Radiative divertor studies in JET high confinement mode plasmas

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Controlled power exhaust is one of the key challenges in reactor scale fusion devices. These devices must maintain heat loads less than 10 MW/m2 at the plasma-facing materials (PFM), while producing gigawatts of fusion power. Furthermore, sufficiently low erosion of and fuel retention in PFMs are required to reach reactor relevant component duty cycles. The presently preferred solution to these challenges is to utilize tungsten PFMs with injection of extrinsic radiating impurities, such as nitrogen or neon. However, significant gaps do still exist in the technology and scientific understanding needed to fully rely that these devices will perform according to their design specifications. Predictive capability for these devices relies on model validation and physics interpretation studies conducted on existing fusion test reactors. In this doctoral thesis, radiative divertor studies with nitrogen and neon injection are investigated experimentally and interpreted with the multi-fluid code package EDGE2D-EIRENE for high confinement mode plasmas in the JET tokamak. The studies include comparison of predicted and measured divertor conditions, investigations of the impact of PFMs and divertor geometry on the divertor performance, and comparison of divertor performance with nitrogen and neon injection. Furthermore, predictions for tungsten retention in the divertor chamber with the Monte-Carlo code DIVIMP were conducted. When imposing the divertor radiation by impurities, the simulations capture the experimentally observed reduction of the low-field side (LFS) divertor peak heat load, radiated power, and their spatial distribution. However, consistent with earlier studies, the simulations underestimate the radiated power by deuterium, indicating a shortfall in the radiation from the fuel species. Due to similar radiative characteristics of nitrogen and carbon, the divertor radiation distributions observed in JET with carbon PFMs can be obtained with nitrogen seeding in JET with the ITER-like wall. Detachment is obtained at similar divertor radiation levels in both PFM configurations. Unexpectedly, divertor geometry is observed to have only a marginal impact on the reduction of the LFS heat load with increasing radiation. It is also observed that similar levels of LFS heat load reduction can be obtained at JET with either nitrogen or neon injection. However, unlike nitrogen radiation, a significant fraction of neon radiation is predicted to occur in the confined plasma, expected to reduce plasma performance. Furthermore, high density, low temperature divertor conditions are predicted to be beneficial for improving tungsten retention in the divertor of JET, and edge-localized modes (ELMs) are predicted to dominate tungsten erosion and leakage out of the divertor chamber in JET.
Translated title of the contributionRadiative divertor studies in JET high confinement mode plasmas
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Groth, Mathias, Supervising Professor
  • Groth, Mathias, Thesis Advisor
Publisher
Print ISBNs978-952-60-6475-8
Electronic ISBNs978-952-60-6476-5
Publication statusPublished - 2015
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • fusion
  • tokamak
  • impurities
  • power exhaust
  • divertor
  • radiation

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