Located in V114A, this vacuum system is used primarily for experiments in the vacuum and thin-film classes. The system is flexible and features a basic vacuum system (capable of vacuum levels in the mid 10-6 torr range) and gauges to which experiments may be attached via one of two NW-40 high-vacuum fittings. The basic system (exclusive of experiments which are "bolted on" to the manifold), as seen in figures 1 through 3 below, consists of:
Connect the experiment (if in use) to one of the NW-40 fittings (i.e. through the MANIFOLD or AUX valves). Usually the fitting off the MANIFOLD valve is used (as shown in the photos on this page).
Turn the main power switch ON (to power the system gauges and pumps). Turn the mechanical pump ON using the switch on the rear of the motor of that pump. Open the FORELINE valve on the top of the mechanical pump followed by the MAIN valve and the MANIFOLD valve (which will allow evacuation of the experiment manifold as well during pumpdown). Turn the CFV100 pump controller ON and START the turbo pump via the switch on the controller. The manifold pressure should be seen to drop. Pump operation may be verified by the lighting of the yellow 'underspeed' indicator on the controller. The pump will slowly accelerate to 27,000 rpm and high-vacuum manifold Baratron gauge will show a decreasing pressure (it will read only after pressure has decreased below 1 torr), eventually reading zero.
At this point, operation of the system is largely determined by the experiment. The Ion gauge may be used by turning the 919 hot cathode gauge controller on, selecting the PRESSURE display function via the front function buttons, and switching the filament ON via the upper left toggle switch. If the pressure is too high, the filament may not stay lit (i.e. it may blink quickly then extinguish), otherwise the filament will be visually observed to lluminate and the gauge will display current pressure. Be sure to limit filament usage and duty cycle to 30 seconds ON, one minute OFF as required.
The mass spectrometer may also be used to analyze gas composition but to ensure pressures are low enough for RGA operation (i.e. total pressure is below 1 * 10-4 torr), use the ion gauge (above) FIRST to verify the pressure before turning the RGA/Mass Spectrometer on.
In order to reduce pressure in the experiment manifold, the MANIFOLD valve may be opened. To introduce gases into the system, a precision metering valves may be used along with absolute-sealing toggle valves. Open the toggle valve to admit gas then use the needle valve to regulate the flow of gases into the manifold. Once pressure is at a desired level, the toggle valves should be closed since needle valve are not absolute selaing and so pressure will continue to rise continually.
If the MANIFOLD valve is closed and a signifcant pressure exists in the experiment manifold, be sure to open the MANIFOLD valve very slowly to avoid 'dumping' the pump (a situation where a high gas pressure is suddenly presented to the pump which is otherwise at high vacuum).
Also available on the experiment manifold, depending on the configuration, is a mass flow controller (MFC) allowing introduction of precise quantity of gases.
The pumping speed is highly dependent on the inlet pressure of the pump as found in this excerpt from the manual. Note that the maximum pressure for continuous operation is 10 Pa (0.075 torr) and operation at inlet pressures above 2 Pa (0.015 torr) will be at reduced pumping speeds.
When the experiment is complete, be sure to turn off any gas supplies at the source (i.e. the supply bottle) and be sure the toggle valves on the manifold are closed so that it is sealed.
Turn off the ion gauge (if currently on).
Close both the MANIFOLD and MAIN valves. Turn the turbo pump OFF. Close the FORELINE valve then turn the mechanical pump OFF. Shut off the main power.
Updated 2018/05/17 by M. Csele