An extended lifetime system for generating neutrons comprising: an external enclosure; an insulating fluid contained within the external enclosure; a high voltage power supply (20, 73); a target at a target location supporting a layer of target material capable of being loaded with hydrogen isotopes selected from the group consisting of: deuterium and tritium; an ion source assembly configured to supply a beam of ions, the ion source assembly comprising: a vessel (10,72) comprising a wall made from an insulator material and having a plasma source cavity containing a plasma source from which a plasma is generated; an anode electrode connected to the high voltage power supply, the anode electrode being configured to bias the plasma; an external applicator (44, 70) that is: electrically connected to an excitation signal source, and configured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material, wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher, and a target electrode electrically coupled to the target, wherein the high voltage power supply is configured to maintain a voltage between the anode electrode and the target electrode between 10 kV and 500 kV; characterised by an insulating fluid contained within the external enclosure; an insulating gap comprising the insulating fluid that separates the external applicator (44,70) and the plasma source cavity. an external enclosure; an insulating fluid contained within the external enclosure; a high voltage power supply (20, 73); a target at a target location supporting a layer of target material capable of being loaded with hydrogen isotopes selected from the group consisting of: deuterium and tritium; an ion source assembly configured to supply a beam of ions, the ion source assembly comprising: a vessel (10,72) comprising a wall made from an insulator material and having a plasma source cavity containing a plasma source from which a plasma is generated; an anode electrode connected to the high voltage power supply, the anode electrode being configured to bias the plasma; an external applicator (44, 70) that is: electrically connected to an excitation signal source, and configured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material, wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher, and a vessel (10,72) comprising a wall made from an insulator material and having a plasma source cavity containing a plasma source from which a plasma is generated; an anode electrode connected to the high voltage power supply, the anode electrode being configured to bias the plasma; an external applicator (44, 70) that is: electrically connected to an excitation signal source, and configured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material, wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher, and electrically connected to an excitation signal source, and configured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material, wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher, and a target electrode electrically coupled to the target, wherein the high voltage power supply is configured to maintain a voltage between the anode electrode and the target electrode between 10 kV and 500 kV; characterised by an insulating fluid contained within the external enclosure; an insulating gap comprising the insulating fluid that separates the external applicator (44,70) and the plasma source cavity.