A Compact Neutral-Particle Analyzer for Plasma Diagnostics

Abstract

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,

Reconstruction of ion temperature profiles from single chord NPA measurements on the TCV tokamak

“…• The limited upper neutral energy range of the NPA was one of the main motivations for the procuring of an analyzer capable of observing hot suprathermal ions. The Compact Neutral Particle Analyzer (CNPA), manufactured by Ioffe Institute [2], was installed on TCV in 2004. Neutral particles are ionized by a thin carbon foil, which features a higher stripping efficiency for fast particles than the nitrogen gas used in the vertical NPA.…”

A simulation study of a windowless gas stripping room in an E//B neutral particle analyzer

“…It is used to determine the bulk ion temperature, the isotopic ratio and the fast ion distribution of the plasma, by measuring the charge exchange neutral particles escaping from the plasma. Different types of NPA have been built in Tokamak facilities worldwide [2][3][4][5][6][7][8][9][10][11][12][13], such as the parallel direction of electric and magnetic fields (E//B) NPA on the Tokamak Fusion Test Reactor (TFTR) [2], the compact neutral particle analyzer (CNPA) on the Wendelstein 7-AS stellarator [3], the low-and high-energy neutral particle analyzers (LENPA and HENPA) on the International Thermonuclear Experimental Reactor (ITER) [10], the solid state NPA (ss-NPA) on the Experimental Advanced Superconducting Tokamak (EAST) [11] and the CP-NPA on the HuanLiuqi-2A (HL-2A) [12].…”

Design of the Electromagnetic Field for an E//B Neutral Particle Analyzer

“…An equipment to detect these escaped neutrals and provide the energy or/and mass spectrum is named neutral particle analyzer (NPA) [1]. Different types of NPA have been built in the world [2][3][4][5][6][7][8]. NPA is the key tool for fast ion physics study [9] and fusion fuel density ratio (T/D) measurement [10].…”