DC Break Research Articles

The erosion and arc characteristics of Ag/CdO and Ag/SnO/sub 2/ contact materials under DC break conditions

Break operation studies have been conducted upon Ag/CdO and Ag/SnO/sub 2/ contact materials under dc conditions between 1-16 A. The apparatus used allows contact materials to be continually tested with a controlled break velocity. Results are presented on erosion data in terms of mass transfer. Surface analysis methods are used, scanning electron micrographs reveal distinct structures and areas on the contact surface, and elemental analysis (EDS) shows migration of metal species with current. The metal-oxide used in the contact is shown to influence the arc and erosion characteristics of break only operations. The Ag/CdO contacts exhibit lower erosion than Ag/SnO/sub 2/ contacts under these controlled conditions.

An advanced high-current low-emittance dc microwave proton source

The high-current low-emittance microwave proton source introduced two years ago act the Chalk River Laboratories has been extensively redesigned. The 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition. The layered microwave window has been replaced by a single plate of aluminum nitride. The solenoids were electrically isolated from the plasma chamber. Only the plasma chamber remains at the extraction potential. The total beam current and the proton beam current have been measured as a function of the microwave power, the hydrogen mass flow and the solenoid positions and currents. More than 95 mA dc of hydrogen ions with a proton fraction in excess of 85% were extracted from a single 2.5 mm radius aperture with only 500 W of microwave power and 2.0 sccm (3 μg/s) of hydrogen mass flow. The perveance at minimum divergence and the minimum emittance have been determined for various extraction geometries. The variation of the perveance with the aspect ratio of the extraction system was found to be virtually identical for microwave and arc discharge ion sources. The normalized rms emittance was less than 0.13 p mm mrad whatever the extraction geometry.

Excess phase in microstrip DC blocks

The letter gives details of excess phase calculations and measurements on microstrip DC breaks. Published microstrip discontinuity data has been used to develop an equivalent circuit which yields very good agreement between experimental and theoretical phase results over the frequency range 8 to 12 GHz.

Corrections to " Contact Erosion Pattern of DC Break Arcs"

Corrections to " Contact Erosion Pattern of DC Break Arcs"

Velocity Distribution of the Moving Cathode Spot in Breaking Contact Arcs

The motion of cathode spot in Au, Ag, Cu, and Ni contacts, which affects the formation of the pip and crater structures, has been precisely observed by utilizing a high-speed camera in moderate current, atmospheric pressure dc break arcs. Dependencies of contact material, current and voltage on the motion of cathode spot were examined experimentally. Behaviors of the cathode spot were evaluated by three factors: 1) the maximum length moved (l <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mx</inf> ) which was defined as a maximum shift distance of the spot in an arcing; 2) the maximum moving width (l <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mw</inf> ) which was the difference between the maximum and minimum distances on the motion of cathode spot; and 3) distributions of velocity of moving cathode spot. For these contact materials, the cathode spot moved rapidly in the sequence of Au > Ag > Cu > Ni. Moreover, the crater structures of each contact have been reasonably explained through the above behavior of the cathode spot.