Prasoon Raj is a 🏷️#physicist at 📝Commonwealth Fusion Systems working on neutron measurement, and first author of the 2024 Review of Scientific Instruments overview of the 📝neutron diagnostics systems for 📝SPARC. Neutrons are the machine's primary route to fusion power: they leave the plasma unbent by the magnetic field, and their rate and energy spectrum carry the 📝D-T reaction rate, the 📝ion temperature and the fuel ion ratio out with them.

The design the paper sets out is demanding and, so far, entirely on paper. It targets 10 percent uncertainty on fusion power across more than eight orders of magnitude of dynamic range, up to 5×10¹⁹ neutrons per second, using four complementary subsystems fed by a shielded midplane port: roughly fifteen 📝neutron flux monitors — ionization chambers and proportional counters — for yield rate; two independent foil 📝activation systems for fluence; a spectrometric radial neutron camera for poloidal emissivity profiles; and a high-resolution magnetic proton recoil spectrometer for the core spectrum. Together they aim at 10 millisecond time resolution, roughly 7 centimeter spatial resolution and better than 2 percent energy resolution at 📝14 MeV. Raj is also a co-author on the spectrometer's ion optical design and hodoscope, on the diamond spectrometer electronics for the neutron camera, and on an evaluation of deuterated xylene as a scintillator — work carried with 📝Università di Milano-Bicocca and CNR-ISTP and the 📝MIT Plasma Science and Fusion Center.