Laser-Heated Nanowires Produce Microscale Fusion

A dense fusion environment was created by irradiating arrays of nanowires using joule-level pulses from a compact, ultrafast laser. The irradiation of ordered nanowire arrays with femtosecond pulses created ultrahigh energy density plasmas in which deuterons (D) were accelerated up to mega electron volt energies, efficiently driving D-D fusion reactions and ultrafast neutron bursts.

Laser-driven controlled fusion experiments are typically done using multimillion-dollar lasers housed in stadium-size buildings. Such experiments are usually geared toward harnessing fusion for clean energy applications.

In contrast, a Colorado State University team worked with an ultrafast, high-powered tabletop laser they built from scratch. To create extremely hot, dense plasmas, researchers used the laser to irradiate a target of nanowires made out of deuterated polyethylene.

Target chamber (front) and ultrahigh-intensity laser (back) used in the microscale fusion experiment at Colorado State University. Courtesy of Advanced Beam Laboratory/Colorado State University.

The volumetric heating of aligned deuterated polyethylene nanowire arrays irradiated at relativistic intensity was shown to produce ultrashort neutron pulses with about a 500× larger number of D-D neutrons than a deuterated flat solid target. A total of 2 × 10⁶ neutrons per joule was generated. Researchers believe this to be the largest D-D fusion neutron yield reported to date for plasmas generated by laser pulse energies in the 1-J range.

A scanning electron microscope image of aligned deuterated polyethylene nanowires (a). The other panels are 3D simulations of the nanowires rapidly exploding following irradiation by an ultraintense laser pulse. Courtesy of Advanced Beam Laboratory/Colorado State University.

Researchers further believe that an increase of the irradiation intensity could shift the deuteron energy distribution to significantly higher energies, which could to lead to a further increase in D-D fusion reactions.

Researchers say this volumetrically heated dense fusion environment could be created at a high repetition rates.

Making fusion neutrons efficiently, at a small scale, could lead to advances in neutron-based imaging and neutron probes to gain insight into the structure and properties of materials. The approach could also lead to the efficient generation of ultrafast pulses of neutrons for ultrafast neutron radiography and spectroscopy. The results could also contribute to a better understanding of the interactions between ultraintense laser light and matter.

The research was published in Nature Communications (doi:10.1038/s41467-018-03445-z).