UPS delivered my first deuterium bottle with all of the nice, brightly colored labels on the box. Next it's on to making up a delivery system to get those D2 molecules into the chamber in an orderly fashion.
I ordered the bottle (50 liter lecture size) with a CGA 110/170 brass valve. I have an adapter for 1/4 NPT.
My near term and longer term strategies for the delivery system (subject to change at any time with comments from this forum) are:
Near term:
The bottle will be connected to a small volume (about 1/4 liter) made from a 2-3/4 CF nipple via a capillary leak and Nupro isolation valve. The volume will be charged to about 100 Torr after a pump cycle to about 0.1 Torr or lower. This will require another valve that connects the volume to a small 2-stage rotary pump. The pressure in the volume will be monitored with a 1000 Torr full scale Baratron capacitance manometer (model 722) and a pressure relief will be on the volume to guard against accidental overpressure.
All components used will be metal connected with metal to metal seals (4-VCR or 1/4 Swagelok) to minimize permeation losses, leaks and contamination.
The delivery valve will be a Bosch injector valve with pulse driver. Pressure monitoring will be via a Granville Phillips Convectron gauge which provides about 25-50% accuracy and about 5-10% repeatability when corrected for the gas type (G-P does have a correction curve for D2).
Longer Term:
The problem with the above is that the pressure control is open loop i.e. you keep messing with the controls until you get the system to the correct pressure and then keep an eye on everything, making adjustments as necessary, to keep the pressure where it needs to be.
So, the next step in the evolution will be to introduce a closed loop pressure control system. This will require a regulator on the lecture bottle, an MKS 1159 or 1179 mass flow controller (MFC) of about 10 sccm full scale and a capacitance manometer (100 mTorr full scale preferred although I may have to settle for 1 Torr FS).
The flow controller and the capacitance gauge can be connected so that the MFC will deliver whatever amount of gas is required to reach and maintain a given set point pressure.
The advantage of scenario 2 is that it is hands-off once the tuning parameters are set. Also, the capacitance gauge gives a true pressure indication regardless of the type of gas (no conversion charts necessary) and accuracy on the order of 1% or better. The disadvantages are cost of the components and possible gas loss if you mess up the tuning parameters.
Steve
Created on Sunday, March 04, 2001 1:05 PM EDT by Steve Hansen