Investigation of first mirror heating for the collective Thomson scattering diagnostic in ITER

Abstract

Collective Thomson scattering (CTS) has the capabilities to measure phase space densities of fast ion populations in ITER resolved in configuration space, in velocity space, and in time. In the CTS system proposed for ITER, probing radiation at 60 GHz generated by two 1 MW gyrotrons is scattered in the plasma and collected by arrays of receivers. The transmission lines from the gyrotrons to the plasma and from the plasma to the receivers contain several quasioptical mirrors among other components. These are designed to produce astigmatic beam patterns in the plasma where the beam shapes will have a direct impact on the signal strength of the diagnostic, the spatial resolution, and the robustness of probe and receiver beam overlap against density excursions. The first mirror has a line of sight to the plasma and is thus exposed to severe neutron streaming. The present neutronics and thermomechanical modeling of a first mirror on the high field side indicates that the mirror curvature may warp due to heating. This may alter the beam quality, and therefore, thermal effects have to be accounted for during the design of the mirror. The modeling further demonstrates that thin mirrors are superior to thick mirrors from a thermomechanical point of view.

High-definition velocity-space tomography of fast-ion dynamics

“…Hence this alternative approach to tomographic reconstruction should be highly useful for FIDA systems with few viewing directions as is common on many machines. Further, the approach should also work for many combinations of fast ion diagnostics installed on many machines [23,29,31], for example based on FIDA and CTS at LHD [54,55], CTS, FIDA, NPA, NES, and GRS at ASDEX Upgrade [5,7,11,[56][57][58][59][60][61][62], NES, GRS and NPA at JET [14,15,63], CTS, GRS, NES, NPA and possibly fast-ion chargeexchange recombination spectroscopy at ITER [64][65][66][67][68][69]. We will demonstrate this method for the two-view FIDA case using experimental data in the next section.…”

Combination of fast-ion diagnostics in velocity-space tomographies

“…Our joint tomography method could also combine the fast-ion charge exchange spectroscopy (FICXS) (that detects light other than D α but is otherwise similar to FIDA) and the CTS diagnostics at the Large Helical Device (LHD) [49,50]. Moreover, joint tomographic inversions could be directly relevant to ITER where the proposed FICXS [51] and the CTS system [52][53][54][55] could be combined even if there is only one CTS view. Measurements from any other fast-ion diagnostic could be included in our joint tomography prescription, if quantitative weight functions describing the measurements such as those for CTS [34] or FIDA [20,56] can be formulated.…”

Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements

“…With our prescription we can compute tomographies for any set of fastion measurements, in particular those obtained with CTS or FIDA or other fast-ion charge exchange spectroscopy (FICXS) that detects other light than D α . A mix of diagnostics would also be possible as will be relevant to the CTS/FIDA system at ASDEX Upgrade, the CTS/FICXS system at LHD [35,36] and the proposed two-view CTS system for ITER [37][38][39][40] in particular if it can be combined with FICXS [32]. However, only one of the two CTS views is an enabled ITER diagnostic.…”