Engineering topics

Ray, Holly B.

Publications and source records attributed to Ray, Holly B..

4 records

DOE OSTI2019

Radial transport modeling of high density deuterium plasmas in proto-MPEX with the B2.5-Eirene code

High density (≥6 × 10 19 m –3 ), low temperature (2–6 eV) helicon discharges in the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) are analyzed with the coupled multifluid plasma, kinetic neutrals code B2.5-Eirene. The interpretative analyses are constrained by data from multiple diagnostics, including Langmuir probes, Mach probes, filterscopes, infrared TV system, Thomson scattering, and baratrons. The objectives of the transport simulations include: investigation of the effects of heating, fueling, and plasma production; pumping, and assumed radial transport models on the calculated density and temperature distributions; plasma flow profiles and power balance. The primary objective in this report is to investigate the effects of the radial transport model in full plasma (the entire length of the plasma column in Proto-MPEX) data-constrained simulations. Results from three assumed forms of the radial transport coefficients are presented, including spatially constant, radially decreasing, and Bohm (D,χ ~T e /|B|). The results from each of the three transport coefficient sets agree qualitatively with the core (near axis) data. With the implicit T e dependence, the Bohm coefficients tend to decrease as functions of radius, although not as strongly as the centrally peaked set. The axial variation in the Bohm coefficients is largely due to the axial structure of the magnetic field. Furthermore, the agreement of the simulations and the diagnostic data with the Bohm set indicates that transport in the plasma column of Proto-MPEX is dominated by Bohm diffusion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Evidence of electron heating at different radial locations on Proto-MPEX

This paper reports on the observation of controlled underdense electron heating for high heat flux applications in the Prototype Material Plasma Exposure eXperiment. The goal of this experiment is to demonstrate the source and heating concepts to create a high intensity plasma at material targets to study plasma-material interactions in similar plasma conditions to magnetic fusion divertors. A 80 kW helicon source at 13.56 MHz is used for the plasma density production and a 15 kW microwave source at 28 GHz is used for electron heating. Moreover, for electron densities ~5 × 10 18 m -3 , the electron temperature at the target location increases from 2 eV to 5 eV and the core heat flux increases by a factor of 5. It is shown that the radial profile of the heat flux delivered at the target can be controlled by either the background plasma density or the magnetic field. In conclustion, analysis suggests that the electron heating is due to heating near the upper-hybrid resonance layer and that this heating scenario may scale up to divertor-relevant electron densities ~5 × 10 19 m -3 by increasing the microwave driving frequency to 105 GHz.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Characterization of the helicon plasma flux to the target of Proto-MPEX

The ITER divertor will have to handle the boundary plasma power exhaust in the form of high heat and particle flux. The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a plasma source development device for the proposed Material Plasma Exposure eXperiment (MPEX), which is intended to create fusion reactor divertor-like plasma conditions for studying plasma material interactions. Here, ion fluxes to various targets within Proto-MPEX are found to be 5 ± 2.5 × 10 23 m –2 s -1 when using only a helicon plasma source. The fluxes along the flux tube are compared for both 30 cm in front of the target and a few cm in front of the target. The emission intensity fall-off distance in front of the target is studied via Balmer series from a visible camera looking at the target. As a result, this fall-off distance of ~2–4 cm and the dissociation and ionization mean free path of D 2 being over 0.5 m leads to a conclusion that Proto-MPEX is not in a high recycling regime with helicon only plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

Plasma source development for fusion-relevant material testing

Plasma facing materials in the divertor of a magnetic fusion reactor will have to tolerate steady-state plasma heat fluxes in the range of 10 MW/m2 for ~107 sec, in addition to fusion neutron fluences, which can damage the plasma facing materials to high displacements per atom (dpa) of ~50 dpa . Material solutions needed for the plasma facing components are yet to be developed and tested. The Materials Plasma Exposure eXperiment (MPEX) is a newly proposed steady state linear plasma device that is designed to deliver the necessary plasma heat flux to a target for this material testing, including the capability to expose a-priori neutron damaged material samples to those plasmas. The requirements of the plasma source needed to deliver this plasma heat flux are being developed on the Proto-MPEX device, which is a linear high-intensity radio frequency (RF) plasma source that combines a high-density helicon plasma generator with electron and ion heating sections. It is being used to study the physics of heating over-dense plasmas in a linear configuration. The helicon plasma is operated at 13.56 MHz with RF power levels up to 120 kW. Microwaves at 28 GHz (~30 kW) are coupled to the electrons in the over-dense helicon plasma via Electron Bernstein Waves (EBW), and ion cyclotron heating at 7-9 MHz (~30 kW) is via a magnetic beach approach. High plasma densities >6x1019/m3 have been produced in deuterium, with electron temperatures that can range from 2 to >10 eV. Operation with on-axis magnetic field strengths between 0.6 and 1.4 T is typical. The plasma heat flux delivered to a target can be > 10 MW/m2, depending on the operating conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