The reference cell system is comprised of three
subsystems--the reference target cell, the gas handling system, and
the control electronics. The reference target cell is mounted inside
the target enclosure, which is located in the beam path immediately
upstream of
the spectrometers. The gas handling system consists of a gas
manifold, which is located in the electronics rack behind the laser hut, and a series of gas
lines that connect the manifold to the reference cell. A control box consisting of electronics that control the solenoid valves of the gas system is also located in the electronics rack. A remote control box, identical to the one in the hall, is located in the counting house. A schematic of the
entire system is shown in figure . The individual
subsystems are depicted in figures
-
.
Under normal operating conditions, the manifold, the reference cell,
and the intervening gas lines will be filled with either He,
N
, or
He gas at high pressure
(typically
atm). The system
may be operated either locally (at the panel) or remotely (via
switches mounted in the counting house). A switch on the
gas panel itself allows one to toggle between local and remote
control. All switches, local and remote, are equipped with LED
displays so that one can readily determine the status of any switch.
The reference cell consists of a very thin-walled glass flask. An
outlet at the opening is joined to a Copper tube by means of a
glass-to-metal seal. This Copper tube is connected to a 1/8" dia.
Copper tube with quick-plug-on gas fittings. High pressure He gas bottle is mounted near the target chamber and is connected to the other end of the 1/8" Copper tube through solenoid valve V3. The rest of the gas system is connected to the 1/8" copper tube by a long 1/2" Copper tube. The reference cell is mounted at the gas fitting. A special coupling tool has been designed to facilitate the coupling/de-coupling the reference cell at the quick-plug-on gas joint.
The gas handling system consists of 8 solenoid-controlled, air-actuated valves,
one hand-set needle valve, two baratron pressure gauges (0-1000 torr
and 0-1000 psia), two pressure relief valves, a bottle of
high-pressure He gas, a bottle of high pressure N
gas, a
bottle of high pressure
He gas, an oil-free turbo pump backed
up by a pre-pump, and sufficient tubing and pipe fittings to
connect them all together. There are 5 basic actions that the
gas handling system must accomplish; pump-out, vent, fill with N
or
He,
and fill with
He. The selection between N
and
He is
done by a special directional solenoid valve (V8).
The reference cell control panel (shown in Fig. ) is comprised of 5 pushbutton
switches, which activate the 5 possible valve setting conditions, a
baratron high-pressure gauge which reads between 0-1000 psia, a
baratron low-pressure gauge which reads between 0-1000 torr, two toggle switches to turn on and off the vacuum pump and a toggle switch to select local or remote operation.
The valve configurations for the five actions are described in Table
.