The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Beam Diagnostics for Beam Commissioning of SPring-S Synchrotron
Tsuyoshi AOKI, Hiromitsu SUZUKI, Norio TANI, Kenji FUKAMI, Naoyasu HOSODA,Toshiaki KOBAYASHI, Soichiro HAYASHI*!, Mitsugu TANIMOTO*!, Shigeki OHZUCHI*2,Kenji OKANISHI*3, Toshihiro SASAKI*4 and Hirota YONEHARAJASRI, SPring-8, Kamigori, Ako-gun, Hyogo 678-12, Japan*1 JAERI, SPring-8, Kamigori, Ako-gun, Hyogo 678-12, Japan*2 TOSHIBA Co., Uchisaiwai-cho, chiyoda-ku, Tokyo 100, Japan*3 SUMITOMO Heavy Industries Ltd., Soubiraki-cho, Niihama, Ehime 792, Japan*4 HITACHI Ltd., Saiwai-cho, Hitachi, Ibaraki 317, JapanAbstract

2. Fluorescent Screen Monitor

The beam commissioning of the SPring-8 synchrotron
was started on December 10, 1996 [1]. We achieved the firstturn of an electron beam at an energy of 1 Ge V on the sameday, the RF capture on December 11 and the acceleration at abeam energy of 8 GeV on December 16. From January toFebruary 1997, fine tuning of the synchrotron was continued.
The beam transport to the SPring-8 storage ring wasachieved in March 1997. The beam monitors were used tomeasure the beam characteristics to decide the optimum
parameters of the machine operation. In this paper, the statusof the beam monitors and the beam diagnostics during thebeam commissioning are reported.
1. Introduction

The SPring-8 synchrotron accelerates an electron beam ora positron beam from an energy of 1 GeV to 8 Ge V at arepetition rate of 1 Hz [2]. Two types of the pulse length ofthe multi-bunched electron beam were used for the beamcommissioning. At first, the bunch length of the electronbeam was chosen to be 40 ns length for adjustment of thebeam injection and for coarse tuning of the beam orbit tosuppress the radiation dose around the synchrotron. Next, thebeam of 1 f!S bunch length was used for fine tuning of thebeam orbit. Table 1 shows the beam monitors installed in thesynchrotron and in the beam transport line from thesynchrotron to the storage ring (SSBT). Most of the beam
monitors were used for the beam commissioning.
Table 1. Beam monitors of synchrotron and SSBTmonitors
Fluorescent screen monitor
Beam position monitor (BPM)
Radiator
Beam loss monitor
High power RF knock-out (RF-KO 1)
Low power RF knock-out (RF-KO 2)
Strip line monitor
DC current-transformer (DCCT)
Fast current-transformer (FCT)
Synchrotron radiation monitor
Fluorescent screen monitor *Strip line-type position monitor (SPM) *Beam charge monitor **in the SSBTquantity
1480
1

5
1
1
1
1

1
1

16
2
1

2.1 Tuning of Injection Orbit

A single-tum injection with the on-axis technique isadopted as the standard injection method of the synchrotron.
Two septum magnets and two kicker magnets are used forthe beam injection from the linac. The beam positions andthe beam profiles of the injection orbit and of the first-tum
orbit in the synchrotron are observed by the fluorescentscreen monitors. These monitors are divided into fixed-type
and movable-type.
The fixed-type screen monitor is installed in front of
every septum magnet. The fluorescent screens are fixed on
the septum magnets across the designed orbit and have arectangular hole around the orbit not to interrupt the. beam.
The injection orbit was adjusted that the beam passed
through the center of the hole. Eight movable-type screen
monitors are installed at the upstream side of the focusing
quadrupole magnets in the synchrotron. The screens · areleaned 45 degrees against the beam axis and are inserted in
the beam duct using compressed air at the measurement. The
area of each screen is 30 x 30 mm 2 for the beam. The fourthscreen monitor is located at the downstream side of theinjection kicker magnets and is used for tuning of theexcitation current of the second septum magnet and two
kicker magnets for the injection.
Mter adjusting the injection orbit, the first-tum and themulti-tum of the beam were confirmed at the energy of 1
Ge V with DC operation. Then the dipole and the quadrupole
magnets were excited and the sextupole and the correction
magnets were not excited. The first-tum of the beam wasconfirmed by the third screen monitor, which was located at
the upstream side from the injection point in the synchrotron.
Figure 1 shows the beam profile on the third screen monitor
at the first-tum of the beam. The beam energy from the linac
was adjusted to 1 GeV by observing the beam position oneight movable-type screen monitors. At the screen monitors,
the value of the· dispersion function in the horizontal
direction (Yix) is about 1 m. An average of the horizontal
beam position of 1 mm on the eight screen monitors
corresponds to a beam energy difference of 0.1 %.
2.2 Tuning of Extraction Orbit

