The magnetic proton recoil neutron spectrometer has been upgraded (MPRu) with a new focal plane hodoscope detector as a major part to improve the immunity to background and to extend the measuring range from 18 down to 1.5 MeV. The MPRu detector project has entailed the
development of the phoswich technique for this application. This was done through tests of prototype scintillators to reach the final design. The article reports on the tests conducted, the projected specification, and demonstrated performance through the first MPRu results obtained at JET.