Diagnostics of low-pressure hydrogen discharge created in a 13.56 MHz RF plasma reactor

Abstract

A 13.56 MHz RF discharge in hydrogen was studied within the pressure range of 1-10 Pa, and at power range of 400 -1000 W. The electron energy distribution function and electron density were measured by a Langmuir probe. The gas temperature was determined by the Fulcher-α system in pure H2, and by the second positive system of nitrogen using N2 as the probing gas. The gas temperature was constant and equal to 450 ± 50 K in the Capacitively Coupled Plasma mode (CCP), and it was increasing with pressure and power in the Inductively Coupled Plasma mode (ICP). Also the vibrational temperature of ground state of hydrogen molecules was determined to be around 3100 and 2000 ± 500 K in ICP and CCP mode, respectively. The concentration of atomic hydrogen was determined by means of actinometry, either by using Ar (5 %) as the probing gas, or by using H2 as the actinometer in pure hydrogen (Q1 rotational line of Fulcher-α system) The concentration of hydrogen density was increasing with pressure in both modes, but with a dissociation degree slightly higher in the ICP mode (a factor 2). Submitted to Physica Scripta

TALIF measurements of hydrogen and deuterium surface loss probabilities on quartz in low pressure high density plasmas

“…At the moment of the calibration, an alumina sample was installed in the chamber instead of the quartz sample. The sample material could affect the atomic density when compared to the full quartz situation, but the order of magnitude obtained here are still comparable to previous measurements realised in steady state plasma [5] since the sample surface was relatively small compared to surface area of the rest of the chamber walls. The absolute atom density at a time delay of 0.05 ms was (9 ± 1) × 10 19 m −3 .…”

“…The absolute atom density at a time delay of 0.05 ms was (9 ± 1) • 10 19 m −3 . The absolute atom density in this experimental set-up and at the same pressure and RF power but in steady state was also determined by Ar actinometry with H β line in H 2 + 5% Ar plasma using a Pyrex tube instead of a quartz one (Figure 14 of reference [5]). The result was ∼ 2.5 • 10 20 m −3 which compares quite well in term of order of magnitude to the present experiment given the slight differences between the experimental conditions (Pyrex tube instead of quartz tube, quartz sample instead of alumina sample, introduction of 5% argon, etc).…”

“…Based on cross sections of [49] (slightly lower than the original cross sections of Ref. [57]) we have calculated dissociative attachment rate for a vibrational temperature of 3300 K [5] ) ion create from one to three atoms [19]. If we assume for the sake of simplicity that all H + 2 ions are converted into H + 3 then the production rate of H atoms through this mechanism is given by the ionisation rate of H 2 (multiplied by a factor from 2 to and 300 K) and an electron density of 1•10 17 m −3 , this production rate reaches 10 m −3 s −1 at T e = 3 eV and 10 23 m −3 s −1 at T e = 5 eV (cross sections from [58]).…”

“…The ultimate goal of our research program is to measure atomic losses at the surface of fusion relevant materials (tungsten as a priority, but also tungsten nitrides, stainless steel, etc). To this end, a low pressure plasma source has been specially developed [5]. It consists of an inductively coupled plasma confined by quartz walls interacting with a sample made of the material of interest, and equipped with Two photon Absorption Laser Induced Fluorescence (TALIF) diagnostics.…”

Low-pressure inductively coupled plasmas in hydrogen: impact of gas heating on the spatial distribution of atomic hydrogen and vibrationally excited states

“…• 325 K is the wall temperature of the reactor, and in the isothermal case it is assumed that all temperature gradients are zero. • 450 K corresponds to the operating conditions of previous experiments [53,65,66]. • 600 K corresponds to the configuration of previously undertaken simulations with an isothermal neutral gas [26].…”