Gas discharge apparatus

Claim 1

A SHAPED EXPLOSIVE CHARGE UNIT COMPRISING: (A) A THICK-WALLED RING HAVING A TOP FACE AND A BOTTOM-FACE, SAID RING HAVING AN AXIAL BORE THERETHROUGH; (B) A GENERALLY CYLINDRICAL PLUG HAVING A BOTTOM FACE AND A TOP FACE, SAID PLUG BEING FITTED TO SAID RING WITH THE BOTTOM FACE OF SAID PLUG CLOSING SAID BORE AT ITS UPPER END; (C) A GENERALLY CYLINDRICAL, THIN-WALLED CASE HAVING A BOTTOM WALL CLOSING THE LOWER END OF SAID CASE, THE TOP OF SAID CASE BEING OPEN, SAID CASE CONTAINING SAID RING AND AT LEAST THE LOWER PORTION OF SAID PLUG WITH THE BOTTOM WALL OF SAID CASE CLOSELY FITTED TO THE BOTTOM FACE OF SAID RING TO CLOSE SAID BORE AT ITS LOWER END, AND WITH THE SIDE WALLS OF SAID CASE CLOSELY FITTED TO THE PERIPHERY OF SAID RING AND TO THE LOWER PORTION OF THE SIDES OF SAID PLUG; (D) MEANS SECURING SAID CASE TO SAID PLUG; (E) CHARGE OF DETONATING EXPLOSIVE MATERIAL IN SAID BORE; (F) SAID BOTTOM WALL OF SAID CASE HAVING AN AXIALLY SYMMETRICAL INDENTATION EXTENDING INTO SAID CHARGE OF EXPLOSIVE MATERIAL TO PROVIDE A DOWNWARDLY FACING, LINED CAVITY IN SAID MATERIAL; AND (G) MEANS TO DETONATE SAID EXPLOSIVE MATERIAL.