Fuel inventory and material migration of JET main chamber plasma facing components compared over three operational periods

Abstract

Fuel retention and material migration results from JET ITER-like wall beryllium limiter tiles are presented for three operating periods. Ion beam analysis results support the general picture of erosion during limiter configurations with local deposition on tile ends far into the scrape off layer. Similar trends of fuel concentrations are observed in all JET operating periods; (i) low on surfaces exposed to high heat flux and erosion and (ii) higher in deposits. The pattern of fuel retention and deposition correlates with heat flux and distribution of limiter plasmas touching inner and outer limiters. The D/Be ratio in the thickest deposit is ~0.01. Global fuel retention attributed to limiters is < 0.01% of injected fuel. Marker coatings reveal a rapid transition from strong erosion to deposition within 15 mm. This work highlights the need to carefully consider the requirements of marker coatings for long exposure studies in high erosion areas.

Evaluation of tritium retention in plasma facing components during JET tritium operations

“…The global retention value has been calculated using the divertor data presented in figure 1(a) with additional data from main chamber beryllium (Be) limiter tiles [4], Be coated inconel (Be-inconel) recessed Inner Wall Cladding tiles (IWC) [16], Tungsten coated Carbon Fibre Composite (W-CFC) recessed inner limiter tiles, passive diagnostics from the outer recessed wall of the vacuum vessel [17] and remote divertor regions [17,18]. Data for these analyses include IBA techniques from VR, Sweden and University of Helsinki, Finland with facilities described in [11].…”

“…Since 2011, when JET started operating with the all metal ITER-Like Wall (JET-ILW) [3], plasma facing components have been periodically removed from the JET vessel for analysis in a laboratory setting, i.e., ex situ analysis. The components are exposed to a varied experimental campaign with ∼20 h of plasma operations [4], consisting in the order of 3000 JET pulses with ∼20 s discharge time per pulse over a 12-18 month period. The results from these components have provided data on ex situ long term fuel retention, experimental evidence for the material migration processes in JET, demonstrated the reduction in fuel retention, erosion and deposition for JET-ILW in line with JET experiments [5,6] and provided benchmarking data for modelling [7,8].…”

Tritium distribution analysis of Be limiter tiles from JET-ITER like wall campaigns using imaging plate technique and β-ray induced X-ray spectrometry

“…The Joint European Torus (JET) has been operated since year 2011 with the ITER-like wall (ILW): beryllium (Be) limiter tiles in the main chamber and bulk tungsten (W) and tungsten-coated carbonfiber composite (W-CFC) tiles in the divertor. The JET-ILW discharges were mainly fueled by deuterium (D) in three consecutive campaigns performed in 2011-2012 (ILW-1), 2013-2014 (ILW-2) and 2015-2016 (ILW-3) [1,2].…”

“…Understanding of fuel retention mechanisms in a fusion device with Be and W walls is important for safety assessment in future fusion devices including ITER. From this viewpoint, distribution of D has been examined through post-mortem analyses of retrieved tiles using various techniques including ion beam analysis (IBA) [2][3][4], secondary ion mass spectroscopy (SIMS) [5] and thermal desorption spectrometry (TDS) [4,6]. These measurements showed that fuel retention with ILW was far smaller than that with carbon wall [7], and the main retention mechanism was co-deposition with Be and other impurities.…”

Application of Ion Beam Analysis in Studies of First Wall Materials in Controlled Fusion Devices

“…These are regions outside the direct plasma line-of-sight, for instance shadowed areas in the inner and outer divertor. Very detailed D analyses performed on material retrieved from JET-ILW, both PFC and wall probes from shadowed regions in the divertor, have consistently shown the decrease of retention by a factor of 10-15 in comparison to the situation in JET-C [50][51][52][53][54][55][56][57][58]. As well as this, the co-deposit thickness was decreased when the direct carbon source on PFC was eliminated.…”