12FEB98
(Sorry about the palette change, this is the way the screen actually looks during the run. I’ve been reversing it for printing purposes.)
Legend
Total Input Power (electrical)
Output Power (heat)
Chamber Wall Temperature (C)
Heater Temperature (C)
Gas Pressure (torr)
Filament Temperature (° C)
Room Temperature (C)
Inlet water Temperature (C)
This was another filament research run. We combined the hydrogen scavenging cycles used in Run 11 with the addition of two getters to the chamber. One was a heavy tungsten filament from a 1500 watt tubular halogen bulb. We wrapped this filament around the cartridge heater so it would be heated and thus activated to some degree. It’s presence in the chamber was passive…only the original filament was driven with electrical power. The second getter was a strip of household Al foil about 3/8″ wide by 8″ long again wrapped around the cartridge heater so it would get hot.
Another change for this run was the removal of the ceramic tube which housed the Tgas thermocouple sensor. We strapped the junction to the body of the cartridge heater and fixed the software so it reports Thtrplotted on a 0-1000° C scale.
The run starts with 2.5 hours of vacuum pumping and cartridge heater bakeout. The thermocouple strapped to the heater indicated a surface temperature of about 550° C. Then we put 10 watts on the filament (and only 20 watts into the heater) for an hour to outgas the filament. As before, note the stable operation of the filament in vacuum indicated by the flat-topped Tfil trace. At hour 4.0, with the filament off, we admitted 15 torr of H2 to the chamber and closed it off. The Press trace shows how the H2 pressure varied only slightly during the 1/2 hour that the gas was in the chamber. At hour 4.5 we evacuated the chamber. At about 4.9 hrs we filled it with 15 torr of H2 again. At 5.4 hrs we evacuated the chamber again. At hour 5.7 we filled the chamber with 2 torr of H2 gas and closed it off. Note the much-improved Press trace. The new DC amplifier (100x gain) is working nicely (yes, we checked its zero and gain adjustments before using it). Shortly thereafter at hour 6.0 we applied 10 watts to the filament in the 2 torr H2 atmosphere. The filament lasted about 1 hour and 20 minutes…perhaps a little longer than usual, but not much! We manually adjusted for some of the power fall-off that occurs as the filament erodes but, when it burned out, we just let the input power fall to the present heater power: about 24 watts. Over the next 3+ hours, the Pout trace approached the Pin trace nicely.
Sigh………