The recoil protons emitted in the forward direction enter a magnetic part of the spectrometer where they are momentum analyzed and focused onto the focal plane.
An array of plastic scintillators coupled to photomultiplier tubes (PMTs) register the spatial distribution of the protons.
At a distance 170 mm behind the end of the collimator is placed a 10 cm2 polythene conversion foil, defining the active area of the spectrometer.
The MPR determines the neutron spectrum from which important plasma parameters can be determined, such as the ion temperature, the collective motion of the main plasma, the fuel ion densities and their velocity distributions.
The thin-foil magnetic proton recoil neutron spectrometer MPRu at JET