Mostly by Gwyn Williams and the JLab Team, Presented by D. Douglas Working Group 4 Diagnostics & Synchronization Requirements Where we are and what needs work… Kevin Jordan Jefferson Lab, Newport News VA

Charge for working group 4 Review what works & why –What good & bad decisions have been made Synchronization –What does one need and how much will it cost? Beam Instrumentation Requirements –Multipass BPMs –Injector Diagnostics – especially phase space tomagraphy –Exploit synchrotron light! Beam Loss & Halo Operational Procedures

LBNL/SLAC To produce an ultra-stable timing and synchronization system with jitter reduced to the few femtosecond level, we have developed a laser-based scheme with optical signals distributed over a stabilized optical fiber. Transmitting precise frequency and timing signals over distances of hundreds of meters, stabilized to a few femtoseconds (a few parts in 108), is accomplished by measuring the phase delay in an optical fiber and actively compensating for differences with a piezoelectric modulator. In our scheme, phase differences at optical frequency are down-converted to 110 MHz. Because phase information is preserved during the heterodyning process, phase differences at optical frequency can be detected at radio frequencies, using conventional RF electronics. The radiofrequency reference signal need not be provided with femtosecond accuracy at the far end of the fiber, because one degree of error at 110 MHz is equivalent to only one degree at the optical frequency, or fs. The system is linear, and signals modulated onto the CW laser carrier at the fiber entrance do not intermodulate with each other. Moreover, the optical power level is significantly below any nonlinear threshold in the fiber. The laser frequency itself must be stabilized, so the laser is locked to an absorption line in an acetylene cell. At present, a 4 km fiber link has been stabilized to the femtosecond level. 2 km of fiber in this link passes under several roads and through several buildings at LBNL, demonstrating that the fiber stabilization system is robust under real-world conditions. This technique will soon be used as a backbone to demonstrate synchronization of mode- locked lasers. Further developments will include integration with controls and low-level RF systems, and high- resolution diagnostics of photon and electron beams, to provide enhanced feedback control of the integrated laser/accelerator systems. We are planning to develop and implement similar systems at the LCLS, and Steve Lidia for the LBNL team

Initial results (LBNL) Simplified setup: lasers co-located on optical bench Cross-correlator delay set to partially overlap pulses Voltage versus time delay is close to linear Error signal sensitivity is 0.13mV/fs 120fs FWHM modelocked laser 1 f1 f2 f3 f4 reprate 1530nm bandpass 1570nm bandpass + free-space output fiber output coarse 100MHz lock electronics modelocked laser 2 cross-correlator 1MHz bandwidth detector cross-correlation: 5.7fs RMS from 1Hz to 100kHz Inter-laser link not stabilized gives short stabilization time Currently no acoustic isolation Can improve loop gain by filtering

Work in Progress: Synchronisation Activities for ERLP and 4GLS Graeme Hirst STFC Central Laser Facility

ERLP/4GLS Summary Synchronisation requirements for ERLP are relaxed. The photoinjector laser needs to be (and has been) locked to the machine RF with jitter <1ps. ERLP will act as a testbed for some of the subsystems needed for 4GLS. A clock is being developed based on an Er fibre oscillator locked at low frequencies to a stable RF source. A fibre distribution system based on laser pulse propagation will be tested. EO timing of electron bunches is planned. Synchronisable commercial lasers are being evaluated. A phase noise measurement system is operational and is being improved. “Local” synchronisation is being developed. A conceptual design for 4GLS synchronisation has been produced. Electron bunch arrival time appears to be the major outstanding problem. Fast electron timing sensors will be implemented and the option of feedback control of timing will be investigated.

Timing for JLab FEL Amplifier Design Since the beam shifts in time due to small RF fluctuations I (S. Benson) have assumed that we can't hold the electron beam timing to better than about 1 psec. The specification for the laser thus has a pulse length of a few picoseconds to ensure that there is reasonable overlap despite the timing jitter –Most of the amplifier designs assume a picosecond FWHM micropulse so you don't gain too much by having jitter smaller than about 100 fsec –Again is doesn't make much sense to have the laser timing jitter much better than the electron beam timing jitter. – If this is done to about 100 fsec it would be fine.

