Development of synthetic diagnostics for ITER First Plasma operation

Abstract

ITER First Plasma (FP) operation aims to produce a plasma with current higher than 100 kA for a duration longer than 100 ms. However, the low values of plasma density and temperature associated with the initiation phase make it difficult to diagnose the plasma accurately. It is therefore essential to develop models for the available diagnostics for ITER FP operation in order to determine the necessary measurement ranges for plasma initiation and use them as inputs for controller development and assessment within the plasma control system (PCS). The use of accurate diagnostic models also helps to optimally prepare for, and analyse, ITER FP operation. A model developed for the H α main chamber visible spectroscopy for FP shows that it is possible to measure H α emission soon after breakdown for plasma temperatures higher than 3 eV and average plasma densities higher than 10 17 m −3 . The diagnostic model for the interferometer shows that for the proposed ITER FP scenarios, accurate measurements are possible for average plasma densities higher than 5 × 10 17 m −3 . The results from modelling of the hard x-ray monitor demonstrate that it can provide signals useful for runaway electron detection and can measure current levels typically down to 3 kA. Thus, these measurements can thus be used effectively by the PCS for runaway electron (RE) detection during FP operation. Improved diagnosis of the plasma state deducing, for example, parameters such as the plasma size and position, is possible by combining the measurements from the different FP diagnostics (density interferometer polarimeter and H α main chamber visible spectroscopy), which will be available for ITER FP operation.

ITER plasma control system final design and preparation for first plasma

“…Due to the limited plasma duration (<3 s) and the gas line delays, density control in the FP phase can only be achieved with feedforward control (figure 3). The peak FP electron density is expected to reach up to 2.5 × 10 18 m −3 [9], which is above the minimum line average density that can be measured by the density interferometer polarimeter of 7.5 × 10 17 m −3 [10].…”

“…Large currents, of order 1.5 MA, will be induced in the highly conductive VV during plasma initiation [9]. Simulations indicate that I p can be measured down to a level of 10-50 kA [10], though methods to take into account the impact of the vessel current contribution are still being developed.…”

Cross-machine comparison of runaway electron generation during tokamak start-up for extrapolation to ITER

“…basically setting V L = 0 for long enough such that the RE can dissipate). At ITER accurate detection of RE and I RE will be available from the start of ITER plasma operation (ITER First Plasma), with such nominal control and exceptions put in place to prevent and avoid start-up RE formation [63,64].…”

From Physics To Project Management: A Multi-Domain Matrix Model For The Distributed Analysis Of Nuclear Fusion Systems

“…Secondly, the XDSM is intended for mathematical models. Although developing such models is an ongoing effort in nuclear fusion (Sinha et al, 2021), detailed simulations of first-of-a-kind systems are generally less available. Highly multidisciplinary systems are often analyzed by a combination of numerical models and hardware tests (Braspenning et al, 2008).…”