Jun. 26th, 2004Brookhaven National Laboratory, USA

Yusa Muroya, Mingzhang Lin, Hokuto Iijima,Toru Ueda, Mitsuru Uesaka, Yosuke Katsumura

Nuclear Engineering Research LaboratoryUniversity of Tokyo, JAPAN

Design and construction ofultrafast pulse radiolysis system using

laser photocathode rf-gun combined with fs laser

Development of new pulse radiolysis system• Time resolution : ~50ps → ≤10ps• Stroboscopic method (pump-and-probe)

- Laser photocathode rf-gun and/or fs laser- Projects in progress in the world

BNL, Pari-sud, Waseda Univ., Sumitomo Heavy Industries,Osaka Univ., ANL etc.

www.utnl.jp/~beamBeam-Material InteractionsIntroduction

t < 0 t > 0t = 0

Dynamics

AbsorptionOptical delay

Precise Synchronization System at NERL www.utnl.jp/~beamBeam-Material Interactions

Laser photo-cathode RF gun

Accelerating Tube Chicane

BS(50%)

RF

18L LinacCompressor

x 6

Temperature control within 1 deg, Clean room (class : 10,000)

Stretcher Regenerative Amplifier with Pulse Selector

Ti:Sapphire Oscillator with Kerr LensMode-Locker

Timing Stabilizer at 9th Harmonics

Diode Pump Laser

Trigger Pulse

CompressorTHG

Multi-pass Amplifier

Fs Ti:Sapphire Laser System

Klystron15MW

x 4

Digitex

MasterOscillator119MHz

50Hz x 1/5

3DB

To Streak CameraTo Pulse Selector

Laser transport line

CherenkovRadiator

Fs Streak Camera

x 1/6

Synchronization System at NERL www.utnl.jp/~beamBeam-Material Interactions

Transport line for femtosecond laser

18MeV linac

Wave guide(7.5MW, 10Hz S-band RF)

Full cellHalf cell

Cathode (Mg)

Beam(4-5MeV, 3nC, ~20πmmmrad

dark current : ~8nA)

www.utnl.jp/~beamBeam-Material InteractionsPhotocathode RF-Gun

• Photoelectron cooler than thermionic emission• Acceleration up to 4MeV by gradient of 100MV/m

Laser(265nm, ~100µJ, 4-6ps,

D=3mm at cathode, 10Hz)

2 getter, 2 ion pumps (140dm3): <10-10Torr

3ω

795nm

-0.500.000.501.001.502.002.503.003.50

30 60 90 120 150 180 210Phase /deg.

40µJ

60µJ

120µJ

www.utnl.jp/~beamBeam-Material InteractionsGeneration of ultra-short electron beam

RF-gun study- QE: ~1.2x10-4

- Emittance: 20π (hor.) and 20π (vert.) mmmrad- >3nC/pulse@90deg

Adopted for pulse radiolysis

Charge transportation- Laser(265nm) : ~100µJ- Gun phase : ~120deg- ACC phase : ~80deg- 80~90% transmission (Oct. 2003)

Optimized electron beam

2ps(FWHM)

1.7-2.0 nC~0.05nC

Linac end(3mm slit)

22±0.1MeV4-5Energy /MeV<17Pulse width /ps

2.3~0.05

2.4~0.05

2.5~0.2

2.5~0.8

Charge /nCDark current /nC

Linac end(no slit)

ChicaneACCPhoto-cathodeSections in linac

www.utnl.jp/~beamBeam-Material InteractionsGeneration of ultra-short electron beam

→ >40Gy/pulse is available

Synchronization System www.utnl.jp/~beamBeam-Material Interactions

σ1 : Timing stabilization in laser oscillator- 100fs by passive mode-lock

σ2 : Fluctuation of RF power & phase

2 factors affecting timing jitter

Independently supplied RF : mutual jitter

Synchronization System www.utnl.jp/~beamBeam-Material Interactions

Fluctuation of RF power/phase Fluctuation of arrival time

Accelerating tube

Fluctuation of energy

Stable acceleration(1) : stable RF

Stable acceleration(2) : mutual jitter

C

RF-gun Accelerating tube RF-gun Accelerating tube

7MW KLY 7MW KLY15MW KLY

No mutual jitter

~7ps(FWHM)2-3nC

Dipole magnets

Trajectory of the beam

2ps(FWHM)2-3nC

1%, 1deg will induce 300fs jitter

~ps <ps

-10

0

10

20

30

40

0 20 40 60 80 100 120

Tim

e di

ffer

ence

[ps]

Time [min.]