JLab ERL FEL Amplifier Design E = 120 MeV 135 pC pulses up to 75 MHz 20/120/1 microJ/pulse in UV/IR/THz 250 nm – 14 microns, 0.1 – 5 THz All sources are simultaneously produced for pump-probe studies Current plan (hope $$) is to use the UV components to demonstrate FEL amplifier 10 kWatt CW FEL amplifier output for direct comparison to oscillator FEL Seed Laser

Synchronization Bottom Line You get what you pay for! State of the Art; LCLS designs –$1M(+) gets you 10s fsec over kilometers of fiber Every System needs a good Master Oscillator –Expect $50k - $100k Small machines (<100 meters) can use temp stabilized copper for ~$150k –1/10 degree, 1.3GHz ~200fsec –100fsec target Seed laser requirement for JLab FEL Amplifier ~100fsec

Tentative parameters of KEK ERL test facility Parameter Injection energy5 MeV (10-15 MeV) Injector beam power500 kW (1MW) Beam energy in arcs~60 MeV ( MeV) SC cavities for main linac 9 cells x 4: single module (two modules) Normalized emittance1 mm mrad(0.1 mm mrad) Beam current10mA – 100mA RMS bunch lengthUsual mode: sz=1-2 ps Short bunch mode: sz ~100 fs

Beam instrumentation for ERL Beam profile measurement –Fluorescence screen for low energy (<10 MeV) –Optical profile monitor by OTR or SR –Wire scanner (SEM or Compton scattering) –High speed gated camera Beam position measurement –BPM (electric) –BPM (SR or OTR) Intensity measurement –DCCT/NPTC –Photocathode, Faraday cup –SR or OTR based intensity monitor

Beam instrumentation for ERL cont. Emittance measurement –Fluorescence screen with slit –Quad Scan + OTR –Wire scanner Beam temporal structure –Streak camera (SR or OTR) (>1 psec bunches) –Incoherent intensity interferometer (SR or OTR) –CSR interferometer –LOLA Streak cavity Beam Halo –Wire scanner or Fork –Coronagraph (SR or OTR) Beam Energy (SR or Dipole +BPM/Viewer at dump) Beam loss monitor

Long term goal is to separate pulses at higher Micropulse Repetition Rate Frequencies. Multi-pass BPMs in the FEL LINAC (under development) 2 nd Pass Pulse 1 st Pass Pulse Micropulse Repetition Rate Frequency (9.425 MHz)

1.16 MHz Multi-pass Solution

Coronagraph for halo measurement at KEK Objective lens Field lens Baffle plate (Lyot stop) Relay lens Opaque disk Anti-reflection disk Baffle plates to reduce reflection

Single bunch 65.8mA Exposure time of CCD : 3msec Exposure time of CCD : 100msec Intensity in here : 2.05x10 -4 of peak intensity 2.55x10 -6 Background leavel : about 6x10 -7 Far tail Observation (KEK) Chronograph

Halo Monitor at JLab FEL Forks on 6” stepper motor driven actuators Not yet fully exploited Able to see nanoamps (or better) –Use with BLM to enhance performance

Differential DCCT to measure current valance (or beam loss) between accelerated beam and decelerated beam Beam Loss (accounting) at KEK Problem is that ~1 microamp is tolerable loss 1 part in 10 3 for 1 milliamp 1 part in 10 5 for 100 milliamp Instrument is not that accurate/stable but if it was the variation in charge in micropulse to micropulse is no better than 0.1%!

Operational Procedures Set the phase of cavity 1-3 (this section was updated to show how to use ITV0F06 viewer instead of IPM0F06 BPM) Note: if you change cavity 1-3 by more than, say, 1/2 degree, you should go back and repeat it all - because it will make the zero crossing go away. (per Dave Douglas) insert ITV0F06 map ITV0F06 to the monitor 17 (to the WesCam) and make image acquisition “Beam X–Position (mm)” needs to be (see shift plan for the right number)?1. If it is, you are done. If it is not, open the injector RF slider screen by clicking the appropriate button on the 4-seater, see Fig. 6. Set the gain on the cavity 1-3 phase slider to 0.1o and adjust the phase to make ITV0F06 “Beam X–Position (mm)” to be the right number?1 –If the ITV0F06 “Beam X–Position (mm)” more than the right number, push the phase positive. –If the ITV0F06 “Beam X–Position (mm)” less than the right number, push the phase negative.

Repository of available procedures Writing procedures saves time during commissioning! Too often they are written after the fact To help Yuri & ERLP I will post written procedures on open web site Any donations will be accepted at This will serve as a starting point ERL commissioning documents

How do we solve the challenges? The Beam is NOT Gaussian! –How can the diagnostics give better information to models –Novel tomagraphic solutions Halo is and will continue to be a problem –What experiments can be done now? Injector requirements –Proper set-up & monitoring (we still have drifts!) Multipass BPMs remain to be a challange Synchronization requirements