p. emma, slacicfa xfel 2004 - july 29, 2004 electron bunch measurements with a transverse rf...

P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004

Electron Bunch Measurements Electron Bunch Measurements with a Transverse RF Deflectorwith a Transverse RF Deflector

P. EmmaP. Emma ICFA XFEL 2004 WorkshopICFA XFEL 2004 Workshop

July 29, 2004July 29, 2004

ICFA Future Light Sources Sub-panel ICFA Future Light Sources Sub-panel Mini-workshop on XFEL Short Bunch Measurement and Timing Mini-workshop on XFEL Short Bunch Measurement and Timing

Stanford Linear Accelerator CenterStanford Linear Accelerator Center, July 26 - 30, 2004, July 26 - 30, 2004


Previous Talks/PublicationsPrevious Talks/Publications

R. Miller, IEEE Trans. Nucl. Sci., June 1965.R. Miller, IEEE Trans. Nucl. Sci., June 1965.

X.-J. Wang, PAC’99, March 1999.X.-J. Wang, PAC’99, March 1999.

J. Frisch, BNL/LCLS Diag. Workshop, March 2000.J. Frisch, BNL/LCLS Diag. Workshop, March 2000.

P. Emma et al., LCLS-TN-00-12, Aug. 2000.P. Emma et al., LCLS-TN-00-12, Aug. 2000.

R. Akre et al., PAC’01, June 2001.R. Akre et al., PAC’01, June 2001.

R. Akre et al., EPAC’02, June 2002.R. Akre et al., EPAC’02, June 2002.

H. Schlarb: H. Schlarb: http://www.desy.de/s2e/ (Aug. 2003).


Transverse RF Deflector in the SLAC LinacTransverse RF Deflector in the SLAC Linac

VV00 20 MV 20 MVzz 50 50 m, m, EE 28 GeV 28 GeV

ee

zz

2.44 m2.44 m

cc pp

90°90°

VV((tt))yy

RFRF‘‘streak’streak’

SS-band-band

RF InputCoupler

BeamDeflection

Irises withmode-lockingholes

RF InputCoupler

BeamDeflection

Irises withmode-lockingholes

built in 1960’s built in 1960’s (G. Loew…)(G. Loew…)

built in 1960’s built in 1960’s (G. Loew…)(G. Loew…)

ffrfrf = 2856 MHz = 2856 MHz


Short Bunch Generation in the Short Bunch Generation in the SLACSLAC Linac Linac

1-GeV Damping Ring1-GeV Damping Ring

z z 1.1 mm1.1 mm zz 50 50 mm zz 12 12 mm

zz 6 mm 6 mmSLAC LinacSLAC Linac

30 GeV30 GeV

FFTBFFTB

Existing bends compress to 80 fsecExisting bends compress to 80 fsec

1.5 Å1.5 Å

compression by factor of compression by factor of 500500

1.5%1.5%

28.5 GeV28.5 GeV

80 fs 80 fs FWHMFWHM

30 kA30 kA

RF DeflectorRF Deflector


Linac InstallationLinac Installation

SPPSSPPS::LL = 2.4 m = 2.4 mff = 2856 MHz = 2856 MHz

TTF-2TTF-2::LL = 3.6 m = 3.6 mff = 2856 MHz = 2856 MHz

LCLSLCLS::L L = 0.5 & 2.4 m= 0.5 & 2.4 mff = 2856 MHz = 2856 MHz

P. KrejcikP. Krejcik


MeasurementsMeasurements

RF Deflector RF Deflector OFFOFF

RF Deflector RF Deflector ONON


3-Point Bunch Length Measurement3-Point Bunch Length Measurement

Asymmetric parabola indicates Asymmetric parabola indicates incoming beamincoming beam tilttilt

Bunch length Bunch length reconstruction:reconstruction:

measure streak at 3 measure streak at 3 different RF phasesdifferent RF phases

Y = A * (X - B)**2 + CA = 1.6696E-02 STD DEV = 1.3536E-03B = 28.23 STD DEV = 3.084C = 1328. STD DEV = 8.235RMS FIT ERROR = 23.63

-80 -40 0 40 80

SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

****

***

**

**

*

****

********

-80 -40 0 40 80


1.7

1.6

1.5

1.4

1.3

X103

E

-80 -40 0 40 80


1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80


1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80


1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80


1.7

1.6

1.5

1.4

1.3

X103

E

MANUAL STEPPING. STEPS = 30

1-APR-03 20:21:16

Cavity on+180°

Cavity off

Cavity on180°

zz = 90 = 90 mm

yy22

RF deflector phase (deg)RF deflector phase (deg)


Practical IssuesPractical Issues

Extracting rms beam size from non-Gaussian, Extracting rms beam size from non-Gaussian, noisy screen imagenoisy screen image

