Review of RF photoinjector for radiation chemistry. Univ. Tokyo A. Sakumi, M. Uesaka, Y. Muroya, Y. Katsumura

Transcription

1 Review of RF photoinjector for radiation chemistry Univ. Tokyo A. Sakumi, M. Uesaka, Y. Muroya, Y. Katsumura

2 Application for ultra-short pulse Radiation Chemistry experiments

3 Application for ultra-short pulse Radiation Chemistry experiments Final target! 0 1fs 1ps 1µs Physical stage Energy deposition Physicochemical stage Ionization&Excitation Recombination Thermalization Reorganization Chemical stage Inhomogeneous spur reactions - diffusion&reaction control

4 Radiation Chemistry Pulse radiolysis method Chemical reaction of water NERS U. Tokyo Y. Muroya et al.,

5 Requirements Pulse radiolysis in a time range of sub-picosecond I Ultra-short bunch and laser II Stable synchronization III Intense electron bunch For Pumping beam For Probe beam Short pulse Single beam, low dark current High intensity Short pulse Synchronization to pumping beam Tunable wavelength fs laser(ti:sapphire laser) + Photocathode RF gun Suitable combination

6 18L Linac Compressor THG Precise Synchronization System at UTNS BS (50%) Laser transport line Compressor Beam-Material Interactions Laser photocathode RF gun Accelerating Tube Chicane Cherenkov Radiator Master Oscillator 119MHz 50Hz x 1/5 Digitex RF x 4 To Streak Camera To Pulse Selector x 6 Trigger Pulse x 1/6 3DB Klystron 15MW Timing Stabilizer at 9th Harmonics Ti:Sapphire Oscillator with Kerr Lens Mode-Locker Fs Ti:Sapphire Laser System Diode Pump Laser Stretcher Fs Streak Camera Multi-pass Amplifier Regenerative Amplifier with Pulse Selector Temperature control within 0.1 deg, Clean room (class : 10,000)

7 Measurement system Beam-Material Interactions Laser (265nm) Linac PD1 PD2 Shutter1 (On/Off) Sample Delay stage BPF( nm) Shutter2 (On/Off) (UV ) VIS IR (<300 -) nm FC White light cell (D 2 O) Dielectric mirror; elimination of 795nm Fs laser (795nm) OPA

8 Preliminary Pulse Radiolysis; 795 nm Beam-Material Interactions Condition l / mm Charge Beam size Pulse width Wavelength Average Time resol. Results - O.D. still low Intensity [a.u.] H 2 O&1M H + 20 mm nC 4mm 7ps 64 30ps I 0 I Charge 795nm H 2 O 5 mm nC 4mm 3ps 16 9ps Charge [a.u.] In In ps H2O 1M H Time /ps ps Time [ps]

9 Time behaviors of e aq - at 700nm Results l /mm O.D. S/N Dose Time resol. /ps Pulse radiolysis using white light continuum Gy 12-13ps Gy 6-7ps Gy 4-5ps Gy <4ps Beam-Material Interactions Optical path : 10 mm 5 mm 2 mm 1 mm Time /ps Time resol. /ps 12.2ps Good agreement 7.2ps 5.2ps 3.2ps Time resolution: δ total δ total δ diff + (δ E 2 + δ L 2 + δ sync 2 ) 1/2 Dominant factor δ diff due to refractive index n= ps ps ps <4ps Time /ps

10 Improvement of the e-beam Beam-Material Interactions Comparison with conventional linac Charge Beam size Dose/shot Pulse width Conventional linac Long-pulse mode Single-pulse mode 8~20nC 0.5~0.6nC 15x6mm 4mm 30~50Gy 7~8Gy ns 10ps Photocathode In 2000 Current 0.8~1.0nC 1.7~2.0nC 4mm 3mm 13~15Gy >40Gy 7ps 3ps Dominant factors for time resolution (1) <3ps : pulse width of EB (2) 100fs : pulse width of laser Not so bad (3) <1ps : synch. jitter (4) 10ps /10mm : Δt EB-L in H 2 O Thinner cell, but OD High-Brightness EB

