Neoclassical Tearing Mode (NTM)

Tearing mode formation induced by internal crash events at differentβN

“…(6) In our example, for otherwise similar plasma conditions, the higher perturbation amplitude led to the faster conversion time. (7) The perturbation amplitude required to seed a tearing modes at high N β is much lower compared to the low N β case. (This was to be expected as high-beta plasmas are more unstable with respect to both ideal modes and tearing modes.…”

“…The driving force due to the bootstrap current is only important for the further island evolution. In low-beta plasmas, where the neoclassical drive is not important, the seeded tearing modes decay, indicating a negative ∆′ in the Rutherford equation [7].…”

“…For example, a large sawtooth crash produces fast relaxations of the core plasma density and temperature, and provides this forced drive at the neighbouring resonant surfaces where a tearing mode is created [2,3]. The neoclassical tearing mode is metastable and can be triggered by other MHD events via the forced magnetic reconnection at much lower N β values compared to the onset value where the seed island grows from noise [4][5][6][7]. (…”

“…When the mode has grown to a critical island width, the pressure profile becomes flat within the island and the neoclassical drive takes over. Small islands are not able to provide significant pressure flattening and might be driven by other mechanisms [7,8]. In this paper, only the mechanisms of the seed island formation by drives due to MHD events in the plasma are investigated in detail.…”