development of s-band rf gun and advanced diagnostics in pal

POSTECHPAL

Development of S-band RF gun and

advanced diagnostics in PAL박용운

(Yong Woon Park, Ph.D.)

포항 가속기 연구소 (Pohang Accelerator Laboratory, PAL)

포항공과대학교 물리학과(Physics department)

(Pohang University of Science and Technology, POSTECH)

March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL

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Contents

1. Facilities in PAL

2. S-band RF gun development in PAL

3. A study of electron beam measurement by using electro-optic crystal

4. Transverse size measurement of electron beam by using interferometer

March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL

Pohang Accelerator Laboratory (PAL), Korea

Fs-THz beam lineTest facility of injector for XFEL

Gun Test facility for XFEL

160-m long 2.5-GeV S-band PLS Linac2.5-GeV 3rd generation Pohang Light Source (PLS)

3/57SLAC National Accelerator LaboratoryMarch 16, 2010

POSTECHPAL

Contents

1. Facilities in PAL

2. S-band RF gun development in PAL

3. A study of electron beam measurement by using electro-optic crystal

4. Transverse size measurement of electron beam by using interferometer

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POSTECHPAL1st - RF gun in PAL, 2005

RF Gun Bellows Goniometer Motion Stages

Slit & Pinhole Screen

View A

View A

RF Gun Bellows Goniometer Motion Stages

Slit & Pinhole Screen

View A

View A

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POSTECHPALEmittance Evolution measurement

JJAP. Vol. 46, p.1751 (2007)

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1st RF gun in PAL, 2005

2005 2008

fs-THz beam line

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OTR FIR Undulator Radiation(future option) Beam energy : 60 MeV max.

Beam Charge : 0.1 – 0.5 nC Beam Emittance: < 5 mm-mrad Beam Pulse Repetition rate: 30 Hz max. Bunch Length

Before chicane: 0.15 - 2 ps After chicane: 20 - 200 fs

Beam Charge

Bunch Length after RF-gun

Bunch Length after Chicane 2

0.2 nC 0.3 ps < 50 fs

0.5 nC 1 – 2 ps < 150 fs

fs-THz Linac Layout

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POSTECHPAL1st RF gun in PAL, 2005

2005 2009

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POSTECHPAL

2nd RF gun in PAL

March 16, 2010 3rd ILC Asian R&D Seminar, SAMEER, MUMBAI

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POSTECHPAL

3rd ILC Asian R&D Seminar, SAMEER, MUM-BAI

March 9-10, 2010

Cavity and Cathode

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Cavity surface – after machining

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30 nm

RMS~4nm

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Cavity surface

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100 nm40 nm, after cleaning

RMS~7nm

RMS~12nm

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Cavity surface

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100 nm40 nm

RMS~10nm RMS~10nm

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before brazing

after brazing

Cathode

E-gun after braz-ing

2nd - RF gun in PAL, 2008

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RF property of 2nd Gun without tuning pin in wave guide

modes π-mode 0-modeResonant frequency 2856.975 2853.600

Coupling β = 1.853 (Over ) β = 0.869 (Under )

Q0 12698 10119

QL 4450 4717

π-mode0-mode

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POSTECHPAL

RF property of 2nd Gun with tuning pin in wave guide

modes π-mode 0-modeResonant frequency 2856.975 2853.600

Coupling β = 1.853 (Over ) β = 0.869 (Under )

Q0 12698 10119

QL 4450 471717/57

POSTECHPAL Gun Test Facility in PAL-2009

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POSTECHPAL Experiment in February 2009

Measured energy spread (squares). The electron beam energy is measured as 2.5 MeV. Solid line is Gaussian fit. Axis on the top is the expression of energy spread in terms of the wavelength from 0.0042 Å. The Laser radius at the cathode is 400um. The electron charge is 1pC. The longitudinal shape of laser is Gaussian. The pulse length of laser is 3ps (FWHM). The laser injection phase is 32.5o.

