Review of state of the art diagnostic presented at BIW06 and DIPAC07

Review of state of the art diagnostic presented at BIW06 and DIPAC07

The workshops are the right opportunity for the distribution of information and the getting together of experts and beginners in particle beam diagnostics and instrumentation. The workshops deal with the state-of-the-art instruments and new concepts of diagnostics for particle accelerators. Real measurements are preferred for posters and presentations.Tutorial session serve as an introduction to relevant topics. (BIW)

High resolution BPMs required

What were the highlights (personal point of view)Part 1:

Recently commissioned and planned accelerators:Diamond, SNS, Soleil – ALBA, PETRAIII

Very Large Accelerators Projects:Beam Instrumentation Requirements for the International Linear Collider (ILC)Challenges for beam diagnostics in the FAIR project at GSILHC Instrumentation: Status and Outstanding Issues

X-ray FELs:Instrumentation for Linac-based X-ray FELsElectron Beam Diagnostics for the European X-Ray Free-Electron LaserFERMI@ELETTRA

Femtosecond Timing:Techniques for Femtosecond Timing and Synchronization in AcceleratorsSub-ps Timing and Synchronization Systems for Longitudinal Electron Bunch Profile Measurements

Bunch length:Bunch length measurements at JLab FEL using coherent transition and synchrotron radiationsSingle Shot Longitudinal Bunch Profile Measurements by Temporally Resolved Electro-Optical Detection

+ a lot of other very interesting topic, (some will be presented at this conference)!…, Feedback Systems, Transversal emittance measurements (huge field, lot of contributions),FPGA in diagnostic instruments, Optical and IR diagnostic methods: OTR, ODR, CSR, …New Acceleration Methods: Physics And Diagnostics Of Laser-Plasma Accelerators Characterization of laser accelerated electron beams with coherent THz….

Components of a Beam Position Monitor

Analog Front End

Analog Pre-processing

Digital Post-processing

Digitizer Calibration Source

Beam

Pickup

Provide a signal that carries beam position information

Ensure long term stability

• Calc. and Σ• Normalization • Monopole-mode rejection

• Filtering• Amplification• Frequency conversion• Detection

• Offset and gain correction• Linearization• Normalization• Filtering

Close proximity and stiff cables for stability

Shielded from radiation

DIPAC’07, Venice, Italy D.M. Treyer, „High Resolution Single-Shot Beam Position Monitors“

Pillbox Cavity Pickup

Single-shot cavity:25 nm at fTM110 = 5712 MHz and Q = 130 at 1 nC in 20 mm beam pipe

[T. Shintake, HEAC’99]

Measurement of noise in RF-BPM triplet yields ~20 nm single-pulse resolution

DIPAC’07, Venice, Italy D.M. Treyer, „High Resolution Single-Shot Beam Position Monitors“

Beam Instrumentation Challenges at the International Linear ColliderBIW2006, P. Tennenbaum

Figure courtesy M. Ross and G. White, SLAC

This example:

DESIGN OF THE CAVITY BPM SYSTEM FOR FERMI@ELETTRAP. Craievich, DIPAC07

20nm X/Y Orbit RMS (BW ≈ 10 Hz)

Diamond* is using 168 Libera EBPMs in its storage ring (Button Pickups).These have served most valuable information from first turns during commissioning of the storage ring, to beam based alignment of the BPM readings to quadrupole centres and slow orbit feedback implemented through the EPICS interface and a MatLab based correction routine.…The FOFB is currently in the commissioning stage and has successfully been running at full rate and with all EBPMs and correctors. …With these preliminary settings, very reasonable suppression could be achieved, in particular for the beam movements around 16 Hz and 25 Hz which have been found to be caused by ground motion…* Alba, PETRAIII, Soleil, DELTA, ESRF, … have it or plan to buy.

