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RISS 인기검색어
- 검색키워드
- 저자 : Bierwage, Andreas (검색결과 3 건)
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Shinohara, Kouji,Bierwage, Andreas,Suzuki, Yasuhiro,Kim, Junghee,Matsunaga, Go,Honda, Mitsuru,Rhee, Tongnyeol IOP 2018 Nuclear fusion. Fusion nucléaire. &n.Illiga Vol.58 No.8
<P>In order to account for the effect of field perturbations on the transport of fast ions in integrated codes used for the simulation of operational scenarios, it is crucial to develop computationally efficient reduced transport models. Such modeling efforts may greatly benefit from a simple method that determines the width of the island-like structures, which are produced by resonant perturbations in the phase space of the fast ion guiding centers and are known to play a key role for fast ion transport enhancement. In this paper, we present a method for estimating the widths of such ‘orbit islands’ for passing particles in the presence of static magnetic perturbations. The method consists of mapping the boundaries of magnetic islands from magnetic flux space (<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/58/8/082026/nfaab170ieqn001.gif'/>) into the canonical angular momentum space (<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/58/8/082026/nfaab170ieqn002.gif'/>) of the fast ions. As a working example, we consider co-passing neutral beam (NB) ions subject to a resonant magnetic perturbation (RMP) in a KSTAR tokamak plasma. The estimated orbit island width deviates by less than 25% from the value obtained from Poincaré plots of the actual guiding center trajectories, even when the magnetic drifts are large (here, up to 50% of the minor radius). Our analysis also shows that most of the fast ion transport can be attributed to the effect of isolated islands, which means that stochastization of particle trajectories due to resonance overlaps does not play a major role in the case studied here. The island mapping method proposed here eliminates the need to compute and analyze Poincaré maps of particle trajectories, so that computation times can be reduced tremendously by several orders of magnitude. A further speed-up may be achieved by the development of a method for estimating the width of magnetic islands under realistic conditions.</P>
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Shinohara, Kouji,Suzuki, Yasuhiro,Kim, Junghee,Kim, Jun Young,Jeon, Young Mu,Bierwage, Andreas,Rhee, Tongnyeol International Atomic Energy Agency 2016 Nuclear fusion Vol.56 No.11
<P>The fast ion dynamics and the associated heat load on the plasma facing components in the KSTAR tokamak were investigated with the orbit following Monte-Carlo (OFMC) code in several magnetic field configurations and realistic wall geometry. In particular, attention was paid to the effect of resonant magnetic perturbation (RMP) fields. Both the vacuum field approximation as well as the self-consistent field that includes the response of a stationary plasma were considered. In both cases, the magnetic perturbation (MP) is dominated by the toroidal mode number <I>n</I> = 1, but otherwise its structure is strongly affected by the plasma response. The loss of fast ions increased significantly when the MP field was applied. Most loss particles hit the poloidal limiter structure around the outer mid-plane on the low field side, but the distribution of heat loads across the three limiters varied with the form of the MP. Short-timescale loss of supposedly well-confined co-passing fast ions was also observed. These losses started within a few poloidal transits after the fast ion was born deep inside the plasma on the high-field side of the magnetic axis. In the configuration studied, these losses are facilitated by the combination of two factors: (i) the large magnetic drift of fast ions across a wide range of magnetic surfaces due to a low plasma current, and (ii) resonant interactions between the fast ions and magnetic islands that were induced inside the plasma by the external RMP field. These effects are expected to play an important role in present-day tokamaks.</P>
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