Coherent Radiation from High-Current

Electron Beams of a Linear Accelerator

and Its Applications

S. Okuda

1987-2002 ISIR, Osaka Univ. 2002- Research Institute for Advanced Science and Technology (RIAST), Osaka Prefecture Univ. Coworkers: 　　　　　　　 Osaka Pref. Univ. R. Taniguchi, T. Kojima Osaka Univ. M. Nakamura, M. Takanaka, R. Kato Kyoto Univ. T. Takahashi Kangwon Univ. S. Nam

High-current electron linear accelerator (linac)

High-current thermionic gun

3 SHBs

Coherent radiation from electron beams

Free-electron lasers

Coherent radiation with a broad spectrum

Applications of the radiation

Electron bunch shape monitor

Absorption spectroscopy

38 MeV L-band linac at Osaka Univ.

Single-bunch electron beam parameters

Repetition rate 120 pps

Energy 27 (38 max.) MeV

Energy spread 1-2.5% FWHM

Maximum Charge 91 nC/bunch

Micropulse length 20-30 ps

Normal. rms emittance 70-200 mm mrad

High-current thermionicelectron gun

Osaka Argonne X-ray SASE (2002) (2002)

Gun, Injector thermionic photocathode photocathode

SHPBs rf (half cell)

rf frequency (MHz) 1300 1300

Repetition rate (pps) 120

Energy (MeV) 27 (38 max.) 14

Energy spread (% FWHM) 1-2.5

Charge (nC/bunch) 91 100 a few

Micropulse length (ps) 20-30 15-40 10

Normalized rms emittance

(mm mrad) 70-200 1700 2

Estimated

Measured

High-current and high-brightness beams

Operational modes of the linac

Density modulation and coherent radiation

Free-electron lasers (FELs)

Features of FELs Tunability Subpicosecond short pulse High peak power (MW)

Single passage (no cavity mirror)High gainX-ray FEL

SASE (Self-amplified spontaneous emission) FEL

First lasing: 1991

Oscillation FEL

Output power of FEL light

Wavelength: 40 mOutput power: 800 J/macropulse

First lasing: 1994

FEL facility at Osaka Univ.

FEL facilities

IR-FIR user facilities

Visible-UV Storage ring FELs

High power IR FELs

Superconducting linacs

X-ray SASE projects

×N (～ 1011)

Coherent radiation from an electron bunch

Phys. Rev. Lett. 1991

Our observation of coherent radiation

High intensity in a submillimeter to millimeter range (THz – 100 GHz)Continuous spectrumCoherencePico-second short pulseSynchronization with the electron bunch

Absorption spectroscopyAnalysis of transient phenomenaImagingCoherent excitationPump and probe analysis

Characteristics of CR

Applications of CR

Applications of the radiation

Electron bunch shape monitor

Far-infrared light source

for absorption spectroscopy

Bunch form factors for various bunch shapes

Gaussian

RectangularIsosceles triangular

Wavelength is normalized by the FWHM bunch length.

Bunch sape monitoring system

Coherenttransition radiation

L-band LINAC

QQ

Bunch compressorAl foil

Al Mirror

Interferometer

Detector

Streak camera

Shielding wall

Detector

Electron beam

Cherenkov radiation

Streak measurement Time resolution 0.9 psMeasurement of the coherent transition radiation Wavelength range 0.4-2 mm Wavenumber resolution 0.2 cm-1 Interferometer: Martin-Pupplet type Detector: Liquid-He-cooled Si bolometer

Time resolution 0.9 psInterference filter 478.5 nm (B. W.: 11.3 nm)

Martin-Pupplet interferometer

Beam splitter

Fixed mirror

Detector for measuring interferogram

Detector for monitoring beam intensity

Movablemirror

Coherenttransition radiation

Beam splitter : wire grid with a wire spacing of 25 m

-60 -40 -20 0 20 40 60-10

-8

-6

-4

-2

0

2

4

Sig

nal (

arb.

unit)

Optical path difference (mm)

Bunch compression with a bunch compressor

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

29ps (FWHM)

Nor

mal

ized

In

tens

ity

Time (ps)

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

29ps (FWHM)

Nor

mal

ized

In

tens

ity

Time (ps)0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

18ps (FWHM)

Rel

ativ

e In

tens

ity

Time (ps)

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

18ps (FWHM)

Rel

ativ

e In

tens

ity

Time (ps)

4 pole chicane-type bunch compressor

Magnetic field 0.105 T

Deflection angle 0.27 rad

Electron beamElectron beam

Single-bunch beam parameters Energy 27 MeV Energy spread 1.1 % (FWHM) Charge/bunch 13.5 nC

Bunch shapes measured with a streak camera

B.C. on

Spectra of CR and bunch form factors

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (29ps)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (29ps)Coherent radiationTriangular bunch (29ps)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al f

orm

fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (18ps)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al f

orm

fac

tor

Wavenumber (cm-1)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al f

orm

fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (18ps)Coherent radiationTriangular bunch (18ps)

Bunch form factor at =1 mm: 10-6 → 10-5

1 10 100

10-13

10-12

10-11

10-10

Inte

nsity

(J/

pul

se/1

%B

.W.)