Digital EBPMs at Diamond: G. Rehm, et al, DIPAC07

Orbit with Fast Orbit Feed Back on

BPM Readout (commercial solution)

THE SOLEIL BPM AND ORBIT FEEDBACK SYSTEMSN. Hubert,et al. DIPAC07

Soleil with slow orbit feedback


Reliability and Damage issues


Very Large Accelerators Projects:Beam Instrumentation Requirements for the International Linear ColliderChallenges for beam diagnostics in the FAIR project at GSILHC Instrumentation: Status and Outstanding Issues





0.01

0.10

1.00

10.00

100.00

1000.00

1 10 100 1000 10000Momentum [GeV/c]

En

erg

y st

ore

d in

th

e b

eam

[M

J] LHC topenergy

LHC injection(12 SPS batches)

ISR

SNSLEP2

SPS fixed target

HERA

TEVATRON

SPSppbar

SPS batch to LHC

Factor~200

RHIC proton

The LHC: Coping with a Huge Stored Beam Energy

Energy to heat and melt one kg of copper: 700 kJ

3 mm2

• The Beam Loss Monitoring system is a vital part of the active protection of the LHC with lot of redundant monitors ( 4000)• Two digital signal paths for very high reliability• Reliability figures have been evaluated using commercial software package (Isograph™). The probability of not detecting a dangerous beam loss was calculated to 10-3, which corresponds to the SIL3 level. • This includes the lifetime of the detector ( 20 years) with an expected radiation dose at some locations of several ten MGy per year.

•LHC Instrumentation Status and Challenges, R. Jones, BIW06•SECONDARY ELECTRON EMISSION BEAM LOSS MONITOR FOR LHC, E.B. Holzer et al, DIPAC

Reliability Issues of the LHC BLM System








Sub-ps Timing systems

Femto-Second Synchronization

The operation of ultra-violet and X-ray free electron lasers requires a bunch arrival-time stability on the order of several tens of femto-seconds between the X-ray pulses and laser pulses of external probe lasers, to be able to take full advantage of the fs-short X-ray pulses in pump-probe experiments.

– What is the currently achievable signal jitter for a reference signal? – How do we measure it and where does jitter in an FEL-based machine come

from?– How and to what level can we get rid of it?

• But one can also measure the delay and sort it into slices to use this information for the pump-probe experiment results.

RF gun

Photocathode Laser

BC3

Undulators

BC2 ACC 23

Diag.

ACC 45ACC 1

Diag.

LOLAISR

L2RFPP-

laser

MasterMasterStabilized link

Stabilized linkStabilized link

Sta

bilize

d lin

kStabilized link

LLRF and Diagnostic

FEL seed laserPC drive laser

EO laser

User laser

All based on stable Synch. Signal

2005 Nobel Prize in Physics awarded to John L. Hall and Theodor W. Hänsch "for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique"

This technology is nearly ready for applications in precision synchronization in accelerators (J. Byrd, BIW2006)

Nobel LecturePassion for Precision Theodor W. Hänsch December 8, 2005, at Aula Magna, Stockholm University. http://nobelprize.org/nobel_prizes/physics/laureates/2005/hansch-lecture.html

All based on stable synch. signal and stabilized links

The timing system will play a crucial role in achieving the expected performance in Linac based FELs due to the sub-ps electron bunch length and to the expanded use of fs-lasers as key components in future light sources.

RF gun

Photocathode Laser

BC3

Undulators

BC2 ACC 23

Diag.

ACC 45ACC 1

Diag.

LOLAISR

L2RFPP-

laser

Few hundred meters up to few km distance

First prototype of an optical cross-correlation based fiber-link stabilization for the FLASH synchronization system; Florian Loehl, Holger Schlarb (DESY, Hamburg), Jeff Chen, Franz Xaver Kaertner, Jung-Won Kim (MIT, Cambridge, Massachusetts), DIPAC07

0.0 5.0 10.0 15.0 20.0 25.0-4

-3

-2

-1

0

1

2

Digital and Analog Phase Detector Comparison

HP8405A

SR560

Hours, 24 Oct 2005

Ph

as

e D

ete

cto

r O

utp

ut

(fs

ec

)

Lab AC cycle

Measure slow drift (<1 Hz) of fiber under laboratory conditions

Compensation for several environmental effects results in a linear drift of 0.13 fsec/hour and a residual temperature drift of 1 fsec/deg C.

