Longitudinal Diagnostics for start-up Christopher Gerth (DESY) On behalf of XFEL WP18 and many others … Workshop on Linac Operation with Long Bunch Trains 23 February 2010 8

Introduction Set-up of the machine = find operating points a) old settings: save&restore b) predicted operating points from simulations Diagnostics: magnets => orbit,matching => transverse diagnostics (BPM, OTR, BLM, …) modules => energy, bunch compression => longitudinal diagnostics => coarse diagnostics needed with large dynamic range (this talk) Stable operation of the machine = lock operating points a) single-bunch resolution b) feedback capability => high-resolution diagnostics needed (talk before lunch)

Injector laser & Gun set-up See talk by Siggi …

Measurement of absolute Beam Energy in BC2 OTR EBPM SR camera Alignment laser BPM 317.6 mm (survey data) BPM Absolute position of alignment laser: ~ ±0.5 mm Absolute BPM measurement: ~ ±0.5 mm Error of beam energy ~ 1mm/300mm ~ ±0.3% Absolute B field of dipoles: ~ ± 0.2% Error of absolute gun energy ~ ± 0.3 MeV => Error of measured energy gain in ACC1 ~ ±0.7% => ± 1MeV @ 130MeV

Minimum bend angle for SR Camera Beam centre: 292 mm ~ 16.5 deg However, best to stay at 18 deg for beam energy measurement if no particular angle is needed. 10 mm + 7 mm 26 mm 317.6 mm Angle under which SR is imaged: 6 mrad

1) Find on-crest phase (OTR,SR Camera in BC2) Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera in BC2) dE <= minimize energy spread (not exactly on-crest) => accuracy ± 0.5 deg Igor’s 1D simulation tool ~ 1 deg towards compression

1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan 9DBC2.3 Weaker signal in case 9DBC2.1 is saturated! ~ on-crest ~ SASE 9DBC2.1

1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan Saturated? Not centered in DR ? …

1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera) 2) Pyro phase scan Save&Restore required for Pyro Parameters! Especially if someone changes the setup! Accuracy ??? Saturated but scan is still working.

1) Find on-crest phase (OTR,SR Camera) 2) Pyro scan Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera) 2) Pyro scan 3) Start slow feedback => Ideally you have an old target value … Noisy signal (averaging required) See talk by S. Wesch Set target ~ 0.6deg in 2 hours Main beam-based slow feedback for compensation of phase drifts!

Save&Restore list for Pyros

1) Find on-crest phase (OTR,SR Camera) 2) Pyro scan Setup of ACC1 phase: 1) Find on-crest phase (OTR,SR Camera) 2) Pyro scan 3) Start slow feedback Proposed operating points for SASE. Igor’s talk 8-2-2010 Now: 2 phases to be set and controlled! Strong compression required if pyro detectors to be used as phase monitors. Other detectors: e.g. antennas in GHz range, EO, SR camera, …? => Operating points for 9mA run with 3rd harmonic need to be studied!

Measurement of Beam Energy in BC3 Only OTR screen at centre of vacuum chamber available Camera not aligned at the moment EBPM will become available for rel. beam energy measurements (has low prioritity) …?

Energy in dogleg/bypass See talk by Raymund Kammering …

Conclusion Absolute beam energy monitoring important for all accelerating sections! Needs proper design - you cannot simply take a dipole … Wrong beam energy (ca. 320MeV instead of 280MeV assumed) was one of the main reasons that prevented us from first lasing at TTF1!