LPPF Research Physicist Dr. Syed Hassan and Chief Scientist Eric J. Lerner continue to prepare FF-1 for the next set of experiments, which aim to rid the device of oxygen that has caused continued high impurity levels. A key step to doing this is a “bake-out” that heats the vacuum chamber and electrodes to drive off oxygen and water molecules that cling tightly to all metal parts. Right now, the scientists are looking for the right temperature to perform the bake-out. An initial attempt to do the bake-out at 150° C was unsuccessful in December, 2015, when several plastic parts overheated and were damaged. Subsequent oven tests showed that the Mylar sheets that separate the top and bottom plates of the device, providing the main electrical insulation, are not, as the manufacturer claimed, good to use at 150° C. At even 140° C the Mylar has shrunk so much as to be permanently distorted and weakened. The shrinking was reported in the data sheets provided by DuPont but were not indicated as a cause of failure. According to DuPont the heat-induced shrinkage is caused by the relaxation of stresses imposed during manufacture.
Abundant reports in the literature indicate that 100° C is too low a temperature for adequate bake out. So LPPF scientists are looking at 120°-130° C as a possible Goldilocks bake-out temperature: not too hot, not too cold. This temperature was considerably exceeded during the last effort, so the team is installing additional thermocouples to control the temperature. In addition, with the help of a volunteer thermal engineer, we are carrying out a thermal simulation of the heat flow during the bake-out.
Replacement of the damaged Mylar and other plastic insulators is going ahead rapidly and we expect to attempt another bake-out in late January or early February, leading to oxygen elimination and renewed firing of FF-1.
