cotr and sase from compressed beams€¦ · fs3 fs4 fs5fs3 fs4 fs5 l5 sta5 225500mev a.h. lumpkin...

COTR and SASE from Compressed Beams from Compressed Beams

Alex Lumpkin, FermilabRoger Dejus and Nick Sereno, ANLg j ,

Presented at FEL08 Gyeongju, KoreaAugust 28, 2008

OUTLINE

• Introduction• Experimental background and facility.• Recent longitudinal space charge (LSC) g g ( )

microbunching instability results via (COTR).• Comprehensive COTR and SASE data sets

from Dec. 20, 2001. • Summary

A.H. Lumpkin et al. FEL08 August 28, 2008 2

Structure in COTR Image Reported in FEL02

• Six years ago we reported a striking localized SASE-induced microbunching as observed via the COTR andin x-λ space of our imaging spectrometer at APS/ANL.

• In FEL02 we postulated there must be a beamstructure induced at the chicane that the SASE processstructure induced at the chicane that the SASE processpreferred.

• At that time there was no theoretical support forlongitudinal space charge (LSC) or coherentsynchrotron radiation (CSR) induced effects at visiblewavelengths.wavelengths.

• We now suggest that those structures were a result ofthe LSC-CSR microbunching instability that the SASE

f 30process preferentially enhanced at 530 nm.


COTR-6 Spectrometer ImageFrom FEL02 Paper

• The structures are ~250 µm (FWHM), 120 µm apart in x, and 2.9 nm apart in wavelength. Calibration: 0.21 nm/ch.

ch)

530 nm

X(c

Wavelength (ch)


Wavelength (ch)

Schematic of the APS Injector Area

• Both rf PC gun and rf TC gun beams available for acceleration, compression, and diagnosis.

150 MeV

FS3 FS4 FS5FS3 FS4 FS5

L5Sta 5 225 500 MeV


Sta-5 225-500 MeV

FIR CTR Detected with Golay Cell

• FIR CTR signal varied dramatically by factor of 300with change in APS L2 accelerating structure phase.Autocorrelation scan’s FWHM=65 µm (at right) withround trip of 130 µm implies sub-0.5 ps FWHM e beam.

A.H. Lumpkin A0 Upgrade Review August 18, 2008 6

A. Lumpkin et al.,BIW08

OTR Beam Image Structures Vary with L2 Phase

• Images develop enhanced peaks in x-y space with compression. Footprint is similar (11-05-07 Data).

13.7 deg 14.1 deg 14.9 deg

YY

15.2 deg 15.3 deg16.3 deg

X

Y


X

Enhanced OTR Images Seen

• Examples of images and profiles for L2 phase at 12 deg. (L-uncompr.) and L2 phase at 14.9 deg.(R-compr.)

Y Y

XX

Intensity

Intensity


X X A. Lumpkin et al.,BIW08

Off-line Analysis on OTR Image Peak IntensityConfirms Phase Effect

• Localized peak intensity from single-column

Peak intensity and image averages processed for

samples of 150-MeV data.

200

375-MeV data.

ensi

ty

140

160

180

200

L2 phase (deg) vs V-peak

OTR

Pea

k In

te

60

80

100

120

11 12 13 14 15 16 17

O

0

20

40


L2 Phase (Degrees)A. Lumpkin et al.,BIW08

First Imaging Spectrometer COTR Results at Linac (07-24-08)

• We report our preliminary evidence of broadband COTR emissions with the spectrometer at Sta-5. The image is x-λ space. Wavelength span is ~180 nm with Grating-4.

YAG:Ce plus Mirror OTR mirror only

550 nmX

(ch)

550 nm

X (c

h)

Wavelength (ch) W l th ( h)


Wavelength (ch) Wavelength (ch)

First Imaging Spectrometer Results

• Preliminary processing of YAG:Ce and COTR images.• Sub-0.4 micron longitudinal spikes implied?g p p

ity sity

YAG Profiles CCD Camera Response

Inte

ns

Inte

ns

COTR t ith

460 550 640

X (ch)λ (nm)

COTR spectra with BG subtraction and 3-ch smoothing. 460 550 640 460 550 640


COTR and SASE Tests (12-20-01)

• Comprehensive z-dependent data sets taken on lateshift on 12-20-01. SASE fundamental at 530 nm.

• Sets taken for both 120 and 300 A peak current.– Both OTR and SASE data taken at each undulator station.

Near field taken for OTR/COTR; Near field taken for SASE– Near–field taken for OTR/COTR; Near-field taken for SASE.• VLD0 is before first undulator; VLDN is the station after

undulator N.B th 500 h t d ND filt d t t k f OTR• Both 500-nm short pass and ND filter data taken for OTR.

• Single SP filter attenuates SASE-induced microbunching at530 nm by 100.

• 100 images taken for each configuration at each VLD.• LSC-related microbunching instabilities are now

recognized as being detectable via visible light COTR.recognized as being detectable via visible light COTR.• Revisit the data to look for new aspect.


