The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

RF system for SPring-S storage ring at the commissioning
Takashi OHSHIMA, Hiroyasu EGO, Masahiro HARA, Naoyasu HOSODA, Yositaka KAWASHIMA,Yuji OHASHI, Hiromitsu SUZUKI, Takeo TAKASHIMA, Hiroto YONEHARA
SPring-S, Kamigori, Ako-gun, Hyogo 67S-12, Japan

Abstract
Three RF stations of the SPring-S storage ring are inoperation. We report the present status of the RF systemof the ring and the performance of the cooling system.
Some troubles occurred during the commissioning are alsopresented.

1 IntroductionSPring-S is a third generation synchrotron radiation
research facility. It consists of a 1 GeV injector linac, anSGeV booster synchrotron and an SGeV storage ring.
There are four RF stations (A, B, C and D) in the storage
ring. The installation of all apparatus at the B, C and Dstations has been completed [1]. The A station will beinstalled near future.
The first phase of the commissioning of the storage
ring was carried out from the middle of March to themiddle of July '97. RF parameters at the commissioning
are shown in Table 1.
Table 1
RF parameters
frequency50S.579343 MHz
harmonic number
2436
revolution frequency
207.7S kHz
number of RF stations in operation
3
number of RF cavities per RF station
senergy loss per turn( without insertion devices )9.2 MeVtotal acceleration voltage
12MV
synchrotron frequency
1.5kHzThe RF acceleration system is composed of thefollowing parts; a timing system which delivers areference RF signal to three RF stations, a low level
control system, a klystron and its power equipment,
transmission lines, RF cavities and a computer control
system.
The reference RF signal from a master oscillator isdelivered to each RF station with a phase-stabilized opticalfiber. The change in the transmission time of the fiber iswithin 5 ps/km/°C in the temperature range from 0°C to30°C [2]. We use a cable which includes 6 fibers.
The low level control system keeps the RF phase andthe acceleration voltage constant. A feedback loop is used
to tune cavities at the fundamental acceleration mode. Allcavities are initially detuned by -5 degrees of the RF phaseto avoid Robinson instability.
The RF output power from the klystron is divided into
eight using seven magic-Ts. The klystron is connected tothe most upstream magic-T by the WRlSOO waveguides.
The cavities are connected to the magic-Ts with WR1500
waveguides. A circulator is inserted between the klystronand the first magic T to protect the klystron against thereflected RF power from the cavities.
The cavities have bell-shaped inner structures to avoid
the beam instabilities caused by higher-order mode
resonances of the cavities [3]. The cavities are evacuatedby three sputter ion pumps and titanium getter pumps.
The RF system is operated from a central control roomwith networking computers. Using an RF main control
panel working on a computer, we can set and monitor theRF frequency, the acceleration voltage, the station phaseand so on.
The stored beam current can be reduced to a set value bychanging the quantum lifetime. The lifetime is controlled
by adjusting an RF phase of one RF station which resultsin decrease of the total acceleration voltage or the overvoltage ratio.

2 Adjustment of RF parameters
2.1 Frequency of the reference RF signal
Before commissioning, the frequency of the reference
RF signal was set to the design value of 508.580000
MHz. The frequency was adjusted to get the maximum
turn number of the beam at the beginning of thecommissioning. Now the frequency is adjusted tominimize the horizontal closed orbit distortion.

2.2 Phases between stations
It is necessary to adjust the station phases to gain amaximum acceleration voltage. Before the beam operation,
the station phases were adjusted by the following
procedure. Figure 1 shows the schematic drawing of thephase adjustment between the E station and the B stationfor example. The reference line 1 was used to deliver thereference RF signal from the E station to the B station.
The signal from the master oscillator was sent by anelectrical to optical transmitter (E/0) through the optical-95-Estation

Bstalim10stallmFig. 1 Schematic drawing of the phase adjustmentof the reference signal

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

fiber. The optical signal was transferred to the electricalsignal by an optical to electrical receiver (E/0). The
electrical signal is divided into two signals; one is used tosend the signal to the next station and the other is used forthe reference RF signal at the B station. To fix the phaseof the B station, another reference line 2 was used. To fix
the phase of the signal of the reference line 2 at the Bstation, two phase shifters (#2, #3) were changed withsame amount so that the phase difference between thesignal sent to the B station and the reflected signal fromthe reflector at the B station (#a) became zero. By thismethod there is an ambiguity in the phase by 180 degrees
because an increase of the length of the fiber by one
wavelength produces the same phase of the reflectedsignal. This ambiguity will be removed by adjusting thephases of reference line 2 with the signal of one halffrequency of 508 MHz. The phase shifter of the referenceline 1 (#1) was adjusted so that the phase difference
between two reference lines (#b) became zero. Sameprocedures were carried out for the C and D stations.
At the beginning of the commissioning, the phase wasadjusted to maximize the turn number of the injected beamwith only one station. The phase of the D station wasdifferent from those of the B and C station by 180 degrees.
The phase relations between three stations weremeasured from the synchrotron frequency. The deviation of
the phases between stations were less than 10 degrees
except the 180 degrees deviation of the D station.
The phase between synchrotron and the storage ring was
adjusted to maximize the injection efficiency and minimize
the horizontal beam oscillation just after the injection.

heat exchanger

25±0.5 ·csingle-cell cavities

Fig. 2 Schematic drawing of the temperature control
system of the cavity cooling watertemperature of the cavity can be changed by adjusting anangle of a valve the cavity. When one of the valve of acavity is changed, a pressure control valve reduces thechanges of the water flow of other cavities.
Figure 3 shows the temperature deviation of the coolingwater when the RF power up to 400 kW is fed to thecavities. The root mean square of the fluctuation of thecooling water temperature was ±0.02 °C which was one
tenth of the specification value.

