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Abstract. On the way to a comprehensive understanding of the properties of a burning plasma the physics of super-thermal particles due to external heating and fusion reactions plays a key role. Especially Alfvén and Alfvén-acoustic type instabilities are predicted to strongly interact with the fast particle population and to contribute critically to the radial redistribution of the energetic ions. This paper focuses on the comparison of the kinetic dispersion relation for BAEs/GAMs [1] with numerical results obtained by the gyrokinetic eigenvalue code LIGKA [2] and experimental findings at ASDEX Upgrade. It is shown that thermal ions with a finite perpendicular energy (circulating and trapped) modify the dispersion relation significantly for low frequencies. The resulting frequency down-shift together with shaping and diamagnetic effects is crucial to explain the mode frequency as measured at ASDEX Upgrade stressing the importance of a kinetic description for frequencies comparable to the thermal ion transit frequency. In the second part the BAE frequency behaviour during a sawtooth-cycle is investigated and the possibility of an accurate q-profile determination via kinetic Alfvén spectroscopy is discussed.

LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above $${1.4 \times 10^{-48}}\, {\hbox {cm}}^{2}$$ 1.4 × 10 - 48 cm 2 for a WIMP mass of $${40}\, \hbox {GeV}/{\hbox {c}}^{2}$$ 40 GeV / c 2 and a $${1000}\, \hbox {days}$$ 1000 days exposure. LZ achieves this sensitivity through a combination of a large $${5.6}\, \hbox {t}$$ 5.6 t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.

Abstract.The confinement of fast particles, present in tokamak plasmas as nuclear fusion products and through external heating, will be essential for any future reactor. Fast particles can be expelled from the plasma through their interaction with Alfvén eigenmode (AE) instabilities. AEs can exist in gaps in the Alfvén continuum created by plasma equilibrium non-uniformities. In ASDEX Upgrade low frequency modes in the Alfvén-acoustic frequency regime, including betainduced Alfvén eigenmodes (BAEs) and lower frequency modes with mixed Alfvén and acoustic polarizations, have been observed. They exist in gaps in the Alfvén continuum opened up by geodesic curvature and finite plasma compressibility. In this paper a kinetic dispersion relation (Lauber Ph et al 2009 Plasma Phys. Control. Fusion 51 124009) is solved numerically to investigate the influence of diamagnetic effects on the evolution of these low frequency modes during the sawtooth cycle. Other distinct but potentially related modes which sweep significantly upwards in frequency towards the end of the sawtooth cycle are also considered. Using information gained from soft x-ray measurements (Igochine V et al 2010 IPP Report 1/338) and electron temperature information from electron cyclotron emission to constrain the safety factor profiles, realistic equilibrium reconstructions for the analysis are obtained using the CLISTE code (Mc Carthy P J 2012 Plasma Phys. Control. Fusion 54 015010). The results for the mode frequency evolution are then compared with experimental results from ASDEX Upgrade.

Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in confinement and pedestal behaviour before and after the ITER-like wall installation have been better characterized towards the development of high fusion yield scenarios in DT. Post-mortem analyses of the plasma-facing components have confirmed the previously reported low fuel retention obtained by gas balance and shown that the pattern of deposition within the divertor has changed significantly with respect to the JET carbon wall campaigns due to the absence of thermally activated chemical erosion of beryllium in contrast to carbon. Transport to remote areas is almost absent and two orders of magnitude less material is found in the divertor.