Page 6 - Demo

ionize the tritium target ahead of the OPCPA accelerated deuteron beam. In such a configuration, the tritium ionized gas is maintained at almost solid density for a short amount of time and the fusion mean free path is greatly reduced.
The reason for subcriticality is safety but also a transmutator fueled with TRUs is difficult to maintain super-critical due to 2 fundamental reasons: (1) TRU fuel has a much smaller percentage (0.2 %) of delayed neutrons vs. uranium (0.7%), (2) in order to fission TRU, fast neutrons are required. To discuss in more details: any machine that fissions actinides has 2 neutron sources: (1) Prompt neutrons with life-time ~10-7 s (fast reactors) - 10-4 s (thermal reactors). (2) Delayed neutrons which are byproducts from FP decay with lifetime ~1-10s. In thermal reactors the average lifetime of a neutron (prompt + delayed) is ~1s, which is easy to maintain as shown with over 450 operational thermal reactors around the world. Due to TRU low delayed fraction, and further, due to TRU only completely fissioning with energetic neutrons (>1 MeV), neutrons are essentially unmoderated and their prompt neutron lifetime ~10-7 s, much shorter than the thermal neutrons. Therefore, in the TRU fueled reactor, the average neutron lifetime is ~10-4 s -- difficult to control and maintain.
An illustrative example of the conceptual design for the liquid phased transmutator is shown in Fig. 2 where Fig. 2A shows the axial view and Fig. 2B the cross section. Fusion