HIGH VOLTAGE EQUIPMENT OF POLARIZED PROTON PREACCELERATOR
Chikashi KUBOTA, Sadayoshi FUKUMOTO, Yoshiharu MORI and Eiichi TAKASAKIKEK, National Laboratory for High Energy Physics
Introduction
Since 1980, a polarized proton preaccelerato r has been built as a threeyear project at KEK. A new building was made adjacent to the operating preaccelerator room. An 800 kV Cockcroft-Wal ton generator (CW), a high voltage
terminal (HVT) and an insulating motor-generat or have been installed in it.
The ion source and its power supplies are being moved into the HVT.
High Voltage Generator
A symmetric CW generator was made to supply an accelerating voltage tothe HVT (Figs. 1 and 2). Its rated voltage is 800 kV with a stability of±
0.2 % and the maximum available current is 5 rnA. The voltage drop ~V andripple oV (p-p) are denoted approximately by~v

=IN

N2fC

32- - - - ( - + 1)

andov

where N is the number of stages, f is the frequency of the driving voltage, Cis the capacitance of the capacitors and I is an output current supplied to aload. For the new generator, N = 4, f = 350 Hz, and C = 0.01 ~F. The control
system and the 350 Hz generator are similar to those of the old CW so thatthey can work with the new and the old CWs.
16 rectifiers were assembled at KEK. Commercially available Si diodestacks (Fuji Electric RBHB24-288D24) were put into a glass tube, then the tube
was filled with oil (Toray Silicone SH200-50EG), evacuated to remove air bubbles and enclosed with flanges (Fig. 3). Deterioration of the oil and thediodes can be observed by visual inspection. No corona discharge is observed
up to 800 kV in a low humidity atmosphere. The voltage drift and fluctuation
are within ± 0.04 % of an output voltage of 760 kV for 24 hours. The rippleof a single stage was measured directly with a 2000:1 probe for an 80 kV output. The observed ripple of 28 V (p-p) corresponds to 1.4 x 10- 3 of the single stage voltage or 20 kV for a load of 0.2 rnA. This agrees well with thecalculated value of 0.143 %. As oV is proportional toN, the ripple of 760 kVcan be estimated by a simple calculation.
High Voltage TerminalThe HVT has a space 3.75 m long, 4 m wide, and 3.2 m high for the polarisource. It is supported by 4 straight porcelain tubes of 60 em inion
zeddiameter and 3.9 m long as shown in Fig. 4. A 10 Mn limiting resistor protects the Si rectifiers of the CW generator from damage from arcing of theaccelerating column, and it serves asca ripple filter with the stray capacitance of the HVT. The ripple of the accelerating voltage is reduced to lessthan 1/10 of the CW ripple. No problems were found up to 795 kV.
Insulating Motor-generat orA 80 kVA generator supplies electric power to the ion source and its
auxiliary equipment in the HVT. It is in a small room attached to the HVT andis mounted on a separate support to isolate the ion source from mechanicalvibrations caused by the generator. The support consists of three 49 em diameter fiber reenforced plastic (FRP) pipes. The generator is driven by three
10 em diameter FRP shafts which are connected with diaphragm couplings. (Eagleindustry 65E308-250-ED ) The shafts are driven by a 90 kW motor. About 300~m-vibrations are detected on the surface of the middle FRP pipe when some 50
kW is fed from the generator to the magnet power supplies in the HVT. It is
reduced to less than 1/10 by resonant dampers which consist of massive iron
donuts and supports of appropriate stiffness.
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The authors wish to express their gratitude to Dr. T. Nakata, Emeritus
Professor of Tokyo Institute of Technology and Chairman of TSS for the resonant dampers.

TO HVTcw

1.1..

::tCONTROLSYSTEM

001.1..

::tN

00

Fig. 1 800 KV symmetric
Cockcroft-W laton generator.

Fig. 2

Schematic Diagram of
the CW generator.

Fig. 3Fig. 4High voltage terminal withinsulating motor-gene rator.

Silicon rectifier andits components.
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