This article describes a neutral particle analyzer/isotope separator (ISEP) developed for measurement of the relative hydrogen isotope composition of Joint European Torus (JET) plasmas. The ISEP deployed on the JET can be regarded as a prototype of an instrument proposed for measurement of the spatial profile of the ratio of the density of deuterium and tritium ions in the plasma, nD(r)/nT(r), in the International Thermonuclear Experimental Reactor (ITER). The ISEP makes simultaneous measurements of the energy distribution of efflux of hydrogen isotope atoms (H, D, and T) from the plasma. From such measurements it is possible to deduce the radial profile of the relative hydrogen isotope ion composition of the plasma and radial transport of ions of one isotope across the plasma of another isotope species. The main elements of the ISEP are (a) use of a thin carbon foil for reionization of the incident atoms, thereby eliminating gas stripping cells and gas sources of conventional neutral particle analyzers (NPAs), (b) acceleration of secondary ions in order to access the regime of higher detection efficiency of the NPA and to better separate ion pulses from neutron/γ-ray induced pulses in scintillator detectors, (c) E‖B dispersion of the secondary ions in specially designed nonuniform magnetic and electric fields to provide focusing in the detector plane, increased throughput and greater contrast between neighboring isotopes, and (d) counting of energy and mass analyzed secondary ions using detectors consisting of thin [1⩽t (μm)⩽7] CsI(Tl) scintillators deposited directly on miniature thin window photomultiplier tubes mounted in vacuum. The ISEP has high contrast between atoms of neighboring masses (⩾103 for E≈5 keV and much greater at higher energies), and high detection efficiency (0.06⩽ε⩽0.83 for atoms of 5⩽ (keV)⩽150. ISEP detectors have very low sensitivity to neutrons and γ rays (⩽10−7 of ion sensitivity), making it feasible to use the ISEP in JET DT experiments without any shielding. Only a modest amount of neutron/γ-ray shielding would be required in the ITER for similar applications of the ISEP. The initial experiments on JET plasmas using the ISEP demonstrate well the capabilities of the instrument for measurement of the hydrogen isotope composition of the plasma and the energy distribution function of isotope ions.

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An overview of the developments postcirca 1980s in the instrumentation and application of charge exchange neutral particle diagnostics on magnetic fusion energy experiments is presented. First, spectrometers that employ only electric fields and hence provide ion energy resolution but not mass resolution are discussed. Next, spectrometers that use various geometrical combinations of both electric and magnetic fields to provide both energy and mass resolutions are reviewed. Finally, neutral particle diagnostics based on utilization of time-of-flight techniques are presented.

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A new Compact Neutral Particle Analyzer (CNPA) [1] has been developed at A.F. Ioffe Physical-Technical Institute. The CNPA is an energy and mass spectrometer of reduced size (169´302´326 mm). It is designed for the simultaneous analysis of H 0 (0.8 -80 keV) and D 0 (0.66 -36 keV) fluxes emitted by plasma. Significant reduction of spectrometer size and weight (42.5 kg) is achieved by two innovations: 1) employing of stripping in a thin (100 Å) diamond-like carbon foil instead of the traditional stripping in gas; 2) using a high-fieldstrength (1 T) NdFeB permanent magnets instead of the traditional electromagnets for generation of the analysing magnetic field. An acceleration of particles scattered in the stripping foil is employed in the CNPA, which together with a magnetic field configuration providing two-coordinate focusing is used to achieve a better detection efficiency. The CNPA has the following significant advantages in comparison with conventional NPAs:1) The compact spectrometer can be installed practically at any position around plasma machine. It can be easily moved or replaced in the case of need.2) The CNPA shielding against n-gamma radiation and against stray magnetic field can be made more compact.3) The arrays of such instruments for a purpose of multichord diagnostic can be easily formed.4) The CNPA has a high detection sensitivity (10-100 times higher than for conventional NPAs) due to wide solid angle of observation and high detection efficiency.5) The CNPA does not require its own high-vacuum pumping system (because of absence of gas inlet) and does not require magnet power supply (because of permanent magnets usage).The CNPA has been tested on the Wendelstein 7-AS stellarator at IPP,