H01J2893/0072—Disassembly or repair of discharge tubes
H01J2893/0073—Discharge tubes with liquid poolcathodes; constructional details
H01J2893/0074—Cathodic cups; Screens; Reflectors; Filters; Windows; Protection against mercury deposition; Returning condensed electrode material to the cathodic cup; Liquid electrode level control
H01J2893/0087—Igniting means; Cathode spot maintaining or extinguishing means