11 Femtosecond electron beam and femtosecond pump-probe experiment in Osaka University Osaka Univ. pulsed radiation Analyzing light time Stroboscopic Method

12 Osaka Univ. A new concept of equivalent velocity spectroscopy for studies of ultrafast electron-induced reactions Femtosecond laser light Femtosecond electron beam Ionization Excitation Relaxation of Vibration Energy Relaxation of Electronic Energy cos 1/n sample n as fs Thermalization of Electron ps ns us Reaction of intermediate Radical Ion, Electron, Excited State, Radical, ms s Final Product Temporal distribution of 98 fs electron bunch measured by the streak camera at 0.17 nc Transient absorption kinetics of hydrated electrons measured in water at wavelength of 800 nm Charge: 0.17nC

13 LEAF LEAF Facility Layout 20.7 m Laser Room Klystron RF System Probe Beam 798 nm UV Beam 266 nm Accelerator Vault Target A Detectors Electron Gun Magnet Supplies (Area for future targets) Target B 13.7 m Mechanical Chase Hood Anteroom Control Room Control Console Experimental Stations Stairway

14 LEAF LEAF Laser System 4 Pro Hz YAG 1 1 Diode Auto 3 TSA-10 Regenerative Amplifier Tsunami Ti:S Oscillator 6 mj compressed 8 mj uncompressed 5 2 Probe compressor 7 Tripler 6 Probe beam to expt. UV to photocathode Auto 8 Topas OPA nm 2 5 1) Diode-pumped Nd:YVO 4 laser, 5 Watts, 532 nm, pumps picosecond Ti:Sapphire laser. 2) Ti:Sapphire oscillator produces ~50 fs pulses, ~ 7 nj energy, 798 nm, at MHz. 3) Pulse stretcher stretches oscillator pulse to > 200 ps, then injects the pulse into the Ti:Sapphire regenerative amplifier. 4) Simultaneously, the doubled, Q-switched Nd-YAG laser pumps the Ti:Sapphire regen. 5) Stretched ~200 ps pulse is amplified to ~12 mj level. Half is compressed to 1-3 ps for THG 6) 7) 1-3 ps pulse is frequency tripled to 266 nm ( 0.4 mj) for excitation of Mg photocathode. Half of regen output compressed to ~100 fs for use as probe or TOPAS OPA pump (8)

15 LEAF Pulse-Probe Experiment Probe Beam Variable λ nm Detectors Delay Faraday Cup Sample Water 800 nm 5 mm cuvette 9 ps FWHM UV Beam Time, ps nm Electron Beam Electron Gun Water, 800 nm 1 cm path Time, ns 6 8

16 LEAF Pulse-probe transient absorption LEAF spectroscopy Time resolution 7 ps A factor of pulse width and sample depth. Optical Parametric Amplifier ( nm) New diodes extend range from 1000 to 1700 nm Color separation needs work, far-field mode varies Better Signal/Noise than before Improved LabVIEW acquisition software Interleaved collection, measurement selection criteria (dose, laser intensity, modulator and laser timing), using consistent cathode recovery time More proficient laser and electron beam alignment Igor-based analysis software Flow system volumes reduced (~4 ml or 15 ml)

17 ELYSE,Orsay ELYSE, Picosecond Pulse Radiolysis

18 ELYSE,Orsay Photoinjector Accelerator Pulse length 7 ps Charge 1 nc Energy 4 to 9 MeV Repetition Rate 50 Hz Energie Dispersion 2,5 % Spot Diameter 2 à 20 mm Pulse-Probe Accelerator build and installed (SERA)

19 Waseda Univ. (Japan) New pulseradiolysis system [improvement ] Stabilizing white light noise decreasing Quadropole for beam de-sizing high time resolution Easy setup Easy to experiment

