Ⅲ-1

Accelerators andInstrumentsⅢ -1. Accelerators and Instruments

Light sources

Measurement of Temporal Response of Transmission-Type Spin-Polarized
Photocathodes
T. Inagaki1, N. Yamamoto1, T. Konomi2, Y. Okano3, M. Adachi4, X. G. Jin1,
M. Hosaka1, Y. Takashima1 and M. Katoh2,3,1
1

Nagoya University, Nagoya 464-8601, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Laser Research Center for Molecular Science, Okazaki 444-8585, Japan
4
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan2

We have developed transmission-type spinpolarized photocathodes with negative electron
affinity (NEA). The spin-polarized electron beam isessential for “International Linear Collider” and so on.
It is also expected to be applied for “Spin-resolved
Inverse Photoemission Spectroscopy” [1].
In order to measure the temporal response ofphotocathodes, we developed the electron pulse
length measurement system with 20 kV DC gun (Fig.
1). In this system by using an rf deflecting cavity, theelectron beam is kicked transversely according to therf phase position and the longitudinal pulse structure
is projected to the transverse plane. We have
employed the resonance mode of TM120. The
resonance frequency is 2614 MHz for the rf cavity
and the resonance frequency corresponds to themultiple of RF acceleration frequency of UVSOR
storage ring, so the laser can be synchronized withUVSOR accelerator is used for the pump laser [2].
Temporal response of the photocathodes is evaluatedby comparing the electron pulse structure and thepump laser pulse length. The pump laser pulses areprovided by a mode-locked Ti:sapphire oscillator. In
the present system by using a pulse stretcher, thepulse length of the pump laser can be selected in therange between 6.1 and 45 ps.
After the installation of the rf cavity to electron gun
system, we carried out the measurement test with the
GaAs/GaAsP superlatticephotocathodewith
thickness of 96 nm. To evaluate its temporal response,
the longitudinal pulse structure of electron beam
projected by an rf deflecting cavity is fitted with atemporal response function which has two decay time
constants, fast and slow temporal response times (Fig.
2). The measurement is carried out with pump laser
length of less than 10 ps. As the results, two decay
time constants are 3.1 ± 0.9 and 14 ± 1 ps,
respectively. We considered that this result is
consistent in a prior research with almost the sameactive layer thickness on front irradiation type [3].
Finally, in near future we are planning to reduce
electron beam size before it is projected to thetransverse plane in order to realize more precisely
temporal response measurement and we will makesystematic
measurementforthevarioustransmission-type photocathodes.

Fig. 1. 20 kV DC electron gun.

Fig. 2. Experimental data and fitted curves for alongitudinal pulse structure of electron beam.
[1] N. Yamamoto, doctoral thesis, Nagoya University(2007).
[2] T. Niwa, master’s thesis, Nagoya University(2013).
[3] X. G. Jin et al., “Picosecond electron bunchesfrom GaAs/GaAsP strained superlattice photocathode”
Ultramicroscopy 130 (2013) 44.

33

Ⅲ -1

Ⅲ -1. Accelerators and Instruments

Light Sources

Narrow Band Coherent Edge Radiation from UVSOR-III Storage Ring
M. Hosaka1,, D. Oodake2, N. Yamamoto1,2, T. Konomi3,4, J. Yamazaki3, K. Hayashi3,
Y. Takashima1,2 and M. Katoh3,41

Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan

Ⅲ -1
We have already succeeded in producing narrow
band coherent THz radiation by manipulating theinteraction between a relativistic electron bunch andan amplitude modulated laser [1]. In the former
experiment, the radiation from a bending magnet
where electrons moving along a circular trajectory, is
extracted. As next step we planned to extract theradiation from edges of bending magnets, where
electrons experience rapid change of magnetic field.
The radiation is called edge radiation and has
distinctive features as compared to normal
synchrotron radiation: highly collimation even in longwavelength region, annular radiation pattern andradial polarization. Applying our technique of
amplitude modulation laser, intense narrow band edge
radiation is expected to be generated. Moreover,radially polarized light can be converted toZ-polarized one by using a high NA lens. Novel new
applications of the radiation, such as surface scienceand solid state physics are expected.
The experiment to observe narrow band edge
radiation was carried out with an electron beam of
600 MeV. Amplitude modulated Ti:Sa of 3 mJ was
injected to BL1U undulator where the interaction
between the laser and the electron bunch occurs. We
have installed a simple beamline consisting of a mirro
and a window port at 0 degree of BL2 to extract edge
radiation from the edges of the bend 1 and bend 2.
The edge radiation from the beamline was detectedusing an InSb hot-electron bolometer. In the initial
experiment, we confirmed that the radiation intensity
is proportional to the square of stored beam current,
as is peculiar to coherent radiation (the figure is notseen in this report). Then we measured radiation
intensity as a function of the THz frequency adjusted
by the laser modulation frequency. Figure 1 shows theexperimental result compared with efficiency
calculations taking account of optical parameters of
UVSOR-III magnetic lattice. As seen in the figure
they agree well except for very low frequency region(~ 5 cm-1) where multi-turn effect [2] dominates,
which we did not take into account in the calculation.
We observed spatial intensity distribution of theradiation by moving the bolometer which is located at
distance of about 7 m from the radiation source point.
In the experiment, we employed a polarizer toextract only horizontal polarized component. Figure 2

