title: Observations of ion-beam formation in a current-free double layer.
abstract: With nonperturbative laser-induced fluorescence measurements of ion flow, we confirm numerical simulations of spontaneous electric double-layer (DL) formation in a current-free expanding plasma. Measurements in two different experiments confirm that the DL is localized to the region of rapidly diverging magnetic field. The measurements indicate that the trapped ion population is a single Maxwellian, that the spatial gradient of the energy of ions accelerated through the DL matches the magnetic field gradient, and that DL formation is triggered when the ion-neutral collisional mean-free path exceeds the magnetic field gradient scale length.
authors.affiliation: Department of Physics, West Virginia University, Morgantown, West Virginia 26506, USA.
authors.forename: Xuan
authors.initials: X
authors.lastname: Sun
authors.forename: Amy M
authors.initials: AM
authors.lastname: Keesee
authors.forename: Costel
authors.initials: C
authors.lastname: Biloiu
authors.forename: Earl E
authors.initials: EE
authors.lastname: Scime
authors.forename: Albert
authors.initials: A
authors.lastname: Meige
authors.forename: Christine
authors.initials: C
authors.lastname: Charles
authors.forename: Rod W
authors.initials: RW
authors.lastname: Boswell