20 Waseda Univ. (Japan) Stability of Probe light intensity Drum cell Achromatic lens Experimental results (right water) Fluctuation 2.3% previous Fig.12 O.D. Fluctuation 12% previous 26[ps] : Current 8[ps]

21 Beam energy Beam Current Beam width Beam size Target path Length Synchronization Laser pulse width Total time Resolution U. Tokyo LEAF,BNL, USA ELYSE, France 4+18= 22MeV 9MeV 4 to 9 MeV 2nC 2-8nC 1 nc 1ps 7 ps 7 ps 3mm 2-20mm 1mm 10mm(ri ght water) <1ps(rm s) Pico-sec. 100fs(532nm- 2600nm)OPA ( nm) white light made by Ti:Sa 100fs( nm)OP A 3ps(white light) >7ps(pulse -probe) ~7ps? Waseda Univ. 4MeV nC 8ps Osaka Univ. 38MeV >0.2nC <1ps 100fs ~5ps

22 Summary Photocathode RF gun with fs laser(tt:sa) is suitable combination for the Application of Radiation Chemistry In order to measure the phenomena at sub-pico or picosecond region, we need; -high brightness beam with short pulse(<1ps) -Thin target(~mm) -Stable system Timing (within 1ps) Position Beam Intensity (both laser and electron beam)

23 Special thanks to LEAF, BNL ELYSE, Orsay Univ. Osaka Waseda Univ. Univ. Tokyo

24 Physicochemical stage Factor of the thermalization distance λ m = (nσ) -1 λ = [-λ m ln (P λ m )]/α Beam-Material Interactions Factor of the cross section of geminate ion recombination σ rec ~ 3 x E x β Branching ratios in physicochemical stage stems from ionization and excitation Probability Decay of the directly excited water molecules Probability Reaction No. H 2 O*(A 1 B 1 ) H 2 O P1 (1) H + OH P2 H 2 O*(B 1 A 1 ) H 2 O + + e - P6 (4) H 2 O (1-P6)P1 (1) dissociation (1-P6)P2 H + OH P3 (2-1) Decay of the excited states results from the recombination 2H + O(3P) P4 (2-2) H 2 + O( 1 D) P5 (2-3) H 2 O* H 2 O P1 (1) dissociation P2 H + OH P7 (3-1) 2H + O(3P) P8 (3-2) H 2 + O( 1 D) P9 (3-3)

25 Ultra-fast pump-and-probe pulse radiolysis study : radiation induced fast processes Fs Ti:Sapp laser Compressor Optical parametric amplifier ( nm) Combination!! Compressor&THG Chicane PROBE! 100fs, nm 22MeV S-band electron linac Laser photocathode Sample PUMP! 2-3ps, ~2nC, 3mmφ Time behaviors of hydrated electrons in water: Solvation time < time resolution < 10ps Optical path: 10mm 0.3 5mm 0.2 ~13ps 6-7ps 2mm ps 1mm 0.0 <4ps Time /ps Time behaviors of solvated electrons in ethanol: Observation of solvation process (e - pre e- sol ) EtOH 1300nm 1500nm 700nm 1100nm 1200nm Time /ps

26 Sub-ps Pulse Radiolysis - Measurement System Beam-Material Interactions, UTNs Laser TK SI5010 SR DG535 HP 37204A HP 54845A GPIB Computer Computer Shutters Stage driver Data acquisition 18MeV linac or 35MeV linac Measurement of laser intensity and charge - B : Both beam and light - L : Light only - P : Beam only - N : Neither beam nor light - Charge I M (B) and I R (B) I M (L) and I R (L) I M (P) and I R (P) I M (N) and I R (N) C ( I M : Main light, I R : Reference light ) Sample PD 1 PD 2 Current monitor FESCA Calculation of precise absorbance I Absorbance log 0 10 I = C ave C log 10 Electron beam Light Signal I M (L) I M (N) I R (L) I R (N) I R (B) I R (P) I M (B) I M (P) (C ave : Average of charges)