Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

RENOVATION OF SR MONITOR AND MEASUREMENT OF EMITTANCE
AT THE PHOTON FACTORY
Yuhji HAYASHI, Toshitada HORI and Toshiyuki MITSUHASHI*1
Department of Physics, Faculty of Science, Hiroshima University,*High Energy Accelerator Research Organization, Oho, Tsukuba, Ibaraki, 305-0801 Japan

Abstract
The SR monitor system at the BL21 was renovated tomeasure the emittance of electron beam at the Photon
Factory after the upgrade. SR-extraction mirror system,
optical relay system, measuring optics are newly
installed in diagnostics beamline BL21. The thermal
deformation of SR-extraction mirror is measured by ray
tracing method. The beam size is measured by the use of
SR interferometer. The energy spread of the electron
beam is also measured trough bunch length measurement
via streak camera. The emittance is evaluated from theresults of beam size and energy spread. The result ofemittance is 38.7nmrad, and it agreed with designed
value in 10%.

system by new mirror system which has a water-cooled
beryllium mirror. A schematic drawing of the beryllium
mirror and its photograph are shown in Fig.1.

1. INTRODUCTION

In the previous SR extraction system, we used acommercially-available glass window for the separationof vacuum to the air. Optical quality of this glass window
is very worth, and we use a metal O-ring sealed glass
widow which has a transparent wavefront error less than
λ/10 [9] in the new system.

Fig. 1: schematic drawing of water-cooled beryllium
mirror and its photograph.

We have upgraded the Photon Factory (PF) to installfour new-straight section for the short gap undulator andto increase the length of existing straight sections [1].
Monitoring the beam profile, beam size, bunch length
based on using the synchrotron radiation (SR Monitor)
will improve greatly the efficiency of the operation of
new scheme of the PF. We have four SR monitors at BL5,BL27, BL21, and beam transport line. The SR monitors
set in BL5, and BL27 are mainly used for machinestudies [2][3][4] and optical monitor developments[5][6][7][8]. The SR monitor set in BL21 is using as thedaily monitoring. In this time, we renovate SR monitor at
the BL21 to measure the electron beam emittance of thenew scheme of PF. At the same time, to measure theperformance of SR-extraction mirror, the Hartmannsquire array mask is installed just after the extraction
mirror to perform the ray tracing based on Hartmannmethod. This Hartmann squire array mask is also used
for a calibration of SR interferometer. After thecalibration of SRI, we measure a current dependence ofbeam size. The energy spread of the beam is alsomeasured through bunch length measurement by streakcamera. Combining results of beam size measurement
and energy spread measurement, we evaluate emittanceof the beam.

2-2. Thermal deformation of the berylliummirror
The thermal deformation of beryllium mirror due tostrong irradiation of X-ray component of SR is one ofserious problem in the SR monitor. We measure thethermal deformation of beryllium mirror by ray tracing
method based on Hartmann method [10]. A schematic
drawing of set up of ray tracing method is shown in Fig.
2. A 10 x 10 squire-array mask is set just after themirror to sample the rays. The diameter of hole is 1mm,and separation between the holes is 5mm.

2mm

e0.15m

2. RENOVATION OF SR MONITOR AT
BL212-1 Replacement of SR extraction system
Ordinary-used SR extraction system in the beamdiagnostics beamline BL21 has a water-cooled cooper
mirror. This cooper mirror was seriously damaged bylong time irradiation of SR. We replaced this mirror
18m

Fig. 2: Schematic drawing of set up of ray
tracing measurement.

Toshiyuki.mitsuhashi@kek.jp-682-Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)

We used the SR as a light source of ray tracing. The
propagations of rays are observed by a screen which set
8m downstream from the squire mask. We measured
current dependence of mirror shape at several ringcurrent. The initial shape of the mirror was deformed byirradiation of SR. Since current dependence of
deformation was rather smaller than this initial
deformation of mirror shape, we measured changes
between the mirror shapes at higher ring current andmirror shape at 300mA. The results of mirror shapechanges in the higher ring current are shown in Fig. 3.

320mA

Fig. 4: Qualitative image of the electron beam observed
by a focusing system.

3. Quantitative measurement of beam size
and its current dependenceby SR interferometer
A Quantitative measurement of the electron beam size
is performed by using the SR interferometer [6]. For
horizontal direction, the SR interferometer having
retro-focus optics [11] was used to measure a large beamsize. Since the actual separation of double slit willchange due to thermal deformation of beryllium mirror,
we mast correct this effect. The intrinsic separation of
double slit when no deformation of the beryllium mirror
is measured by ray tracing using a one hole of squire
array mask [6][10] of the Hartmann ray-tracing system.
Results of intrinsic separation of double slit in both ofhorizontal and vertical direction are shown in Fig. 5.

340mA

horizontal

Vertical
35

530
425

360mA

400mA

32015210
1
50

050

100

150

200

250300

CURRENT [mA]

430mA35040050100150200250300350

CURRENT [mA]

Fig. 5: Results of intrinsic separation of double slit inboth of horizontal and vertical direction.

450mA

Fig. 3: The results of mirror shape changes in the higher
ring current from the mirror shape at 300mA.

