Light Sources

Development of Pulse Duration Measurement System
for Coherent Harmonic Generation Experiments
H. Zen1, M. Adachi2,3, S. Tanaka2 and M. Katoh2,31Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan1 ps or shorter. Moreover, we are now planning toinstall thinner crystal (1 mm, 0.5 mm) to obtain better
temporal resolution.

The Coherent Harmonic Generation (CHG) from
relativistic electron beam through the interaction withhigh power laser is promising way to generate shortpulse EUV coherent radiation [1]. However,saturation limits the number of photon in a pulse [2].
In conventional laser, Chirped Pulse Amplification(CPA) technique is commonly used to avoid damage
or saturation and to obtain high power laser beam. We
proposed utilization of CPA to CHG technique toovercome the saturation problem [3].
We are planning to make proof of principle
experiment at the wavelength of 266 nm whichcorresponds to the 3rd harmonics of Ti-sapphire laser.
For the experiment, we need a pulse duration
measurement system and an UV pulse compressor.
In this fiscal year, we have designed and developed
the pulse duration measurement system. We selected
an optical cross correlation as the way to measure theUV pulse duration, since 150-fs Ti-sapphire laser isavailable in UVSOR for the pump beam of crosscorrelation. Figure 1 shows the schematic diagram ofpulse duration measurement system. Fundamental of
Ti-sapphire laser (800 nm) and 266-nm radiationfrom CHG is focused together to BBO crystal which
is optimized for Difference Frequency Generation(DFG). Then, 400-nm radiation is generated from
DFG crystal when the fundamental and CHG
radiation enter to the crystal at the same time. Bymeasuring the dependence of the 400-nm radiation
intensity on the time delay between the two pulses,
we can measure the temporal profile of UV light.
Figure 2 shows the photo of the developed pulse
duration measurement system.
To check the properties of developed system, we
generated UV laser beam from 800-nm laser beam(150 fs-FWHM) and 3rd harmonic generation crystals.
Figure 3 shows the result of cross correlation
measurement of the UV laser beam. The measured
pulse duration was 0.8 ps in FWHM. This value ismuch longer than the expected pulse duration of UV
laser beam (around 150 fs). Since we used DFG
crystal of 2-mm thickness in this experiment to obtainlarger signal, group velocity mismatch of 800-nm and266-nm light in the crystal causes 0.75-ps slip of
those pulses. Therefore, the measured result (0.8 ps,
FWHM) indicates the temporal resolution of thedeveloped system. This value is acceptable for the
proof of principle experiment, because we will
generate 10-100 ps UV radiation and compress it to

Vertically
Polarized 800 nm

Retroreflector (RR)
Auto Stage
SGSP20-85,
Sigma Koki

E
Probe Light

Horizontally
Polarized 266 nm

Lens(f = 200 mm)

Bandpass Filter(400 nm)DetectorE
Measured LightBBO Crystal
for DFG

Fig. 1. Schematic drawing of pulse duration
measurement system.

Fig. 2. Photo of the developed pulse duration
measurement system.

Fig. 3. Result of cross correlation measurement.
[1] R. Prazeres et al., Nucl. Inst. Meth. A 304(1991)72.
[2] T. Tanikawa et al., Appl. Phys. Exp. 3 (2010)2702.
[3] H. Zen et al., Proc. of FEL2011 (2012) 366.

33

Light sources

Development of an Electron Beam Bunch Length Measurement System for
the Transmission-type Polarized Electron Source
N. Yamamoto 1, T. Niwa 2 , T. Inagaki 2, M. Hosaka 1, A. Mano 1, Y. Takashima 2,1 ,T. Konomi 3, M. Adachi 3, M. Katoh 3,1, K. Sakaue 4 and T. Takatomi 5
1

Nagoya University Synchrotron Radiation Research Center, Nagoya, Aichi, 464-8603
2
Graduate School of Engineering, Nagoya University, Nagoya, Aichi, 464-8603
3
UVSOR Facility, Institute for Molecular Science (IMS), Okazaki, Aichi, 444-8585
4
Research Institute for Science and Engineering, Waseda University (RISE), Tokyo, 169-8555
5High Energy Accelerator Research Organization (KEK), Ibaraki, 305-0801