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POSTECHPAL Low energy case with FED condition

(a) Measured energy (filled dot) vs injection phase. (b) Measured energy spread (filled dot) vs injection phase. Electron beam energy is measured as 2.5 MeV. Theory (solid line), PARMELA simulation (diamond).

(a) (b)

20 1 sin sin sin

2 f fW m c kL kL kL 00

1W dWW W d

0

0

1 2152sin

6

f

20 0/qE m c k

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POSTECHPAL Energy spread effect on FED

(a) Diffraction pattern of polycrys-talline Al without the energy disper-sion

(a) (b)

1/ 22 2 20/ ,r k l m L a

where a0 = 4.05 Å is the lattice constant, L is the distance from the sample to the detector, λ is De Broglie wavelength of the electron, and (k, l, m) are Miller indices for the diffraction plane in the alu-

minum.

J. Korean. Phys. Soc. Vol. 54, p. 2247.

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(b) Blurred image of the diffraction pattern with 200 keV energy dispersion. Beam energy is 2.5 MeV.

POSTECHPAL High energy cases

March 16, 2010 3rd ILC Asian R&D Seminar, SAMEER, MUMBAI

Measured energy spread . The electron beam energy is measured as 4.8, 5.0, 5.2 MeV. The Laser radius at the cathode is 400um. The electron charge is ~100 pC. The longitudinal shape of laser is Gaussian. The pulse length of laser is 3ps (FWHM).

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POSTECHPAL

RF Gun development project2008~2012

Budget: 1 M$ (0.2 M$/year)

March 16, 2010 3rd ILC Asian R&D Seminar, SAMEER, MUMBAI

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POSTECHPAL

Cavity + 1 PortCavity Cavity + 2 Ports

Cavity + 4 Ports

y

x

zE

Basic Concept of Four Ports method

By SLAC

By POSTECH

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POSTECHPALImprovement of RF gun

Quadrupole mode elimi-nation by adding two side cavities

By POSTECH

Emittance reduction by four ports in full cell

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POSTECHPALTest cavity design: four ports RF gun for low power test• Test cavity type: BNL/SLAC/UCLA 1.6-cell photocathode RF gun with input wave-

guide and three symmetric vacuum ports.

March 9-10, 2010 3rd ILC Asian R&D Seminar, SAMEER, MUM-BAI

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POSTECHPALField measurement set up

cathode

xy

z

θ xρ = 10 mm

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POSTECHPALLow power test result: |Ez|

Case 1: Cavity + 1 waveguide Case 2: Cavity + 1 waveguide + 1 vacuum port

Case 3: Cavity + 1 waveguide + 3 vacuum ports

θ xρ=10 mm

y

Coordinates system

Simulation result

Experimental resultRed fitting line

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3rd RF gun for fs-THz Facility

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Requirements:

Vacuum : < 5x10-10 torr

Emittance: < 1 mm mrad

Operating frequency: 2.856 GHz

Field balance(*Eh/**Ef)of π mode: ~1

Mode separation(fπ-f0): ~10 MHz

Coupling factor : ~1

Pulse repetition rate: >30 Hz

*Eh: Maximum E-field in half cell**Ef: Maximum E-field in full cell

Cold model

In real gun, the tuners will be removed and the ports will be used as vacuum ports.

3rd RF Gun for fs-THz Facility at PAL

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POSTECHPAL

3rd ILC Asian R&D Seminar, SAMEER, MUM-BAI

March 9-10, 2010

Cavity and Cathode

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POSTECHPALThermal analysis

heat generation by the rounded port

temperature distribution 59.172 ℃ ~ 107. 406 ℃

temperature distribution 31.408 ℃ ~ 63.149℃

ΔT ~ 48 ℃ ΔT ~ 21 ℃

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POSTECHPAL

Brazing of RF Gun and Wave guide

brazed at February 2010

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Yesterday

SLAC National Accelerator LaboratoryMarch 16, 2010

POSTECHPAL

Contents

1. Facilities in PAL

2. S-band RF gun development in PAL

3. A study of electron beam measurement by using electro-optic crystal

4. Transverse size measurement of electron beam by using interferometer

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POSTECHPAL

Electro-Optic crystal

March 16, 2010 SLAC National Accelerator Laboratory

The refractive indices of the Electro-optic crystal are changed by the electric field from the electron beam.

