Physical and technical basis of Materials Plasma Exposure eXperiment from modeling and Proto-MPEX results^*

Abstract

The Materials Plasma Exposure eXperiment (MPEX) is a steady-state linear plasma device that will address plasma-material interaction (PMI) science and enable testing of fusion reactor-relevant divertor plasma-facing materials. The MPEX source concept consists of a helicon plasma source to generate the plasma, electron cyclotron heating (ECH) for electron heating, and ion cyclotron heating (ICH) for ion heating. The MPEX source plasma is then transported axially to the PMI material target region to test material samples in fusion reactor-relevant divertor conditions. This paper will summarize the physical and technical basis of MPEX. The paper will first define the MPEX parameters and scenarios at the target relevant to PMI science for various fusion reactor-relevant divertor conditions and show plasma transport modelling results to set the MPEX source parameters. Recent experimental and modeling results from Proto-MPEX, a short-pulse experiment to develop the plasma production, heating, and transport physics for MPEX, will be shown. From these results, it will be shown that MPEX can reach its desired scenarios. The MPEX physical and technical basis will also determine important functional requirements for magnetic field, radiofrequency (RF) power, RF frequency, and neutral pressure in the helicon, ECH, ICH, and PMI regions that are required to achieve the desired MPEX scenarios. The necessity for key in-vessel components such as skimmers, limiters, and microwave absorbers will also be highlighted.

Analysing the effects of heating and gas puffing in Proto-MPEX helicon and auxiliary heated plasmas *

“…The Material Plasma Exposure Experiment (MPEX) is a linear plasma device presently being constructed at Oak Ridge National Laboratory with the goal to investigate the physical mechanisms of PMI and divertor issues under reactor-relevant conditions [9,10]. The unique features of MPEX compared to present linear plasma devices will be (1) high plasma fluxes to the target, (2) long pulse steady-state operation up to 10 6 s, (3) a plasma heating system able to provide electron temperatures and ion temperatures in front of the target representative of those in a fusion reactor divertor, and (4) the ability to expose a priori neutron irradiated samples at relevant ambient material temperatures.…”

“…The unique features of MPEX compared to present linear plasma devices will be (1) high plasma fluxes to the target, (2) long pulse steady-state operation up to 10 6 s, (3) a plasma heating system able to provide electron temperatures and ion temperatures in front of the target representative of those in a fusion reactor divertor, and (4) the ability to expose a priori neutron irradiated samples at relevant ambient material temperatures. In MPEX, long pulse operation will be achieved via a steady-state high power helicon antenna, electron cyclotron heating (ECH), and ion cyclotron resonance frequency (ICRF) [9,10]. This enables independent tuning of electron and ion temperatures.…”

“…This enables independent tuning of electron and ion temperatures. To address the RD issues associated with MPEX, a smaller device, Proto-MPEX, was constructed to study the heating scenarios and magnetic field configurations required to achieve fluxes that extrapolate to the MPEX design requirements [9][10][11][12][13][14][15][16][17].…”

“…These experiments raised an important research issue, in that ECH heating caused a plasma density drop towards the target. It is necessary to clarify the physical processes of these actuators to reduce the risks in achieving the MPEX design goals [9,10]. In this paper, plasma simulations with auxiliary heating are performed to better understand the impact of heating on achieving reactorrelevant target fluxes.…”