shows the spatial distribution obtained in theexperiment with the wavelength adjusted to 20 cm-1.
We expected horizontally separated distribution (Fig.
2 (b) ); however, the experimental result does notclearly reproduce the expected distribution. We think
the spatial distribution is affected by diffraction due
to a narrow beam duct. We are planning a similar
experiment with shorter THz wavelength. We are also
going to make a simulation taking account of thediffraction effect.

Fig. 1. Intensity of edge radiation as a function of
wavelength.

Fig. 2. Spatial distribution of horizontal polarizedcomponet of edge radiation: (a) experiment (b)calculation.
[1] S. Bielawski et al., Nat. Phys. Rev. Lett. 4 (2008)
390.
[2] C. Evain et al., Phys. Rev. ST Accel Beam 12 9(2010) 090703.

34

Ⅲ -1. Accelerators and Instruments

Light sources

Beam Injection with a Pulsed Multipole Magnet at UVSOR-III
1

N. Yamamoto1, H. Zen2, M. Hosaka1, M. Adachi4, K. Hayashi3,
J. Yamazaki3, Y. Takashima1 and M. Katoh3,1Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
2
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki, 444-8585, Japan
4
High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan

Ⅲ -1

The pulsed multipole injection scheme wasdeveloped at KEK-PF and KEK-AR [1,2]. In thisscheme, the injection beam is captured into theaccelerator acceptance as a result of pulsed multipole
kicks, and the stored beam passes through the centerof the multipole magnet, where the field strength isalmost zero. The scheme thus avoids exciting
coherent oscillation in the stored beam and delivers ahigh quality photon beam for synchrotron radiation
users.
To introduce pulsed multipole injection into the
UVSOR-III storage ring, we designed arectangular-shaped pulsed multipole magnet (Fig.1)
and tested it for electron beam injection[3]. The goalof the design was to compensate for residual
magnetic fields by using thin ferrite bars applied tothe pre-manufactured magnet.
The injection experiments demonstrated thatmultiturn injection, which uses the pulsed multipole
magnet, is successful technique for UVSOR-III. Thisis the successful result of the pulsed multipole
injection in case of as many as 7–9 kicks being
applied to the same injected bunch on consecutive
turns.
After optimizing the injection conditions, we
obtained a maximum injection efficiency of 23% andan electron beam injection up to 300 mA. The
injection efficiency obtained was less than expectedfrom beam simulations, but the efficiency was
sufficient to maintain the top-up operation at 300 mA.
We suggest that the quality of the injection beam may
have caused the lower injection efficiency because an
injection efficiency lower than expected also occurred
when using conventional dipole magnets. Thus, toobtain a higher injection efficiency, we shall focus
our future investigations on the injector system.
Finally, this work demonstrates that thefield-compensation technique based on using thin
ferrite bars to cancel the residual magnet field is an
economical and powerful way to improve
performance. Coherent oscillations were drasticallysuppressed by applying this technique topre-manufactured magnet (Fig. 2).

