Speaker
Description
ITER will be among the first experiments with extensive number of fusion-born alpha particles. The research plan of ITER includes studying this burning plasma physics domain. However, to learn from these experiments, a necessary requirement is to be able to measure these fusion-born alphas. To this end, ITER is limited to measure confined distributions using gamma-ray spectroscopy and collective Thomson scattering. For the lost alphas, the only measurement capable of producing relevant physics input will be scintillator-based fast-ion loss detector (FILD). Within this contribution, we overview the numerical modeling efforts using the ASCOT orbit-following code towards the design of the FILD diagnostic for ITER.
The design of the ITER FILD diagnostic has been strongly supported by a modeling effort to understand the expected signal levels, to estimate the signal to noise ratio, to optimize the poloidal location for the FILD within the vacuum vessel, and to confirm that relevant physics phenomena can be measured using the design without compromising the integrity of the diagnostic. The ASCOT code has been selected as the main tool for the modeling with its capability to track the most important transport processes. In particular, the ASCOT model enables usage of the full 3D geometry of both the magnetic field and the first wall. The FILD is modeled as part of the 3D wall mesh, allowing to post-process the fast-ions that would intersect with the FILD probe head. An interface from ASCOT model to FILDSIM has been built to model the synthetic images at the scintillator plate, including all instrument effects from the alphas entering the pinhole to images being recorded with the fast-cameras or signals been recorded using photomultiplier tubes.
Within this contribution we will concentrate on the modeling of 15 MA baseline H-mode. The inputs include 3D perturbations due to TF ripple, ferritic inserts, TBMs, and the effect of ELM control coils including the plasma response. However, MHD quiescent conditions are assumed except for including a neoclassical tearing mode in some simulations. Both alpha particles and neutral beam ions have been simulated with ASCOT. The main results of the work are the following. An optimal location in the first wall was found by studying the velocity space coverage. Radial scans, using this poloidal location, has been carried out to study the signal levels with different insertion depth. This allows to compromise the signal level against the thermal load. The essential role of plasma response calculations has been acknowledged. The lost alpha particles will produce signal higher than the background noise at acceptable thermal load. The fingerprints of alpha particles and neutral beam ions on the scintillator plate are partly overlapping, but the tomographic reconstructions should allow the separation of the signals. When NTMs are present, the signal can be measured from deeper in the plasma. The next steps of the work foresee inclusion of Alfven Eigenmodes in the ASCOT model, updating the scenario to be aligned with the new rebaseline with full tungsten first wall.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
| Presentation type | Oral |
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