GAS PURIFICATION .SYSTEM
M. Uraki and T. Itahashi
Research Center for Nuclear Physics, Osaka University
Abstract
3 He recovery and pur.ification system based on a special polymer film wasdeveloped and purified gas was analyzed by a quadrupole mass filter with adifferential pumping system.

1.

Introduction

All cyclotron has to equip a recovery and purification system at theacceleration of 3 He particles due to a high cost of 3 He gas. The purification
system usually is based upon absorption by liquid nitrogen cooled absorbents.
RCNP AVF cyclotron also equipped the purification and recirculation gas
handling system. Alternative He recovery and purification system was developed and was tested.
2.

Principle of purification

Principle of 3He purification is based upon different permeabilities ofvarious gas on the polymer film. Diffusion of gas through the wall of thepolymer thin tubes is described by the equation;
dqi _ Kat - iwhere,

A~

ddqi · gas flow rate at STP
dt 'permeability constantKi~ptotal surface areapressure difference across the tubing walldwall thickness.

AThe permeability constants for He, N2 and 02 are K(He)=l.4xlo- 1 0, K(0 2)=
The large difference of between He and Oz, Nz
3.9x1Q-l2, K(N 2)=5,2xlo- 13
suggests to purify He from contaminant gas.
3.

Gas purification and analyzing system

The system for gas purification used a special polymer film offered by
Nippon Sanso Co.. It is mainly composed of diffusion sells and diaphragm
compressors. Gas circulation under almost the same condition as the cyclotron
gas handling system was simulated by a large vacuum chamber(3000 ~), an·evacuating diffusion pump(3000 ~/min) and a leak tight rotary pump. Gas
analysis system was composed of a quadrupole mass filter, a variable conductance value and a small chamber evacuated by a diffusion pump (EdwardDiffstak 160/700 with santovac-5 fluid). The system is shown in fig. 1.
4.

aperation and results

Purified gas was introduced into a small chamber at pressure of ~sxl0- 8Torr through a variable conductance valve. If there are residual gas in thechamber, the chamber was heated with tape heaters up to about 200°c, After-6 3-evacuating for 5 or 6 hours, pressure of the chamber came to 10- 8 Torr. A
typical measurement has been done under the vacuum of about 5xl0- 8 Torr atanalyzing chamber and 500 Torr at exit of purificati on system. Before andafter mass analysis, partial pressure of residual gas in the chamber atanalyzing system has been measured. After purified gas was sampled by avariable conductan ce valve and the measurement of mass analysis was completed ,partial pressure of purified gas was obtained from the difference between theanalysis of residual gas and that of purified gas. In order to know thepurificati on of output depending on that of the input gas, several mixturesof helium and argon were tested. The results are as follows;
Input Gas

Output Gas

HeAr

3.0 cc/min

1.0 cc/min

2,0
2.0

He/other gas (%)
2 cc/min

98.0

1.0

II

98.0

2.0

II

97.0

If the helium content is larger than SO%, purity of gas can be expected to beover 97%.
Another test at making large leak at a chamber has been done. Gas
circulate s from a chamber with a leak tight rotary pump to purificati onsystem and gas flow rate into a chamber was regulated by an electro-m agneticalgas flow controlle r. At the helium gas flow rate of 1 cc/min, purificati onof helium was about 97%. After measurein g it about 3 lus argon gas wasintroduced into a chamber, the mass analysis has been measured during one
hour. In that analysis, the purificati on of helium decreased to 96% andpartial pressure of H, H20 increased by about 1% respectiv ely, but argon was
not observed. When the more leak about 60 lus was introduce d, 0.6% argon wasdetected. The system, recently was operated with cyclotron and it worked
successfu lly.

Mltary''""II(lull: ti'lntlFig.

l~Gas purificatio n and analyzing system-6 4-