Optical diffraction - transition radiation interferometry beam divergence diagnostics

1
Optical diffraction - transition radiation
interferometry beam divergence diagnostics 

• R. B. Fiorito and A.G. Shkvarunets Institute
  for Research in Electronics and Applied Physics
  University of Maryland,
•   T. Watanabe and V. Yakimenko ATF, Brookhaven
  National Laboratory
• J.Power, M. Conde, W. Gei
• AWA, Argonne National Laboratory
• D. Snyder Dept. of Physics, Naval Postgraduate
  School

2

• 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

3
Spectral-angular distribution
q
Radially Polarized AD Pattern Centered
on Direction of Ve
E
Polarized OTR pattern
P
q
4
Effect of Beam Divergence on OTR Convolution of
single electron OTR with 2D distribution of beam
trajectory angles
x
gs 0.2
5
OTR Interferometry provides greater sensitivity
to beam parameters
Formation or coherence length

• Visibility of OTR interferences is a measure of
  divergence
• when gs gtgt ( DE/E and gsscattering
  )
• OTRI visibility measure of divergence in any
  radial direction
• gtgt 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
6
Optical Diffraction-Transition Radiation
Interferometry
7
DIFFRACTION RADIATION FROM A SINGLE APERTURE

• radiation impact parameter a-1 gl/2p ,
• a-1 is 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
8
Calculation of ODR from a Perforated
Foil Simulation Code needed to calculate
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.
9
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)
10
Closer Look at the Radiation Components in
an ODR-OTR Interferometer
backward OTR
ODR(u) ODR(s)
Beam
mirror (Foil 2)
perforated foil 1
ODR(u) ODR(s) OTR(u) OTR(s)
11
(No Transcript)
12
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
13
Interferences produced by unscattered and
scattered ODR from the mesh with OTR from the
mirror
14
OTR and ODTR Interferometers Designed for
Electron Beam Divergence Measurements
L g2 l
ODTRI AD Pattern
Electron beam
OTRI AD Pattern
15
Experimental Setup for OTRI or ODTRI RMS
Emittance Measurement
Beam magnetically focused to x or y waist
condition at mirror
erms,n bgltxgt1/2ltxgt1/2
Far Field Pattern Camera
Lens focused to Infinity
Bandpass Filter
Pellicle Beam Splitter
Qobserv 10/g
Image Plane Camera
OTRI, ODTRI
mirror
Beam
16
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
17

Comparison of ODTR and OTR Interference Patterns
at an x waist
OTRI
s 1.2
ODTRI
s 1.2

18
Fitted beam parameters for NPS beam Y and X
waists.
Waist Method Scan Energy (MeV) 0.2 Comp1 (Tot) 5 s1 (mrad) 5 Comp2 (Tot) 5 s2 (mrad) 10 L (mm) 0.2
Y OTRI Vert. 93.5 72 0.58 28 1.4 37.2
Y ODTRI Vert. 93.5 69 0.56 31 1.5 36.5
X OTRI Horiz. 93.5 100 1.2 37.2
X ODTRI Horiz. 93.5 100 1.2 36.5
19
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
20
Comparison of ODTRI and OTRI ( Tune 2 x 0.18
mm, y 0.15 mm, sx 0.37 mad and sy 0.75 mrad
)
21
Fitted beam parameters for ATF beam tunes 1 and 2
22
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
ODRDOR
23
EFFECT of UNSCATTERED BEAM DIVERGENCE on
ODR-DOF INTERFERENCES
24
(No Transcript)
25
ODR-Dielectric Foil Radiation Interferences at
ANL-AWA E 14.2 MeV
Qv
QH
26
Optical Method for Mapping Transverse Phase Space
Unfocussed beam
detector
collimator
27
Optical Pepperpot Technique
Bandpass Filter
OTR, ODR Interferometer
Farfield Camera
Optical Mask
Polarizer
Profile Camera
beam
28
OTR Phase Space Mapping Scan with a 1mm Pinhole
Vert. Scan of OTRI passing through pinhole
29
OTR Phase Space Maps