### Abstract

A detailed Monte Carlo-based numerical analysis of ASDEX
Upgrade discharges is presented, examining the
applicability of neutral particle analysers (NPAs) for
measuring the central ion temperature from the neutral
particle spectra above the neutral beam injection energy.
The analysis is motivated by an earlier work carried out
for TFTR (Fiore C L et al 1988 Nucl. Fusion 28 1315),
where the beams were quite tangential. This work is now
extended to investigate the applicability of the method
when the beams are perpendicular. The Monte Carlo
simulations take fully into account the effects due to
finite orbits and realistic magnetic geometry, and reveal
that the fast ion distribution above the beam energy,
generated by collisions, reflects the background
temperature with good accuracy. However, it is found that
the use of NPA tends to give temperature values that are
up to 30% lower than the on-axis temperature Ti(0)
assumed for the background. This is because the neutral
fluxes measured by NPA originate from a wide radial
region, and thus the measured spectrum is a
chord-averaged one. A fairly tangential viewing is found
to be optimal because in that case the signal originating
from the centre of the plasma is enhanced relative to the
signal from outer radii. It is concluded that, in
discharges where the slowing down from electrons does not
dominate the beam ion dynamics, NPA can give a reliable
estimate of an average central temperature, Ti( =
0,...,0.3).

Original language | English |
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Pages (from-to) | 475-491 |

Journal | Plasma Physics and Controlled Fusion |

Volume | 44 |

Issue number | 5 |

DOIs | |

Publication status | Published - 2002 |

MoE publication type | A1 Journal article-refereed |

### Keywords

- Monte Carlo
- Monte Carlo simulation
- plasma
- fusion energy

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## Cite this

Kurki-Suonio, T., Sipilä, S., Heikkinen, J., Fahrbach, H-U., Khudoleev, A., & Team, ASDEX. U. (2002). Monte Carlo simulations of central ion temperature measurements using neutral particle analysers.

*Plasma Physics and Controlled Fusion*,*44*(5), 475-491. https://doi.org/10.1088/0741-3335/44/5/302