Fig. 1. Cross-section of the pulsed
magnet with calculated magnetic field.

multipoleFig. 2. Measured stored beam movements withpulsed dipole magnet (open circles) and pulsed
multipole magnet with ferrite bars (close circles)
and without ferrite bars (open triangles).
[1] K. Harada, Y. Kobayashi, T. Miyajima and S.
Nagahashi, Phys. Rev. ST-AB 10 (12) (2007) 123501.
[2] H. Takaki, N. Nakamura, Y. Kobayashi, K. Harada,
T. Miyajima, A. Ueda, S. Nagahashi, M. Shimada, T.
Obina and T. Honda, Phys. Rev. ST-AB 13 (2010)
020705.
[3] N. Yamamoto, H. Zen, M. Hosaka, T. Konomi, M.
Adachi, K. Hayashi, J. Yamazaki, Y. Takashima and
M. Katoh, Nucl. Inst. and Meth. A 767 (2014) 26.

35

Ⅲ -1. Accelerators and Instruments

OthersPerformance Evaluation of Mass Production Nuclear Emulsion for 2015
Balloon-Borne Experiment
N. Otsuka1, H. Kawahara1, H. Rokujo1, K. Ozaki2, S. Aoki2, E. Shibayama2, S. Takahashi2,
S. Tawa2, F. Mizutani2, K. Yamada2, Y. Tateishi2, T. Kosaka2 and GRAINE collaboration
1

2

Ⅲ -1

Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
Department of Human Environment Science, Kobe University, Kobe 657-8501, JapanWe are promoting GRAINE project. GRAINE
project is a balloon-borne experiment to explore the
gamma-ray astrophysics. We load a balloon with
nuclear emulsion to observe cosmic gamma-rays.
Nuclear emulsion is able to record the 3-dimensional
trajectory of a charged particle within a 1-um
accuracy. Nuclear emulsion is made of a plastic baseand silver halide emulsion which is coated on aplastic base. After development the emulsion films,
we can observe track made of silver grain by charged
particles under a microscope. We observed
electron-pair which created of cosmic gamma-rays inemulsion and reconstruct each gamma-ray todetermine which way the gamma-ray come from.
Figure 1 shows how track of charged particle look
like in nuclear emulsion under microscope.
We produced nuclear emulsion at Nagoya
University for next balloon-borne experiment. Next
balloon-borne experiment will operate in May 2015,
Australia. We were required to product about fiftysquare meters of nuclear emulsion for 2015
experiment. Mass production of silver halide
emulsion for 2015 experiment is started at February
2014 and it finished in January 2015. Figure 2 showstime profile of the total amount of produced
emulsions. We produce emulsion with R&D machine(1L tank) until November 2014. Thereafter, we
introduced mass production machine (3L tank).
We need to evaluate performance of each silver
halide emulsion. I will explain how to evaluate
performance of silver halide emulsion. We expose
electron beam to films made of silver halide emulsion
to evaluate at UVSOR. Exposed film has trajectories
of electron. We measured Grain Density (GD), countsof silver grains per 100um, by observed trajectories in
emulsion under microscope. GD would be high whenemulsion has high sensitivity to charged particle.
Figure 3 shows results of measurement of GD forall emulsions. The high density silver halide emulsion
has an average GD of 50.6 and the middle density
silver halide emulsion has an average GD of 45.8.
Since next experiment demand more than 40 for GD,
mass production of emulsion was stable. Moreover,the mass production machine is able to produce
emulsion as the R&D machine.
Sufficient performed emulsions were coated onplastic bases at Nagoya University. These films are
become detector for 2015 experiment.

Fig. 1. Microscopic view of emulsion recorded
charged track.

Fig. 2. Time profile of mass production for 2015
experiment.

Fig. 3. Performance of produced silver bromide
emulsions.

36

Ⅲ -1. Accelerators and Instruments

OthersDevelopment of the Backward-Illuminated Photocathode for SRF GUN
T. Konomi1, R. Inagaki2, M. Hosaka3, N. Yamamoto3,Y. Takashima2,3and M. Katoh1,3
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Nagoya University Synchrotron Radiation Research Center, Nagoya 464-8603, Japan2