2.3 Acceleration voltage

500
The total acceleration voltage was set to enough leveltaking account of the quantum lifetime. The acceleration
voltage was measured by three methods. One was using acalibrated pickup signal. Second was using the wall lossof the cavity which was measured by a calorimetricmethod. Third was using measured synchrotron
frequencies. Each result agrees within 10 %.

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The cavity temperature is stabilized by keeping thecooling water temperature constant. Figure 1 shows theschematic drawing of the temperature control system of
the cavity cooling water. The temperature of the water iscontrolled in three steps. 1) The water flow fed from theutility to the heat exchanger is controlled. The coolingwater after passing through the cavities is cooled down by
the heat exchanger to 29.6±0.5 °C. 2) The heat moment of
the water tank averages out the temperature to 29.6 ±0.3°C. 3) The temperature is finally controlled to
30.0±0.2 oc by the heater installed between the tank andthe cavities. The temperature of the water is measured byusing with Platinum 200 .Q resistor. The accuracy of thetemperature indication is 0.005 °C at 0 °C and 0.01 °C at
25 °C , 30 °C and 35 °C. The maximum heater power is50 kW. The total water flow is 950 liters/min; a part ofthe flow (45 liters/min) is passing through the ion
exchange resin to keep the water resistivity high. The~uwH••n.atua••l ~~,tn~J\jf~· · · temperature ll·~~0p..

3 Cavity cooling system

400~(tin....;. . . . . . . . . . . . . . . -130.100~~~LL~U-~~~~LL~~~030
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Fig. 3 The temperature deviation of the cavity
cooling water and the klystron output power.
4 Troubles during the commissioning
4.1 Faults occurred during the commissioning

The beam commissioning of the storage ring wastripped by RF interlock signals. The sources of theinterlock signals were a beam abort signal, low flow ofcooling water for the klystron power supply, circulator-96-

The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

large peak was detected in a mass number of 18. Possible
leak points were a water channel of a cavity, a tuner, an
RF coupler or a photon absorber. After we drained thewater from the water channels, helium leak test was donefor each cooling water channel. But frozen ice in· the leak
path prevented the helium gas from diffusing into the leakpath. By pressurizing each cavity unit with nitrogen gas
one by one, we could detect the increase of the vacuum
pressure when the cooling water channels of the number 3cavity unit was pressured. To remove the ice from the leakpath, we baked the cavity to 150 °C for one hour and we
blew the cooling water channel with a blower. We could
find the leak point in the cooling water channel of a tuner.
We replaced this tuner by a plunger with fixed length. The
lost time due to the leakage was five days. The
replacement of the plunger to a spare of the tuner was
carried out during the summer shut-down period.

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Fig. 4 Number of RF faults occurred during fourmonths operation of the commissioning.

5 Conclusionarc, an RF power reflection from cavities and so on.
During the commissioning, about forty interlock signals
were detected. Figure 4 shows the number of faults foreach source. Beam abort signals mainly came from a raiseof the vacuum pressure of the ring, a large deviation of thebeam position and so on. Concerning the RF devices
themselves, the circulator arc and cavity reflections
happened at about 2 and 1 times/month, respectively.
Failures in database system, interlock signals from
communication errors of programmable logic control unitsof the safety system were also occurred. No beam
instabilities due to higher-order mode resonances of thecavities have been observed at the beam current of 20 rnA.

The RF system is stably operated. The temperature of
the cavity coo!ing water was kept 30.44±0.02 °C at theklystron output of 400 kW.
Stored beam current was 20mA at present. No beam
instabilities due to higher-order mode resonances of thecavities have been observed.
The beam commissioning of the storage ring wastripped by interlock signals of the arc of the circulator,
large reflection from cavities and so on. The faults fromRF devices occurred less than 3 times/month. A waterleakage at a movable tuner was detected but it wasrecovered in five days. The faults will be decreased by
improvement and maintenance of the RF system.
References

4.2 Vacuum leakage at a tuner

On May 27 in 1997, the vacuum pressure of the RF D
station was degraded to 5xl0·6 Pa at the beam current of
about 18 rnA. The value of the pressure was ten times
worse than normal value. The pressure was changing witha period of a few minutes. Figure 5 shows the trend plotof the stored current and the vacuum pressure of the RF Dstation.
From the mass spectrum in the vacuum chamber, a[1] M. Hara et al.; PAC97 to be published[2] H. Suzuki et al.; 9th Symp. on Ace. Sci. Tech.
(1995) 249-251[3] H. Ego et al., Nucl. Inst. and Meth. A383 (1996)
325

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pressure of the RF D station.

-97-