Diagnostics Overview for the LCLS

Presented by Josef FrischFor the LCLS

ANL / LBNL / LLNL / SLAC

250 MeV 4.3 GeV

3.2-15 GeV

OTR or YAG screen

BPM in dispersive location

Wire Scanner

Pyroelectric bunch length monitor

Laser Heater

Tune-up Stopper

Beam arrival time cavity

X-ray Gas Detector

RF structure - S-band

RF structure – X band

Transverse Cavity

Quad scanned for emittance measurements

135 MeV

500 eV-10 KeV

X-ray Gas Attenuator

Primary LCLS Diagnostics

BPMs distributed throughout machine not shown

Undulator

3

Stripline Beam Position Monitors

Reso lu tion 4 .8 m icro ns

4.8 micron resolution at 200pC

S. Smith et. al.

4

X-Band Cavity BPM

Horizontal

Attenuator/bandpass

filterLow Noise Ampl

Power Limiter

Lowpass Filter

IF Amplifier

Low Noise Ampl

Power Limiter

Low Noise Ampl

Power Limiter

LO Ampl

119 MHz Beam Synchronized

Reference

Receiver Chassis

Ib

Reference cavity

Dipole cavity

40 MHz IF signals

To ADC

Attenuator/bandpass

filter

Attenuator/bandpass

filter

Termination

Vertical

Reference

Phase Locked Local oscillator

15 Volts/control I/O

11.424 GHz Local Oscillator

Power Distribution and Control

Vertical

Horizontal

Reference

Low Gain Bypass

Low Gain Bypass

Low Gain Bypass

Lowpass Filter

IF Amplifier

Lowpass Filter

IF Amplifier

Cavity Beam Position Monitors

~300nm Resolution250pC

Expect ~2 micron resolution at 20pC

Note: good resolution has been demonstrated in high Q cavity bpms for multi-bunch beams (ATF Japan)

5

Beam Orbit (stripline BPMs)

UndulatorBC2

LINAC Orbit tooSmall to see

6

Undulator Orbit (cavity BPMs)

7

Transverse Orbit FeedbacksGunLaunch

Injector launch

X-bandlaunch

L2 Launch

L3 Launch

Sector 28Launch

BSYLaunch

DL2ADL2B

LTU Undulator Launch

Orbit Feedbacks operate independantly at ~10 Hz. Provide stabilization, not jitter supression

Time slot control (120Hz) in near future. Possible cascading for better bandwidth

8

Electron Beam Transverse Screens

Ce:YAG Cathode Emission Image at 6 MeV

Ce:YAG in 135 MeV spectrometer TCAV on

OTR in 135 MeV bend, TCAV on

135 MeV OTR image

COTR makes OTR screens useless above 250 MeV

10,000X enhanced COTR

9

Wire ScannersNo Jitter Correction

With JitterCorrection

10

TCAV Bunch Length Measurement

ee

zz

ee

zz

2 .4 m2.4 m2.4 m2.4 m

yy

R FR F‘‘s treaks treak ’’

yyyyyy

R FR F‘‘s treaks treak ’’VV (( tt ))

SS -- band (2856 M H z)band (2856 M H z)

transve rse R F de flec to rtransve rse R F de flec to r

VV (( tt ))VV (( tt ))

SS -- band (2856 M H z)band (2856 M H z)

transve rse R F de flec to rtransve rse R F de flec to r

o ffo ff -- a x is sc re e na x is sc re e n

s in g les in g le -- sh o t, a b so lu te b u n ch sh o t, a b so lu te b u n ch le n g th m e a su re m e n tle n g th m e a su re m e n t

Can't measure bunch lengths <~20 femtoseconds RMS with S-band

X-band TCAV 4X F, 2X VResolution to ~2fs RMSX-band with SLED?

TCAV with wire scanner

11

Relative Bunch Length Monitor

Pyroelectric detector good from 100GHz to light(response is not flat)

Si transmits from mm-wave to ~20 um and 7um to 1um

12

Precision Timing SystemPhaseCavity

FiberSystem

Experiment

LaserSystem

Phase cavity measures electron beam timing Noise ~10fs, drift ~100fsec Note that X-ray timing may not exactly match

electron beam timing Fiber system (LBNL) transmits time information

~100M to Near Hall laser. ~20 fs stability Laser system locking ~25fs stability

13

Phase Cavity System

Standard Deviation of single cavity ~100fs RMS

Time Difference between Cavities ~100 fs drift over 1 day

Standard deviation of difference between cavities ~15 fs RMS

PhaseCavity

AdjustableAttenuator

Mixer

2805 MHz

X6Multiplier

476 MHzReference

51 MHz

¼Divider

Digitizer16 Bit

2856 MHz 119 MHz

PhaseMeasurement

Software

Trigger

14

MasterSource MDL

PLL

Injector L2 L3

BC1

DL2Undulato

rPCA

VAMO

PLL

Optical / RFphase

Detector

Opticaltransmitt

er

Optical / RF phaseDetector

ΔΦ

X6 X6

PhaseDet

PhaseDet

PCAV

BPFilte

r

BPFilte

r

BPFilte

r

BPFilte

r

ΔΦ

Feedback

Feedback

LengthsMatched

Laser

BPFilte

r

Laser

Diode

Feedback

476 Out(unused)

HighPowerRF

HighPowerRF

HighPowerRF

BLDBLD

Full timing sytsem ~50 fs timing (offline reconstruction)

