Dynamic outgassing of deuterium, helium and nitrogen from plasma-facing materials under DEMO relevant conditions. (1st November 2016)

• Record Type: Journal Article
• Authors: Möller, S.; Matveev, D.; Martynova, Y.; Unterberg, B.; Rasinski, M.; Wegener, T.; Kreter, A.; Linsmeier, Ch.
• Is Part Of: Nuclear fusion. Volume 57:Number 1(2017:Jan.)
• Publication Date: 2016-11-01
• Subjects: hydrogen retention -- tungsten -- plasma-surface-interaction -- dynamic inventory -- outgassing -- PSI-2 -- DEMO; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/57/1/016020
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: In confined plasma magnetic fusion devices significant amounts of the hydrogen isotopes used for the fusion reaction can be stored in the plasma-facing materials by implantation. The desorption of this retained hydrogen was seen to follow a t α law with α ≈ −0.7 in tokamaks. For a pulsed fusion reactor this outgassing can define the inter-pulse waiting time. This work presents new experimental data on the dynamic outgassing in ITER grade tungsten exposed under the well-defined conditions of PSI-2 to pure and mixed D2 plasmas. A peak ion flux of 10 22 D + m −2 s is applied for up to 6 h at sample temperatures of up to 900 K. Pure D2 and mixed D2 + He, D2 + N2 and D2 + He + N2 plasmas are applied to the sample at 68 V bias. The D2, He, N outgassing at 293 K and 580 k are observed via in-vacuo quadrupole mass spectrometry covering the range of 40 s–200 000 s after exposure. The outgassing decay follows a single power law with exponents α = −0.7 to −1.1 at 293 K, but at 580 K a drop from α = −0.25 to −2.35 is found. For DEMO a pump-down time to 0.5 mPa in the order of 1–5 h can be expected. The outgassing is in all cases dominated by D2 .