Proceedings of IBIC2012, Tsukuba, Japan

MOPB86BETATRON TUNE MEASUREMENT AND AUTOMATIC CORRECTIONSYSTEMS AT NEWSUBARU STORAGE RING
S. Hashimoto#, Y. Hamada, S. Miyamoto, NewSUBARU, Hyogo, JapanAt the NewSUBARU electron storage ring, twodifferent kinds of systems for betatron tunes have beendeveloped: a high-precision tune monitor and a real-timemeasurement and automatic correction system. The highprecision tune monitor has the resolution of 0.0002 anduses frequency analysis methods such as SRSA, zoom
FFT, in addition to usual FFT. Fluctuations of tune due
to a slight difference of filling pattern in the top-up
operation and tune shifts due to the decrease of stored
current in the decay operation can be observed with thismonitor. The tune monitoring and automatic-correcting
system has been developed to compensate tune shifts
during the energy ramp from 1.0 to 1.5 GeV. This system
can measure and correct betatron tunes every 0.5 sec tokeep tunes to the optimal values. The system also has atune survey function that can automatically measure thebeam lifetime in a tune diagram to find the optimal
operating point experimentally.

INTRODUCTION
The NewSUBARU synchrotron radiation facility [1,2]of University of Hyogo [3] is located in the SPring-8 siteand has a 1.5 GeV electron storage ring. Synchrotron
radiation in the soft X-ray regime is applied to industrial
purposes such as EUV Lithography, LIGA, thedevelopment of new materials, and the generation ofgamma ray by Compton scattering. Electron beams are
injected from 1.0 GeV Linac of SPring-8. The ring
operates in the top-up mode at 1.0 GeV and the decay
mode at 1.5 GeV. The main parameters of the ring areshown in Table 1.

mode operation, (2) dependence on a slight difference offilling pattern in the top-up operation, (3) during energy
ramping from 1.0 to 1.5 GeV. In our ring a stripe-line
kicker shakes electron beams vertically to enlarge theTouschek lifetime. Thus horizontal and vertical tunes canbe usually observed even during user time.
In this paper we introduce two different kinds ofsystems concerning betatron tunes, the one is for precise
measurement and the other is for real-time tune
correction.

BETATRON TUNE MONITOR
To measure betatron tunes with a high resolution wedeveloped a precise tune monitor. Although the update
rate is relatively slow, the monitor has the resolution of0.0002 and can measure a slight change of tune or its finestructure.

HardwareSignals from four electrodes of a Beam Position
Monitor are analyzed using a BPM signal processing
circuit (bergoz LRBPM). The output signals representing
horizontal and vertical beam positions are digitized by adigital oscilloscope (NI PXI-5102) in a PXI chassis. The
digitizer has 15MHz bandwidth and 20MS/s sampling
speed. The PXI system was connected to a PC through
Ethernet. The digitized waveform data in time domain,
whose typical number of samples per channel is 25600,
was transferred to the PC. The application softwaredeveloped by National Instruments (NI) LabVIEW
performs frequency analysis from the position data. ThePC runs as a virtual machine on a host machine using
VMware workstation.

Table 1: Main Parameters of the NewSUBARU Ring
Beam energy

1.0 – 1.5 GeV

Circumference

118.7 mRF frequency

499.955 MHz

Stored Current

500 mA (max.)

Harmonic Number198Synchrotron Frequency

6 kHz

Betatron Tune

6.28 (H) / 2.22 (V)Operation mode in usertime

220 mA Top-up @1.0GeV
350 mA Decay @1.5GeV

One of the problems on machine operation is a betatrontune shift during user time. Tune shifts were observed in
the following cases: (1) current dependence in the decay____________________________________________#hashi@lasti.u-hyogo.ac.jp

Figure 1: Layout of the precise tune monitor.

Frequency Analysis
The advantage of performing frequency analysis at thePC is that resources of high-performance PC can be used
for the frequency analysis requiring a huge amount ofISBN 978-3-95450-119-9
Tune Monitors

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Abstractc 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○MOPB86