Environmental factors

• Temperature: 0.5-1 fsec/deg C

• Atmospheric pressure: none found

• Humidity: significant correlation

• Laser Wavelength Stabilizer: none

• Human activity: femtosecond noise in the data

Compare phase at the end of fiber with reference to establish stability.

J. Byrd, Progress in femtosecond timing distribution and synchronization for ultrafast light sources BIW06

Bunch timing jitter sources

Timing jitter behind BC

Gradient Phase IncomingTiming jitter

C compression factor (20)R56 ~ 100 mm XFEL /180 mm FLASHkrf: wavenumber RF acceleration (27.2/m)

XFEL: 3.3 ps/%FLASH: 5.5ps/%

2 ps/deg 0.05 ps/ps

A. Winter: Sub-ps Synchronization Systems for Longitudinal electron bunch profile measurementsDIPAC07

How to measure?: Use of standard beam diagnostic instruments with a “clever” correlation to other machine parameters

Measurement: Bunch arrival monitor ()

A Sub-50 Femtosecond bunch arrival time monitor system for FLASH; F. Loehl, Kirsten E. Hacker, H. Schlarb (DESY, Hamburg) DIPAC07

Gradient Jitter of Accelerating Module

RF gun

Photocathode Laser

BC3

Undulators

BC2 ACC 23

Diag.

ACC 45ACC 1

Diag.

LOLAISR

L2RFPP-

laser

The horizontal beam profile is imaged (using SR) by a telescope onto a gated, intensified CCD camera. The energy distribution of a 10 ps FWHM electron bunch with a residual energy spread of only a few keV shows a steep rising edge at high energies with a low energy tail, as plotted in Fig. 4. Phase variation of the acceleration module changesthe tail distribution, while gradient variations shift the entire profile. To determine the energy stability, the offset value of a linear fit on the rising edge is used. lower energy higher energy

Measurement of energy stability

Typically, an energy stability of 2.7·10−4 is measured, where values as small as 1.5·10−4 have been recorded. This corresponds to an arrival jitter of about 140 fsec or 75 fsec, respectively.

Ch. Gerth; “SYNCHROTRON RADIATION MONITOR FOR ENERGY SPECTRUM MEASUREMENTS IN THE BUNCH COMPRESSOR AT FLASH”, DIPAC 2007, 20-23. May

2007, Venice, Mestre, Italy. DIPAC07

Phase Jitter of Acceleration Module

Off-crest acceleration provides an energy chirp that leads to a compression of the electron bunch in a magnetic chicane.

Compression is monitored at FLASH using a diffraction radiator after the chicane and a pyro-electric sensor that records the emitted coherent Terahertz radiation power. When the phase of ACC1 is scanned the compression monitor detects, within a narrow phase range

of about 4◦ FWHM, a large coherent signal. The monitor signal varies strongly with the ACC1 phase and the slope of the linear fit provides the calibration factor.The phase stability over 10 minutes is shown

in Fig. 7(b) and amounts to 0.067◦ (= 134 fs). Beam injection and the RF gun phase jitter is still included, so the quoted value is an upper limit on the phase stability achieved by the low level RF regulation.

Beam Based Measurements of RF Phase and Amplitude Stability at FLASH; Holger Schlarb, Christopher Gerth, Waldemar Koprek, Florian Loehl, Elmar Vogel (DESY,

Hamburg); DIPAC07

RF Gun Phase Jitter

RF gun

Photocathode Laser

BC3

Undulators

BC2 ACC 23

Diag.

ACC 45ACC 1

Diag.