Screen calibrationScreen calibration

Limited field of view on screenLimited field of view on screen

RF phase drift during measurementRF phase drift during measurement

Inadequate RF voltageInadequate RF voltage

Clumsy softwareClumsy software

Data acquisition time vs. beam drift timeData acquisition time vs. beam drift time


Voltage/Screen CalibrationVoltage/Screen CalibrationB

PM

B

PM

yy-p

ositi

on a

fter

def

lect

or (

mm

)-p

ositi

on a

fter

def

lect

or (

mm

)

RF deflector phase (deg)RF deflector phase (deg)

BPM calibration is only BPM calibration is only accurate to ~10% level: accurate to ~10% level:

……better to calibrate better to calibrate amplitude on screen and amplitude on screen and get pixels/deg (P. Krejcik)get pixels/deg (P. Krejcik)

RF phase setting is RF phase setting is highly accuratehighly accurate


Screen Pixel Calibration ErrorsScreen Pixel Calibration Errors

Errors on Errors on xx-axis produce bias in standard linear regression techniques…-axis produce bias in standard linear regression techniques…

T. Lohse, P. Emma, SLAC-CN-371, Feb 1989.T. Lohse, P. Emma, SLAC-CN-371, Feb 1989.

nono noise on noise on xx-axis:-axis:slopeslope = = 3.5 exactly3.5 exactly

SimulatedSimulated

beam

pos

ition

beam

pos

ition

RF phaseRF phase

noise on x-axis:fitted-slope = 2.6 (true = 3.5)

SimulatedSimulated

beam

pos

ition

beam

pos

ition

RF phaseRF phase

(from H. Schlarb’s 2003 talk)(from H. Schlarb’s 2003 talk)


Screen Pixel CalibrationScreen Pixel Calibration(from H. Schlarb’s 2003 talk)(from H. Schlarb’s 2003 talk)

100% klys. drive:100% klys. drive:0.427 mm/deg0.427 mm/deg

50% klys. drive:50% klys. drive:0.0415 mm/deg0.0415 mm/deg

50% klys. drive:50% klys. drive:4.92 pix/deg4.92 pix/deg

less sensitive to timing jitterless sensitive to timing jitter

scre

en

scre

en yy

-pos

ition

(pi

x)-p

ositi

on (

pix)

BP

M

BP

M yy

-pos

ition

(m

m)

-pos

ition

(m

m)

BP

M

BP

M yy

-pos

ition

(m

m)

-pos

ition

(m

m)


RF Deflector as Arrival Time MonitorRF Deflector as Arrival Time Monitor

At 14 GeV, a 10-At 14 GeV, a 10-m BPM resolution can m BPM resolution can resolve resolve <10 fsec<10 fsec timing error – but must timing error – but must also consider RF phase jitter.also consider RF phase jitter.

EE00 28 GeV, 28 GeV, VV00 24 MV, 24 MV, yy 50 m 50 m


Location of Main Linac DiagnosticsLocation of Main Linac Diagnostics

5+ energy spread meas. stations (optimized with small )5+ energy spread meas. stations (optimized with small )

...existing linac...existing linac

L0L0

rfrfgungun

L3L3L1L1 XX L2L2

xx,,yy xx,,yy xx,,yy xx,,yy

xx,,yy

EE EE EEEE

5+ emittance meas. stations designed into optics (x,y)

slice measurements possible with transverse RF (L0 & L3)BPMs at or near most quadrupoles and in each bend syst.

RF deflectors for slice and E measurements

EE

EE EEEEEE EE

T-cav.T-cav.

T-cav.T-cav.

xx,,yy??


Slice-Emittance Measurement SimulationSlice-Emittance Measurement SimulationRF-deflector at 1 MVRF-deflector at 1 MV

slice OTR 10 timesslice OTR 10 times

yy bunch length bunch length

scannedscanned quadquad


Slice-Emittance Measurement SimulationSlice-Emittance Measurement Simulation

slice-5slice-5

Injector at 135 MeV with Injector at 135 MeV with S-band RF-deflector at 1 MVS-band RF-deflector at 1 MV = meas. sim.

= calc.= y distribution= actual

(same SLAC slice-(same SLAC slice- code used at BNL/SDL) code used at BNL/SDL)

(slice-y-emittance also simulated in BC1-center)


Slice Energy Spread Measurements in LTUSlice Energy Spread Measurements in LTU

LTU at 14 GeV with S-band LTU at 14 GeV with S-band RF-deflector at 24 MVRF-deflector at 24 MV

FEL goalFEL goal

EE//E E 104

x 12 m

p. emma, slacicfa xfel 2004 - july 29, 2004 electron bunch measurements with a transverse rf...

Documents

slacicfa xfel

emma icfa xfel

ka rf deflector slide

transverse rf deflector

measurements rf deflector

screen rf phase drift

accurate slide

krejcik slide