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

1. 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)

2. High resolution BPMs required What were the highlights (personal point of view) Part 1:

3. Components of a Beam Position Monitor • Calc.  and Σ • Normalization • Monopole-mode rejection Ensure long term stability Shielded from radiation Close proximity and stiff cables for stability • Filtering • Amplification • Frequency conversion • Detection • Offset and gain correction • Linearization • Normalization • Filtering Provide a signal that carries beam position information DIPAC’07, Venice, Italy D.M. Treyer, „High Resolution Single-Shot Beam Position Monitors“

4. Pillbox Cavity Pickup Single-shot cavity: 25 nm at fTM110 = 5712 MHz and Q = 130 at 1 nC in 20 mm beam pipe Measurement of noise in RF-BPM triplet yields ~20 nm single-pulse resolution Figure courtesy M. Ross and G. White, SLAC [T. Shintake, HEAC’99] Beam Instrumentation Challenges at the International Linear Collider BIW2006, P. Tennenbaum DIPAC’07, Venice, Italy D.M. Treyer, „High Resolution Single-Shot Beam Position Monitors“

5. This example: DESIGN OF THE CAVITY BPM SYSTEM FOR FERMI@ELETTRA P. Craievich, DIPAC07

6. BPM Readout (commercial solution) Orbit with Fast Orbit Feed Back on 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. 20nm X/Y Orbit RMS (BW ≈ 10 Hz) Digital EBPMs at Diamond: G. Rehm, et al, DIPAC07

7. Soleil with slow orbit feedback THE SOLEIL BPM AND ORBIT FEEDBACK SYSTEMS N. Hubert,et al. DIPAC07

8. What were the highlights (personal point of view) Part 2: Reliability and Damage issues

9. 3 mm2 The LHC: Coping with a Huge Stored Beam Energy Energy to heat and melt one kg of copper: 700 kJ

10. Reliability Issues of the LHC BLM System • LHC Instrumentation Status and Challenges, R. Jones, BIW06 • SECONDARY ELECTRON EMISSION BEAM LOSS MONITOR FOR LHC, E.B. Holzer et al, DIPAC • 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.

11. What were the highlights (personal point of view) Part 3: Sub-ps Timing systems

12. Photocathode Laser ACC 1 BC2 ACC 23 ACC 45 BC3 Undulators Diag. ISR Diag. LOLA PP-laser L2RF 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

13. Master Stabilized link Stabilized link Stabilized link Stabilized link FEL seed laser Stabilized link PC drive laser User laser EO laser LLRF and Diagnostic 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)

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

15. Few hundred meters up to few km distance Photocathode Laser ACC 1 BC2 ACC 23 ACC 45 BC3 Undulators Diag. ISR Diag. LOLA RF gun PP-laser L2RF 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.

16. Compare phase at the end of fiber with reference to establish stability. 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 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 J. Byrd, Progress in femtosecond timing distribution and synchronization for ultrafast light sources BIW06

17. Bunch timing jitter sources Timing jitter behind BC Gradient Phase Incoming Timing jitter XFEL: 3.3 ps/% FLASH: 5.5ps/% 2 ps/deg 0.05 ps/ps C compression factor (20) R56 ~ 100 mm XFEL /180 mm FLASH krf: wavenumber RF acceleration (27.2/m) How to measure?: Use of standard beam diagnostic instruments with a “clever” correlation to other machine parameters A. Winter: Sub-ps Synchronization Systems for Longitudinal electron bunch profile measurements DIPAC07

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

19. Photocathode Laser ACC 1 BC2 ACC 23 ACC 45 BC3 Undulators Diag. ISR Diag. LOLA RF gun PP-laser L2RF Gradient Jitter of Accelerating Module 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 changes the 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

20. 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

21. 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

22. Photocathode Laser ACC 1 BC2 ACC 23 ACC 45 BC3 Undulators Diag. ISR Diag. LOLA RF gun PP-laser L2RF RF Gun Phase Jitter 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).

23. What were the highlights (personal point of view) Part 4: Sub-ps bunch-length

24. Kicker ~ z - - e e • 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) z Transverse Cavity vertical streak  c S phase advance best:  = 90o • Translates longitudinal into transverse beam profile when operating at RF zero crossing • Temporal resolution limited by unstreaked spot size Courtesy of P. Krejcik, P.Emma Christopher Gerth; Electron Beam Diagnostics for the European X-Ray Free-Electron Laser, DIPAC07

25. SRF Linac TDS Dipole OTR Quad Dump Quad Slice emittance measurement Slice energy spread • 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. • Screen in large dispersive section and small b • Resolution of ΔE ~ 7.2 keV was achieved

26. 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 becomes • COHERENT. (   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 pC N  8.4108 P. Evtushenko et al.; Bunch length measurements at JLab FEL using coherent transition and synchrotron radiation, BIW06

27. Interferometers Two different interferometers; essentially both are a modification of the Michelson interferometer. The two interferometers differ in implementation; Beam splitter Polarizer Detector Focusing element Mirror position measurements! Michelson interferometer: (rapid scan device 2 sec/scan) beam splitter (silicon) detector (pyroelectric) focusing (parabolic mirrors) mirror position is measured by another built-in interferometer Used with CSR 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 motor Used with CTR P. Evtushenko et al.; Bunch length measurements at JLab FEL using coherent transition and synchrotron radiation, BIW06

28. Measurements Since there is no phase information, the pulse reconstruction may be carried out using the Kramers–Kronig analysis. Bunch length measurements using a Martin-Puplett interferometer at the VUV-FEL. L. Froehlich Hamburg DESY - DESY-TESLA-FEL-05-02

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

30. Femtosecond Bunch Length Measurements  Steven Jamison, at all, EPAC'06 Spatial encoding: This approach has many similarities to the scanning delay line approach, but instead allows for a single-shot measurement. By sampling the Coulomb field with an optical pulse obliquely incident to the EO crystal and the Coulomb field propagation direction, there is a spatial to temporal mapping introduced for the relative delay 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, 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 FIR pulse, 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 from time jitter between the laser and electron bunch; however, in even the first demonstration, scanning rates of 2ps per μs were achieved, and over such short measurement periods very 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

31. 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

32. Comparison of EO and LOLA signals ACC1 phase 3° overcompression EO at first bunch, LOLA at second bunch in the same bunch train SASE conditions Preliminary unpublished Data

33. Summary High resolution BPMs required Reliability and Damage issues Sub-ps Timing systems Sub-ps bunch length

34. The End Question?