LOLAISR

L2RFPP-

laser

To measure the gun phase stability, a current transformer (toroid) for bunch charge measurements is used. First, the gun phasing is performed by scanning the RF cavity over 360◦ while recording the bunch charge. The result of a scan is shown in Fig. 1. With a slew rate of typically 0.05 nC/deg, marked as a red line in Fig. 1, and a single shot toroid resolution of 2-3 pC/bunch, the phase jitter can be determined bunch-by-bunch with a precision

of 0.05◦ (100 fs).








Sub-ps bunch-length

Transverse Cavity

• Translates longitudinal into transverse beam profile when operating at RF zero crossing

• Temporal resolution limited by unstreaked spot size

c

ee

z

~ z

vertical streak

phase advance best: = 90o

S

Courtesy of P. Krejcik, P.Emma

Kicker

• Parasitic operation with kicker and off-axis screen (pulse stealing mode)• Single shot absolute bunch length measurement• It’s like a beam based streak camera• LOLA = named after its designers G. LOew, R. Larsen, O. Altenmueller (1964)

Christopher Gerth; Electron Beam Diagnostics for the European X-Ray Free-Electron Laser, DIPAC07

0 0.5 1 1.50

5

10

15

20

xnorm

[mm

mra

d]

t [ps]

x

[mm

]

-1.5

-1

-0.5

0

0.5

1

density profile [a.u.]slice boundaries

0

50

100

150

200

250

Measurement resolution: 60 fs Lasing part: ~ 25 fs

• Two density ‘islands’ visible within a slice: smaller emittance for each island

• Quadrupole scan using 6 Magnets

• Measurement destructive to SASE operation! Scan takes about 30 min.

Slice emittance measurement Slice energy spread

• Screen in large dispersive section and small

• Resolution of ΔE ~ 7.2 keV was achievedSRF Linac

Dump

OTR

Quad

Quad

DipoleTDS

Bunch length measurements using coherent radiation

Transition (synchrotron) radiation is produced when the electron bunch passes a boundary of two media(magnetic field).

Response time is zero. Shape of the radiation pulse is a

“copy” of the electron bunch shape.

When the wave length of the radiation becomes more than the bunch length the radiation becomesCOHERENT. ( L )

Power is proportional to:intensity of incoherent radiation N intensity of coherent radiation N2

Measurements of the radiation spectrum give information about the bunch length.

An interferometer could be used to measure the spectrum.

at 135 pCN 8.4108

P. Evtushenko et al.; Bunch length measurements at JLab FEL using coherent transition and synchrotron radiation, BIW06

Interferometers

Two different interferometers;essentially both are a modificationof the Michelson interferometer.

The two interferometers differ inimplementation; Beam splitter Polarizer Detector Focusing element Mirror position measurements!

Modified Martin-Puplett interferometer:(step scan device 2 min/scan) beam splitter & polarizer (wire grids) detector (Golay cell) focusing (Plano-convex lens) mirror position is set by step motorUsed with CTR

Michelson interferometer:(rapid scan device 2 sec/scan) beam splitter (silicon) detector (pyroelectric) focusing (parabolic mirrors) mirror position is measured by another built-in interferometerUsed with CSR

P. Evtushenko et al.; Bunch length measurements at JLab FEL using coherent transition and synchrotron radiation, BIW06

Measurements

Bunch length measurements using a Martin-Puplett interferometer at the VUV-FEL. L. Froehlich Hamburg DESY - DESY-TESLA-FEL-05-02

Since there is no phase information, the pulse reconstruction may be carried out using the Kramers–Kronig analysis.

The investigation of the longitudinal charge distribution in the electron bunches on a bunch-by-bunch basis is an important issue for optimizing the operation of the machine. The new single-shot spectrometer uses diffraction gratings as dispersive elements and an array of pyroelectric detectors with multi-channel readout. Profiles with a leading peak in the bunch as short as 15 fs were detected.

single-shot spectrometer

H. Delsim-Hashemi;“THz Spectroscopic Methods as longitudinal Diagnostics for FELs”, DIPAC07

Scanning delay sampling: This is the simplest and first demonstrated example EO bunch diagnostics. A short(sub-50fs) laser is used to sample fixed parts of the FIRpulse, and an integrated intensity change in the optical probe is measured. Scanning the relative delay between laser and electron bunch allows the build up of the profile. Multi shot measurements such as this do suffer fromtime jitter between the laser and electron bunch; however,in even the first demonstration, scanning rates of 2ps per μswere achieved, and over such short measurement periodsvery small timing jitter (<50 fs) can be achieved.

