K.Y. Watanabe

National Institute for Fusion Science (NIFS-Repository)

§69. MHO Property for FFHR Watanabe, K.Y. We have studied the MHD equilibrium and stability and the neoclassical transport property of FFHR (1=3/m=18,Rc=20m, ac=3.33m, rc=l.O) with some magnetic axis. 1. Vacuum Magnetic Surface The plasma aspect ratio of FFHR is about 10. Straight 1=3 helical system has zero rotational transform in the plasma center as well known. Sip.ce FFHR is slender 1=3 helical system, its rotational transform is nearly zero in the case that its magnetic axis is near device center. FFHR is sensitive to quadrupole magnetic field component from helical coil or/and poloidal coils, and its magnetic axis is likely to split, which isn't unfavorable aspect according to the prediction that pressure profile become flat in the region where the magnetic axis splits. However, the magnetic axis touros inward or outward shifts prevent it from splitting magnetic axis. 2. MHD Equilibrium and Stability Analysis Here, we decide the equilibrium beta limit from the convergence condition of VMEC. Mf.ID stability is estimated by Mercier analysis. Figure 1 shows stability beta limit with various rriagmetic configuration. Stability beta limit is defined by the condition that the region D1>0.2 does not exist, where D1 corresponds to D1=-1/4 in vacuum. D1>0 corresponds to the Mercier mode (high m limit) unstable and D1>0.2 to the low-n mode unstable. The configuration with Roo (a) ~20.1m has the stability beta limit 2%, which corresponds to the ignition condition for B0= 12T. 3. :Neoclassical Ripple Transport Figure 2 shows the geometric factor of helical ripple: loss for FFHR estimated by means of multi··helicity model of ripple transport. Here G is the geometric factor, where is equal to c? tE312 h for simple magnetic field model. For FFHR, geometric factor decreases as magnetic axis shifts outward, which is different from the property of 1=2 helical system. This is why that the side band of Fourier component of main helicity in FFHR is 1=2/4 and change of quadrupole component is dominant effect here. We get the results that magnetic field The MHD equilibrium of FFHR with various c~nfiguration with certain outward touros axis vacuum magnetic axes is calculated by VMEC shift is favorable for both MHD equilibrium and code. All configurations with R v ax=18.7 ----20.8m stability, and neoclassical ripple transport in have almost same equilibrium beta limit, ~(f4%. FFHR 2.0 [ripple ·= -(f:!Jn E 2 E3h/2](_I_).2v -1. dn • C;s . ' . e~B : dr I 10-3 . .. ....... ....... •• .. .. ! : : ~/ ! ~ i r;p>---- J 1.5 J ::~ ~;- ~ :P:f~ -~ , :v, ; [ \ : //:/,t/ ~ : ~ 1=2/m=lO, eta=0.16, E11a=0.2 \', : r./ I [!' . : -e-- R0 ox=20.2m !.... 10~ .... ·t .... : ·:;·y·· ·: ··· ... : ...... ;... ~- 20.0m en 1' . ;~ : i : --~-- 19.8m 0 1 f.'/ : I : • • + • - 19.6m --E 10-7 c .. .... .. . ;/ .. ...... ... ;... .. r .... , .. . e- ..... 19.4m I I 1.0 0.50 • 0.0 L_ _ __..L __ --'-. __ _.~,....__~ 19.00 19.50 20.00 20.50 21.00 Raxis for Outer Most Mag.Surf. (m) Fig.l MHD stability beta limit for various FFHR configuration. E _ _._ 0 t /: ' 19.3m - 10-' L. -K I l 0.0 0.20 0.40 0.60 0.80 1.0 Minor Radius Fig.2 Geometric factor of helical ripple transport in various vacuum FFHR configuration. 75 

MHD Property for FFHR

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MHD Property for FFHR

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