A." Sagara

J. Miyazawa

R. "Sakamoto

T. Goto

National Institute for Fusion Science (NIFS-Repository)

Pellet refueling conditions to allow self-burning hasbeen investigated by extrapolating conﬁnement prop-erty of the LHD plasma to clarify essential requirementsfor pellet refueling in FFHR-d1. In order to evalu-ate the self-burning property taking the time evolutionof plasma proﬁles into consideration, the plasma pro-ﬁle evolution was calculated by the combination of thesimple particle diﬀusion equation and the direct proﬁleextrapolation (DPE) method in which the normalizedplasma pressure proﬁle obtained from the LHD experi-ment is directly extrapolated into a burning plasma byassuming gyro-Bohm type parameter dependence. Oneof the signiﬁcant improvements from the previous re-search is a revaluation of the particle diﬀusion coeﬃcient,which degrades with increasing heating power density.To investigate eﬀects of the pellet penetration depth onthe density proﬁle formation and the self-burning prop-erty, the pellet velocity is decided so that the pellet pen-etration depth become preset ﬁxed value. The pelletsize is assumed to be about 5 % of the particles in thebackground plasma, namely, 2 × 1022 atoms in particlenumber, to suppress the fusion output variation.Under too shallow pellet penetration conditions be-low λ/a = 0.3, the self-burning condition cannot be sat-isﬁed due to the insuﬃcient fusion α output as a result oflacking in the core refueling particles. And furthermore,the boundary plasma density easily beyond the densitylimit in such a shallow pellet refueling conditions. Theself-burning solutions are found when the pellet refuel-ing particles are deposited beyond λ/a = 0.3. Figure1 shows the pellet penetration depth dependence of thedensity and temperature proﬁles at the minimum fusion3210ne   [1020 m-3]15105Te    [keV]λ/a=0.93210ne   [1020 m-3]151050Te    [keV]λ/a=0.73210ne   [1020 m-3]151050Te    [keV]λ/a=0.53210ne   [1020 m-3]1.00.50ρ151050Te    [keV]λ/a=0.3(fP=1.05) (fP=1.14)(fP=1.30) (fP=1.52)1.00.50ρFig. 1: Density and temperature proﬁles just before(broken line) and after (solid line) pellet injection.output to satisfy the self-burning condition. In the caseof λ/a = 0.3, the density proﬁle inside the pellet de-posited radius (ρ < 0.7) remain nearly unaﬀected andﬂat density proﬁle is formed. The density proﬁle be-come peak as the pellet penetration depth deepens andthe peaking factor which is deﬁned by ne(0)/n¯e become1.52 at λ/a = 0.9.The pellet penetration depth dependence of theself-burning plasma properties under the minimum fu-sion output conditions are shown in Figure 2. The pelletpenetration depth aﬀect to the self-burning plasma prop-erties through the changing plasma proﬁles and the fol-lowing tendency are seen as the pellet penetration deep-ens. (a) Central density increase and central temper-ature decrease, (b) moderation of the minimum fusionoutput and increase of the burning rate which is deﬁnedas a ratio between the burned particles and fueled par-ticles, (c) suppression of the required fueling rate pro-longing the pellet injection interval. It seems reasonableto conclude that the deep pellet fueling allows to moder-ate the technological diﬃculties. On the other hand, (d)very high-speed pellet injection beyond 10 km/s, whichcannot be attained in present-day injection technology,is required to allow the deep pellet fueling. Although useof larger mass pellet can alleviate the diﬃculty of high-speed pellet injection, the eﬀect is restricted because thelarge pellet size may cause unacceptable fusion outputvariation.(a)(b)(c)(d)20100Velocity   [km/s]1.00.80.60.40.20/a Np=2.0E22        (~5 % of plasma) Np=4.0E22         (~10 % of plasma) Np=8.0E22        (same rate as LHD)3210ne   [1020 m-3]151050Te    [keV] neave. ne(0) Teave. Te(0)6004002000Injection interval   [ms] 20151050Fueling rate   [1022 /s] Injection interval Fueling rate1.51.00.50P [GW],   Wp [GJ]3210Burning rate   [%] P Wp Burning rateFig. 2: Dependence of the self-burning plasma param-eters on the normalized pellet penetration depth.270§8. Pellet Refueling Scenario to Allow  Self-burning on FFHR-d1Sakamoto, R., Miyazawa, J., Goto, T., Sagara, A.

Pellet Refueling Scenario to Allow Self-burning on FFHR-d1

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