Even though the current is carried by electrons, the good ions returning on the cathode allow the conduction path to become mainly unaffected by the Room charge outcomes which limit the efficiency of vacuum tubes. As a result, the valve can carry significant currents at lower arc voltages (normally 20-30 http://valvesandfittings29493.getblogs.net/18100453/a-simple-key-for-arc-valves-unveiled