Four bump, three kicker and four septum magnets areused for the beam extraction of the synchrotron. The fixedtype screen monitors are installed in front of every septum
magnets and are used for tuning of the extraction orbit. The
beam was extracted successfully without adjustment of the-246-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

excitation current of the pulse magnets for the beam
extraction. As the extracted beam orbit was tilted slightly inthe vertical direction, a local bump orbit was made with thethree vertical correction magnets that the tilt became
negligibly small.

Fig.1 Beam profile on the fluorescent screen monitor after
the first-tum of the beam.

3. Beam Current Monitors
The multi-tum of the beam and its lifetime were observed
by a fast current-transformer (Fer). The Fer has asensitivity of 2.5 V/A and a rise time of 500 ps. Figure 2
shows the waveform of first five turns of the beam observedby the Fer. The bunch length of the beam was 40 ns. Thebeam intensity in the synchrotron was measured by a DC
current-transformer (DCCT), which has a bandwidth fromDC to 4.2 kHz.
r11- IIttCh~

I_d LAli k_ ......... _1\j(\ A_/'

t" '~ !'fV Ivv v IV L.J'Itk+v

II-Hrf\ .N -""" ~ / r--..... ~Ch2h3-+ ·r-.f}"fC::h1tCh3I-"'""",(Iy-....rs.oomvo ~g~ .00 v M .00MS Ch4 [\.
s.1oomvf
I 5 00I1~

4. Beam Position Monitor
4.1 Measurement of COD
The beam position monitors (BPMs) are located in frontof every quadrupole magnets to measure closed orbit
distortions (CODs) [3]. Each BPM has four button-type
electrodes which are mounted on the wall of the vacuum
chamber. The diameter of the electrodes are 18 mm. Output
signals from the four electrodes are selected one after
another by fast PIN-diode switches which are placed near
the electrodes. These signals are detected by a heterodyne
circuit at a monitor room for 20-BPMs. Four detection
systems are used at the same time for 80-BPMs, and it isexpected that the time of data taking of all the BPMs is lessthan 30 ms. The accuracy of calibration and the installation
error of the BPMs are less than 0.1 mm and 0.3 mm,respectively.
After tuning of the RF capture of the injected electron
beam at the energy of 1 GeV, the CODs were measured bythe BPMs. It was confirmed that there was no timedependence on the COD by changing the timing of the BPM
measurement. Next, the beam was accelerated from theenergy of 1 GeV to 8 GeV and the COD was measured at 8GeV. The power supplies for the dipole, the quadrupole andthe sextupole magnets were excited with a trapezoidal
current pattern at a repetition rate of 1 Hz. The RF
accelerating-voltage was achieved by changing the RF phasebetween two klystrons [4]. The maximum CODs in thehorizontal and in the vertical directions at the beam energy of8 GeV without the COD correction were 2.53 mm and 2.92mm, respectively.
4.2 COD Correction
The COD was corrected by the method based on asensitivity matrix (Smatrix) [5]. The Smatrix represents therelation between the excitation current of each correction
magnet and the variations of the beam positions measured atevery BPMs. To correct the CODs, the excitation current of
all the correction magnets are evaluated by the most effective
corrector method using the measured Smatrix. As the result,the maximum CODs in the horizontal and in the verticaldirections at the beam energy of 8 GeV are decreased to 2.22mm and 1.40 mm, respectively. The route mean square of thehorizontal and of the vertical CODs at the beam energy of 8GeV are 0.47 mm and 0.38 mm, respectively.

5. Measurement of Betatron Tune- .6rr1VIFig.2 First five turns of the beam observed by the FCT.
The waveform is shown at Chl. Ch2 shows the waveformof the injection kicker magnet and Ch4 shows thewaveform observed by the wall current monitor at thetransport line from the linac.

