JAERI-Conf 95-021

PB10
A DESIGN OF THE BEAM PROFILE MONITOR FOR THE HIGH BRILLIANCE
LATTICE OF THE PHOTON FACTORY
Toshiyuki MITSUHASHI
Photon Factory, National Laboratory for High Energy Physics,Oho,Tsukuba,Ibaraki, 305 Japan

Abstract
A beam profile monitor by means of animaging the visible part of synchrotron radiation
beam was designed for the high brilliance lattice
The design consistsof the Photon Factory.
extraction mirror for SR beam, adaptive optical
A Fourier opticalsystem, and focusing system.
Aanalysis of the system has been done.
preliminary result of the monitor will be
described.

windows those place in series. The windows are
made of BK7 and SF11 ,those having a surface
quality of A./10 (A.=500nm now). The first window
separates ultra-high vacuum of the ring and nexthigh vacuum room of 1o- 6 Pa. The second widow
separates high vacuum room and atmosphericenvironment.
The extraction mirror must withstand themaximum angular power of the synchrotron lights
given in Table 1.
Table 1
Parameters of the bending magnet and angularpower of the SR light

1. Introduction
The beam profile monitor based on an imagingof the synchrotron radiation will give a visible
beam profile, which greatly improves theefficiency of the commissioning of the new highbrilliance configuration of the Photon Factory.
By digitizing the image data, transverse beam
size can be obtained, and with the knowledge ofthe lattice parameters, various beam parameterssuch as beam emittance and horizontal- vertical
coupling can be deduced. The dependence of thebeam size measured with this device on the beam
current gives some information on the collective
Furthermore, by using a streak camera
effects.
or photon counting system, the longitudinal
profile of the beam bunch can be observed. in thispaper presents the design of the optical beamprofile measurement system for high brilliantA
configuration of the Photon Factory.
alsoissystemtheofpreliminary result
described.

Bend radius

8.66m

Dipole field

0.96T

Angular power of SR

13.2W/mrad at 350 rnA

Beam size (90deg latice)

cr,: 450J1m, cry: 95 Jlm

An optimum design of a water-cooled Be mirror
has been designed and constructed. The outline ofthe Be-mirror is shown in Fig.2. Nevertheless, athermal deformation of the optical flatness of themirror can exceed the tolerance of thediffraction-limited optics such as Rayleigh'scriterion(about wave front error < A./8).
Extraction mirror

Active

2. Extraction of the visible synchrotron light andcorrection of the thermal deformation of theextraction mirror by use of corrective mirror
array

Since the focusing system will be placed in theatmospheric environment, which is separated
from the accelerator, the visible synchrotron
light must be extracted from the ring through aThevacuum-tight optical quality window.
window system consist of two optical grass

Laser

SR beamFig.1 The schematic design diagram of thecorrective system-275-JAERI-Conf 95-021

IS 0.0000 ll:G

There maybe also the mirror deformation
caused by the mechanics of mounting and coolingwater.
To correct such errors corrective
optical system is designed2). It is basically afeedback system based on an active(corrective)
mirror that makes the point response function of
the two-mirror system as correct as possible: A
schematic diagram of the corrective system isshown in Fig.1. Because of the wave front of theSR light is spherical, the point response between
two mirror must be modified by distance of tow
mirrors.
cooling water tube

3. Focusing system
The optical image of the beam is produce by adiffraction limited focusing system placed in theexperimental room under the accelerator tunnel.
The focusing system consists a ED doublet lenshaving a diameter of 80mm and focusing length of
1OOOmm which optimized to the wave length of
550nm. The theoretical remaining longitudinalaberration and modulation transfer function(MTF) on axis are shown in Figures 2 and 3. The
designed wave front error is about less thanA./100. So the geometrical aberrationby thislens is negligible small and image will bediffraction limited near by on axis. Transverse
magnitude is designed to 0.141.

