postech pal development of s-band rf gun and advanced diagnostics in pal 박용운 (yong woon park,...

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


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 Linac

2.5-GeV 3rd generation Pohang Light Source (PLS)

3/57SLAC National Accelerator LaboratoryMarch 16, 2010

POSTECHPAL

Contents





March 16, 2010 SLAC National Accelerator Laboratory 4/57

POSTECHPAL

1st - 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


POSTECHPALEmittance Evolution measurement

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


POSTECHPAL

1st RF gun in PAL, 2005

2005 2008

fs-THz beam line


POSTECHPAL

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

9/57

POSTECHPAL

2nd RF gun in PAL

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

10/57

POSTECHPAL

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

March 9-10, 2010

Cavity and Cathode

11/57

POSTECHPAL

Cavity surface – after machining

12/57

30 nm

RMS~4nm

POSTECHPAL

Cavity surface

13/57

100 nm40 nm, after cleaning

RMS~7nm

RMS~12nm

POSTECHPAL

Cavity surface

14/57

100 nm40 nm

RMS~10nm RMS~10nm

POSTECHPAL

before brazing

after brazing

Cathode

E-gun after braz-ing

2nd - RF gun in PAL, 2008

15/57

POSTECHPAL

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

modes π-mode 0-mode

Resonant frequency 2856.975 2853.600

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

Q0 12698 10119

QL 4450 4717

π-mode0-mode

16/57

POSTECHPAL

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

modes π-mode 0-mode

Resonant 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

18/57

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.


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 dW

W W d

0

0

1 2

152sin

6

f

20 0/qE m c k

20/57

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


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).

22/57

POSTECHPAL

RF Gun development project2008~2012

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


23/57

POSTECHPAL

Cavity + 1 PortCavity Cavity + 2 Ports

Cavity + 4 Ports

y

x

zE

Basic Concept of Four Ports method

By SLAC

By POSTECH

24/57

POSTECHPAL

Improvement of RF gun

Quadrupole mode elimi-nation by adding two side cavities

By POSTECH

Emittance reduction by four ports in full cell

25/57

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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POSTECHPAL

Field measurement set up

cathode

x

y

z

θ xρ = 10 mm

27/57

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 result

Red fitting line28/57

POSTECHPAL

3rd RF gun for fs-THz Facility

29/57

POSTECHPAL

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

30/57

POSTECHPAL

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

March 9-10, 2010

Cavity and Cathode

31/57

POSTECHPALThermal analysis

heat generation by the rounded port

temperature distribution 59.172 ℃ ~ 107. 406 ℃

temperature distribution 31.408 ℃ ~ 63.149℃

ΔT ~ 48 ℃ ΔT ~ 21 ℃

32/57March 16, 2010 SLAC National Accelerator Laboratory

POSTECHPAL

Brazing of RF Gun and Wave guide

brazed at February 2010

33/57

Yesterday

SLAC National Accelerator LaboratoryMarch 16, 2010

POSTECHPAL

Contents






POSTECHPAL

Electro-Optic crystal


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

35/57

POSTECHPAL

E

Coordinates


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 E

c

mE

nm

E


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


POSTECHPAL

SNR enhancement with wave plates

/ 2

/ 2

/ 4

/ 4

/ 2

/ 2

cos sin

sin cos

0

0

0

0

0

0

i

i

i

i

i

i

R

eEO

e

eQ

e

eH

e

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

21

, , 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


POSTECHPAL

=0 , 1

NIMA 586 (2008) p.452

SNR enhancement


POSTECHPAL

Analysis of the electro-optic measure-ment at FLASH

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

247.6

I

With Electron beam

0

= 2

7.13

=800 MeV

2

GaP d = 180

=0.8 nC

100

E

r mm

m

Q

FWHM fs

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

II


POSTECHPAL

laser

electron beam

E

X = [-1,1,0]

Y = [0,0,1]

yor

o

o

cos

tan

R r

y

r

R

y EO crystal

electron beamX

(a) (b)

polarization

polarization

Experimental setup


POSTECHPAL

Change of laser delay


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


( )A B

dn n

c

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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

45/57

0A B

dn n

c

POSTECHPAL

Origin of low signal


laser

E

laser

E

POSTECHPAL

Contents






POSTECHPAL

Source

Slit

Screen

LD

P

RdO

x


POSTECHPAL

Simulated interferogram

2

12sin( )2 1 cos

J vuI

u v

/u kax R

max /v k d L

/kdx R


max min

max min

I IVisibility

I I

49/57

POSTECHPAL 1B1 diagnostics beam line in PAL

J. Sync. Rad. Vol. 16, p. 642


Uniform distribution

Gaussian distribution

Experimental result

50/57

POSTECHPAL Fourier transform and visibility


max min

max min

I IVisibility

I I

POSTECHPAL Inverse Fourier transformation


POSTECHPAL Reconstruction of transverse distribution


POSTECHPAL

2 2

2sin( )( ) 2 1 exp cos

2

uI P v

u

/u kax R

/v kd L

/kdx R

2

sin( )2 1 cos

A 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


POSTECHPAL

Experimental pattern

Theoretical calculation

with point source


with finite size source31m

10m

100 m

s

d

r

r

a

35 m

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POSTECHPAL

Study on the visibility

2

0 2/ exp

8 tc

aV V

l

20

0 20

4 3cos

4

a aV

a a

Eq. (8) Eq. (9)

20

4 d s

s d

r ra

r r

31m

10ms

d

r

r

18keV


with point source


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.


POSTECHPAL

Thank you for your attention


POSTECHPAL

60/47

Bunching part of the electron beam

Charge distribution

Gaussian-Bunching Part

2

20

exp2 22 2 to t

t q tE t

r r c


POSTECHPAL

3D Refractive indices


POSTECHPAL

Refractive indices

2 2 2 2 2

2 2 21 2 3

2 2 2 2 2

2 2 21 2 3

2

sin 1 cos cos 1 cos sin

2

cos 1 cos sin 1 cos sin

A

L L L L L

B

L L L L L

n

n n n

n

n n n


POSTECHPAL

Analysis and simulation

or 3mm

or 2.5mm

or 2mm

Simulation resultExperimental result


postech pal development of s-band rf gun and advanced diagnostics in pal 박용운 (yong woon park,...

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