At JET, special attention has always been given to the measurement of neutrons, which are produced in the fusion reactions. Neutrons carry vital information on the rate and location of fusion reactions in burning plasmas. JET’s ability to produce neutrons in both Deuterium-Deuterium and Deuterium-Tritium fusion reactions, provides a unique opportunity for development of neutron diagnostics and data analysis methods for future fusion reactors.

Magnetic Proton Recoil detector at JET

Magnetic Proton Recoil Spectrometer

A Magnetic Proton Recoil Spectrometer (MPR) measures energies of protons released from a special target in head-on collisions with the tracked neutrons. Protons are electrically charged and can precisely be measured via their deflection in a well-defined magnetic field. The kinetic energy of protons is then almost precisely equal to the energy of incident neutrons. Of course, MPR needs heavy shielding against JET’s powerful magnetic fields to avoid interference. The JET MPS measures high energy neutrons produced by Deuterium-Tritium fusion as well as lower energy Deuterium-Deuterium fusion neutrons.

Schematic of Time Of Flight for Optimised Rate (TOFOR)

Time Of Flight for Optimised Rate
A Time Of Flight for Optimised Rate (TOFOR) measures energy spectra from Deuterium-Deuterium fusion neutrons.
Every proton recoil is registered in a small scintillation detector in the bottom of the device. Some of the recoiled neutrons are registered again in the top “umbrella-like” set of detectors. All pulses are seeded by a system of automated data analysis so that only the incidences of both bottom and top counts are followed up. The original energy of each neutron is then derived from the time that elapsed between the first count in the bottom detector and the second count in one of the top detectors.