RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-8. Accelerator

Construction of new amplifiers for RILAC†
K. Suda,∗1 E. Ikezawa,∗1 N. Sakamoto,∗1 K. Yamada∗1 Y. Touch,∗2 T. Ohki,∗3 K. Oyamada,∗3 K. Kaneko,∗3
M. Tamura,∗3 H. Yamauchi,∗3 A. Yusa,∗3 and O. Kamigaito∗1
RILAC consists of six variable frequency cavities(tanks) constructed in 19781) . The first amplifier wasconstructed in 1977 as a prototype for tank #1. Fiveother amplifiers were constructed the next year. The#5 and #6 amplifiers were upgraded in 1999 for experiments super heavy element synthesis. Three finalstage plate DC power supply (plate PS) were upgradedat the same time; one PS supplies DC voltage to two
amplifiers.
In recent years, several issues related to amplifiers#1 to #4 were encountered, such as water leaks fromcooling pipes and damages to the socket for the tetrodecaused by insufficient contact. The contact between
the socket and tetrode is shallow and a careful alignment is necessary. In particular, the design of the #1
amplifier was the oldest, so it became difficult to maintain it. Therefore, the amplifier #1 was upgraded in
FY 2013 along with #2, because the plate PS was common for #1 and #2, and its control system had to beupgraded at the same time.
The new amplifier, as well as those for #5 and#6 are based on a tetrode RS2042SK coupled with aRS2012CJ from THALES/SIEMENS with a grounded
grid circuit, that were originally designed for RRC2) .
The maximum RF signal of 0.01 W (10 dBm, 18 to40 MHz) is amplified by pre-, driver- and, final-stage
amplifiers up to 150 kW. In 14 years of operation of theRILAC #5 and #6, we have experienced several parasitic modes, which might damage the tank and/or theamplifier itself. One is caused by a coupled oscillation
between the 99-MHz G1-G2 resonance of RS2042SK
and the output circuit including a feeder line to thetank. The other example is the 7th harmonic mode
observed in RILAC #5. In order to avoid such parasitic modes, a 50 kW dummy load was installed at aplate stub.
In a factory, matching conditions for input and output circuits of driver- and final-stage amplifiers weremeasured and/or tuned. (1) The gain of the input
circuit for a driver amplifier called as “All Pass Network” was measured and confirmed to be sufficient. (2)An input circuit for the final amplifier was tuned bya vacuum variable capacitor (INCAP) and a movable
shorting stub located at a cathode input. The following was performed after installation in an accelerator
hall: (3) An output impedance of the final amplifier
was matched by changing a plate stub and a capacitor(OUTCAP). Details are described in Ref.3) .
∗1
∗2
∗3

RIKEN Nishina CenterSumitomo Heavy Industries
SHI Accelerator Service Ltd.

Fig. 1. Result of dummy load tests for two amplifiers (#1,#2). Voltages of plate (Ep ), currents of plate (Ip ),screen (Ig2 ) and control grids (Ig1 ), and the increase intemperatures of the cooling water (∆T ) for the driverand final amplifiers are shown.

The old amplifiers were removed in December 2013,
and the new ones were installed in January 2014.
Dummy load and power tests were performed in February 2014. In dummy load tests, a water-cooled 250 kW
dummy load was connected to the output of the amplifier. It succeeded in obtaining an output power of
150 kW at three frequencies (Fig. 1). Then, load tests
were performed at 36.5 MHz. The required acceleration voltages of RILAC #1 and #2 were successfully obtained. Beam service using the new amplifiers
started on schedule on March 10th, 2014. A few problems occurred during operations. One was the leakageof cooling water from a rf power feeder of #14) . Thiswas partly due to heating at the output flange of theamplifier. The parameters of the amplifier were tuned,so that the temperature of the flange decreased. The
other problem was that an automatic tuning control
system stopped its sequence abnormally. This happened in both amplifiers in some cases since May 2014.
The PLC program was corrected in October 2014.
References
1) M. Odera et al., Nucl. Instrum. and Methods, 227, 187(1984).
2) T. Fujisawa et al., Sci. Papers I.P.C.R. 80 (1985).
3) K. Suda et al., Proc. of LINAC14, MOPP12, 339 (2015).
4) E. Ikezawa et al., In this report.

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