Wavenumber (cm-1)

BC offBC on

1 10 100

10-13

10-12

10-11

10-10

Inte

nsity

(J/

pul

se/1

%B

.W.)

Wavenumber (cm-1)

BC offBC on

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (29ps)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

0 5 10 15 20 25

10-7

10-6

10-5

10-4

Lon

gitu

din

al F

orm

Fac

tor

Wavenumber (cm-1)

Coherent radiationTriangular bunch (29ps)Coherent radiationTriangular bunch (29ps)

Spectra of CR

Bunch form factors

B.C. on

Radiation loss of the single-bunch beam energy

in the bunch compressor

Coherent synchrotron radiation light source

CSR power1 J/%B.W. at 1 mm0.3 mJ at 0.7-1.4 mm (>30 MW peak power)

Beam conditions Energy: 27 MeV Electron charge: 30 nC/bunch Bunch length: 5-10 ps

Submillimeter to millimeter wave

light sources

Peak power (at =1 mm) Averaged power

1 Coherent radiation (100 Hz) 1

10-5 Terahertz radiation source 10-1

(10 MHz)

10-12 Incoherent SR source 10-4 (10 MHz)

10-20 Blackbody source (DC) 10-5

Experimental setup for absorption spectroscopy using CTR

Detector

Detector

Monochromator

Splitter

Shielding wall

Sample

Plane mirror

L-band linac

Transition radiation

Al plate

Quadrupole magnets

Electron beam

Window Concave mirror

Detector

Detector

Monochromator

Splitter

Shielding wall

Sample

Plane mirror

L-band linac

Transition radiation

Al plate

Quadrupole magnets

Electron beam

Window Concave mirror

Absorption spectroscopy for water

Incident LightQuartz

Water

Incident LightQuartz

Water

Temperature: 22 ℃Thickness of the sample: 186 m

(a)

(b)

1.5

2

2.5

3

9 10 11 12 13 14 15

0

50

100

150

200

9 10 11 12 13 14 15

Wavenumber (cm -¹)

Ab

sorp

tion

Co

effi

cie

nt

Re

fra

ctiv

e In

de

x(

Np

cm

-1)

Wavenumber (cm -¹)

(a)

(b)

1.5

2

2.5

3

9 10 11 12 13 14 15

0

50

100

150

200

9 10 11 12 13 14 15

Wavenumber (cm -¹)

Ab

sorp

tion

Co

effi

cie

nt

Re

fra

ctiv

e In

de

x(

Np

cm

-1)

Wavenumber (cm -¹)

Resolution: 1%

Setup for imaging 　

X-Y Stage

Collimator

Sample

Sample

Collimator (Al plate)

CTR

CTR

X-Y Stage

Collimator

Sample

X-Y Stage

Collimator

Sample

Sample

Collimator (Al plate)

CTR

CTR

MonochromatorDetector

Detector

SampleBeam Splitter

X-Y Stage

Collimator

Oscilloscope X-Y Stage Controller

CTR

MonochromatorDetector

Detector

SampleBeam Splitter

X-Y Stage

Collimator

Oscilloscope X-Y Stage Controller

CTR

Dried

1 cm 1 cm

Dried

1 cm 1 cm

Imaging with CTR

PrintPeak wavenumber : 11.1 cm-1

Wavenumber width: 0.2 cm-

1

Resolution: 0.8 mm

8 mm8 mm

Transmission (%) 0 25 50 75 100

Transmission (%) 0 25 50 75 100

LeafPeak wavenumber : 10.7 cm-1

Wavenumber width: 3.5 cm-

1

Resolution: 0.8 mm

Other application

Summary

High-current electron linac

91 nC/bunch (kA peak current)

Coherent radiation from electron beams

FELs

Coherent radiation

Applications of the coherent radiation

Electron bunch shape monitor

Absorption spectroscopy

Other applications

Research Center for Radiation and RadioisotopesRIAST, Osaka Prefecture Univ. Electron accelerators　　 18 MeV Linac　　 600 keV Cockcroft-Walton accelerator Ion accelerators　　 3 MeV Tandem accelerator Cobalt-60 gamma ray sources 4 x 1015 Bq (105 Ci ） 4 irradiation rooms and a water pool facility Radioisotope facilities

Water pool for 60Co -ray sources

Cherenkov radiation from 60Co -ray sources installed

in a water pool