A Particle-in-Cell Simulation of Double Layers and Ion-Acoustic Waves

Abstract

Double layers and ion-acoustic waves are investigated by using a one-dimensional electrostatic particle-in-cell simulation code. Our results show that double layers can be formed even when the drift velocity between electrons and ions is less than the electron thermal velocity. Electron and ion density depressions were clearly seen. Electrons gradually developed a distribution comprising both background and beam components. In fact, as the initial electron-ion drift velocity was less than the electron thermal velocity, intense ion-acoustic waves could be found only at the places where the electron beam was located, suggesting that they are excited by the self-consistently developed electron beam. Besides the Langmuir waves and ion-acoustic waves, the beam mode excited by electron beams produced in our simulation has been clearly found.

Numerical analysis of high Mach flow and flow reversal in the experimental advanced superconducting tokamak divertor

“…[9] The Eirene code was developed by Reiter et al [11] The SOLPS4.0 code has been allowed by the IPP-Garching to be used in the Institute of Plasma Physics, China, and has been applied to the simulation of the EAST plasma. [7,10] In the present analysis of the EAST, the single null divertor configuration is considered and the schematic diagram of the SOL and the divertor plasma is shown in Fig. 1.…”

“…Sputtering coefficient Y ch = 2.0% is used at all material surfaces, which is a typical value for the divertor plasma conditions in the present machine. [7] The anomalous diffusion coefficients are set as D = 0.3 m 2 • s −1 and χ i = χ e = 1.0 m 2 • s −1 . The recycling coefficient for deuterium is set to unity at the target plates and the vacuum vessel walls for the envisaged long pulse operation in the EAST.…”

“…As a result, most of the particle flux incident on the target plates is prevented from escaping back into the SOL and reemitting towards the separatrix below the X-point. [7] Since the SOL flow shows different behaviour, such as the flow reversal and the high Mach flow associated with plasma regimes in the edge tokamaks, we first discuss the divertor operation regime before proceeding to the detailed analysis of the SOL flow. We can see from Fig.…”

“…The engineering design of the EAST requires that the maximum power flux to the target plates during the first operation phase is below 1 MW/m 2 to ensure a long pulse (> 100 s) operation, which dictates that the EAST must be operated close to the plasma detachment condition. [7] In the present paper, numerical analyses of the SOL flow in the EAST divertor region in the detachment and the high recycling regimes are performed by using the SOLPS4.0 code package. To investigate the driving mechanisms and the formation condition for the SOL flow, we focus on the profiles of the ionization sources.…”

Numerical analysis of divertor asymmetry induced by differential divertor biasing

“…The outer/inner divertor asymmetry has been found in both experiments and simulations of tokamaks such as JET [1] and EAST [2,3]. The asymmetry of the heat load on the divertor plates, i.e.…”