Photocathode electron gun is a key component of
the high brightness synchrotron radiation source suchas free electron laser, energy recovery linac, etc.
Superconducting RF gun has advantages on the highgradient and high duty operation because CW highpower RF operation is capable. Figure 1 shows thesuperconducting RF gun cavity under development[1]. The cavity is made of pure niobium, and RF
surface resistance is 1/1,000,000 compared with purecopper cavity. Therefore the gun can accelerate highcurrent beam with high accelerating field.
Backward illumination with a transparent
photocathode is desirable from the good laser
operability point of view because it gives better laser
pointing stability, laser shape operability with fiber
bundle and a high numerical aperture lens. Figure 2
shows the shame of the gun. The excitation light(laser) is illuminated to the backside of thephotocathode, and the electron beam emitted fromfront side of the photocathode and accelerated in RF
field.
We studied the backward illumination for thetransparent photocathode in a superconducting RF
gun and we found that a combination of a transparent
superconductor LiTi2O4 and the high brightness
photocathode K2CsSb is a candidate. Figure3 shows
the structure of the photocathode. The transparent
superconductor LiTi2O4 is epitaxially grown ontransparent substrate MgAl2O4 [2]. RF is reflected at
LiTi2O4 because RF Skin depth of the superconductor
is several hundred nm. It's possible to protect thesubstrate with the insulation breakdown voltage.
Photocathode parameter was measured separately.
The critical RF magnetic field was measured by
SQUID (Fig.4). The operation RF magnetic field of
SRF gun is 4.3 mT on the photocathode. The
photocathode has double margin about RF field at
5K.
The quantum efficiency has the peak at green
wavelength range (Fig.5).
We will develop SRF gun development such as
laser development by using these cathode data.

Ⅲ -1

Fig. 1. Superconducting RF gun cavity.

Fig. 2. Shame of developed electron gun.

Fig. 3. The photocathode structure.
11
LiTi2O4
LiTi2O4+k2CsSb

9

H

c

RF

(mT)

10

8

7

1

2

3

4

5

Temperature (K)67Fig. 4. Critical RF magnetic Field of LiTi2O4.

Quantum Efficiency (%)

10

1

0.1






Photon Energy (eV)Fig. 5. Quantum efficiency of the photocathode.
[1] R. Matsuda et al., PASJ11, MOOL13, 2014.
[2] A. Kumatani et al., Appl. Phys. Lett. 101 (2012)
123103.

37

Ⅲ -1. Accelerators and Instruments

BL1U, Accelerators

Generation of Laser Compton Scattered Gamma-Ray
Using a 1.95-μm Fiber Laser at UVSOR Facility
H. Zen1, Y. Taira2, T. Konomi3,4, J. Yamazaki3, T. Hayakawa5, T. Shizuma5, T. Kii1,
H. Toyokawa2, M. Katoh3,4 and H. Ohgaki1
1

Intitute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
5Japan Atomic Energy Agency, Tokai-mura 319-1184, Japan
2

High energy and quasi-monoenergetic gamma-rays
can be generated by Compton backscattering between
high energy electron beams and laser beams [1]. The
gamma-rays are called as LCS (Laser Compton
Scattering) gamma-ray and have unique and good
features such as energy tunability, variable
polarization and good directivity. Therefore, the LCS
gamma-rays are very useful for various purposes. In
order to generate narrowband and intense LCS
gamma-ray, high current, low emittance and smallenergy spread electron beam must be provided.
In the UVSOR facility, high current (300 mA,
top-up), low emittance (17.5 nm-rad) and smallenergy spread (5.26×10-4) electron beam circulatingin the UVSOR-III storage ring with electron energyof 750 MeV is available [2]. Those features ofelectron beam are very good for generating
narrowband and intense LCS gamma-ray. Therefore,
we proposed development of LCS gamma-ray sourcein the UVSOR facility.
In this fiscal year, we installed a 1.95-μm fiber
laser in the downstream side of BL1U and performed
LCS gamma-ray generation experiment. The
experimental setup is shown in Fig. 1. Laser beamwith 1.95-μm wavelength was injected fromdownstream side of BL1U and scattered by electron
beam circulating in the storage ring. The
characteristics of the fiber laser are listed in Table 1.
The energy spectrum of generated LCS gamma-ray
include detector efficiency is shown in Fig. 2. We
have successfully generated LCS gamma-rays whose
maximum energy of about 5.4 MeV. The gamma-ray
yield with the beam current of 300 mA and laser
power of 5 W is expected to be about
3×105 photons/s in 3% bandwidth.

