Impurity re-distribution in the corner regions of the JET divertor

Abstract

The International Thermonuclear Experimental Reactor (ITER) will use a mixture of deuterium (D) and tritium (T) as the fuel to generate power. Since T is both radioactive and expensive the Joint European Torus (JET) has been at the forefront of research to discover how much T is used and where it may be retained within the main reaction chamber. Until the year 2010 the JET plasma facing components were constructed of carbon fibre composites (CFC). During the JET carbon (C) phases impurities accumulated at the corners of the divertor located towards the bottom of the chamber in regions shadowed from the plasma where they are very difficult to reach and remove. This build-up of C and the associated H-isotope (including T) retention were of particular concern for future fusion reactors therefore, in 2010 JET changed the wall protection to (mainly) Be and the divertor to tungsten (W)-the JET ITER-like Wall (ILW)-the choice of materials for ITER. This paper reveals that with the JET ILW impurities are still accumulating in the shadowed regions, with Be being the majority element, though the overall quantities are very much reduced from those in the C phases. The strike points for corner discharges are the principle source of the material transporting into the shadowed regions, but particles typically have about a 75% probability of reflection from lineof sight surfaces, and multiple reflection/scattering results in deposition over all surfaces.

Ion beam analysis of fusion plasma-facing materials and components: facilities and research challenges

“…Specifically designed diagnostics aiming at providing time resolved erosion/deposition patterns [5,152], gross deposition and sticking coefficients [82] of deposited material have been deployed in fusion devices. Such diagnostics are typically installed in locations remote from the plasma, thus providing data on long range material migration to remote regions [83].…”

Fuel retention and erosion-deposition on inner wall cladding tiles in JET-ILW

“…Three experimental campaigns with deuterium (D) fueling were completed in JET-ILW: 2011-2012 (ILW-1), 2013-2014 (ILW-2) and 2015-2016 (ILW-3). Gas balance measurements [2,3] and a range of ex situ analyses have been performed over the years to quantify the content and depth distribution of hydrogen isotopes in all types of PFC [4,5], in remote areas of the divertor [6] and also in dust [7]. An overall objective has been to obtain a detailed erosion-deposition pattern: plasma-induced modification of wall materials and composition of codeposited layers.…”