Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Abstract

Radio frequency (RF) driven helicon plasma sources are commonly used for their ability to produce high-density argon plasmas (n > 1019 m−3) at relatively moderate powers (typical RF power < 2 kW). Typical electron temperatures are <10 eV and typical ion temperatures are <0.6 eV. A newly designed helicon antenna assembly (with concentric, double-layered, fully liquid-cooled RF-transparent windows) operates in steady-state at RF powers up to 10 kW. We report on the dependence of argon plasma density, electron temperature and ion temperature on RF power. At 10 kW, ion temperatures >2 eV in argon plasmas are measured with laser induced fluorescence, which is consistent with a simple volume averaged 0D power balance model. 1D Monte Carlo simulations of the neutral density profile for these plasma conditions show strong neutral depletion near the core and predict neutral temperatures well above room temperatures. The plasmas created in this high-power helicon source (when light ions are employed) are ideally suited for fusion divertor plasma-material interaction studies and negative ion production for neutral beams.

PISCES-RF: a liquid-cooled high-power steady-state helicon plasma device

“…We also find that in the core plasma, direct collisional effects are more dominant, primarily due to the very high densities. Measurements of the ion temperature in argon plasma, using LIF [42], are consistent with results of a 0-D, volumeaveraged global model where collisional heating is balanced by diffusive radial losses and convective end losses. Hence it seems that near the core, collisional heating is the dominant heating mechanism.…”

“…Hence it seems that near the core, collisional heating is the dominant heating mechanism. In addition, measurements of the radial profiles of the electron temperature shows an elevated contribution near the edge [42], where the effect of the Trivelpiece-Gould (T-G) mode is expected to be maximum. Preliminary modeling of our device using COMSOL also shows this enhanced energy absorption by the electrons in this spatial region.…”

“…However, it is clear that the presence of the DI water coolant does not hinder high density plasma production. In a companion paper [42], we show systematic scans of argon plasma density, electron temperature and ion temperature as measured by laser induced fluorescence (LIF), as well as numerically computed profiles of the argon neutral density and temperatures. We show that the RF source design is stable enough to allow us to use a novel compact portable LIF design [43], which needed several minutes of integration of the emitted light for good signal-to-noise ratios to measure the ion velocity distribution functions of argon.…”

Estimation of erosion phenomena within helicon plasma sources through a steady-state explicit analytical model

“…The source parameters used in the estimation are listed in Table 3. It was found that the axial model was able to predict the behavior of the axial density profile, Comparison of the radial plasma density distribution estimated by Ahedo's radial model [12,20] and experimental data published by Burin et al [21], Castro et al [22], and Thakur et al [5,23].…”

“…The chosen versions of these models are the asymptotic, magnetized regimes. For the case of the radial model [12,20], Figure 3 shows the normalized radial profile of the plasma density, compared to experimental data from the CSDX device published by Burin et al [21], from the VX-CR device by Castro et al [22] and from the PISCES-RF device by Thakur et al [5,23], from experimental runs using argon gas as the feedstock in all cases. The published experimental parameters obtained from these experimental data sets are described in Table 2.…”