Spin polarized electron sources are expected aselectron sources for next high energy accelerators,
such as the International Linear Accelerator (ILC).
In the development of the transmission-type spinpolarized electron sources, the electron spinpolarization of ~90 % and he high beam brightnessof ~2 × 107 A.cm-2.sr-1 were already achieved at
Nagoya University [1, 2].
For the next step of the development, the time
response of the transmission-type photocathode has
to be characterized. Then we designed andmanufactured an electron beam bunch length
measurement system using a radio frequency (rf)deflecting cavity [3].
The system consisted of a laser injection systemusing a mode-locked Ti:Sapphire laser, an rf
deflecting cavity and a beam profile monitor. The
system was modified for 20-keV electron beams,
which corresponds to the Lorentz factor ȕ of 0.272.
At low energy, the difference between velocities ofrf waves and electron beams is important for
designing the cavity structure. Concerning beam
dynamics, stretching of bunch length due to spacecharge effect is also non - negligible.
Parameters of the deflecting cavity are shown in
Table 1. The deflecting cavity is made of
Oxygen-Free Copper and has one cell rectangularstructure with six frequency tuners. Electron beams
are deflected by magnetic field of TM120 mode in
deflecting cavity. The resonance frequency is2612.9 MHz that is 29 times of beam reputations(90.1 MHz). The longitudinal length was chosen to
be 46.81 mm with consideration for beam
deflecting efficiency. The deflecting efficiency ismaximized when the longitudinal length is equal tothe product of the rf half-wavelength and theLorentz factor ȕ.

Agilent N5230A Network Analyzer. The frequency
tuning range is 2.9 MHz from 2611.2 to 2614.1 MHz.
The loaded and unloaded quality factors are 10,155
and 20,565 respectively and in good agreement withthe calculation (only just 4% below). The gradient ofmagnetic field along with longitudinal direction was
also measured by the bead-pull method andconfirmed by the HFSS simulation.
The deflecting cavity and beam profile monitor
were installed in the downstream of the polarized
electron gun at UVSOR. The operation test by using
20-keV CW beams was done and it is demonstrated
that the performances of the cavity are enough todeflect the 20-keV beams.
We are preparing the picosecond laser injection
system for generation of pulsed electron beams. By
using this system consisting of grating dispersion
compensators and an 30m photonic crystal fiber, thelaser pulse duration can be changed in the range of a
few to several tens picoseconds.
In near future, the systematic measurements of thetemporal response of electron sources are scheduled
and the results will be feed backed for thephotocathode developments to realize fast temporal
response, highly brightness and highly spin polarized
simultaneously.
Table 1. Parameters of the RF cavity
Size
Width
121.01 mm
Height129.98 mm
Longitudinal length
46.81 mmResonance mode
TM120
Resonance frequency
2612.9 MHz
Quality factor (Loaded)
10,155
Quality factor(Unloaded) 20,565
Input coupling factor
1.02
Magnetic field at 1 W
1.57 G (Max.)

Most of cavity designs are made by analytical
calculation from Maxwell equations and a 3-D
simulation cord ANSYS HFSS are also used fordesigns of rf input and monitor ports.
The fabrication and assembling of the cavity was
made at Equipment Development Center of IMS and
Mechanical Engineering Center of KEK. After them,a set of rf measurements was performed with an[1] N. Yamamoto, T. Nakanishi et al., J. Appl. Phys.
103 (2008) 064905.
[2] X.G. Jin, N. Yamamoto et al., Appl. Phys. Ex. 1(2008) 045002.
[3] T. Niwa, N. Yamamoto et al., Proc. of the 9th
Annual Meeting of PASJ, pp. (2012) 1100.

34

Light Sources

Pulsed Sextupole Injection in UVSOR-III
Y. Hida1, H. Zen2, T. Konomi3,4, N. Yamamoto5, M. Adachi3,4, M. Hosaka5, K. Hayashi3,
J. Yamazaki3, Y. Takashima1 and M. Katoh3,41

Graduate School of Engineering, Nagoya University, Nagoya, Aichi, 464-8603, Japan
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
5
Nagoya University Synchrotron Radiation Research Center, Nagoya, Aichi, 464-8603, Japan
2

Since 2010, the top-up injection of electron beam
to storage ring has been started to keep the beam
current almost constant during user experiments in
UVSOR [1]. For the electron beam injection, weessentially require kicking the electron beam inhorizontal direction and the kick induces betatronoscillation of electron beam. This oscillation disturbs
user experiments and causes undesired spikes inmeasured data. To prevent this effect, beamline users
are required to stop their measurement for ten
seconds during the injection and for five seconds after
the injection.
A new injection scheme called as pulsed multipole
injection has been developed in KEK [2, 3]. We
decided to introduce this scheme with pulsed
sextupole magnet (PSM) to UVSOR to increase theefficiency of user experiments. Based on the
numerical experiments, the PSM has been designed
as Fig. 1 and fabricated as Fig. 2(a). The magnet wasmade of 0.2-mm-thick laminated silicon steel sheets
to reduce eddy current effects. The coil is formed by a
one-turn cupper bar with a diameter of 5 mm.
Figure 2(b) shows the photo of PSM after installation
to the UVSOR-III storage ring. The main
specification of the designed PSM and its power
supplies are summarized in Table 1.

