Electron Bernstein Wave (EBW) current drive profiles and efficiency for STEP

Wilson, Thomas E.; Freethy, S. J.; Henderson, M.; Köhn-Seeman, Alf; Konoplev, Ivan; Saarelma, S.; Speirs, David; Vann, R. G. L.

doi:10.1051/epjconf/202327701011

Cited by 5 publications

(7 citation statements)

References 8 publications

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“…This makes EBCD a very promising avenue and would significantly lower the re-circulating power requirements for the reactor. Access to radii less than ρ tor ≃ 0.5 is limited primarily by a combination of Doppler broadening of the resonance and the non-monotonic B-field profile typical of the high-β ST reactor [8]. The radial restriction was approximately the same across the ST concepts we examined.…”

Section: Penetration and Current Drive Efficiencymentioning

confidence: 91%

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Microwave current drive for STEP and MAST Upgrade

Freethy

Figini²,

Henderson³

et al. 2023

EPJ Web Conf.

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The UK’s Spherical Tokamak for Energy Production (STEP) reactor design program has recently taken the decision to use exclusively microwave-based heating and current drive (HCD) actuators for its reactor concepts. This is based on a detailed assessment considering all viable HCD concepts, covering the grid to plasma efficiency, physics applications, technology maturity, integration, maintenance, and costs. Of the two microwave techniques: Electron Cyclotron (EC) and Electron Bernstein Wave (EBW), EC was deemed the lowest risk and EBW is retained as a potential path to a more efficient, higher performing device. To assess the ECCD efficiency, the GRAY beam tracing code was employed to perform detailed scans of the launcher position, toroidal and poloidal launch angle, and frequency over the first 3 cyclotron harmonics. For EBW, GENRAY/CQL3D were used to estimate the CD efficiency, demonstrating promising results. To reduce the physics uncertainties in present models for EBW coupling and current drive, MAST Upgrade will install two dual frequency (28, 34.8 GHz), 900kW, 5s gyrotrons from Kyoto Fusioneering, as part of the MAST Upgrade enhancements package. This will be accompanied by a flexible 2D steering launcher system to allow midplane coand counter-CD and above midplane launch for co-direction off-axis CD. Coupling efficiency is quantified by measuring the heating induced by reflected (i.e. non-coupled) power to a plate inserted in the reflected beam path. The experiments will also include EBW driven solenoid-free start-up, increasing power and pulse length by a factor of 10 compared to previous MAST experiments. This presentation will discuss the STEP microwave studies and the MAST Upgrade physics design and capabilities.

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Section: Penetration and Current Drive Efficiencymentioning

confidence: 91%

“…5 shows equilibria, density, temperature profiles for three of these. For more a more detailed account of the study, see [8].…”

Section: Penetration and Current Drive Efficiencymentioning

confidence: 99%

Microwave current drive for STEP and MAST Upgrade

Freethy

Figini²,

Henderson³

et al. 2023

EPJ Web Conf.

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“…Significant damping occurs for β ⩽ αβ th (where β th ≡ v th /c and α ≈ 3.5 [35]) due to a non-negligible resonant electron population. One then expects strong damping to occur when the following condition is satisfied [2]: In other words, Y − /Y and Y + /Y bound a Dopplerbroadened resonance domain, and strong damping is expected when the domain overlaps with an integer ℓ. The domain widens with increasing |N ∥ | and T e .…”

Section: Ray-tracing + Linear CD Simulationsmentioning

confidence: 99%

“…It is therefore important to understand where linear models break down. It is expected, based on numerical quasilinear calculations, that linear ECCD models are valid as long as 2Q e [MW m −3 ]/n 2 19 < 1 [38], where n 19 is electron density in 10 19 m −3 . Experiment on DIII-D suggests this is in fact a conservative limit [39].…”

Section: Power Threshold For Quasilinear Effectsmentioning

confidence: 99%

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Application of linear electron Bernstein current drive models in reactor-relevant spherical tokamaks

Biswas,

Speirs,

Freethy

et al. 2023

Nucl. Fusion

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Electron Bernstein current drive (EBCD) systems in spherical tokamaks are sensitive to plasma and launch conditions, and therefore require large parametric scans to optimise their design. One particular bottleneck in the simulation workflow is quasilinear modelling of current drive efficiency. Linear adjoint models are an attractive alternative, offering a ~1000x speed-up compared to quasilinear codes. While linear models are well-tested and commonly used for electron cyclotron current drive (ECCD), they have seen little use in EBCD modelling. In this work, variants of the linear model are applied to EBCD and compared to quasilinear results in a reactor-relevant plasma, i.e. Spherical Tokamak for Energy Production (STEP). This comparison reveals it is important to accurately model the collision operator and finite Larmor radius effects in the linear model. When done properly, good agreement is found with quasilinear calculations, at least for normalised minor radii $\rho < 0.7$ and at low power densities. The power density threshold for quasilinear effects during EBCD is found to be significantly lower than that of ECCD. This is attributed to the much lower group velocity of the electron Bernstein wave. Thus, the linear model is only valid for EBCD modeling at low power densities (e.g. $\lesssim 1 MW launched EBW power in STEP). This may be satisfied in present-day experimental devices, but certainly not in reactors targeting non-inductive operation.

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The optimisation of the STEP electron cyclotron current drive concept

Freethy,

Figini,

Craig

et al. 2024

Nucl. Fusion

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A fusion reactor based on the spherical tokamak is very likely to be completely non-inductive for the majority of the plasma ramp-up and steady-state phases, due to the limitations imposed on the central coil assemblies by the compact design. Efficiency gains from solenoid-driven current cannot be relied upon. It’s also critical that an electricity-producing plant maximises the wall-plug efficiency of its heating and current drive (HCD) system, this being one of the largest consumers of recirculating power. It is therefore essential that the HCD system is well-optimised for current drive efficiency in order to meet the goal of net electricity production. The UK’s Spherical Tokamak for Energy Production (STEP) reactor design program has recently taken the decision to use exclusively microwave-based heating and current drive actuators for its reactor concepts. We present the optimisation of an electron cyclotron current drive scheme for a spherical tokamak reactor, based around the STEP concept, arriving at a solution which overcomes the limitations imposed by the spherical tokamak geometry in terms of microwave access and high trapped particle fraction. The solution is modified to account for the changing conditions during the non-inductive plasma ramp.

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Electron Bernstein Wave (EBW) current drive profiles and efficiency for STEP

Cited by 5 publications

References 8 publications

Microwave current drive for STEP and MAST Upgrade

Microwave current drive for STEP and MAST Upgrade

Application of linear electron Bernstein current drive models in reactor-relevant spherical tokamaks

The optimisation of the STEP electron cyclotron current drive concept

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