Proceedings of IBIC2012, Tsukuba, JapanTUPB77

MEASUREMENT OF THE FREQUENCY SPECTRUM
ON THE BEAM PROFILE CONTROLLED BY RF KICKER
Y. Yamamoto, Ritsumeikan University SR Center, Kusatsu, Shiga, JapanThe frequency spectrum on the beam profile wasmeasured at the compact superconducting storage ring ofRitsumeikan University. The radiation detector was used
an avalanche photodiode module with a high frequency
response of 1 GHz for the visible ray. Signals from thedetector were transferred to a spectrum analyzer. Thebeam profile was magnified strongly by a conventional
profile monitor system. We scanned the beam profile invertical direction by shifting the detector. The distributionof peak intensity as a function of the position on beamprofile was obtained.

INTRODUCTION
The world smallest electron storage ring AURORA
with a super conducting magnet was developed by
Sumitomo Heavy Industries [1]. Ritsumeikan University
installed this storage ring in 1996. Since then, the SRcenter was utilized for synchrotron radiation researches[2]. There are 14 beamlines (XAFS, PES, Imaging andLIGA) and 2 beam-monitor-lines operated in the center.
The number of registered users in last year was 405 in
total, in which number of outside users was 149.
AURORA is the weak focusing type with the simplest
lattice composed of a single bending magnet, which
produces an exactly axial symmetric magnetic field withlittle error magnetic field. The vertical beam size wasmeasured to use the SR-interferometer by Mitsuhashi et alin 1997 [3-4]. The result of the size to be 10.5 m showedability of the SR-interferometer. At the user operation, wecontrolled the vertical beam size to keep 130 m by
RFKO to extend beam lifetime [5-6]. We tried to measure
the frequency spectrum on the beam profile to monitor
any instability by RFKO.
Table 1 lists the parameters of the injector and the ring.
Figure 1 shows the storage ring and beamlines in theexperimental hall.

Table 1: Parameters of the Injector and Storage Ring
Injector parameters
Energy150 MeV
Repetition
3 Hz
Peak current
1 mA
Pulse width
2 sStorage ring parameters
EnergyStored current
Circumference
Radius of curvature
Field strength
RF frequency
Number of cavities
Harmonic number
Critical energy of radiation
Vertical beam size()Vertical beam size: user operation()Horizontal beam size()Beam lifetime

575 MeV
300 mA
3.14 m
0.5 m
3.8 T
190.86 MHz
12844 eV
0.0105 mm
0.13 mm
1.1 mm
300 min

EXPERIMENTAL SETUP
Measurement system which was composed by theradiation detector (APDM: avalanche photodiode module,
C5658 HAMAMATSU), spectrum analyzer (U3200
ADVANTEST) and PC was constructed behind the beam
extraction port BL-9 and BL-16 at the atmosphere [7]. A
thick beryllium flat mirror was set to reflect the primary
ray by 90° to extract the visible component in the vacuumchamber. This visible ray through the optical glass
window to divide the vacuum and atmosphere wasreflected again by an aluminium mirror, and introduced
into the measurement system.
___________________________________________

y-yama@st.ritsumei.ac.jp

Figure 1: Photograph showing the storage ring andbeamlines in the experimental hall.
The stored beam profile was magnified strongly by theconventional profile monitor using objective lens andmagnifying lens. The radiation detector was scanned withusing the micrometer on the beam profile in verticaldirection. For the operating condition of the kicker forRFKO, the center of frequency was 57.6 MHz inagreement with vertical betatron frequency (fy), deviationof frequency modulation 200 kHz, sweep frequency 1, 3or 10 kHz. Stored beam current was about 200 mA atevery measurement.
ISBN 978-3-95450-119-9

Transverse Profiles, Screens & Wires Monitors

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Abstract

TUPB77

Proceedings of IBIC2012, Tsukuba, Japan-20(A)190.9MHz
57.6MHz
75.7MHz-25-30

Intensity [dBm]frf-35-40-45-50-55-60-4-3-2-10

12345Position [mm]-20c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 2 shows an example of the observed frequency
spectrum. frf is the RF frequency of 190.9 MHz. Peakfrequencies showed by bold-red arrows are given by fyand frf ± fy, and these intensities are almost same values
at the each scanning position. Similarly, peak frequenciesof blue arrows are 75.7 MHz and frf ±75.7 MHz. The
frequency of 75.7 MHz doesn’t agree with the horizontal
betatron frequency ( fx = 76.1 MHz) but agree with thefrequency given by frf –2fy.
Figure 3 (A), (B) and (C) show measured peakintensities as a function of the vertical scanning positionon the magnified beam profile for the sweep frequency of1, 3 and 10 kHz, respectively. Distributions of plotted
points for 190.9 MHz are consistent with the beam profile,and these intensities are in proportion to the stored beam
current. On the distributions for 57.6 MHz, there are
double peaks on both sides of the center of beam profile,and these intensities decrease dependent on the sweep
frequency. This result suggests that the bunching beam
size repeat increase because of the resonant oscillation
using RFKO and decrease owing to the radiation dumping.
This suggestion is consistent with that the dumping time
constant of vertical betatron oscillation is 0.63 ms, and thetune spread is about 30 kHz and smaller than the deviation
frequency of the modulation of RF kicker. We confirmedthat the intensity of 57.6 MHz increased with every half ofsweep time by using the real time spectrum analyzer(RSA230: SONY TEKTRONIX).
On the distributions for 75.7 MHz, there are single
peaks at the center of beam profile. That tendency is
obviously different by comparison with one for 57.6 MHz.
The origin of 75.7 MHz isn’t the vertical betatronoscillation, RF frequency or those sum peak effect. We
guess that electrons kicked by RFKO oscillate inhorizontal with the frequency of 75.5 MHz. The horizontal
tune is 0.797 at the normal operation, and is 0.792 at thethird order resonance given by x+2y=2.

190.9MHz
57.6MHz
75.7MHz-30

Intensity [dBm]

RESULTS AND DISCUSSION(B)-25-35-40-45-50-55-60-4-3-2-1012345Position [mm]-20(C)-25

190.9MHz
57.6MHz
75.7MHz-30

Intensity [dBm]

Figure 2: Frequency spectrum measured by APDM at
BL-9. The center is 150 MHz, and the span 300 MHz.
The unit of vertical axis is dBm.

-35-40-45-50-55-60-4-3-2-1012

345Position [mm]Figure 3: Observed peak intensity as a function ofscanning position. (A), (B) and (C) show results for 1 kHz,
3 kHz and 10 kHz of the sweep frequency of themodulation, respectively. Diamonds show the results for
190.9 MHz of peak frequency, squares for 57.6 MHz andcircles for 75.7 MHz, respectively.
Hence, x is horizontal tune, y vertical tune: y = fy /frev,
and frev revolution frequency: 95.4 MHz. We think thehorizontal oscillations are induced by RFKO using
vertical betatron frequency duo to the effect of third orderresonance. Figure 4 shows the generation of resonant
oscillation and dumping of frequency of 75.7 MHz

ISBN 978-3-95450-119-92Transverse Profiles, Screens & Wires Monitors

Proceedings of IBIC2012, Tsukuba, JapanTUPB77

REFERENCESACKNOWLEDGEMENTS
We would like to thank Mr. S. Okada and Mr. T.
Yoshino for their aid in data collection.

ISBN 978-3-95450-119-9
Transverse Profiles, Screens & Wires Monitors

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 4: Time dependent change of peak intensity for
75.7 MHz measured by APDM (R263VF MATSUSADA)
at BL-16. Sweep time is 1.0 ms.

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