STRAW - A Hydrogen-Specific Pressure Gauge for XHV

A fundamental issue with high average current photoelectron guns is the generation of stray electrons and ions which can damage the photoemitter. Both the photogenerated electron bunch and any field emitted electrons can potentially directly impact the photocathode, desorb molecules from the gun structure and act as ionization agents for backgroundgas atoms. Ion backbombardment of the photoemitter can alter or damage both the photoemitter and the activation layer, resulting in diminished lifetime and poor photoyield, hampering efficient operation. The source of damaging gas ions is inadequately low residual gas pressure in the gun structure. Lower pressures need to be achieved by the application of extreme high vacuum techniques. Development and routine application of extreme high vacuum has been delayed by the inability to routinely and accurately measure the extreme high vacuum residual gas pressure. The goal of this program is to develop an inexpensive and accurate pressuremeasuring gauge for the extreme high vacuum range through the use of conductivity changes in titania nanotubes when exposed to hydrogen. Titania nanotube sensors were packaged and tested for hydrogen sensitivity in vacuum using a custom test fixture. They were characterized for sensitivity as a function of base resistance, noise figure, optical excitation response and were shown to maintain hydrogen sensitivity following a vacuum chamber bake. The hydrogen absorbing titania nanotube sensors will be optimized for vacuum sensitivity, demonstrated to operate well at extreme high vacuum pressures, quantified for optimal operating conditions and be integrated into a control system including the process for crosscalibration. The optimal method for sensitivity restoration in vacuum will be established. Commercial Applications and Other Benefits: Reduced gas ion damage to photocathodes, due to routine operation in extreme high vacuum, will allow less robust photocathodes to be used in properly designed accelerator injector guns. Other markets that require extreme high vacuum will also benefit, such as extreme ultraviolet photolithography for semiconductor mask production (benefitting IBM, Intel, and AMD, among others), MEMS manufacturing and space simulation efforts.