The onset distribution of rotating m,n=2,1 tearing modes and its consequences on the stability of high-confinement-mode plasmas in DIII-D
Abstract Analysis of a multi-scenario database of over 13 000 DIII-D H-mode discharges shows that the magnetic islands are dominantly pressure gradient driven, stochastically triggered non-linear instabilities at all edge safety factor ( ) values. The instability onset time closely follows the exponential distribution in intermediate and high scenarios and is characterized by near constant onset rate ( λ ), in accordance with Poisson-point processes. This implies that the plasmas are operated in marginally stable conditions, characterized by a small threshold for instability growth and variations in the trigger amplitude and/or the stabilizing mechanisms with temporally uniform random distribution in this database. While the majority of the tearing modes occur in the first current-profile relaxation time of the flattop, constant λ throughout the flattop shows that the tearing onset is insensitive to the evolution of the equilibrium current profile. In low scenarios, where a large fraction of the plasmas are operated at low torque, λ increases over the course of the flattop, showing that these plasmas evolve toward more unstable conditions. The onset rate rapidly increases with , while it does not show a clear dependence on the current gradient at the mode rational surface. Overall, these observations support that the majority of the analyzed 2,1 tearing modes are non-linear, neoclassically driven instabilities and classical stability does not play a dominant role in their onset.
- Research Organization:
- General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
- Grant/Contract Number:
- AC52-07NA27344; FC02-04ER54698
- OSTI ID:
- 2204433
- Alternate ID(s):
- OSTI ID: 2202878; OSTI ID: 2203187
- Report Number(s):
- DOE-GA-54698
- Journal Information:
- Nuclear Fusion, Journal Name: Nuclear Fusion Vol. 63 Journal Issue: 12; ISSN 0029-5515
- Publisher:
- IOP PublishingCopyright Statement
- Country of Publication:
- IAEA
- Language:
- English
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