Three-body collisions in a plasma in a strong laser field
- PDF / 296,460 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 194 Views
R PLASMA
Three-Body Collisions in a Plasma in a Strong Laser Field A. A. Balakin and M. G. Tolmachev Institute of Applied Physics, Russian Academy of Sciences, ul. Ul’yanova 46, Nizhni Novgorod, 603950 Russia Received January 16, 2008
Abstract—Electron–ion collisions in a high-density plasma in strong electromagnetic fields are considered. The applicability condition for the approximate model of pair collisions in strong fields are determined. It is shown that this condition is identical to the condition for the plasma to be transparent. Investigations were carried out by the test particle method generalized to the case of several scattering centers. An accurate calculation of short-range collisions is provided by a “jump” method that is based on the exact solution to the problem of the motion of a particle in a Coulomb potential. This method can also be applied in other approaches to simulating a collisional plasma (such as particle-in-cell and molecular dynamics methods). PACS numbers: 52.20.Fs, 52.50.Sw, 52.35.Mw DOI: 10.1134/S1063780X08080047
1. INTRODUCTION Electron–ion collisions in strong electromagnetic (EM) fields differ from those in weak or high-frequency fields [1–5] in some qualitative respects, such as the attraction and bunching effects occurring during a collision event [6–8], more intense Joule heating [6, 7], and the generation of coherent radiation harmonics [8] and fast particles [9]. By collisions in a strong EM field is meant the collisional regime in which the amplitude of electron oscillations in an EM wave, rosc = vosc/ω (with ω being the wave frequency), exceeds the size of the region dominated by the Coulomb field of an ion, 2
rE = e Z/E (with E being the wave amplitude and e and Ze being the charges of an electron and an ion, respectively). The dimensionless parameter Ω = r E /r osc can serve as a measure of how strong the field is. In the nonrelativistic case, the parameter Ω is the only one that determines the structure of the phase space of the scattered particles [10]. It is this circumstance that reflects the fundamental difference between the scattering in strong (Ω 1) and weak (Ω 1) fields.1 Thus, in weak fields (Ω 1), the amplitude of electron oscillations is small in comparison with the main spatial scale characteristic of a collision event, so an electron moves as if in an averaged potential. This is why, for high-energy electrons such that v (e2Zω/m)1/3, the collision frequency can be described by the same classical expression as that in [1–3] and, for low-energy electrons such that v < (e2Zω/m)1/3, it is suf1 Instead
of the strong and weak fields, it would be more correct to speak of low-frequency (Ω 1) and high-frequency (Ω 1) ones, because the intensity of the weak fields can be large in absolute value. But the present paper will make use of the terminology introduced in [6].
ficient to use a relatively simple quantum description [4, 5]. For strong fields (Ω 1), the situation is opposite. The amplitude of electron oscillations is large in comparison with t
Data Loading...