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5

3

4~0a
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SPATIAL FREQUENCY IN CYCLES PER MILLIMETER

Fig. 3 The calculated MTF of the rens
4. Fourier optical analysis of the focusing system

Fig.2 Design of the Be-mirror-t!L~I£'01:0a . 7

4-1 Transverse diffraction effects
The finite aperture of the entrance pupil of thefocusing system produce a diffraction.
With theFresnel approximation of the diffraction theory
and the paraxial lens transfer function, the point
spread function (PSF) of the system is a Fouriertransform of the generalized pupil function of thesystem 1 ).
A wave front error of the lens or mirrors aretreated by means of wave front aberration inthese approximation, but now they will be
negligible small after the corrective system. Anamplitude transmittance of the generalized pupil
function is modified by a vertical angularintensity distribution of the SR.
To create a
simple generalized pupil function, an apodization 2)
for the entrance pupil of the system is required.
The apodization filter must have an antiamplitude transmittance which corresponds to thevertical intensity distribution of the SR light.
This apodization filter will create a flat intensity
distribution on the entrance pupil, and the pupil
will give a increase of the higher components ofspatial frequency.
Results of calculation of a
PSF with the apodization for the system is shownin Fig.4. The optical parameters of the focusing
system are given in Table 2.

0.0001

Fig.2 The expected longitudinal aberration of thelens

Fig.4 The PSF of the focusing system. The side
length of the 3-dimensional plots is 119J.Lm.

-276-JAERI-Conf 95-021

Table 2
Optical parameters of the focusing system.
All the unit is in mmglass

Surface nunber Radius of surface thickness7763

source point

I

573.36

8.00

2-222.3936-1.00

3-226.5498

5.00

4-1212.2

1126.00

FPL52ZSL7

The rms widths of the central peak of the PSF
are 5.9f.l.m in vertical and 12.8 J.l.m in horizontal.
The image of the beam is given a convolution of
the PSF and the geometrical image. Very small
vertical beam size as in table 1 must analyzed byfor the observed
lest square fitting method
PSF of the real
ThePSF.
ofusebyimage
analysis.
thisformeasured
bemustsystem

4-2 iongitudinal diffraction and the field depth
The field depth of the diffraction limited
focusing system is dominated by the longitudinal
Figure 5
diffraction along the optical axis 1>.
diffraction
shows the calculated longitudinal
Frompattern on axis of the focusing system.
toplanethis figure, the field depth around image
Effect of the longitudinal aberration
be 500f.l.m.
as discussed in section 3 is small enough for thisThe system appears to be diffraction
lens.
The
limited also in the longitudinal axis.
curvature effect in the horizontal beam size ofthe beam trajectory by the this field depth will tobe.

The surface quality of the Be-mirror before
mounting to the holder was A./4. After themirror was mounted to the mirror holder and150deg backing, theapplying two times ofas like as apermanently
bentmirror surface washorizontal).
indistortion
parabola in vertical (nothe BL-27ininstalled
The extraction mirror was
Maximum differencein the Photon Factory.
between center and edge was about 5J.l.m. The
corrective mirror system for the correction of
the extract mirror and the focusing system are.now under construction.
A preliminary measurement of a beam profile
without corrective system has been done. The
nomal doublet lens MELLES GRIOT LA0366 is used
for focusing system. A result of observed beam
image is shown in Fig.6.

Fig.6 A beam image of the Photon Factory beam
current is 2mA.

references
1)M.Born and E. Wolf,"Principles of Optics,
Pergamon press. (1974).
2)R.K.Tyson, "Principles of Adaptive Optics,
Academic press.(1991 ).

1.00000.90000.80000.70000.60000.50000.40000.30000.20000.10000.00004~-1.00

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1.00

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distance from focus point(mm)Longitudinal diffraction pattern of theFig.5
focusing system.

5. Performance of the Be mirror and preliminary
experiment at present Photon Factory-277-