30E01P
トカマク中のヘリカルフェライト鋼設置による共鳴磁場摂動とペデスタルプラズマ輸送	 
Resonant Magnetic Perturbation by Helical Ferritic Steel Inserts in Tokamakand Transport of Pedestal Plasma	 滝塚知典1,	 清水勝宏2,	 星野一生2,	 福田武司1
Tomonori TAKIZUKA1, Katsuhiro SHIMIZU2, Kazuo HOSHINO2, Takeshi FUKUDA1
阪大工1, 原子力機構2
Osaka Univ.1, JAEA2
Edge localized mode (ELM) must be eliminated which enhances the erosion of divertor plates in theH-mode operation of tokamak reactors. Suppression of ELM has been experimentally achieved by theresonant magnetic perturbation (RMP) with multipartite coils [1]. In a DEMO reactor with strong neutron
flux, however, it is desired the coils near the first wall not to be put in. We proposed an innovative concept of
the RMP for tokamak DEMO reactors without installing coils but inserting ferritic steels of the helicalconfiguration [2]. Helically perturbed magnetic field is naturally formed in the axisymmetric toroidal
magnetic field through the helical ferritic steel inserts (FSIs). The perturbation amplitude in the plasmapedestal region can easily be set above several 10 −4 of the toroidal field strength in the DEMO reactor
condition (B0 ~ 6 T), which is enough for the RMP to mitigate/suppress ELMs [3]. Figure 1 shows thedependence of the relative perturbation | δH/H0 |PED at the pedestal position (r = 0.95a) on the relative radiusof the FSIs bF ≡ aF/a (a: plasma minor radius).
FSs are located in the region aF – d < r < aF + d. FS thickness€2d is normalized by κ = m/aF (m: poloidal mode number of helical FSIs). For m ~ 10 and a ~ 2.5 m, helical
FSIs with 2d ~ 0.5 m (κd ~ 1) easily generate the RMP of | δH/H0 |PED ~ 10 −3 , even when FSs are placed notnear by the plasma surface bF ~ 1.5. The helical FS configuration can be attained by the helical arrangementof blanket modules, but the FS materials occupy only a part of the FS region not to reduce thetritium-breeding ratio. A dashed curve in Fig. 1 corresponds to€ the blanket utilization assuming the 15%
FS-occupation. We see that the condition, | δH/H0 |PED > 3 × 10 −4 , is still satisfied for bF < 1.3.
Three-dimensional fluid simulations have been performed, and shown that the electron heat transport ismuch enhanced in the RMP stochastic field [4]. But this result did not agree well with the DIII-Dexperiments for low-collisionality regime, where€ the density was appreciable pumped out while electron
temperature was affected little [1]. We will discuss about possible models of the reduced heat transportconsidering the kinetic effects.

Fig. 1. Relative perturbation | δH/H0 |PED at thepedestal position vs bF for various κd values. A
dashed curve corresponds to the blanket utilization
with 15% FS-occupation and κd = 1.

[1] T.E. Evans et al., Nature Phys., 2, 419 (2006).
[2] T. Takizuka et al., “Helical Ferritic SteelInserts for Resonant Magnetic Perturbation toSuppress ELM in Tokamak DEMO Reactor”,
Plasma Conference 2011 / 28th JSPF Annual
Meeting, 2011, Kanazawa.
[3] T. Takizuka et al., “Resonant Magnetic
Perturbation for ELM Suppress ELM with HelicalFerritic Steel Inserts in Tokamak DEMO
Reactor”, 9th Int. Conf. on Open Magnetic
Systems for Plasma Confinement, 2012, Tsukuba;
to be published in Trans. Fusion Sci. Technol.
[4] I. Joseph et al., J. Nucl. Mater., 363-365, 591(2007).