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POSTECHPAL

E

Coordinates

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POSTECHPAL

Principal refractive indices

30 41

1 0

30 41

2 0

2

2

n r En n

n r En n

31 2 0 41

0

3 12

9

9 6

2( )

2 *200( ) *(2.7) *4.0*10 *800( )

2 *19.68*10 *

360 *20*10 *10

7.2

d dn n n r Ec

m Enm

E

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320 41

1 0

320 41

2 0

sin 1 3cos2

sin 1 3cos2

n r En n

n r En n

POSTECHPAL

150m

in Tunnel

TEO

Courtesy from A. Azima

Timing EO setup

March 16, 2010 SLAC National Accelerator Laboratory 38/57

POSTECHPAL

SNR enhancement with wave plates

/ 2

/ 2

/ 4

/ 4

/ 2

/ 2

cos sinsin cos

00

00

00

i

i

i

i

i

i

R

eEO

e

eQ

e

eH

e

1, , 1 sin sin 2 4 cos cos 2 cos 2 42

1, , 0 1 cos 2 cos 2 42

I

I

10 1 . . . . . . . / 4 . . / 4 .

0vE R H R R Q R R EO R

, ,I

, , 0I

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POSTECHPAL

=0 , 1

NIMA 586 (2008) p.452

SNR enhancement

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POSTECHPAL

Analysis of the electro-optic measure-ment at FLASH

44660 , 2 , 1 sin sin 2 ( 2 ) cos cos 2 ( 2 ) cos 2 ( 2 )2

47.6

I

With Electron beam

0

= 2

7.13

=800 MeV2

GaP d = 180 =0.8 nC

100

Er mm

mQFWHM fs

0, , 1 sin sin 2 4 cos cos 2 cos 2 42II

March 16, 2010 SLAC National Accelerator Laboratory 41/57

POSTECHPAL

laser

electron beam

E

X = [-1,1,0]Y = [0,0,1]

yor

o

o

cos

tan

R ryr

R

y EO crystal

electron beamX

(a) (b)

polarization

polarization

Experimental setup

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POSTECHPAL

Change of laser delay

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laser

X = [-1,1,0]Y = [0,0,1]

y

E

laser

X = [-1,1,0]Y = [0,0,1]

y

E

POSTECHPAL

2 21 2

2 21 2

21 sin(2 ) 1 sin(2 )

21 sin(2 ) 1 sin(2 )

A

B

n

n n

n

n n

An

March 16, 2010 SLAC National Accelerator Laboratory

( )A Bd n nc

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A

B

45

A

X

Quantification of polarization change

POSTECHPAL

Quantification of polarization change

J. Opt. A:Pure Appl. Opt., vol. 11, p.105704 (2009)

or 2mm

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0A B

dn n

c

POSTECHPAL

Origin of low signal

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laser

E

laser

E

POSTECHPAL

Contents

1. Facilities in PAL

2. S-band RF gun development in PAL

3. A study of electron beam measurement by using electro-optic crystal

4. Transverse size measurement of electron beam by using interferometer

March 16, 2010 SLAC National Accelerator Laboratory 47/57

POSTECHPAL

Source

Slit

Screen

LD

P

RdO

x

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Simulated interferogram

212sin( )2 1 cosJ vuI

u v

/u kax R

max /v k d L

/kdx R

March 16, 2010 SLAC National Accelerator Laboratory

max min

max min

I IVisibility

I I

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POSTECHPAL 1B1 diagnostics beam line in PAL

