title: Using neutral beams as a light ion beam probe (invited).
abstract: By arranging the particle first banana orbits to pass near a distant detector, the light ion beam probe (LIBP) utilizes orbital deflection to probe internal fields and field fluctuations. The LIBP technique takes advantage of (1) the in situ, known source of fast ions created by beam-injected neutral particles that naturally ionize near the plasma edge and (2) various commonly available diagnostics as its detector. These born trapped particles can traverse the plasma core on their inner banana leg before returning to the plasma edge. Orbital displacements (the forces on fast ions) caused by internal instabilities or edge perturbing fields appear as modulated signal at an edge detector. Adjustments in the q-profile and plasma shape that determine the first orbit, as well as the relative position of the source and detector, enable studies under a wide variety of plasma conditions. This diagnostic technique can be used to probe the impact on fast ions of various instabilities, e.g., Alfvén eigenmodes (AEs) and neoclassical tearing modes, and of externally imposed 3D fields, e.g., magnetic perturbations. To date, displacements by AEs and by externally applied resonant magnetic perturbation fields have been measured using a fast ion loss detector. Comparisons with simulations are shown. In addition, nonlinear interactions between fast ions and independent AE waves are revealed by this technique.
authors.affiliation: Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.affiliation: University of California Irvine, Irvine, California 92697, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Heidbrink
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Van Zeeland
authors.affiliation: Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kramer
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Pace
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Petty
authors.affiliation: University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Austin
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Fisher
authors.affiliation: Columbia University, New York, New York 10027, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Hanson
authors.affiliation: Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543, USA.
authors.forename: R
authors.initials: R
authors.lastname: Nazikian
authors.affiliation: University of California Los Angeles, Los Angeles, California 90095, USA.
authors.forename: L
authors.initials: L
authors.lastname: Zeng