A. Sagara

O. Mitarai

O. Motojima

National Institute for Fusion Science (NIFS-Repository)

§70. Ignition Analyses for the Helical-type Fusion Reactor FFHR-2 with the H-mode Power Threshold Mitarai, O.(Kyushu Tokai University) Sagara, A., and Motojima, 0. Ignition characteristics in the D-T high field helical reactor, two times bigger than the LHD are analyzed by the "operation path method" on the Ph(t~-T plane and "POPCON". Machine parameters of R = 8 to lOrn, a= 1.0 to 1.3m and Bo= lOT are considered for the experimental demonstration of the ignited operation in a stellarator reactor. Based on the LHD scaling law, R = lOrn, a= LOrn and the magnetic field around Bo =lOT in FFHR with force-free helical coil configuration is chosen as a reference one. In this helical reactor, the ignited operation is possible down to the fusion power 1.0 GW and low beta value of about 2.0 % with the high confinement enhancement factor 3 over LHD scaling. The H-mode power threshold observed in W7-X must have a hysteresis effect to maintain the operating point in the ignition regime. While the high magnetic field makes the empirical density limit higher and then the ignited operation regime becomes wider, it makes the H-mode power threshold higher and the ignited operation regime narrower. Table 1 Machine and plasma parameters for Compact FFHR. Major radius Major radius : R =10m Minor radius : a = 1 m External heating power : PExr = 100 MW Effective plasma volume: Vo =197m3 Effective plasma surface area : So = 395 m 2 Enhancement factor over LHD scaling : YH = 3.0 Effective ion charge: Zeff = 1.5 a density fraction: fa= 1 %for the start-up phase fa= 5 % in the ignition regime Alpha particle heating efficiency: lla = 0.7 Reflectivity for synchrotron : Reff = 0.9 Hole fraction for synchrotron: fH = 0.1 Density profile: an = 1.0 Temperature profile: aT= 1.0 Table 2 Operation pQints in the ignition regime Toroidal field Bo 9T 10 10 Fusion power Pt l.OGW 1.0 1.5 Neutron power Pn 0.8GW 0.8 1.2 Alpha loss paw 58MW 59 63 Alpha heating Pap 142MW 141 210 Energy loss : Bremsstrhalung P b 20MW 20 26.5 Synchrotron P s 0.5 MW 16.8 25.5 Conduction P L llOMW 104 156 Electron density n(O) (xl02° m-3) 2.93 2.78 3.14 Temperature T(O) 24.5 keV 26.5 30.3 Beta value < (3 > 2.2% 1.8 2.3 Neutron wall loading W n (MW /m 2) 1.85 1.86 2.8 5 4 (') IE 3 0 N 0 X 2 ..._..-,.-... 0 -....... c 1 0 0 20 40 60 Ti (0) ( keV) Fig. 1 POPCON analysis for R = 10 m, a = 1.0 m, Bo= 10 T and YH = 3.0. The H-L boundary shown by the dotted line for the hysteresis effect with AHL = Arn/2 = 0.012 and PExr = 0 MW divides the H and L-mode regimes. Ignition exists in the H-mode regime, and not in the L-mode regime. The density limit for the ignition boundary is also shown by the hatched line for PExr = 0 MW. The operating point is 1.0 GW. We note that the H-mode power threshold is given by PH[MW] > Arn ii[x10 20m-3] Bo[T] So[m2], with Arn = 0.024. 75 

Ignition Analyses for the Helical-type Fusion Reactor FFHR-2 with the H-mode Power Threshold

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