arXiv subjects

C. Nührenberg

Publications and source records attributed to C. Nührenberg.

3 recordsLinked to original sources

arXiv2023

Critical gradient turbulence optimization toward a compact stellarator reactor concept

Integrating turbulence into stellarator optimization is shown by targeting the onset for the ion-temperature-gradient mode, highlighting effects of parallel connection length, local magnetic shear, and flux surface expansion. The result is a compact quasihelically symmetric stellarator configuration, admitting a set of uncomplicated coils, with significantly reduced turbulent heat fluxes compared to a known stellarator. The new configuration combines low values of neoclassical transport, good alpha particle confinement, and Mercier stability at a plasma beta of almost 2$\%$.

physics.plasm-ph↗

arXiv2023

Enhanced transport at high plasma pressure and sub-threshold kinetic ballooning modes in Wendelstein 7-X

High-performance fusion plasmas, requiring high pressure $β$, are not well-understood in stellarator-type experiments. Here, the effect of $β$ on ion-temperature-gradient-driven (ITG) turbulence is studied in Wendelstein 7-X (W7-X), showing that subdominant kinetic ballooning modes (KBMs) are unstable well below the ideal MHD threshold and get strongly excited in the turbulence. By zonal-flow erosion, these sub-threshold KBMs (stKBMs) affect ITG saturation and enable higher heat fluxes. Controlling stKBMs will be essential to allow W7-X and future stellarators to achieve maximum performance.

physics.plasm-ph↗

arXiv2018

Properties of a new quasi-axisymmetric configuration

A novel, compact, quasi-axisymmetric configuration is presented which exhibits low fast-particle losses and is stable to ideal MHD instabilities. The design has fast-particle loss rates below 8\% for flux surfaces within the half-radius, and is shown to have an MHD-stability limit of a normalised pressure of $\langleβ\rangle=3\%$ where $\langleβ\rangle$ is volume averaged. The flux surfaces at various plasma betas and currents as calculated using the SPEC equilibrium code are presented. Neoclassical transport coefficients are shown to be similar to an equivalent tokamak, with a distinct banana regime at half-radius. An initial coil design study is presented to assess the feasibility of this configuration as a fusion-relevant experiment.

physics.plasm-ph↗