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Optical diffraction - transition radiation interferometry beam divergence diagnostics

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## Optical diffraction - transition radiation interferometry beam divergence diagnostics

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**Optical diffraction - transition radiation interferometry**beam divergence diagnostics R. B. Fiorito and A.G. Shkvarunets Institute for Research in Electronics and Applied PhysicsUniversity of Maryland, T. Watanabe and V. Yakimenko ATF, Brookhaven National Laboratory J.Power, M. Conde, W. Gei AWA, Argonne National Laboratory D. SnyderDept. of Physics, Naval Postgraduate School**Beam Parameters Accessible to OTR and ODR Diagnostics**• Incoherent OTR and ODR • ‘Near Field’ Imaging (spatial distribution) • size (x, y) • position (x, y) (offset) • Far Field Imaging (angular distribution) • divergence (x’, y’) • trajectory angle (X’,Y’) • energy and energy spread • Coherent TR and DR • bunch length and shape**Spectral-angular distribution**q Radially Polarized AD Pattern Centered on Direction of Ve E Polarized OTR pattern P q**Effect of Beam Divergence on OTR:Convolution of single**electron OTR with 2D distribution of beam trajectory angles x gs = 0.2**Forward OTR**backward OTR Beam FOTR +BOTR OTR Interferometry provides greater sensitivity to beam parameters Formation or coherence length • Visibility of OTR interferences is a measure of divergence • when gs >> ( DE/E and gsscattering ) • OTRI visibility measure of divergence in any radial direction • >> can be used to separate and measure rms x’ and y’ at • an x or y beam waist • Center of pattern measures trajectory angle of particle • Fringe position measures beam energy (E) qx qy**Extends OTRI diagnostics to low energy and/or low emittance**Perforated first foil overcomes scattering limit of conventional OTRI mirrored foil (OTR source) ODR Beam perforated foil (ODR source) ODR+OTR Optical Diffraction-Transition Radiation Interferometry**DIFFRACTION RADIATION FROM A SINGLE APERTURE**radiation impact parameter: a-1 = gl/2p , a-1is the range of the radial E field of the charge: Ee~ K1 (ar) DR from a circular aperture with radius a and position offset r Forward DR a-1 e geometric factor Backward DR**Calculation of ODR from a Perforated Foil**Simulation Code needed tocalculate the fields and intensities of ODR produced by an electron passing through a perforated foil at any position in the hole or screen. (No analytic solution is available for multiple aperture radiator) Huygens-Kirchoff Integral is used to calculate the x, y components of electric and magnetic radiation fields produced by a source field that is proportional to field of the particle passing through the hole or through a solid portion of the screen, R is the distance from dSf, the differential element of area at the foil to the observation plane, ux,y is the Fourier component of the free space radial field of the electron.**Calculation of the two ODR component from a grid of**rectangular holes in a metal screen: ODR from Unscattered and Scattered Electrons) Unit cell used to calculate DR for a particular electron position in the beam ( scattered and un- scattered)**Closer Look at the Radiation Components in an**ODR-OTR Interferometer ODR(u) +ODR(s) backward OTR Beam mirror (Foil #2) perforated foil #1 ODR(u) + ODR(s) +OTR(u) + OTR(s)**ODR - OTR Interferences**I. Simulation Code calculates and adds up the intensity distributions at foils 1 and 2 for U and S beam fractions. generalized phase: where L is the spacing between the foils, qe is the electron trajectory angle within the beam and q is the observation angle. II. Convolution of I with Distribution of Beam Angles as for OTR**Interferences produced by unscattered and scattered ODR from**the mesh with OTR from the mirror**OTR and ODTR Interferometers Designed for Electron Beam**Divergence Measurements L ~ g2 l ODTRI AD Pattern Electron beam OTRI AD Pattern**Experimental Setup for OTRI or ODTRI RMS Emittance**Measurement Experimental Setup for OTR-ODR RMS Divergence Measurements Far Field Pattern Camera Lens focused to Infinity Bandpass Filter Pellicle Beam Splitter Qobserv ~ 10/g Image Plane Camera OTR-ODR Interferometer Beam magnetically focused to x or y waist condition mirror Beam Beam magnetically focused to x or y waist condition at mirror erms,n = bg<x>1/2<x’>1/2 Far Field Pattern Camera Lens focused to Infinity Bandpass Filter Pellicle Beam Splitter Qobserv ~ 10/g Image Plane Camera OTRI, ODTRI mirror Beam**Comparison of y divergence measurements at y beam waist**(E = 95 MeV, I = 0.5mA, l =650 x 70 nm) OTRI (t= 60s) qy ODTRI (t =90s) s1 = 0.57 qx**Comparison of ODTR and OTR Interference Patterns**at an x waist OTRI s = 1.2 ODTRI s = 1.2**Comparison of ODTRI and OTRI at ATF**( Tune 1: x = 0.18 mm, y = 0.27 mm, sx = 0.31 mrad and sy = 0.22 mrad ) l = 650 x 10nm ) ODTRI 480s OTRI 360s**Comparison of ODTRI and OTRI**( Tune 2: x = 0.18 mm, y = 0.15 mm, sx = 0.37 mad and sy = 0.75 mrad )**Tune**Method Scan Energy MeV Comp1 % Tot s1mrad Comp2 % Tot s2mrad L mm sEmrad 1 OTRI H 50.7 28 0.35 72 1 47 0.31 1 OTRI V 50.7 38 0.3 62 1 47 0.22 1 ODTRI H 50 33 0.28 67 1 44.5 0.31 1 ODTRI V 50 55 0.28 45 1 44.5 0.22 2 OTRI H 50.3 33 0.5 67 1.6 47 0.37 2 OTRI V 50.3 33 0.75 67 1.6 47 0.75 2 ODTRI H 49.3 33 0.4 67 1.6 44.5 0.37 2 ODTRI V 49.3 33 0.65 67 0.8 44.5 0.75 Fitted beam parameters for ATF beam tunes 1 and 2**Low Energy (Injector) Diagnostics using ODR and OR from**Dielectric Foil PROBLEM: for low energy beams the inter-foil spacing L required is too small to directly observe backward reflected OTR or ODR from a mesh -metal foil e.g. L ( 8 MeV, 650 nm ) ~ g2l ~ 1 mm SOLUTION: observe interference between forward directed ODR from mesh and forward dielectric optical radiation(DOR). dielectric foil mirror BEAM micromesh ODR+DOR**EFFECT of UNSCATTERED BEAM DIVERGENCE on ODR-DOF**INTERFERENCES**ODR-Dielectric Foil Radiation Interferences**at ANL-AWA E = 14.2 MeV Qv QH**Optical Method for Mapping Transverse Phase Space**Unfocussed beam detector collimator**Optical Pepperpot Technique**Bandpass Filter OTR, ODR Interferometer Farfield Camera Optical Mask Polarizer Profile Camera beam**OTR Phase Space Mapping**Scan with a 1mm Pinhole Vert. Scan of OTRI passing through pinhole