Proceedings of IBIC2012, Tsukuba, Japan

calculation and that various methods of frequency
analysis can be used. As frequency analysis methods, weused zoom FFT, SRSA (Super-Resolution SpectralAnalysis) in addition to FFT which is the most popular
frequency analysis method. Zoom FFT analysis [4] is anefficient computation on a subset of frequencies ofinterest, and can save an amount of processing power andtime compared to computing the FFT for entire
frequencies. SRSA is a model-based analysis method. It
needs smaller datasets of sample points and priorknowledge of the input signal, that is, an estimate of thenumber of sinusoidal components in the input signal.
Horizontal tune spectrums at the 1.0 GeV top-up
operation obtained by the three methods are shown inFig. 2. Peak frequency of 726 kHz corresponds tofractional tune of 0.287. The resolution of the FFT is0.0002 in tune. In both sides of the main lobe sidebands
are observed which are separated by a synchrotron
frequency of 6 kHz from the main peak. The elapsed
times for computing one waveform are 15.4 ms in FFT,
4.5 ms in zoom FFT and 10.0 ms in SRSA.
Magnification of the zoom FFT is about 80. The zoom
FFT has relatively lower resolution than the FFT butsmaller elapsed time for computing. SRSA can the peakfrequency but it is hard to obtain fine structure and needcomputing time longer than the zoom FFT.

time [5]. The ratio of bunch charge between a bunch in
70 bunch trains and the full-fill part is about 3 to 1. The
beam from the linac can be injected in the order of bucket
address or to a selected bucket which charge is smallest
compared to the other bunches [6]. When beams are
injected in the order of bucket address, observed tunes arefluctuated as shown in Fig. 3 due to a slight and relative
variation of a filling pattern. When the address of an
injected bunch is selected, no fluctuation was observed,
but slow drifts of tunes in both horizontal and verticalwere observed. These drifts may arise from a temperaturedrift such as magnets, vacuum chambers. Our facility
stops machine operation at night and starts to operate
power supplies in morning for energy saving everyday.
The dependence of tune on the stored current is shownin Fig. 4. Tune slowly decreases according to thedecrease of the current for ten hours of the 1.5 GeV decay
mode operation.

Figure 3: Measured tune variation during user-time inhorizontal (left) and vertical (right). Bunch selection is
OFF (upper) and ON (lower).

Figure 2: Horizontal tune spectrums analyzed by FFT(upper), zoom FFT (middle) and SRSA (lower).

Measurement Results
Temporal changes of horizontal and vertical tunes
during top-up operation, where the stored beam current of
220 mA is kept constant for eight hours, are shown in
Fig. 3. In our ring the number of harmonic number is 198
and “70+70 over Full-Fill” filling pattern, which means
two 70 bunch trains plus fulfilling, is used in usual user

Figure 4: Horizontal (upper) and vertical (lower) tunes
during 1.5 GeV decay mode.

AUTOMATIC TUNE CORRECTIONSYSTEM
The second system is the tune measurements andautomatic correction system. In the NewSUBARU
storage ring, horizontal and vertical tunes drift orISBN 978-3-95450-119-92

Tune Monitors

Proceedings of IBIC2012, Tsukuba, Japan

Tune Measurement for Correction
The layout of the tune correction system is shown inFig. 5. To measure both horizontal and vertical tunes
simultaneously, beam signals from diagonally displaced
two electrodes of a BPM are used. The intensity andphase of the two signals are adjusted using attenuatorsand phase shifters. And subtracted signal is generated by
180-degree hybrid. After being amplified, this signal isfrequency analyzed by the spectrum analyzer(ADVANTEST U3751). The spectrum data is transferred
to a PC through GPIB and Ethernet. In the PC raw
spectrum data is analyzed and tunes are evaluated in realtime using the application software developed byLabVIEW.

averaging and a smoothing, the processed waveform
becomes clear and suitable for peak detection. In thesoftware the peaks are carefully analyzed so that there isno detection error, taking into account that the beam
signal intensity varies according to the stored beam
current and a spectrum is largely disturbed in top-up
operation if the timing of measurement is overlapped witha beam injection.

Tune Correction
A flow chart for the tune correction scheme is shown in
Fig. 7. The PC detects two peaks of tunes in the spectrum
waveform and determines that it should be corrected if
the measured tunes are largely shifted from the desiredones. The PC calculates correction amount of tune andcorresponding currents for power supplies (PS).
To adjust tunes we attached the additional windings toquadrupole magnet Q1, Q2 families. For the additional
winding, power supplies that can be controlled separatelyfrom the main power supplies for Q1 and Q2 areprovided. The PC sends current setting for Q1 and Q2
windings to the PS controller, which controls the PS
through Programmable Logic Controller network. The
control loop speed is 0.5 sec.
Because these power supplies are monopolar from thepoint of view of cost, a simple polarity switcher that canbe controlled by external high/low voltage from theremote I/O device (NI compact Fieldpoint) is used. To
avoid an over-correction due to measurement errors, incase of tune shifts larger than 0.02 in one cycle, thecorrection is not performed.