Gamma-ray

Fiber Laser
Exit

Collimator

IR BeamGermanium
Detector

Fig. 1. Setup of LCS experiment at the downstreamof BL1U.
Laser Power = 1.2 W, Beam Current = 0.61 mA
w/ Laser Focusing, w/o Collimator, 600 s
1500Counts [# / 1 keV]

Ⅲ -1

5.4 MeV

1000

500

BG (0.51 mA)
0

Table 1. Characteristics of the 1.95-μm Fiber Laser
Parameter
Specification
Operation mode
CW
Operation wavelength 1950 nm
Max. output power
5W
Spectral linewidth< 1 nmBeam quality, M2< 1.1
Output polarization
Linear

0

1

2

3

4

5

6

7

8

Energy [MeV]Fig. 2. Measured gamma-ray spectrum with andwithout laser injection.
[1] F. V. Hartemann et al., Phys. Rev. ST Accel.
Beams 8 (2005) 100702.
[2] M. Adachi et al., J. Phys.: Conf. Ser. 425 (2013)
042013.

38

Ⅲ -1. Accelerators and Instruments

BL1U

Observation of Light’s Orbital Angular Momentum from Helical Undulator
Harmonics
S. Sasaki1, A. Miyamoto1, M. Hosaka2, N. Yamamoto2, T. Konomi3 and M. Katoh3
1

Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
2
Nagoya University Synchrotron Radiation Research Center, Nagoya, 464-8603, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki, 444-8585, Japan

The phenomenon of higher harmonic radiationfrom a helical undulator carrying orbital angularmomentum (OAM)[1] attracts a great deal ofattention because this novel property may be used asa new probe for synchrotron radiation science[2] thatwould be performed in a diffraction limited lightsource facility.
Although a diffraction limited x-ray source does
not yet exist, the 750 MeV UVSOR-III is already adiffraction limited light source in the ultra violet(UV) wavelength region. In this ring, atandem-aligned double-APPLE undulator system
similar to that in BESSY-II [3] is installed for FEL
and coherent light source experiments. Using thisset-up, we observed spiral interference patterns
between two different harmonic radiations with ascanning fiber multi-channel spectrometer and a CCD
camera placed at the end of BL1U Beamline. By
these measurements, various interference patterns
such as single, double, and triple spirals wereobserved which concur with the theoretical prediction
for every mode in the right or left circularpolarization[4]. Figure 1 shows the layout of
undulator system and beamline.
A schematic view of experimental set-up for theinterference mesurements with a CCD cameara isshown in Fig. 2.
Figure 3 shows examples of interference patterns.
The rotation of an interference pattern by rotating apolarizer was also observed as shown in Fig.4.

Ⅲ -1

Fig. 2. Experimental
set-upformeasurements with a CCD camera.

interference

Fig. 3. Double spiral by interference between 1st &3rd harmonic.E = 500 MeV, ε0 = 8 nmrad, λ= 250 nm.

Fig. 4. Spiral rotation, 1st & 2nd harm.interference.
Rot. Angle: TL: 0º, TR: 30º, BL: 60º, BR: 90º.
[1] S. Sasaki and I. McNulty, Phys. Rev. Lett. 100(2008) 124801.
[2] M. VanVeenendaal and I. McNulty, Phys. Rev.
Lett. 98 (2007) 157401.
[3] J. Bahrdt, et al., Phys. Rev. Lett. 111 (2013)
034801.
[4] S. Sasaki, A. Miyamoto, M. Hosaka, N.
Yamamoto, T. Konomi and M. Katoh, to be
published.

Fig. 1. Drawings of undulators and BL-1U beamline.

39

Ⅲ -1. Accelerators and Instruments

BL2B

Reconstruction of the Beamline BL2B for Development of Photoelectron
Spectroscopy for Organic Materials II
S. Kera1,2, K. R. Koswattage3, K. Yonezawa2, Y. Nakayama2, K. K. Okudaira2 and H. Ishii2,3
1

Institute for Molecular Science, Okazaki 444-8585, Japan
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
3
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan

2

Ⅲ -1

The beamline BL2B has been reconstructed forcharacterizing the wide range of molecular materials
via angle-resolved photoelectron spectroscopy(ARPES) to achieve the fundamental understandingof charge transport properties, adsorption properties,
interface energetics, chemical reactivity and so on,
since September 2013.
The BL2B originally consists of M0, and M1
pre-focusing mirrors, entrance slit, monochromator,
movable exist slit and M4 refocusing mirror. The
monochromator consists of G1, G2, and G3 sphericalgratings and M2 and M3 plane mirrors system [1, 2].
The monochromator was designed to cover the energy
range of 23 – 205 eV and used for gas phase
experiments till 2012.
In the initial process, the beamline was mainly
reconstructed solving a malfunction of the M2 andM3 mirror system in the monochromator, introducing
a UHV chamber (monitoring chamber) downstreamof the M4 mirror chamber, building a new interlock
system, placing a new end-station for the ARPES
equipped with a hemispherical analyzer (SCIENTA
R3000) [3]. Then, the beam line was carefully aligned
starting from adjusting M0, M1, and subsequently
adjusting the optics in the monochromator and M4
mirror. A typical spot size after the M4 refocusing
mirror is roughly estimated to be about 1.5 mm × 0.8
mm (vertical × horizontal) for exist slit of 300 μm by
a four directional slit (in between the M4 mirror & themonitoring chamber) edges scan.
The photon flux for an exit slit width of 300 μm are
estimated to be 1× 1010 – 3× 1010 , 4× 1010 – 2× 1011 ,and 1× 1010 – 2× 1010 photons/s for G1 (80 – 150eV), G2 (50– 120 eV) and G3 (25 – 55 eV) gratings,
respectively using a silicon photodiode (AXUV-100,
IRD) and Au mesh in the monitoring chamber. The
estimated photon flux is one order of magnitude
smaller than the expecting value from the references[1, 2] and the decrement may be due to contaminationof the optics, a slight misalignment of the light and soon.
The contribution of the second order light wasestimated to be 10% at 28 eV and it can be reduced to
2.4% by inserting a metal filter (Al20nm/Mg300nm/Al20nm/Ni70nm, LUXEL) in the monitoring
chamber. The accuracy of the photon energy at 28 eV
was checked by measuring Fermi edge of gold
considering the first and second order light, leading a
difference of -0.04 eV.

The beamline resolution was determined bymeasuring Fermi edge of gold at low temperature ~13
K. Refereeing a preciously determined energy
resolution of the analyzer (ΛR=2.3meV at passenergy (Ep) of 2eV and analyzer slit of 0.2mm) by Xegas cell experiments, the photon energy resolution isestimated to be 14 ± 1 meV at 28 eV, and the value isconsistent with the literature (E/ΛE = 2,000 @Slit
500μm) [1]. Consequently, one can obtain the ARPES
data for a Au(111) surface as shown in Fig.1.
M0 mirror is cooled by water cooling system toimprove the stability of the synchrotron light,
however currently the cooling system having aproblem where the mirror system cannot be cooled.
Thus, the stability of the photon energy and flux has
been carefully checked repeatedly measuring thebinding energy and intensity of Au 4f at the photon
energy of 110 eV. The result confirms that a stability
to a certain extent of the light for a 24 hours
continuous measurements which may not be a
drawback for future experiments at BL2B.

Fig. 1. ARPES of a clean Au(111) surface taken at
15 K and hν = 28 eV. (a) Valence band (VB) region isrecorded for 5min and (b) surface state region isrecorded for 40min to obtain an image.
[1] H. Yoshida and K. Mitsuke, J. Synch. Rad. 5(1998) 774.
[2] M. Ono, H. Yoshida and K. Mitsuke Nucl. Instrum.
Meth. Phys. Res. A 467-468 (2001) 577.
[3] S. Kera et al., UVSOR Act. Repo2013 41 (2014)38.

40

Ⅲ -1. Accelerators and Instruments

BL6B, BL1U

Microbunching Instability in Relativistic Electron Bunches: Direct
Observations of the Microstructures Using Ultrafast YBCO Detectors
E. Roussel1, C. Evain1, C. Szwaj1, S. Bielawski1, J. Raasch2, P. Thoma2, A. Scheuring2,
M. Hofherr2, K. Ilin2, S. Wünsch2, M. Siegel2, M. Hosaka3, N. Yamamoto3, Y. Takashima3,
H. Zen4, T. Konomi5, M. Adachi5, S. Kimura5 and M. Katoh5
1

2

Laboratoire PhLAM, Université Lille 1, 59655 Villeneuve d'Ascq, FranceInstitute of Micro- and Nanoelectronic Systems, Karlsruhe Institute of Technology, 76187 Karlsruhe, Germany
3
Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
4
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
5
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