(a)(b)
Fig. 2. Photo of the manufactured sextupole magnet(a). Photo of the sextupole magnet after installation to
the storage ring (b).
Table 1.

Specification of the sextupole magnet.

Sextupole Magnet
Core Length
Vertical Gap
Horizontal Gap
InductancePower Supply
Peak Excitation Current
Pulse Width

240 mm
45 mm
136 mm2.15 PH
2200 A
1.3 PsWe have performed test experiments of electron
beam injection with PSM. After optimization ofhorizontal and vertical tune of the UVSOR-III storage
ring, we achieved maximum injection efficiency of
23% and electron beam injection up to 300 mA in
multi-bunch filling (12 bunches in 16 RF buckets).
We have already observed the drastic suppression ofhorizontal electron beam movement with PSM
injection.
For further improvement of injection efficiency, themaximum excitation current will be increased andplace of PSM will be moved.

Fig. 1. Geometry of designed sextupole magnet andmagnetic flux lines calculated by Poisson.

[1] H. Zen et al., Proc. of IPAC10 (2010) 2576.
[2] K. Harada et al., Phys. Rev. ST Accel. Beams 10(2007) 123501.
[3] H. Takagi et al., Phys. Rev. ST Accel. Beams 13(2010) 020705.

35

Light Source

Saturation of the Laser-Induced Narrowband Coherent Synchrotron
Radiation Process
M. Hosaka1, N. Yamamoto1, Y. Takashima1,2, C. Szwaj3, M. Le Parquier3, C. Evain3,
S. Bielawski3, M. Adachi4, H. Zen4, T. Tanikawa4, S. Kimura4, M. Katoh4, M. Shimada5
and T. Takahashi61

Nagoya University Synchrotron Radiation Research Center, Nagoya 464-8603, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Universit´e des Sciences et Technologies de Lille, F-59655 Villeneuve d’Ascq Cedex, France
4
UVSOR, Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan
5
High Energy Accelerator Research Organization, KEK, Tsukuba, 305-0801, Japan
6
Research Reactor Institute, Kyoto University, 590-0494, Japan

In a bending magnet, a relativistic electron bunch
can radiate narrowband terahertz coherent synchrotron
radiation when its longitudinal distribution issinusoidally
modulated.
We
havealready
demonstrated this by creating the modulation using
interaction between an electron beam and a laser pulse
containing a sinusoidal amplitude modulation. We
have also demonstrated that the emitted powerincreases with the beam current and the laser power
and the scaling is quadratic. However, when the laser
power is arbitrarily increased, a departure to thisquadratic increase with laser power is also expected,
eventually leading to a decrease of emitted power withlaser.
In order to observe the saturation phenomenon in
the long pulse regime, we used higher energy pulses(by means of a new amplifier), and realized apulse-shaper able to provide modulated pulses withadjustable duration and modulation period. The
experiment is performed with an electron energy of
600 MeV and a laser pulse modulation period of 2.38
ps (i.e., a terahertz emission spectroscopic
wavenumber of 14 cm-1), near the maximum
efficiency of the system. In the present conditions,departures from quadratic scaling are typicallyobserved, as is shown in Fig. 1. Near maximum laser
pulse duration available from the pulse shaper (191 ps
FWHM), only a slight (though noticeable) departurefrom quadratic scaling is observed [Fig. 1 (b)].
However, when the laser pulses are further
compressed [down to 28.5 ps FWHM in Fig. 1(c)], astrong saturation effect is observed, leading to theappearance of a maximum.
In order to analyze the process in detail, we use thetheoretical approach introduced in the framework oflaser-induced CSR. We have calculated an integrated
form factor of the CSR as a function of modulationenergy. We have also estimated the modulated energy
as a function of laser energy and pulse duration. The
calculated result is compared with the experimental
one. Although not shown here, the theoretical valuesof the integrated form factor is consistent with theexperiment [2]. Future extensions of this work concern
studies of the consequences of this saturation

Fig. 1. Typical scalings of terahertz signal versus laser
power, for three power ranges. (a): reference
quasi-quadratic behavior that was already observed at
low power, with a 2 mJ amplifier and 300 ps longpulses.
effect in various situations. This may be important inorder to compare the ultimate limits due to saturation
effects (in particular in THz pulse energy and peak
power) due to the saturation effect, in the cases ofslicing, and modulated pulse based strategies.