Previous : 3.5ps (rms)

Recent data : <1.6ps (rms)

Cherenkovradiation

Laser

Synchronization of electron beamand laser by FESCA

• Timing jitter during minutes: <500fs(rms)- Stabilized RFs, passive mode-lock- Simulation by PARMERA : 330fs(rms)

• Large drift(1) Cooling system in ACC: ∆T < 0.01K(2) Temp. control in rooms: ∆T < 0.5K(3) N2 purge in 50m transport line

• Pulse radiolysis : 40~60min./data → <1ps(rms)

Synchronization experiment

www.utnl.jp/~beamBeam-Material InteractionsProgress of synchronization system

• Xe chamber used for Cherenkov radiator

0 10 20 30 40 50

Inte

nsity

[a.u

.]

Time [ps]

700fs(FWHM)

1.3ps(FWHM)

In 1999

Current

The laser transport line is 50 m long, and 14 bellows are used.

• In the chembers… Vacuum Atmospheric pressure N2 gas.

Mirror

(i) The chamber of transport line is expanded and contracted by a change of temperature.

(iii) The mirror chamber with flexibility due to the bellows is moved by the pressure.

To suppress the pressure effect!

VacuumAir

(ii) The pressure difference between inside and outside of the transport line chamber applies the force to the mirror chamber.

BellowsTransport line chamber

www.utnl.jp/~beamBeam-Material InteractionsProgress of synchronization system

www.utnl.jp/~beamBeam-Material InteractionsImprovement : problems solved

Time resolution vs. dose(1) 2~3ps : pulse width (EB)(2) 100fs : pulse width (laser)(3) <1ps : synch.(4) 5ps /5mm : ∆t passing through H2O

→ Thinner cell & focused EB

OK

Note: O.D. = ε C l l↓ for better time resolution, but O.D.↓then, C↑ for O.D.→

>40Gy/pulse13-15GyDose2ps3psPulse width

3mm4mmBeam size1.7-2.0nC0.8-1.0nCChargeCurrentPrevious

Introduction of white light continuum- 795nm → white- Worse stability of intensity- S/N↓ then average↑

CurrentPreviousWhite

400-1100nmFundamental

795nmWavelength

6416Average~0.015 OD~0.005 ODNoise

Improvement

Dose increase&

Wide measurement wavelength

-0.050.000.050.100.150.200.250.300.35

0 50 100 150 200 250Time /ps

Optical path : 10 mm

5 mm

2 mm1 mm

-0.050.000.050.100.150.200.250.300.35

-10 -5 0 5 10 15 20 25 30Time /ps

12-13ps

6-7ps

4-5ps

<4ps

• Time behaviors of eaq- at 700nm

Results

Time resolution: δtotalδtotal = δdiff + (δE

2 + δL2 + δsync

2 )1/2

Dominant factor： δdiffdue to refractive index n=1.33

Radiolysis of water measured at 700nm www.utnl.jp/~beamBeam-Material Interactions

50Gy50Gy47Gy40GyDose

<4ps4-5ps6-7ps12-13psTimeresol. /ps

0.043

0.085

0.1910

0.3215

O.D.S/N

12510l /mm

12.2ps 3.2ps5.2ps7.2psTime resol. /ps

Good agreement

www.utnl.jp/~beamBeam-Material InteractionsSummary

• A new pulse radiolysis system combined withlaser photocathode rf-gun and fs white light continuumhas been developed.

• Some problems have been pointed out. Consequently,most of those were improved.

• <4ps time resolution has been attained.

• Future worksIntroduction of OPA for extending measurement wavelength