CURRENT DRIVEN DRIFT WAVES IN REVERSED FIELD PINCHES
Current driven drift waves stability in slab geometry with sheared magnetic field may be reduced to analysis of the eigenmodes equation with outgoing wave boundary conditions for large /x/. In limit b = (k**2-ya**2-i) << 1 where w-o = w*-e eta(1-b), xi is the electron streaming parameter, eta = T-i/T-e, x-j/x - w-o/k-"v thj-, lambda = (1-w/w-o)(eta+b)/(1+eta). Solution by matched asymptotic expansion technique and distinguishing two shear regimes: theta=L-s/L-n(m-e eta/M-i)**1/3 b**2/3 (1-b)/(eta+b) << 1 and theta >> 1. In the first regime the wave becomes unstable when xi > xi-cr ? L-n/L-s with growth rate y =w*-e xi. In the second regime we find marginal stability (y = O). Applied to a Reversed Field Pinch (RFP) equilibrium the high value attained by the streaming parameter in the external region causes instability in an annulus around the reversal surface, seen in Fig. 1, where the adopted equilibrium profiles (n-n(O)(1-(r/a)**2)**2, T-T(O)(1- (r/a**3), B-oe-B(O)J-o(2.8 r/a), B-OE=B(O)J-1(2.8 r/a)) are shown along with the instability regions corresponding to four different values of the on-axis streaming parameter. The perturbation is then predicted to propagate in the direction of B-oe. Both localization and propagation direction of the perturbation are in agreement with the results of density fluctuations measurements performed in ZT-40M using interferometric signal correlation techniques.
Bibliographic Reference: 12TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, BUDAPEST (HUNGARY), SEPT. 2-6, 1985 PP. 31-34 WRITE TO SERVIZIO STUDI E DOCUMENTAZIONE - ENEA, CENTRO RICERCHE ENERGIA FRASCATI, C.P. 65 - 00044 FRASCATI, ROMA (ITALY), MENTIONING REPORT RT
Record Number: 1989125009300 / Last updated on: 1987-01-01
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