[1] S. Bielawski, et al., Nature Physics 4 (2008) 390.
[2] M. Hosaka et al., Phys. Rev. ST Accel Beams 16(2013) 020701.

36Light Source

Design and Performance Test of a Buncher Magnet for a New Optical
Klystron at UVSOR-III
Y. Uematsu1, M. Hosaka2, S. Sekita1, Y. Asano1, N. Yamamoto2
Y. Takashima1,2, M. Adachi3, H. Zen3, S. Tanaka3, T. Konomi3 and M. Katoh3
1

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

New coherent sources using a relativistic electron
beam are being developed at UVSOR-III storage ring.
An optical klystron consists of two undualtors
separated by a buncher magnet plays an important role
for the sources, especially for the coherent harmonic
generation. We adapted apple-II type undulators madeof permanent magnets and an electromagnet buncher
magnet with 3 poles for the optical klystron. The
buncher was designed under the conditions that itshould be sufficiently compact to be installed in alimited space between the two undulators (the length
along the propagation direction of the electron beam
should be less than 400 mm) and the magnetic field is
sufficient strong:R56 > 70 Pm, with vanishing firstand second field integrals. Taking into account the cost,
we have adapted indirect cooling for the coils andtherefore the maximum current density is limited
around 4 A/mm. The numerical magnetic fieldcalculation was performed with Radia code [1] andoptimization of the magnetic field was carried out.
Figure 1 shows 3-D drawings of the buncher createdby Radia. The shape of the field poles is speciallydesigned in order to increase magnetic field around theelectron beam path. After the designed work, thebuncher was fabricated. Magnetic field of theconstructed buncher was measured and the result isvery consistent with the simulation calculation using
Radia [3]. The bucher was installed between the two
undulators already installed at UVSOR-III 1S. It canbe said that then construction of the optical klystron
was finally completed.
The performance test of the buncher was carried byobserving spontaneous radiation from the opticalFig. 2. Measured (blue) and calculated (red) spectra of
spontaneous radiation from optical klystron.
klystron. Since the spontaneous spectrum as a result ofinterference between two undulators, is sensitive to thebuncher magnetic field, we can characterize thebuncher by analyzing the spontaneous spectra. The
experiment was made with the electron energy of 600
MeV and the fundamental wavelength of theundulators of 800 nm. Figure 2 shows examples ofmeasured spectra changing excitation current of thebuncher. Calculated spectra using spectra [3] are alsoplotted in the figure. The agreement between
measured and calculated spectra reveals that theperformance of the bucher is as designed.
Soon we are going to make an experiment on
coherent harmonic generation using the optical
klystron.
[1] O. Chubar, P. Elleaume, J. Chavanne, J.
Synchrotron Rad. 5 (1998) 481.
[2] Y. Uematsu, Master’s Thesis, Nagoya University(2013).
[3] T. Tanaka and H. Kitamura, J. Synchrotron Radiant.
8 (2001) 1221.

Fig. 1. 3-d drawing of the designed bucher.

37

Light Sources

Combined-Function Bending Magnets for UVSOR-III
K. Hayashi, M. Adachi, T. Konomi, J. Yamazaki and M. Katoh
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

In the first major upgrade, from UVSOR to
UVSOR-II, in 2003, most of the storage ring magnets
were replaced, but the bending (dipole) magnets wereleft untouched for later upgrade. In the next major
upgrade, to UVSOR-III, in 2012, all eight bending
magnets were replaced with newly designed
combined-function ones to reduce emittance from 27
to 17 nm-rad.
The parameters of the new and old bending
magnets are listed in Table 1. The quadrupole
component of the magnetic field is achieved byadjusting the cross-sectional shape of the pole. The
sextupole component is generated by adjusting thelongitudinal end-shape of the pole. The mass of the
new magnets was reduced, but a sufficient good-fieldregion (<0.1%) of ±3 cm was retained.

