title: Positron production by x rays emitted by betatron motion in a plasma wiggler.
abstract: Positrons in the energy range of 3-30 MeV, produced by x rays emitted by betatron motion in a plasma wiggler of 28.5 GeV electrons from the SLAC accelerator, have been measured. The extremely high-strength plasma wiggler is an ion column induced by the electron beam as it propagates through and ionizes dense lithium vapor. X rays in the range of 1-50 MeV in a forward cone angle of 0.1 mrad collide with a 1.7 mm thick tungsten target to produce electron-positron pairs. The positron spectra are found to be strongly influenced by the plasma density and length as well as the electron bunch length. By characterizing the beam propagation in the ion column these influences are quantified and result in excellent agreement between the measured and calculated positron spectra.
authors.affiliation: University of California, Los Angeles, California 90095, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Johnson
authors.forename: D
authors.initials: D
authors.lastname: Auerbach
authors.forename: I
authors.initials: I
authors.lastname: Blumenfeld
authors.forename: C D
authors.initials: CD
authors.lastname: Barnes
authors.forename: C E
authors.initials: CE
authors.lastname: Clayton
authors.forename: F J
authors.initials: FJ
authors.lastname: Decker
authors.forename: S
authors.initials: S
authors.lastname: Deng
authors.forename: P
authors.initials: P
authors.lastname: Emma
authors.forename: M J
authors.initials: MJ
authors.lastname: Hogan
authors.forename: C
authors.initials: C
authors.lastname: Huang
authors.forename: R
authors.initials: R
authors.lastname: Ischebeck
authors.forename: R
authors.initials: R
authors.lastname: Iverson
authors.forename: C
authors.initials: C
authors.lastname: Joshi
authors.forename: T C
authors.initials: TC
authors.lastname: Katsouleas
authors.forename: N
authors.initials: N
authors.lastname: Kirby
authors.forename: P
authors.initials: P
authors.lastname: Krejcik
authors.forename: W
authors.initials: W
authors.lastname: Lu
authors.forename: K A
authors.initials: KA
authors.lastname: Marsh
authors.forename: W B
authors.initials: WB
authors.lastname: Mori
authors.forename: P
authors.initials: P
authors.lastname: Muggli
authors.forename: C L
authors.initials: CL
authors.lastname: O'Connell
authors.forename: E
authors.initials: E
authors.lastname: Oz
authors.forename: R H
authors.initials: RH
authors.lastname: Siemann
authors.forename: D
authors.initials: D
authors.lastname: Walz
authors.forename: M
authors.initials: M
authors.lastname: Zhou