Controllers for high-performance nuclear fusion plasmas

A succesful nuclear fusion reactor will confine plasma at hig temperatures and densities, with low thermal losses. The workhorse of the nuclear fusion community is the tokamak, a toroidal device in which plasmas are confined by poloidal and toroidal magnetic fields. Ideally, the confirming magnetic fields form a set of nested tori. A repetive magnetohydrodynamic (MHD) event in the plasma core (the sawteeth instability) perturbs the confirming magnetic field by producing seed islands. In low-pressure plasmas the seed islands will self-heal. In high-pressure plasmas the seed islands can grow and saturate. These neoclassical tearing models (NTMs) reduce the plasma performance or lead to plasma disruption. This sets the resistive pressure limit in tokamaks. High-performance operation in tokamaks therefore implies the control or amelioration of the NTMs. Controllers for the sawteeth and the NTMs will be discussed, with special emphasis on the development of dedicated sensors and models for MHD control

Electron transport barriers in tokamak plasmas

+139hlm.;23c

The construction of knowledge-based economies versus knowledge societies: The cases of Germany and Singapore

In the past decades, terms such as knowledge-based economy (KBE)\u27, and \u27information/knowledge society\u27 have been adopted by governments worldwide in order to underline their interest in developing their economies and societies further and assure future growth. Many governments used these catchwords as labels for government programs and action plans aiming at economic and social prosperity. This aim of national governments to construct knowledge-based economies, information/knowledge societies, the actions taken and especially the ability or disability to do so, is the topic of this paper. As two cases of comparison act Singapore and Germany. (DIPF/Orig.

Determination of localized heat transport in fusion plasmas

Abstract only

Experimental stabilisation of 2D vortex patterns using time-dependent forcing

Experimental results of the effect of time-periodic and "chirped" (electro-magnetic) forcing on vortex patterns in shallow-water-layer flows are presented. Analogously to vibrational control, the use of a time-periodic forcing results in stabilisation of otherwise unstable vortex patterns. Chirped frequency forcing yields self-organising patterns that are different from those in stationary and periodically forced experiments. The results are shown to be consistent with theoretical analysis of 2D Taylor-Green vortices, i.e. unstable analytical solutions of the 2D Navier-Stokes equation. These results imply that, compared to the more often analysed stationary forced flows, time-varying forcing can stabilise different vortex patterns in shallow-water-layer flows

Feedback control using divertor multi-spectral imaging diagnostics

The heat and particle exhaust in tokamaks is guided to a dedicated region called the divertor. Unmitigated, the expected power fluxes impacting the divertor targets during reactor relevant operation exceed present-day engineering limits [1]. Real-time feedback control of plasma detachment, aregime characterized by a large reduction in plasma temperature and pressure at the divertor target,is required to maintain a sufficient reduction of these fluxes [2, 3]. During plasma detachment atemperature gradient along the divertor leg is established. This gradient gives rise to a sharp opticalemission fall-off, frequently referred to as a front. These fronts are indicative of a local electron temperature, and their location can be used as a measure of detachment strength. A real-time algorithmfor detection of these radiation fronts using multi-spectral imaging was recently developed [4], andexperimentally demonstrated [5] on the Tokamak à Configuration Variable (TCV) [6] utilizing themulti-spectral imaging diagnostic MANTIS [7].In this talk, we will show the state-of-the art and further development of using MANTIS for feedback control of the divertor plasma. Including: 1) feedback-control of the C-III emission front usingdeuterium fueling and the N-II emission front using nitrogen seeding, and 2) the use of system identification techniques to obtain control-oriented models for offline controller design. We conclude withour view towards multi-input, multi-output (MIMO) control of the divertor plasma using MANTIS,fully exploiting its 10 available cameras. Specifically, combining multiple spectrally filtered imagesto obtain real-time information on the loss processes driving detachment.References[1] R. Pitts et al., Nucl. Mat. Ener. 20, 100696 (2019)[2] B. Lipschultz et al., Nuclear Fusion 56, 056007 (2016)[3] A. Leonard, Plasma Phys. Control. Fusion 60, 044001 (2018)[4] T. Ravensbergen et al., Nucl. Fusion 60, 066017 (2020)[5] T. Ravensbergen et al., Nat. Commun. 12, 1105 (2021)[6] S. Coda et al., Nucl. Fusion 59, 112023 (2019)[7] A. Perek et al., Rev. Sci. Instrum. 90, 123514 (2019)<br/

Sawtooth period pacing and locking by EC power control on TCV

Abstract #TP9.127 submitted for the DPP11 Meeting of The American Physical Society

Kalman filter density reconstruction in ICRH discharges on ASDEX Upgrade

Plasma density is one of the key quantities that need to be controlled in real-time as it scales directly with fusion power and, if left uncontrolled, density limits can be reached leading to a disruption. On ASDEX Upgrade (AUG), the real-time measurements are the line-integrated density, measured by the interferometers, and the average density derived from the bremsstrahlung measured by spectroscopy. For control, these measurements are used to reconstruct the radial density profile using an extended Kalman filter (EKF). However, in discharges where ion cyclotron resonance heating (ICRH) is used, the measurements from the interferometers are corrupted and the reconstructed density is false. In this paper, the existing EKF implementation is improved, implemented and experimentally verified on AUG. The new EKF includes a new particle transport model in the prediction model RAPDENS as well as a new representation of ionization and recombination. Furthermore, an algorithm was introduced that is capable of detecting the corrupt diagnostics; this algorithm is based on the rate of change of the innovation residual. The changes to the RAPDENS observer resulted in better density reconstruction in ICRH discharges where corrupt measurement occur. The new version has been implemented on the real-time control system at AUG and functions properly in ICRH discharges.</p

Mathematical equivalence of non-local transport models and broadened deposition profiles

Old and recent experiments show that there is a direct response to the heating power of transport observed in modulated electron cyclotron heating (ECH) experiments both in tokamaks and stellarators, which is commonly known as non-local transport. This is most apparent for modulated experiments in stellarators such as LHD and W7-AS. We show that this power dependence and its corresponding experimental observations such as the so-called hysteresis in flux [Inagaki, NF, 113006, 2013] can be reproduced by broadened ECH deposition profiles. In other words, many mathematical models proposed to describe non-local transport are equivalent to an deposition (effective) profile in its linearized forms [vanBerkel, NF, 106042, 2018]. This also connects with new insights on microwave scattering due to density fluctuations in the edge plasma which shows that in reality the deposition profiles are much broader than expected [Chellai, PRL, 105001, 2018] but it is unclear if this effect is sufficient to explain non-local transport. These relationships can be further studied by separating the transport in a slow (diffusive) and a fast (heating/non-local) time-scale using perturbative experiments