Fig. 2. End-shape of the new bending magnet.
The shape details were investigated by using the
2D calculation code Poisson for cross-sectional shapeand the 3D calculation code Opera for longitudinal
end-shape. The magnets (Fig. 3) were made by NEC
TOKIN Corporation, Japan.

Table 1. Design parameters of bending magnets.
New
Old
Bending radius (m)2.2
2.2
Bending angle
45°
45°
K1
(m–1)
–1.2
0
(quadrupole)
K2(m–2) –2.43 (u2)0(sextupole)
Good field region
±3
±5
(cm)
Pole width (cm)1418
Gap at center (cm)5.5
4.8
Mass (metric ton)
3.3
4.3
Material
SUY1
S10C

Fig. 3. A new bending magnet (lower half is shown).
The measured magnetic field-strength distribution
is shown in Fig. 4. For unknown reasons thequadrupole field strength, which is represented by thegradient of the graph, is about 3% smaller than thedesign value. The good field region was about ±3 cm.
The effective magnetic length was within 1 mm of thedesign value, 1.728 m.

The pole shape is shown in Figs. 1 and 2. To
generate the quadrupole defocusing magnetic field aswell as the dipole magnetic field, the pole face istaper-shaped. The sextupole magnetic fieldcomponent is achieved by shaping the end section of
the bending magnets like a paraboloid so that theeffective magnetic-field length varies according to thehorizontal orbit position of the electrons.

Fig. 4. Horizontal distribution of magnetic field.
The new bending magnets were installed in the
UVSOR storage ring in April 2012 and have been
operational since August.
We are very grateful to Dr. Y. Shoji of New
SUBARU for his kind collaboration.

Fig. 1. Cross-sectional view of combined-function
bending magnets (upper half is shown).

38

Light SourcesTurn-By-Turn BPM for UVSOR-III
K. Hayashi1, T. Toyoda2, M. Adachi1, T. Konomi1, J. Yamazaki1 and M. Katoh1
1

2

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Instrument Development Center, Institute for Molecular Science, Okazaki 444-8585, JapanThe signal-switching box is shown in Fig. 3.
Because the BPM signal is a weak (tens of mVs to
sub-mV) high-speed pulse (a 100-ps bunch length
corresponds to a frequency region of several GHz),
we use coaxial switches (Teledyne Coax Switches) to
switch signals at low attenuation.
We use a digital oscilloscope (5-GHz sampling
frequency, 1-GHz analog signal band) to record four
signals from one BPM head; the heads are selected
one by one. The data are analyzed off-line.

A major upgrade of the electron storage ring at the
UVSOR facility started in April 2012. To help in thecommissioning procedure we have developed aturn-by-turn Beam Position Monitor (BPM) system,
which consists of a signal-switching circuit, a digital
oscilloscope, and software [1].
The UVSOR-III storage ring has 24 BPMs, each ofwhich consists of four button electrodes (Fig. 1). We
use a commercial signal-processing system (BergozCo.) for regular operation.

Fig. 1. Layout of BPM electrodes.
At commissioning— especially before the successof the beam storage is confirmed—we need to findout such things as the number of turns the beam has
made and where the beam has been lost. Most ofthese things can be determined by using aturn-by-turn BPM system, but such a system is notnecessary for daily operation. We therefore decided toconstruct a turn-by-turn BPM system, as follows:•The system was constructed as cheaply and simply
as possible.
•We used an existing digital oscilloscope forwaveform observation and recording.
•We used existing RF cables that were normally used
to connect the BPM heads and the Bergoz signal
processing system.
•We set up the oscilloscope in the ring and controlled
it via a LAN.
•We developed a signal-switching box that could becontrolled via the LAN.
Fig. 2 is a block diagram of the system.

Fig. 3. BPM switching box.
We control the coaxial switches with an “mbed”
microcontroller (NXP Semiconductors), which can becontrolled remotely through the LAN. The control
application for the BPM system was constructed inHTML (and CSS), which implements a JavaScript
library that can handle I/O ports. When we access the
mbed from the web browser, the mbed responds as an
HTTP server and a control application is displayed in
the web browser.
An example of the injection beam trajectory is
shown in Fig. 4. By using this system, we have beenable to determine not only the orbit but also thebetatron tune. At commissioning, the system was very
powerful in achieving beam storage.

Fig. 4. Example of an injection orbit.
[1] T. Toyoda, K. Hayashi and M. Katoh, Proc.
IBIC2012 (2012) MOPA28.

Fig. 2. Block diagram of the BPM system.

39