler 100 kw rf window coaxial cable <40 kw short-gap rf cavity rf gun e-beam

12 KU-FEL Upgrade Scheduled Next Year BPMs for beam feedback control Under way Cs 2 Te, BNL AUG 2011 FEB 2011 Undulator Parameter Comparison present new length [m] # of periods period [mm] min. gap [mm] max. field [T] max. K Optical cavity needs to be rearranged. Design will be presented by Mr. Ueda.

13 Why Mid-Infrared FEL? O H(stretch) 2.8μm N H(stretch) 3.0μm C H(stretch) 3.4μm C = O(stretch) 5.8μm C = C(stretch) 6.1μm N H(rotation) 6.5μm C H(rotation) 7.3μm H C H(scissors) 6.8μm.. Fingerprint region Si C : 12.6μm Si H : 11.2μm Si N : 10.4μm Si O : 9.8μm selective excitation/breaking of chemical bonds Surface treatment, processing, soft annealing high conversion efficiency PV cell, long-life FC, etc..

14 Interaction between Phonon & Electron may affect the electrical and physical properties of wide band-gap semiconductors, e.g. SiC, TiO 2, ZnO, for such applications as photocatalyst, solar cell and power device. lattice vibration FEL C.B E selective excitation of phonon by FEL PL hω hν hν Phonon Atom To be studied in terms of PL & resistivity measurements V.B k

15 PL Measurement System Filter FEL He-Cd He-Cd Laser(325 レーザー nm, ( nm, 445 nm) nm) PE 60 mm Pipe Elliptic mirror cryostat PL measurement box Filled box with N2 50 cm Flat mirror Transport line Ellipse mirror PL analysis He-Cd Laser He-Cd レーザー PL Parabolic mirror FEL 40 cm Parabolic mirror cryostat 70 cm

16 Photon- & Nano-Technology Research Facility Budget provided by MEXT FY2010 ultracentrifugation PL spectroscopy high-speed li chromatogra laser system for photocathode in-air photoemission spectroscopy ICP atomic em spectrometry Nd:YAG 263nm 100 pulses scanning prob microscope FEL transport line

17 Summary Energy compensation methods against backbombardment in thermionic rf-gun was developed μm MIR-FEL with peak power of 5 MW was achieved. The goal (stability, 5-20 μm or more) needs further R&Ds. Electron beam feedback control system is to be development. Photocathode system & new undulator will be installed next year. Thermionic cathode material investigation is under way. Triode rf-gun, proof-of-principle experiments will be started. PL spectroscopy system with MIR-FEL is ready for phonon-electron interaction study in semiconductors. Other user stations are under construction.