During the synchrotron radiation process, eachelectron is exposed to the radiation emitted by theothers. At high electron bunch charge, this collective
effect is at the origin of an instability that leads to thespontaneous formation of spatial structures inside theelectron bunch: the microbunching instability (orCSR
instability).
This
very
fundamental
electromagnetic phenomenon is known as a limitationin various types of accelerators, and at the same time
as a great opportunity for the generation of giant
pulses of Terahertz radiation (Coherent Synchrotron
Radiation or CSR). This phenomenon is also
suspected to be at the origin of coherent emission insolar flares.
Although this is a well-known fact, direct
experimental observations of the structures, or thefield they emit (CSR), remained up to now an open
problem. In the present work, we attempted toobserve directly such a structure in a storage ring, andfollow its evolution over many turns [1].
The experimental setup is displayed in Fig. 1. TheUVSOR-III storage ring was operated in single bunch,
above the microbunching instability threshold. The
spontaneously formed structure (with ~9 mmwavelength) emitted a coherent radiation (at the same
wavelength). This radiation was detected using an
ultrafast detector developed by the Institute of Microand Nanoelectronic Systems (KIT, Germany). Thisdetector has the capability to measure the total
electric field evolution, with a time resolution that isbetter than fastest oscilloscope speeds (17 ps at thetime).
The experimental recordings immediately revealed
that we had access to the full shape of the CSR pulses(including envelope and carrier), and which are adirect “image” of the microstructures (Fig. 2). Then,the data quickly appeared as a powerful and severereference for the tests of theoretical models.
Comparison with numerical simulations quickly
revealed model limitations, and how the models
should be refined to reproduce the experimental data.
These studies were also performed in presence oflaser perturbations, using the slicing setup installed at
BL1U (see Ref. [1] for details).
More generally, the possibility to “see” directly the

microstructures shape and its evolution at each turnopens the way to tests of models, and control
strategies that were not possible before.

Fig. 1. Experimental setup.

Fig. 2. (a) Typical pulse shape associated to a burstof CSR radiation that carries the information on theelectron bunch microstructure. (b). Series of pulse
shapes at successive round-trips in the ring.
[1] E. Roussel et al., Phys. Rev. Lett. 113 (2014)
094801.
http://dx.doi.org/10.1103/PhysRevLett.113.094801.

41

Ⅲ -1

Ⅲ -1. Accelerators and Instruments

BL7B

Evaluation of the VUV Coating Performed on the Flight Mirrors of the
CLASP Sounding Rocket
N. Narukage1, M. Kubo1, R. Ishikawa1, Y. Katsukawa1, S. Ishikawa1, T. Kobiki1, G. Giono1,
R. Kano1, T. Bando1 and S. Tsuneta2
1

National Astronomical Observatory of Japan, Mitaka 181-8588, Japan
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan

2

Ⅲ -1

Our team consisting of Japan, US, Spain, France,and Norway is developing a Chromospheric
Lyman-Alpha SpectroPolarimeter (CLASP), which is
proposed to fly with a NASA sounding rocket in 2015
[1, 2]. CLASP will explore the magnetic fields in thesolar atmosphere (the upper chromosphere andtransition region) via the Hanle effect in the
Lyman-alpha (Lyα) line (121.6 nm) for the first time.
This experiment requires precise spectropolarimetricobservations with a polarimetric sensitivity of 3σ ~0.1% and a wavelength resolution of 0.01 nm.
In order to achieve the polarimetric sensitivity of3σ ~ 0.1%, CLASP requires the high throughput for
suppressing the photon noise. For this purpose,
CLASP is consists of minimum number of reflective
mirrors [3]. And, we have developed three types ofhigh-efficiency VUV reflective coatings, namely, areflective narrow band filter coating [4], a highreflectivity polarizing coating [5], and a highreflectivity mirror coating.
In 2014, we fabricated the flight mirrors andperformed the high-efficiency VUV reflective
coatings on such flight mirrors. In order to evaluate
the performance of the flight coatings, witness
samples (whose diameters are 1 inch or 30 mm) were
coated simultaneously with the flight mirrors. Using
these witness samples, we evaluated the performanceof the flight coatings at UVSOR BL7B with ourmeasurement system shown in Fig. 1 (see the details
in Narukage et al. [5]).
The reflective narrow band filter coating wasapplied to the 290 mm diameter primary mirror (seeFig. 2). The measured reflectivity in Lyα is about
56%. Meanwhile, the reflectivity in visible light andinfrared is less than 5 % in average. Hence, thiscoating can efficiently remove the unwanted visible
light and heat, which are the dominant components inthe solar spectrum. Additionally, this coating isenough uniform across the entire 290 mm diameter tosuppress the polarization caused by the
non-uniformity of the coating to less than 10 -3 % [6].
The high reflectivity polarizing coating on theflight polarization analyzer has a performance of Rs ~55 % and Rp ~ 0.3 % at their Brewster’s angle of 68
degree in Lyα, where Rs and Rp are reflectivity for sand p-polarized beam, respectively. This coating has~ 2.5 times higher efficiency than MgF2, and highpolarization power ( ≡ (Rs–Rp) / (Rs+Rp)) of 98.9 %.
Other mirrors, namely, secondary mirror and two

