Control of low pressure d.c. arc discharges

Claim 1

A DIRECT CURRENT LOW-PRESSURE SWITCH COMPRISING: A POSITIVE ELECTRODE; A NEGATIVE ELECTRODE AXIALLY ALIGNED WITH THE POSITIVE ELECTRODE; OPERATING MEANS WHEREBY THE ELECTRODES CAN BE MOVED TOWARD AND AWAY FROM EACH OTHER IN AN AXIAL DIRECTION; A CYLINDRICAL SPIGOT PROVIDED ON THE FACE OF THE POSITIVE ELECTRODE AND CONFRONTING THE NEGATIVE ELECTRODE; THE NEGATIVE ELECTRODE HAVING A CAVITY FACING AND AXIALLY ALIGNED WITH SAID SPIGOT, AN ANNULAR SHOULDER ON THE NEGATIVE ELECTRODE SURROUNDING THE CAVITY, SAID CAVITY HAVING A CROSS SECTION SLIGHTLY LARGER THAN THAT OF THE SPIGOT SO THAT THE SPIGOT MAY ENTER SAME WITH AN ANNULAR CLEARANCE THEREAROUND, SAID CAVITY HAVING A DEPTH LESS THAN THE LENGTH OF THE SPIGOT SO THAT THE SPIGOT WILL ENGAGE THE CAVITY BOTTOM BEFORE THE FACE OF THE POSITIVE ELECTRODE BUTTS AGAINST THE ANNULAR SHOULDER ON THE NEGATIVE ELECTRODE; AT LEAST ONE BLIND RECESS EXTENDING RADIALLY OUTWARDLY FROM THE CAVITY; A GAS TIGHT ENVELOPE ENCLOSING THE FIRST AND SECOND ELECTRODES AND PERMITTING AXIAL MOVEMENT THEREOF; AND GAS UNDER A LOW PRESSURE FILLING THE ENVELOPE; WHEREBY UPON THE OPERATING MEANS SEPARATING THE TWO ELECTRODES THE DIRECT CURRENT ARC BETWEEN THE SPIGOT AND THE CAVITY BOTTOM ESTABLISHES A PLASMA ORIGINATING FROM CATHODE SPOTS ON THE SAID CAVITY BOTTOM, AND THESE SPOTS ARE THEN MUTUALLY REPELLED TO MOVE RADIALLY OUTWARDLY INTO THE BLIND RECESS, WHERE THE CATHODE SPOT AND THUS THE PLASMA BECOMES EXTINGUISHED.