ast neutrons have applications in neutron radiograghy, imaging, fast neutron therapy, and material testing. The primary advantage of laser based neutrons is the reduction of the charged particle acceleration distance from meter scale to millimeter scale due to the high electrical fields supported by plasmas. Another advantage is the high instaneous neuron production rates due to the short pulse duration of the laser and corresponding acceleration times. It has been previously demonstrated experimentlly that high intense lasers can be used to produce neutrons by accelerating deuterons through clusters Coulomb Explosion.
In our experiments, short neutrons were generated by deutrium clusters. As a form of matter intermediate between molecules and bulk solids, atomic clusters have been intensively studied. Many research results, including theoretical arguments and experimental data, have shown that laser clusters interaction is extremely energetic due to the fact that the density within the clusters is nearly that of a solid. The clusters can exhibit the large absorption efficiency usually associated with solid targets. We experimentally demenstrated the deuterium clusters fusion induced by an intense femtosecond laser pulse. The laser deliverd pulses of 300 mJ in a duration of 30 fs, The laser is focused by an f/12 lens to a 10 µm diameter (FWHM) spot at the edge of clusters gas jet. In our experiment, deuterium clusters are generated by the adiabatic expansion of high pressure gas through a cylindrical nozzle with a orifice of 0.5 mm. The nozzle assembly is cooled down by liquid Nitrogen. The cryogenic pulsed valve  is set to work at 80 K with the backing pressure 50 bar. The opening time of the valve is 2 ms. An calorimeter  was employed to monitor the laser energy absorption efficiency.The average neutron yield of 5×10³ per shot was observed. The fusion neutrons at different laser intensity were observed. We found the neutron production mainly come from the high temperature plasma region, while the beam target fusion, occuring from the close vicinity is negligible.
In summary, we have shown the DD reactions within an intense laser-produced plasma, using cryogenic deuterium clusters. Table-top neutron source is of great interest for time resolved material damage studies and medical application. With further optimization of the parameters in the experiment or increasing the laser energy, we believe the neutron yield can be increased.
 

cluster,intense,fusion