camera mirrors, were coated with the high reflectivity
mirror coating. The measured reflectivity is morethan 80 % in Lyα.
On the bases of these measurements with BL7B,
we confirmed that all of the coatings on the CLASP
flight mirrors satisfy the specifications determined forthe polarimetric sensitivity of 3σ ~ 0.1%.

Fig. 1. Photo of our measurement system.

Fig. 2. Photo of the CLASP primary mirror.
[1] R. Kano et al., SPIE 8443 (2012) 84434F.
[2] K. Kobayashi et al., Proc. Fifth Hinode Science
Meeting, Astronomical Society of the PacificConference Series 456 (2012) 233.
[3] N. Narukage et al., Applied Optics 54 (2015)
2080.
[4] N. Narukage et al., UVSOR Activity Report 201240 (2013) 46.
[5] N. Narukage et al., UVSOR Activity Report 201240 (2013) 47.
[6] R. Ishikawa et al., Solar Physics 289 (2014) 4727.

42Ⅲ -1. Accelerators and Instruments

BL7B

The Improvement and Evaluation of VIS-VUV Ellipsometry1

Y. Kubo1, K. Fukui1, K. Yamamoto2, T. Saito3 and T. Horigome4

Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan
2
FIR Center, University of Fukui, Fukui 910-8507, Japan3
Department of Environment and Energy, Tohoku Institute of Technology, Sendai 982-8577, Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Recently, the need for quantitative measurementsof ultraviolet (UV) - vacuum UV (VUV) radiation isincreasing with the expanding applications of theradiation for sterilization, curing, etc.. However, mostwidely used Si photodiodes, have a serious problem
of degradation under UV exposure. To develop stable
new UV detectors, accurate optical constants ofalternative materials, especially of wide bandgap ones,
composing a detector are necessary. Althoughcommercially available spectroscopic ellipsometers(SE) are known as a powerful tool to obtain opticalconstants with high accuracy, the highest photon
energy limit is typically in the near UV. Therefore, we
are improving a visible (VIS) – VUV SE which isdesigned by an AIST group [1] to optimizing for theuse at BL7B. In this report, we show present status ofa VIS-VUV SE at BL7B.
Figure 1 shows the side view of VIS-VUV SE. In
this SE, an oblique incident photodiode and a sample
chamber are rotated along the incident beam axis (βand α rotations) instead of the rotations of an analyzer
and a polarizer, respectively. Then, both rapid andaccurate 5-axis adjustable mechanical system to alignmechanical α rotation axis with the light axis isrequired. To realize computer controlled adjustable
mounting at the narrow working space of BL7B, we
design and construct a mount using parallel linkmechanism. Measurement accuracy drasticallyincreases after installing this mount.
Figure 2 shows both the refractive index n and theextinction coefficient k of Au mirror as a function ofphoton energy. Color symbols represent measurement
results under various experimental conditions. The
solid lines show the standard table data of Au [2] forcomparison. Although measurement errors mainly
affect the accuracy of extinction coefficient k
according to the measurement principles, k shows
good agreement with reference data in the wholemeasurement photon energy range. However, theaccuracy of n is not enough at present and further
improvement is needed, though absolute values of nare in agreement with rough surface Au thin film [3]Ⅲ -1

Fig. 1. Side view of a visible - vacuum ultraviolet
spectroscopic ellipsometer at BL7B.

Fig. 2. Photon energy dependences of both refractive
index and extinction coefficient of Au mirror.
[1] T. Saito, M. Yuri and H. Onuki, Rev. Sci. Instrum.
66 (1995) 1570.
[2] D.E. Gray ed., American Institute of Physics
Handbook 3rd edition (McGraw-Hill, 1972) 6-136.
[3] M. L. Theye, Phys. Rev. B 2 (1970) 3060.

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