Schematic of APS Linac

• Flexible system with three guns and one bunch compressor.


Intraundulator Diagnostics Stations Used to Track Evolution of Microbunching and SASE.

14A.H. Lumpkin et al. FEL08 August 28, 2008

PC rf Gun Beam Setup (12-20-01)

Parameter Uncompressed Compressed

Beam Energy (MeV) 217 MeV 217

i f fEmittance x(mm mrad)

4.6 after chicane

4.1 after chicane

Emittance y( d)

4.3 after hi

4.2 after hi(mm mrad) chicane chicane

Peak Current (A) 120 300

Bunch Length (ps 1 6 0 65Bunch Length (ps rms)

1.6 0.65

Charge (pC) 450 450Energy Spread (%) 0 1 0 2 < 0 1Energy Spread (%) 0.1-0.2 < 0.1


COTR/SASE Gain Curves at 300 A with LSC(12-20-01 data)

• Gain saturates by the end of undulator 5 on average with 300 A beam and the LSC microbunching inducements.

cts)

1000

ts)

ensi

ty (x

105

c

10

100VLD# vs 300-ACOTR

ensi

ty (x

105

ct

1e+4

1e+5

1e+6 300-A UR HM-DS4 300-A UR HM-DS5

OTR

Imag

e In

te

0.1

1

UR

Imag

e In

te1e+2

1e+3

Z Position (VLD #)0 2 4 6 8 10

O

0.01

Z Position (VLD #)0 2 4 6 8 10

U1e+1


VLD0: OTR Before Undulator 1

• For similar charge, OTR Images at 120 A (L) and 300 A (R) have quite different intensities with structures seen in the latter.

120 A: ND 0.0 300 A: ND 0.5

Y(ch)

X(ch) X(ch)


VLD1: OTR/COTR after Undulator 1at 300 A Peak Current

• Shortpass filter blocks the 530-nm fundamental microbunching signal (L). (12-20-01 Data)

500 nm SP:LSC COTR ND1.0: LSC- + SASE-Induced COTR

Y(ch) Y(ch)

X(ch) X(ch)

( ) ( )

X(ch) X(ch)

nten

sity


X(ch) X(ch)

In

VLD6: COTR and SASE Images

• Imaging spectrometer shows structures in x-λ space near 530 nm fundamental (12-20-01 data)near 530 nm fundamental. (12 20 01 data)

COTR SASE

h) h)

X (c

h

X (c

h530 nm 530 nm

W l th ( h) Wavelength (ch)


Wavelength (ch) Wavelength (ch)

SUMMARY

• LSC-CSR related microbunching instabilities are nowrecognized as being detectable via visible light COTR.– Identified now in 2001 APS OTR experimental data.

• We report strong evidence for the effects on a pastvisible light SASE FEL experiment at APS by thevisible light SASE FEL experiment at APS by thespatially localized LSC-CSR-induced microbunchingbeam structures that evidently encourage startup.

• Need start-to-end simulations with Genesis or Ginger runs to improve understanding.

• Explore other data in visible UV and VUV at APS• Explore other data in visible, UV, and VUV at APS.– Will structures seen in vis-UV be enhanced in VUV also?

• How many other FEL experiments showed LSC-relatedeffects?


ACKNOWLEDGEMENTS

• The authors acknowledge the support of M. Wendt ofFermilab and R. Gerig and K.-J. Kim of the ArgonneAccelerator Institute.

• They also acknowledge discussions with K.-J. Kim andY -C Chae of Argonne and Z Huang of SLACY.-C. Chae of Argonne and Z. Huang of SLAC.

• They acknowledge W. Berg and S. Shoaf of Argonne forrelocating the optical spectrometer with controls to thelinac optics lab.


COTR and SASE Gain Curves

• Gain saturates by the end of undulator 4 on average with 300-A beam and the LSC microbunching inducements.

2D Graph 3

05 cts

) 100

1000

2D Graph 7

105 c

ts)

10

100

VLD# vs 120-A COTR

120 A

Imag

e In

tens

ity (x

10

0.1

1

10

VLD# vs 300-ACOTR

Inte

grat

ed In

tens

ity (x

0.01

0.1

1

120 A Gain

300 AGain

VLD #

0 2 4 6 8 100.01

2D Graph 6

cts)

10000

VLD# vs 120-A-UR HM-2

VLD #

0 2 4 6 8 10

2D Graph 4

1e+6

Inte

grat

ed In

tens

ity (x

105 c

100

1000

Imag

e In

tens

ity (x

105 c

ts)

1e+3

1e+4

1e+5

VLD# vs 300-A URHM


VLD #

0 2 4 6 8 1010

VLD #

0 2 4 6 8 10

1e+2

cotr and sase from compressed beams€¦ · fs3 fs4 fs5fs3 fs4 fs5 l5 sta5 225500mev a.h. lumpkin...

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