J. Sync. Rad. Vol. 16, p. 642March 16, 2010 SLAC National Accelerator Laboratory

Uniform distribution

Gaussian distribution

Experimental result

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POSTECHPAL Fourier transform and visibility

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max min

max min

I IVisibilityI I

POSTECHPAL Inverse Fourier transformation

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POSTECHPAL Reconstruction of transverse distribution

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POSTECHPAL

2 2

2sin( )( ) 2 1 exp cos2

uI P vu

/u kax R

/v kd L

/kdx R

2sin( )2 1 cosA BxI E Cx D

x

A = 2.281,B = 0.4145, C = 7.995, D = 1.817, E = 0.7943.

Measurement result in February 2010

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POSTECHPAL Reconstruction of transverse distribution

Reconstructed shape of electron beam

Measured phasesMeasured visibilities

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Experimental pattern

Theoretical calculation with point source

Theoretical calculation with finite size source

31m10m100 m

s

d

rra

35 m

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Study on the visibility

2

0 2/ exp8 tc

aV Vl

20

0 20

4 3cos4

a aVa a

Eq. (8) Eq. (9)

20

4 d s

s d

r ra

r r

31m10 m

s

d

rr

18keV

Theoretical calculation with point source

Theoretical calculation with finite size source

57/57March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL Summary1. RF gun development - I have many experiences on development of RF electron gun for the XFEL. To design the RF gun, I used the POISSON code and PARMELA also. For the three dimensional analysis of the field distribution in the cavity, I used CST Microwave Studio. As postdoctoral position in Pohang Accelerator Laboratory, I carried out a big Project for the development of RF gun for 4th generation light source XFEL, as you can see in the Ref. [3]. I worked with three Ph.D. candidates whom work under my supervisor. I believe that I can lead a group to carry out a project. I fully understand the emittance compensation process in the injector part of the XFEL.

2. Electron beam diagnostics- I have also many experiences on the diagnostics of electron beam using electro-optic crystal. To measure very short electron beam such as 100 fs bunch length and measuring the arrival timing for the pump and probeexperiment in XFEL, this technique is very promising method. I made myself simulation code to simulate many situations of electron beam diagnostics in accelerator such as bunch charge, bunch length, beam energy, etc. I also have experience working on FLASH machine in DESY during 5 months. I made a contribution to upgrade the EO diagnostics setup with my simulation code. I found the origin of low signal in the EO setup. Many papers are published with this subject as you can see in the list of publications, as you can see in the Ref. [1, 5, 7, 8].

3. XFEL design experience-In my Ph.D. course, I am involved also to the design of the 4th generation light source XFEL. This XFEL is called PAL-XFEL as you can see in the Ref. [13, 15] in the publication list. I can simulate the electron beam dynamics with PARMELA, ELEGANT.

4. Storage ring experience- I also have many experiences on the machine study of Pohang Accelerator Laboratory such as transverse beam size measurement with interferometer in diagnostics beam line, as you can see in the Ref. [2]. I also have many interesting on the dynamics of electron beam in the 3rd generation storage ring.

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POSTECHPAL

Thank you for your attention

March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL

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Bunching part of the electron beam

Charge distribution

Gaussian-Bunching Part

2

20

exp2 22 2 to t

t q tE tr r c

March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL

3D Refractive indices

March 16, 2010 SLAC National Accelerator Laboratory 61/53

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Refractive indices

2 2 2 2 2

2 2 21 2 3

2 2 2 2 2

2 2 21 2 3

2sin 1 cos cos 1 cos sin

2cos 1 cos sin 1 cos sin

AL L L L L

BL L L L L

n

n n n

n

n n n

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Analysis and simulation

or 3mm

or 2.5mm

or 2mm

Simulation resultExperimental result

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