When discussing timing systems, need to ask “stability relative to WHAT reference?“

Longitudinal Feedbacks

3.2-15 GeV

135 MeV

Undulator

Energy →amplitude

Energy and bunch length →Amplitude and phase Energy and bunch length →

Amplitude and phase

Energy → amplitude (phases of 2 sectors)

Longitudinal feedbacks operate independently at ~5Hz (MATLAB)In L2 and L3 amplitude is controlled by moving phases in opposite directions

1.5 Å

EE

tt

over-compressed

EE

tt

under-compressed

EE

tt

ffullycompressed

peak currentpeak currentMonitor (CSR)Monitor (CSR)

gasgasdetectordetector

Ultra-short Bunch OperationOperate at 20pc near full compression, estimate 5 femtosecond FWHM bunch length

Challenge for diagnostics – low charge, better timing precision desired

3.2-15 GeV

Undulator

Quick-change Diagnostic (ST0)

Port 1: Test samples for wavelenth filters, diffraction slits, visible light blocking filter, X-ray attenautors

Port 2: Ce:YAG screen, thermal sensor (future)

Port 3: B4C Stopper to protect downstream safety stoppers

Designed for rapid changes

3.2-15 GeV

Undulator

X-ray YAG: YAGXRAY

100um Ce:YAG Screen

YAGXRAY

10KeV

SaturationCurve

YAG saturatesAt high intensity orLong wavelength

19

Primary FEE Diagnostics

Gas Detector

Gas Attenuator

Direct Imager(Scintillator)

FEL Offset Mirror Systems

Beam Direction

SolidAttenuators

K-Monochromator

Thermal Sensor

Slit

Collimators

Pop-in cameras

Pop-in cameras

Reticule

C0 collimator (in e- beam dump

Fixed Mask

GasDetector

Originally designed to help find lasing

R. Bionta

20

Direct Imager YAG Screen

ScintillatorsYAG::Ce

NFOV Camera

(12 x 12 mm)WFOV

Camera(60 x 60 mm)

UV and visible light

sources

ND filter wheels

3.2-15 GeV

Undulator

X-ray YAGs: Direct ImagerDirect ImagerMultiple Ce:YAG screens5um, 100um, Wide and narrow field of view

Direct Imager WFOV

20pc at 800eV NFOV

Gas and solid attenuators allow adjustment of intensity to avoid saturation

Speckle from Be Attenuator

Pop-in monitors

22

Gas Detector

FEL

Primary photoelectrons cause N2 molecules to fluoresce in the near UV

N2 gas inletPhoto detector

Photo detector Magnet coils

Removable aperture

Vital for user operations: Provides non-invasive shot by shot pulse energy to users and accelerator operations

23

Gas Detector Calibration

Energy loss scan, vary steering measure energy loss from DL2 to dump

10 MeV2.5mJ

Calibration of gas detector against energy loss (linearity check)

24

Monocromator

DatumAxis

Set to pass 8.17 KeV

Scan of K-mono transmission vs beam energy

Can use harmonics for calibration at longer wavelengths

Would like a Spectrometer

25

Total Energy Monitor

Raw signal from total energy sensorCalibration of TE sensor against energy loss

Cryogenic pulsed temperature rise sensor

By the time this was operational we were trusting calibration from the e-beam energy loss

26

Critical Diagnostics for Operations

BPMs: High stability low noise BPMs critical to machine operation

Relative bunch length monitor Wire Scanners: For us these are the ONLY

option for electron beam size measurements Single shot beam time monitor X-ray YAG screens: Versatile diagnostic. Gas Detector: Non-invasive pulse energy

diagnostics.

27

What we need: Near Term

Calibrated thermal X-ray pulse energy monitor Needs to be compact and inexpensive for

installation after each X-ray mirror X-ray spectral measurement

Can probably use the SXR experiment spectrometer with K-edge foils for absolute calibration

Electron bunch length measurement for ultra-short bunches

Multi-bunch diagnostics

28

What we need: Longer Term

Non-invasive X-ray bunch length measurement Non-invasive, single shot X-ray to Laser relative

time measurement with 1fs resolution Non-invasive single shot X-ray spectral

measurement

Above measurements need to work over full operation range (500eV to 10 KeV)

Difficult Problems – Will keep us busy!

29

Comments

Diagnostics are critical: Tolerances in XFELs are too tight for operation "as built".

Need resources to build diagnostics after operation begins. New machines are likely to produce surprises. Some surprises are good!

Close integration with experiments is important: XFELS have more flexibility and more variability than synchrotron sources. Experimenters need extensive online beam instrumentation.