Strong Perpendicular Velocity-space Diffusion in Proton Beams Observed by Parker Solar Probe

Academic Article


  • Abstract The SWEAP instrument suite on Parker Solar Probe (PSP) has detected numerous proton beams associated with coherent, circularly polarized, ion-scale waves observed by PSP’s FIELDS instrument suite. Measurements during PSP Encounters 4−8 revealed pronounced complex shapes in the proton velocity distribution functions (VDFs), in which the tip of the beam undergoes strong perpendicular diffusion, resulting in VDF level contours that resemble a “hammerhead.” We refer to these proton beams, with their attendant “hammerhead” features, as the ion strahl. We present an example of these observations occurring simultaneously with a 7 hr ion-scale wave storm and show results from a preliminary attempt at quantifying the occurrence of ion-strahl broadening through three-component ion VDF fitting. We also provide a possible explanation of the ion perpendicular scattering based on quasilinear theory and the resonant scattering of beam ions by parallel-propagating, right circularly polarized, fast magnetosonic/whistler waves.
  • Authors

  • Verniero, JL
  • Chandran, Benjamin
  • Larson, DE
  • Paulson, K
  • Alterman, BL
  • Badman, S
  • Bale, SD
  • Bonnell, JW
  • Bowen, TA
  • de Wit, T Dudok
  • Kasper, JC
  • Klein, KG
  • Lichko, E
  • Livi, R
  • McManus, MD
  • Rahmati, A
  • Verscharen, D
  • Walters, J
  • Whittlesey, PL
  • Status

    Publication Date

  • January 1, 2022
  • Has Subject Area


  • astro-ph.SR
  • physics.plasm-ph
  • Digital Object Identifier (doi)

    Start Page

  • 112
  • End Page

  • 112
  • Volume

  • 924
  • Issue

  • 2