Figure 5: Layout of the automatic tune correction system.

Figure 7: Scheme of tune correction.

Correction Results

Figure 6: Spectrum waveform before (upper) and after(lower) ten times averaging and a smoothing.
In Fig. 6 measured spectrum waveforms are shown.
The raw data from the spectrum analyzer is very noisy, sothe estimation of signal peaks is difficult. After ten times

Results of tune correction during energy ramping areshown in Fig. 8. Without corrections, horizontal andvertical tunes vary in the range of 0.01 to 0.02 during
energy ramping. These changes come from discrepancyof magnetic field during energy ramping. The trajectory
in a tune diagram during energy ramping is shown inFig. 9. The large shift is one of reasons of a partial lossof beams or a beam abort.
With tune corrections, the range of tune shifts become
be kept within 0.005 and stable ramping is possible. Thetune trajectory with the correction in a tune diagram isalso shown in Fig. 9.

ISBN 978-3-95450-119-9
Tune Monitors

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○fluctuate during energy ramping in addition to the filling
patterns and the stored current as mentioned above. Tune
shifts during the ramping come from asynchronous
ramping speeds among magnets, eddy currents and an
inadequate reproducibility of magnetic field strength. It
is desired to compensate tune shifts in real-time for astable operation.

MOPB86

MOPB86

Proceedings of IBIC2012, Tsukuba, Japan

Figure 8: Time variation of horizontal and vertical tunes
without and with correction.

Figure 10: Contour plot of the measured beam lifetime intune diagram. The circle denotes typical operating point.

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

Figure 9: Tune trajectory during energy ramp from 1.0 to1.5 GeV without (left) and with (right) tune real-timecorrection.

AUTOMATIC TUNE SURVEY
The tune correction system has an automatic survey
function, which can measure automatically beam lifetime
with varying operation points. Figure 10 shows theexperimental results of tune survey of the beam lifetimeat 1.0 GeV, 200 mA. Because of the insufficient numberof windings and the lack of capability of power supplies,
a survey area is divided into three parts. All data wastaken within one hour. Some resonance lines and theusual operating point (6.28, 2.21) are also plotted. It isobvious that there are the decrease of lifetime due toresonances near 3νx=19 and νx - νx =4.
At the usual operating point, the product of current andlifetime Iτ is about 1000 mA hour. On the other hand, it
is found that Iτ around νx =6.31 increases about 40 %.
This optimal area is relatively large but close to the strong
resonance 3νx=19. Without tune corrections, ramping inthis area may cause the reduction of lifetime or a beamabort, considering that tunes shift about 0.02 as shown in
Fig. 8. Thus it is necessary for the stable operation tooperate and ramp in this area with the tune correction.

In the NewSUBARU electron storage ring, the twokinds of betatron tune monitors have been used. The one
is for the high-precision measurement and the other is forthe real-time automatic correction.
Although the high-precision monitor is slow monitor,
the resolution of tune measurements is 0.0002. In
frequency analysis three methods such as FFT, zoom
FFT, SRSA were compared. Small fluctuations of tunes
during the top-up operation can be observed using thismonitor.
The tune correction system can automaticallycompensates tune shifts every 500 ms, if measured values
are shifted from the desired values. The automatic tune
survey of the beam lifetime is useful for study of beamdynamics.

ACKNOWLEDGMENT
The authors are very grateful to Mr. T. Shinomoto, Mr.
Y. Takemura and Dr. Y. Minagawa of JASRI/SPring-8
for their help in developing the monitor systems andoperating the NewSUBARU storage ring.

REFERENCES[1] A. Ando et al., J. Synchrotron Rad. 5, pp. 342-344(1998).
[2] http://www.lasti.u-hyogo.ac.jp/NS-en[3] http://www.u-hyogo.ac.jp/english/index.html[4] R. G. Lyons, “Understanding Digital SignalProcessing”, Prentice Hall.
[5] S. Hashimoto et al., ”Photo Stimulated Desorption
Phenomena at The NewUBARU Storage Ring”, SRI
2003, pp. 525-528 (2003).
[6] Y. Minagawa et al., “Bunch current monitor systemfor NewSUBARU”, Proceedings of 7th Annual
Meeting of Particle Accelerator Society in Japan,(2010).

ISBN 978-3-95450-119-9
4Tune Monitors