A GAS FEED SYSTEM WITH PIEZOELECTRIC VALVES
Y. Sakurada, T. Yamazaki, T. Honma, H. Ogawa* , M. Sekiguchi, M. Fujita,
T. Tanabe, K. Sato, Y. Ohshiro and N. Yamazaki
Institute for Nuclear Study, University of Tokyo, Tanashi-shi, Tokyo* National Institute of Radiological Sciences, Chiba
1.

Introduction
Fine control of the gas flow rate is indispensable for efficient operationof a cold-cathode PIG ion source in addition to a wide dynamic range of theflow rate extending from 0.1 to 10 cm 3 /min. Conventional gas-feed system with amotor-driven needle valve is insufficient from this point of view.
A new gas-feed system controlled by piezoelectric valves has been installed
for the ion source of the INS SF cyclotron. The piezoelectric valves driven byelectronic pulses have characteristics suitable for heavy ion sources; a quick
responce, fine controlability and a wide dynamic range of the flow rate. Thesystem is equipped with two gas-feed lines to provide a mixture of two different gasses. Each line has a piezoelectric valve in it. The second line wasdesigned to feed a support gas to strike an arc easily or a subsidiary gas toincrease the beam intensity.
At the same time the 3He gas recovery system witha charcoal trap in aliquid nitrogen bath for purification, has been replaced with an evacuated3bottle of He gas storage. This method eliminated the use of liquid nitrogen
during the 3He beam time.
2.

Gas Feed System
A block diagram of thegas-feed system is shown in
Fig. 1. This system is similar to the one used at theTexas A & M cyclotron 1 ).
Each line has a low-pressure
regulator and a piezoelectricvalve. The regulator commercially available for propane
PV1,2 o PIEZOELECTRIC VALVEgas, was modified to beFig. 1vacuum tight for the presentpurpose. It is operated with

Block diagram of the gas-feed systema spring and it keeps theoutput pressure at a level-6 5-

higher than the atmospheric pressure by
0.03 kg/em~ for the input pressure range.
2of 0.1 - 3.0 kg/em (above the atmosphericNe(P\11)

Ar(PV2)

pressure). The piezoelectric valves arealso commercially available from Veeco,
U. S. A.• It uses the displacement of apiezoelectric crystal and can be opened
234567\W.VE !:RIVE PU.SE tu<BER/ SEC.

either by a pulse voltage or a DC voltage.
In the case of DC operation, the stabilityof the flow rate is very poor. In pulse
operation, the flow rate can be controlledeither by the frequency of the pulses orFig. 2Gas flow rate vs valve-drive pulserate. In the case of Ne, thefirst line was used and for AR
the second was used.

by the height. We usually use a frequency
mode of operation with a constant pulse
voltage of 90 V and the pulse length of 2.4 ms.
Fig. 2 shows the results measured for two different gasses. It should be
noted that the flow rate is linear to the pulse number per second. More important is the fact that the flow rate can be reduced to zero. This allows us tocompare the effects of mixed gas on the beam intensity with those of pure gas.
The system employs 12 electromagnetic valves, which are actuated by asequence controller (OMRON SCY-PO), thus avoiding the use of bulky electromagnetic relays. The main line is connected to six gas inlets which can beselected by a remote control.
3.

Gas Mixing Experimant
100

It is reported 2 • 3 ) that the beam intensity of somekinds of ions can be increased by adding nother kind of~....
zgas to the PIG arc. By using this gas-feed system we"'a:tried to observe this effect. An example is shown inFig.3, in which a large increase of the 115-MeV 20 Ne 6+~ 10beam was observed by adding nitrogen gas. However, theintensity was not so much increased by an optimum
addition of 0.3 cm 3 /min argon gas. Finer tuning of thearc and the cyclotron is needed to get a more definite

~0~a:

....
1:i

N2 1>1£. SUPPORT GAS(em'/min)conclusion.

Fig. 3

1. Y. Sakurada et al., Nucl. Instr. Meth. 164(1979) 196
2. E. D. Hudson et al., IEEE Trans. Nucl. Sci.
NS-24 (1977) 1950
3. Y. Sakurada et al., IEEE Trans. Nucl. Sci.
NS-26(1979)2175-6 6-The extracted beam currentof the 115-MeV Ne beam asa function of the flowrate of nitrogen supportgas