To measure the betatron tune, the beam is kicked out
horizontally or vertically by the magnetic field which isgenerated from the knock-out electrodes in the beam duct. Acertain frequency of the field is related to a fractional part ofthe betatron tune. Figure 3 shows the RF knock-out system.
The knock-out electrode is a strip line-type and the length is
1 m. The impedance of each electrode is adjusted to 50 Q.
The maximum output power of the wide-band amplifier is
200 watts and the power is divided among four electrodes
equally. To measure the vertical betatron tune, the beam iskicked out vertically with an RF phase shift of 180 degrees at
the A-electrode and at the B-electrodes. At the horizontal-247-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

betatron tune measurement, the beam is kicked out
horizontally by switching over the RF phase of the Belectrode and of the D-electrode. The maximum strength ofthe magnetic field, which generated by the RF power of 200
W from the amplifier, is 7.1 x 10·6 T. It correspond to a kickangle of 4.3 x 10·6 rad at the beam energy of 1 GeV. Whenthe resonance between the knock-out frequency and thebetatron tune takes place, the amplitude of betatronoscillation is increased and the beam is lost on the beam duct.
At the resonance points, the beam current is decreased tozero for about 10 ms and the knock-out frequency is decidedusing the DCCT. The relation between the knock-out
frequency and the betatron tune is expressed as follows.

with the DCCT in the synchrotron.
2 ,-----------------------------------------,--~0&.

0.59mmy.=-o.57mm
ax= 50.7,rnm= 39.711m

Horizontal (x)"E.5. 0.5
li~

Xa=

Beam position at SPM1 ('97.3.18)

1.5-------------------~

Vertical (y)E -0.5! -1

Wll:'lif ;t . .\111*"*1:': '*~:t·J~:.•Je:·•·!li:·SE"llliw i!lt '1Hil"1il.l!IAA~lll M.·ll< lill w ~;t·:W'~~< ~w'*~l!O·lii!W <lit ~w·ll!"'!!w l!f~lill:wM*l: ae111!w"* a-1.5~L-------~------~------~------~------~
16:30
16:45
17:00
17:15
17:30
17:45
Timefknockout = frevolution X( n±( Vx,y- Int ( Vx,y)))2 ,---------~------------------------------,
X.= 0.12 mm
Beam position at SPM2 ('97 .3.18)

n : 0 or positive integer
Yx,y : horizontal or vertical betatron tune

1.5

Y•=·1.17mm
ax= 53.S,.m
m= 74.71Lm
Horizontal (x)Vertical (y)·1·1.5~L-------~------~------~--------~----~
14:00

14:30

15:00

15:30

16:00

16:30

TimeFig.4 Beam positions at the strip line-type position
monitors of SSBT.

Fig.3 RF knock-out system for the measurement of thebetatron tune.

7. Conclusion

To adjust the betatron tunes to the designed values, theexcitation currents of the focusing and the defocusing
quadrupole magnets were varied from the designed values.
The horizontal and the vertical tune values were selected to11.796 and S.7S33, respectively.

The beam commissioning of the SPring-S synchrotron
was carried out successfully and the beam was supplied tothe storage ring with good efficiency. The beam monitors
were useful for the beam commissioning.

6. Beam Monitors of SSBT

References

The SSBT is the beam transport line from the synchrotron
to the storage ring. The length of the SSBT is 310m and thebeam line of the storage ring is 9 m higher than that of thesynchrotron. Sixteen fluorescent screen monitors were used
to adjust the beam positions. The excitation currents of thedipole and the correction magnets were adjusted to theoptimum values, that the beam passes through the center ofthe quadrupole magnets observing the beam positions on thescreen monitors. If the beam does not pass the center of thequadrupole magnet, the beam position on the screen monitormoves when the excitation current of the quadrupole magnet
is decreased from the present value. Two strip line-type
position monitors (SPM) were installed at the end section ofthe SSBT to measure the stability of the beam position. The
accuracy of calibration and the installation error of the SPMs
are less than 0.1 mm and 0.5 mm, respectively. Figure 4
shows the result of the measurement of the beam positions atthe SPMs. The stability and the repeatability of the beam
position and of the beam angle between the SPMs are lessthan 0.1 mm and 0.1 mrad, respectively. It was confirmedthat the beam loss in the SSBT was negligibly small with abeam charge monitor installed at the end of the SSBT and[1] H. Suzuki et al., "Beam Commissioning of the SPring-S
Synchrotron", to be published in Proc. 6th International
Conference on SRI 97.
[2] H. Yonehara et al., "Synchrotron of SPring-S", Proc.
Particle Ace. Conf., pp.2039 (1993)[3] T. Aoki et al., "Beam Position Monitor for the SPring-S
Synchrotron", Proc. Syn. Rad. Instr. 1995.
[4] H. Suzuki et al., "Status of the booster synchrotron forSPring-S", Proc. 5th International Conference on SRI94,
Rev. Sci. Instrum., 66 2 (1995) 1964.
[5] H. Nishimura et al., "Orbit control at the ALS based onsensitivity matrices", Proc. Particle Ace. Conf., LBL36443 (1995).

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