Spectral decoding (SD): The measurement of the optical spectrum can be used to directly infer the field temporal profile if a chirp is first applied to the optical pulse, so that there is a known time-frequency relationship in the sampling laser pulse. SD characterization of the in-beam-line Coulomb field has been demonstrated at several facilities, including FELIX, NSLS, and FLASH. The technique has also been demonstrated for single shot characterisation of CSR, and CTR

Spatial encoding: This approach has many similarities to the scanning delay line approach, but instead allows for asingle-shot measurement. By sampling the Coulomb field with an optical pulse obliquely incident to the EO crystaland the Coulomb field propagation direction, there is a spatial to temporal mapping introduced for the relativedelay of the laser arrival time at the crystal. Imaging the EO crystal, and the intensity changes as a function of spatial position, therefore allows the determination of the field induced intensity changes as a function of relative arrival time at the crystal.. This approach has been demonstrated at SLAC FFTBand at DESY on FLASH. At the FFTB EO signals of 270 fs FWHM were measured, while at FLASH ∼ 300 fs FWHM signals have been obtained.

Temporal decoding (TD): The time structure of the electric field of the electron bunch is encoded onto a chirped laser pulse. In the electro-optic crystal the stretched laser pulse acquires an elliptic polarization with an ellipticity which is proportional to the electric field of the electron bunch and encodes its temporal structure. The analyser, turns the elliptical polarization into an intensity modulation, which is then sampled by the gate pulse in a single-shot cross-correlator, using a second harmonic BBO crystal. TD has been demonstrated at FELIX, and more recently at FLASH. In these later experiments an electro-optic signals with FWHM duration of 118 fs were observed. Single Shot Longitudinal Bunch Profile Measurements by Temporally Resolved Electro-Optical DetectionP. J. Phillips, et al.; 8th DIPAC 2007,

Femtosecond Bunch Length Measurements Steven Jamison, at all, EPAC'06

Temporal Decoding

GaP

- the chirped laser pulse behind the EO crystal is measured by a short laser pulse with a single shot cross correlation technique

- approx. 1mJ laser pulse energy necessary

4.4 4.6 4.8 5 5.2

LolaB 2006 03 01 01 43 3380

time [ps]

EO

sig

nal/s

qare

d LO

LA s

igna

l

EO

S@

VU

V-F

EL

by F

ELI

X, D

ES

Y, D

unde

e, D

ares

bury

30-

Apr

-200

6

110fs FWHM80fs FWHM

Comparison of EO and LOLA signals

3.5 4 4.5 5 5.5 6 6.5

LolaB 2006 03 01 01 43 3380

time [ps]

EO

sig

nal/sqare

d L

OLA

sig

nal

EO

S@

VU

V-F

EL b

y F

ELIX

, D

ES

Y, D

undee, D

are

sbury

01-M

ay-2

006

squared Lola signalEO signal

EO at first bunch, LOLA at second bunchin the same bunch train

SASE conditions

ACC1 phase 3° overcompression

7 7.5 8 8.5 9 9.5 10

LolaS 2006 03 01 03 08 0719

time [ps]

EO

sig

nal/s

qare

d LO

LA s

igna

lE

OS

@V

UV

-FE

L by

FE

LIX

, DE

SY

, Dun

dee,

Dar

esbu

ry 0

1-M

ay-2

006

Preliminary unpublished Data







Summary

Reliability and Damage issues

Sub-ps Timing systems

High resolution BPMs required

Sub-ps bunch length

The End Question?

Documents

Review of state of the art diagnostic presented at BIW06 and DIPAC07