ASTA Bunch Length Interferometer, et al… Randy Thurman-Keup ASTA Science Mtg Feb 21, 2014

Bunch Length Measurements Streak Camera – Good down to ~0.5 ps, see talk by Alex Interferometry of coherent radiation from bunch (CTR, CDR, CSR, CER, etc…) – Good from 0.15 to ~0.5 ps, passable up to 1 ps Narrow band coherent radiation intensity – See talk by Charles Electro-optic sampling – Any plans for that?

Transition (or Diffraction) Radiation View from Top Transition Radiation Electron Bunch CoherentIncoherent

Martin-Puplett Interferometer View from Top Motorized stagePolarizing Splitter Polarizing Splitter Input Polarizer Mirrors Pyro Detector 1 Pyro Detector 2 Off-axis Paraboloidal Focusing Mirror

Coherent Radiation - Ignore incoherent terms - Assume I 0 is flat in ω View from Top Transition Radiation Electron Bunch CoherentIncoherent

How do we get the phase, etc? No phase information in S(  ) Also no low frequency information Kramers-Kronig minimal phase approximation – Need to reconstruct low frequency Rough guess unless you know the approximate beam profile – Then construct the minimum phase through mathematical smoke ‘n’ mirrors Phase retrieval using iterative approach – S. I. Bajlekov et al., PRSTAB 16, (2013) Start with measured spectrum and random phase Transform to time domain and force signal to be positive with reasonable time bounds Transform back to full spectrum and constrain known region Repeat until convergence Done in 2D crystallography where it has unique solutions etc… – No such luck in the 1D world See Tanaji’s talk ??

Interferometer Data Autocorrelation Spectrum

Layout Streak Camera Optics Crosspoint And THz Devices 4” SS316L Sanitary Piping 4” Flat Mirrors Dipole 3 Port Dipole 4 Port X121 CTR/CDR Port w/ Off-axis Paraboloidal Mirror Entrance Beam Off-axis Paraboloidal Mirrors

Transport Line Boxes 90 Degree Bend 4” Flat Mirror 90 Degree Off-Axis 3” Paraboloidal Mirror f = mm Manual Stage 6” Access Hatch

Dipole Ports Dipole 4 Slits Cross Two 4” x 4” Flat Mirrors 4” Schedule 10 Pipe OD is 4.5”, same as 4.5” CF flange(?) Dipole 3 Beam One 4” x 4” Flat Mirror Off-Axis Focusing Mirrors

Optics Crosspoint Interferometer From X121 From Dipole 3 From Dipole 4 To Streak Camera Broadband Dielectric

Interferometer From 0.15 to 1 ps bunch lengths – Low end due to wire grids 10  m diameter 45  m spacing – High end due to low frequency cutoff Pyros have ~150  s time constant with present electronics – Trade off between response time and signal level Not a single shot Needs more than one bunch but depends on bunch length – Nice signal at A0 with 40ish bunches and 0.5 ps bunch length

Status Need X121 position finalized Ready to order many parts – Mostly short lead times (few days to 2 weeks) – Need functioning task code Boxes need to be made (somewhat costly) – Possibly NIU physics Haven’t thought much about mounting – 80/20 off the girder most likely – Hang from ceiling and wall Probably want to run dry nitrogen through system