Resonant Excitation of Shear Alfv\'en Perturbations by Trapped Energetic Ions in a Tokamak

A new analytic expression is derived for the resonant drive of high n Alfvenic modes by particles accelerated to high energy by Ion Cyclotron Resonance Heating. This derivation includes finite orbit effects, and the formalism is completely non-perturbative. The high-n limit is used to calculate the complex particle response integrals along the orbits explicitly. This new theory is applied to downward sweeping Alfven Cascade quasimodes completing the theory of these modes, and making testable predictions. These predictions are found to be consistent with experiments carried out on the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)].Comment: 31 pages, 6 figure

Fusion Technology Activities at JET in Support of the ITER Program

AbstrAct Among the technological activities performed at JET in support of the scientific objectives of both JET and ITER, a significant effort is devoted to the investigation of the erosion, transport and deposition of wall materials, and of their fuel retention properties. With the analysis of wall tiles retrieved in the 2010 shutdown, the full characterization of the previous JET carbon wall is obtained. In order to confirm the expectations on properties of the new ITER-Like Wall (ILW) installed in 2011, a large number of marker tiles and profiled tiles have been prepared and installed both in the main wall and in the divertor. These will be retrieved from the vessel during a short shutdown at the end of 2012 and analysed. The major changes introduced by the new ILW materials in JET required also a new nuclear characterization of the machine. Neutronics measurements have been performed to obtain the neutron/g-ray field changes inside and outside the JET machine. The experimental data are also used to validate neutronics codes used in ITER design. A new calibration of neutron detectors, scheduled in the 2012 shutdown and adopting the same procedure as in ITER, has been prepared based on extensive neutronics calculations. IntroductIon The JET research program includes technological activities in support of the scientific objectives of both JET and ITER. To this purpose, in 2010-11 the JET machine has undergone a major change to replace the previous carbon wall with a new ITER-Like Wall (ILW) making use of beryllium and tungsten in plasma facing components The erosion/deposition of wall materials in JET is characterized by net erosion on the main chamber wall and outer divertor, and migration of eroded material mainly to the inner divertor. During the 2009-10 shutdown phase, dust was collected from JET vessel [2] and several removed tiles were selected for analysis of deposits and surface. In this paper, first results of analyses on tiles exposed in 2007-2009 are presented. Considering also all previous results of erosion and deposition studies, a full characterization of the C wall in JET will be derived for comparison with the new ILW. Presently, one of the major objectives of the JET program is the investigation of the wall material transport, erosion/deposition and the fuel retention properties in the ILW. It is expected from laboratory experiments that the main mechanism for the fuel retention in the ILW is co-deposition in Be-layers. Implantation is the main mechanism for the retention in W, but it is expected to play a negligible role in comparison with the Be co-deposition. In order to confirm these expectations, and the results obtained during first ILW plasmas from gas balance method The major changes introduced by the new ILW materials in JET required also a new nuclear characterization of the machine. Neutronics analyses have been performed to calculate the neutron/gray field changes inside and outside the machine, the material activation and the shutdown doserat

The effect of ionization on the populations of excited levels of C IV and C V in tokamak edge plasmas

The main populating and depopulating mechanisms of the excited energy levels of ions in plasmas with densities <1023-1024 m-3 are electron collisional excitation from the ion's ground state and radiative decay, respectively, with the majority of the electron population being in the ground state of the ionization stage. Electron collisional ionization is predominately expected to take place from one ground state to that of the next higher ionization stage. However, the question arises as to whether, in some cases, ionization can also affect the excited level populations. This would apply particularly to those cases involving transient events such as impurity influxes in a laboratory plasma. An analysis of the importance of ionization in populating the excited levels of ions in plasmas typical of those found in the edge of tokamaks is undertaken for the C IV and C V ionization stages. The emphasis is on those energy levels giving rise to transitions of most use for diagnostic purposes. Carbon is chosen since it is an important contaminant of JET plasmas; it was the dominant low Z impurity before the installation of the ITER-like wall and is still present in the plasma after its installation. Direct electron collisional ionization both from and to excited levels is considered. Distorted-wave Flexible Atomic Code calculations are performed to generate the required ionization cross sections, due to a lack of atomic data in the literature.Comment: 29 pages, 5 figures. This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics B. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i