Array of neutral particle analyzers at DIII-D

Local measurements of the fast-ion distribution in auxiliary-heated plasmas are key to understanding the behavior of energetic particles under a variety of conditions, such as beam–ion transport during Alfvén instabilities and the acceleration of beam ions by fast waves. For the first time at DIII-D, line-averaged and local measurements of the energetic-particle density (for E=5–75 keV) are possible using an array of four compact charge–exchange analyzers [P. Beiersdorfer et al., Rev. Sci. Instrum. 58, 2092 (1987)]. The installation consists of three vertically viewing analyzers with fixed sightlines, measuring particles with χ=90° (where χ is the angle between the particle’s velocity and the toroidal direction), and one horizontally viewing analyzer with a variable sightline, measuring particles with 2°≲χ≲60°. All the analyzers can make passive measurements while three detectors, with sightlines that intersect deuterium heating beams, can make active charge–exchange measurements.