Synchrotron radiation from electron beams in plasma-focusing channels

Abstract

Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma focusing channel is analyzed and applications to plasma wakefield accelerator experiments and to the ion channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter a β , which plays a similar role to that of the wiggler strength parameter in a conventional FEL. For a β > ∼ 1, radiation is emitted in numerous harmonics.Furthermore, a β is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. The radiation spectrum emitted from an electron beam is calculated by averaging the single electron spectrum over the electron distribution. This leads to a frequency broadening of the radiation spectrum, which places serious limits on the possibility of realizing an ICL.03.65. 02.60.Cb, Typeset using REVT E X 1

Efficient numerical modelling of the emittance evolution of beams with finite energy spread in plasma wakefield accelerators

“…e.g. [32]). This frequency depends on the individual electron energy γ e as well as on the local plasma frequency ω p ðzÞ ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4πnðzÞe 2 =m e p .…”

Bright spatially coherent synchrotron X-rays from a table-top source

“…These oscillations occur at the betatron frequency ω β = ω p / √ 2γ , where ω p is the plasma frequency and γ is the Lorentz factor of the electron beam 17 . As this betatron wavelength (λ β ≈ 2πc/ω β ) is much smaller than the period of comparable external wigglers, again as a result of the extremely large electric fields of the wakefield, the wavelength at which these particles radiate (of order λ ≈ λ β /γ 2 ) can be in the X-ray region for γ ∼ > 200, that is, for an electron beam of energy W > 100 MeV.…”

“…As K → 1, radiation also appears at harmonics. For large K 1 (that is, large-amplitude wiggler limit) a synchrotron spectrum with broad emission consisting of closely spaced harmonics is produced 17 .…”

Laser-plasma electron acceleration in dielectric capillary tubes

“…It is clearly seen that most of the X-rays are generated in the region where electrons reach their maximum energy. The emitted power scales with γ 4 [11] and, therefore, the X-ray emission is maximum when the electrons have their maximum energy. The spatial profile is calculated with the assumption that the X-rays are absorbed at the capillary wall.…”

“…Moreover, their observation provides insight into the laser-plasma interaction itself, because their production is directly linked to the trapping and acceleration of electrons. For large amplitude oscillations of electrons, the radiation emitted close to the axis can be shown [11] to have a synchrotron-like spectrum, which is a broadband spectral distribution peaked close to the critical energy E c = 3/2 Kγ 2 ω β , with γ m e c 2 the electron energy [12]. The betatron frequency ω β = ω p / √ 2γ and the betatron strength parameter K = γ r β ω β /c describe the trajectory of an electron oscillating with an amplitude r β .…”