Patent Number: 
Section: claims

1. A system for generating neutrons, the system comprising:a target positioned at a target location, the target including at least a target substrate suitable for supporting a target assembly layer;an anode electrode biased at a positive voltage relative to the target;an ion source configured to generate ions for acceleration by an electric potential difference between the anode electrode and the target; anda target maintenance system configured to perform one or more of the group consisting of:in situ deposition, onto the target substrate in order to form the target assembly layer and replenish the target assembly layer after it has been formed, of target material capable of being loaded with at least one of deuterium and tritium, wherein the target assembly layer is formed of the target material; andin situ regeneration of the target material forming the target assembly layer to repair or reform the target assembly layer. 2. The system according to claim 1, wherein the target maintenance system is configured to perform only in situ deposition of target material. 3. The system according to claim 1, wherein the target maintenance system comprises a source of target material for in situ deposition onto the target substrate. 4. The system according to claim 3, wherein the target maintenance system is configured to perform in situ deposition of target material onto the target substrate during one or more of the group consisting of: initial fabrication of the system, discrete intervals during operation of the system, maintenance cycle of the system, and continuous operation of the system. 5. The system according to claim 1, further comprising a source of target material that is one of the group consisting of: a coating on one or more surfaces of parts of the neutron generator, one or more surfaces of parts within the neutron generator, electrodes of the neutron generator, a reservoir, and an evaporator assembly. 6. The system according to claim 1, wherein in situ deposition, onto the target substrate in order to form or replenish the target assembly layer, of target material includes one or more of the group consisting of: evaporation, sublimation, chemical vapor deposition, physical vapor deposition, sputtering, beam deposition, and flowing of liquid target material. 7. The system according to claim 1, wherein the target assembly layer is between 2 microns and 3 microns in thickness. 8. The system according to claim 1, wherein the target maintenance system is further configured to maintain a thickness of the target assembly layer. 9. The system according to claim 1, wherein in-situ regeneration of the target material to repair or reform the target assembly layer comprises one or more of the group consisting of: induction, direct beam impingement, coolant reduction, resistive heating, convective heating, radiative heating, chemical heating, electrical discharge, radiative cooling, conductive cooling, convective cooling, thermoelectric cooling and conduction from an external thermal source through the target substrate. 10. The system according to claim 1, wherein the target maintenance system is configured to perform in-situ regeneration of the target material to repair or reform the target assembly layer is performed during one of the group consisting of: discrete intervals during operation of the system, a maintenance cycle of the system, and continuous operation of the system. 11. The system according to claim 1, further comprising a target degradation sensor configured to detect degradation of the target and to trigger one or more of the group consisting of: in-situ deposition and in-situ regeneration. 12. The system according to claim 1 wherein the target material forming the target assembly layer has properties that include one or more of the group consisting of: effective atomic number less than 21, stable hydride formation, thermal conductivity greater than 23 W/m/K, impurity solubility, hydrogen diffusion, hydrogen retention, and neutron-producing secondary reaction capability. 13. The system of claim 1, the system further comprising a suppression electrode biased to a negative voltage with respect to the target. 14. The system according to claim 1, wherein the target assembly layer comprises lithium. 15. The system according to claim 12, wherein neutron producing secondary reaction capability includes the capability to produce one of the group consisting of: D-6Li fusion reactions, D-7Li fusion reactions, T-6Li fusion reactions, or T-7Li fusion reactions. 16. The system according to claim 1, wherein the target is thermally connected to one or more of the group consisting of: a thermal management system and an external enclosure. 17. The system according to claim 1, further comprising a hydrogen isotope implanter, the hydrogen isotope implanter configured to perform in-situ implantation of hydrogen isotopes into the target assembly layer, the hydrogen isotopes provided by one or more of the group consisting of: a particle source, a secondary plasma source, and an electrolytically-driven source. 18. A method for maintaining a system for generating neutrons, the system including a target having at least a target substrate capable of supporting a target assembly layer, an ion source configured to generate ions for acceleration by an electric potential difference between an anode electrode and the target, and a target maintenance system, the method comprising:performing, by the target maintenance system, in situ deposition, onto the target substrate in order to form or replenish the target assembly layer, in situ deposition, onto the target substrate in order to form or replenish the target assembly layer, of target material capable of being loaded with one or more of deuterium and tritium, wherein the target assembly layer is formed of the target material; andperforming, by the target maintenance system, in situ regeneration of the target material forming the target assembly layer to mitigate target assembly layer degradation and preserve neutron production efficiency over the lifetime of the system. 19. A method for generating neutrons having a selected energy spectrum, the neutrons being generated by a system including a target having at least a target assembly layer supported by a target substrate, an ion source configured to generate ions for acceleration by an electric potential difference between an anode electrode and the target, and a target maintenance system, the method comprising:establishing a ratio of 6Li to 7Li isotopes in a target assembly layer by performing, by the target maintenance system, in situ deposition of target material including one or more of 6Li and 7Li; andestablishing a selected electric potential difference between the anode electrode and the cathode to adjust the incident particle energy to generate different sets of neutron energy spectra, wherein the neutron energy spectra is adjusted by the ratio of 6Li to 7Li isotopes in the target assembly layer; anddirecting the ions generated by the ion source and accelerated by the electric potential difference between the anode electrode and the target at the target assembly layer to cause secondary neutron producing reactions involving the ions and at least one of the 6Li and 7Li isotopes. 20. The method according to claim 19, wherein the method yields neutrons with energy greater than 3 MeV without the use of radioactive tritium and without acceleration potentials higher than 500 kV. 21. The system according to claim 1, wherein the target maintenance system is further configured to maintain a purity of target material forming the target assembly layer within a beam interaction layer.