High current density advanced cold cathode facility

Summary form only given. We report the design, construction and initial operation of an advanced, high-current-density, field emission cathode facility. The facility is designed to examine the nanophysics of field emission from advanced Al, C, CsI, Mo and other material cathodes that operate in the 1-1000 A/cm² regime. Operation is designed for UHV vacuum (10^-10 torr) and achieved with bake-out up to temperatures of 450 C to eliminate residual water vapor or other contaminants. The vacuum chamber is a stainless steel six-way cross. We use a scroll pump, turbo pump and a Vacion pump to achieve the UHV vacuum. We bake the system at 450 C for several days to eliminate contaminants inside. An optical fiber, pyrometer and spectrometer are used to measure the temperature of the cathode and possible plasma formation. An emitting tungsten filament is used to clean the anode surface. The current-voltage characteristics including field emission, work function, space charge limitation and the Fowler-Nordheim coefficients are examined. With a Glassman high DC voltage supply and a DEI high voltage pulse supply, 0~50 kV, 1-100 mus duration negative pulses with rise time less than 60 ns are applied between cathode and anode to get the current-voltage characteristics. A Tektronics high voltage probe is used to monitor the voltage across cathode and anode. Another Glassman high DC voltage supply provides negative 2 kV between the outer and inner conductors of the anode to increase the collection efficiency. A Lesker manua linear shifts is used to adjust the gap between the cathode and anode from 0-2.5 cm with a resolution less than 0.1 mm. Both Rogowski current meter and a resistor voltage measurement setup in series with anode are applied to measure the wide range of cathode current level. Measurements are presented on a 1 cm diameter cathode, consisting of laser-ablated-lines on an aluminum plate. This series of hills and valleys has a 0.35 mm period; hills - re 0.1 mm wide and 0.07 mm high, while valleys (grooves) are 0.1 mm wide and 0.04 mm deep. Both single sharp tip and multi tips cathodes made of different materials will be tested, in order to determine the interference between local neighboring tips during electron emission. Initial data will be presented