In these measurements, the actual separations of double
slits are 4mm in horizontal and 30mm in vertical. Since
the magnification of retro-focus optics in the horizontal
SR interferometer is set 2, the actual separation of double
slit is about twice of intrinsic separation. Rather a largedifference between actual and intrinsic separation invertical direction is due to permanent deformation ofberyllium mirror. Current dependences of intrinsic
separations due to change of the mirror shape are also
observed. By using measured intrinsic separations ofdouble slit, we measured current dependence of beam
sizes in horizontal and vertical directions in the current
region from 50mA to 400mA. Results of current
dependence of beam sizes before and after this correction
are shown in Fig. 6. In the vertical direction, currentdependence of the beam size is small. In the horizontal
direction, the beam size is almost constant from 50mA to
270mA, but sudden jump of beam size is observed
around 270mA. The beam size in beam current larger

The mirror was deformed by 6µm by the ring current
increase from 320mA to 450mA. This deformation ismore than 10 times larger than average wavelengthof visible SR, and we cannot do any quantitative
beam size measurement by the SR monitor without
any correction of these deformations.

2. Qualitative observation of beam profileby a focusing system
We have installed a focusing system to observe aqualitative image of the electron beam. To reduce theeffects of thermal deformation of beryllium mirror as
mentioned in upper, we limited entrance aperture of theobjective lens of focusing system by a squire-aperturemask. A typical image of the beam is shown in Fig. 4.

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Proceedings of the 5th Annual Meeting of Particle Accelerator Society of Japanand the 33rd Linear Accelerator Meeting in Japan (August 6-8, 2008, Higashihiroshima, Japan)
3than 270mA is about 20% larger than its size in lower
than 270mA.
Energy spread

60640560

beam size[μm]beam size [μm]0.0015

480
400
320
240
16050

4030

2.5

20.001

1.5

10.0005

0.5

20050

100

150200

250

300

350

400

50100

150

80
0200

250

300

350

400

current [mA]

10current [mA]
050

100

150200

250

300

350

400

50

100

150

200

250

300

350

400

CURRENT [mA]

CURRENT [mA]

Fig. 7: (a): The result of energy spread. Red line
denotes energy spread evaluated from bunch length.
Blue line denotes energy spread evaluated from beamsize. (b): Ratio between energy spread evaluated frombeam size and it from bunch length.

Fig. 6: Results of current dependence of beamsizes. Red line denotes beam size evaluatedusing actual separation of double slit. Blue line
denotes beam size evaluated using intrinsic
separation of double slit.

4. Evaluation of electron beam emittance
Since the ratio between two results of energy spreadis almost constant in measured range of beam current,
we can conclude increase of horizontal beam size upper
than 270mA is due to increase of energy spread. Small
current dependence of horizontal beam size as shown inFig. 6 is also can explain by current dependence ofenergy spread. From these evidences, we can conclude
emittance of the electron beam has almost no current
dependence. The result of emittance and coupling aresummarized in table 1 with designed values.

4. Measurement of energy spread of theelectron beam
To investigate beam size jump in horizontal direction
around 270mA, we have measured energy spread of theelectron beam via bunch length measurement by using
streak camera. Since the dispersion function is not zeroat the source point of BL21, the information of energy
spread is also necessary to evaluate the emittance of theelectron beam. Results of longitudinal beam profile
measured lower than 270mA and upper than 270mA is
shown in Fig. 7.

Table 1 The result of emittance and coupling withdesigned values.
σx [µm]σy [μm]ε [nmrad]ε [nmrad]Coupling(%)

Measurement
result

416±5

48±1

38.7 ±1.30.244±0.001

0.63±0.11%

designed

413

59.4

35.5

0.355

1%

(a)

(b)

yThe result of emittance is agreed with designed value
in 10%.
REFERENCES[1] T. Honda, et al. Proc. PAC05, p.2678 (2005).
[2] S. Sakanaka, Y. Kobayashi, T. Mitsuhashi and T.
Obina, Jan. J. Appl. Phys., Vol.42, p.1757 (2003).

Fig. 7: Longitudinal beam profile measured below
270mA (a) and upper 270mA (b).

[3] A. Ueda and T. Mitsuhashi, Proc. PAC05, p.2717(2005).
[4] S,Sakanak, T. Obuna and T. Mitsuhashi Proc.
EPAC08, p.1269(2008).
[5] T. Mitsuhashi and M. Tadano, Proc.EPAC02,

Result of bunch length lower than 270mA is 33psec.
Upper than 270mA, the bunch length measurement
results are 40ps in shorter one and 60psec in longer one.
Relationship between bunch length and energy spread isgiven by following equation.

σ τ = T0xp.1936 (2002).
[6] T. Mitsuhashi , Proceedings of BIW04 (2004).
[7] T. Mitsuhashi, Proc. DIPAC05, p.7 (2005).
[8] T. Mitsuhashi and M. Tadano, Proc. PAC07, p.3368(2007).
[9] T. Mitsuhashi and K. Kanazawa, Proc. 13th Sym.

αE0⎛ ∆E ⎞⎜⎟2πheVrf sin φs ⎝ E ⎠ .

The result of energy spread evaluated by using thisequation is shown in Fig. 7 (a). The energy spread
evaluated from the result of horizontal beam size byusing the designed emittance is also shown in Fig. 7 (a).
The ratio between energy spread evaluated from beam
size and it from bunch length is shown in Fig 7 (b).
These two results are agreed within 10%.

on Accel. Sci. and Tec., p387(2001).
[10] T. Mitsuhashi and M. Tadano, Proc. APAC01,p.704 (2001).
[11] J.W. Flanagan H. Hukuma, S. Hiramatsu and T.
Mitsuhashi, PAC05, p.3150 (2005).
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