Optimal condition for oscillating field current drive in a bootstrapped tokamak

Weening, R. H.

doi:10.1088/0741-3335/39/8/007

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(2 citation statements)

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“…Kessel et al [1] showed that, with the stabilizing effect of an ideally conducting wall, high normalized beta can be achieved at bootstrap fractions close to 100%. On the other hand, in the absence of wall stabilization, the beta limits are rather modest if the bootstrap fraction is significant [16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

“…Before discussing the results of the optimization, it is worthwhile to recall the difficulty in achieving simultaneously high beta and a high bootstrap fraction [16,17]. Reference [17] shows that the product of the bootstrap fraction and beta is limited by where c geom 0.1(1 + κ 2 ) is a geometrical (and weakly profile dependent) factor related to the efficiency of bootstrap current generation, κ the elongation, β N = β(%)/I N the normalized beta and I N = I p (MA)/(a(m)B 0 (T)) the normalized plasma current.…”

Section: Introductionmentioning

confidence: 99%

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MHD beta limits for advanced scenarios on JET

et al. 1999

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Ideal MHD limits to beta and bootstrap fraction are computed for pressure profiles similar to those of JET discharges with both internal and H mode transport barriers. Several non-monotonic current profiles are tested, and the pressure profile is constrained so that no negative current drive is required in steady state. Calculations are made both with and without an ideally conducting wall. The main result is that, for such peaked pressure profiles, the limits to beta and bootstrap fraction improve at low internal inductance, in particular when wall stabilization is taken into account. The highest limits to beta, and often also to normalized beta, occur for the maximum plasma current. There is also a weak dependence on qmin , for which three favourable regions have been identified. A highly advantageous region is found at qmin 1.6, where the limits to β * are 7.0% with, and 4.8% without, wall stabilization. The corresponding limits are 68 and 50%, respectively, for the bootstrap fraction and 4.0 and 2.9 for the normalized beta. These equilibria have low internal inductance, li = 0.62. For higher inductance, an optimum occurs when qmin 1.2, where the limit to β * is 5.3% with a wall and 4.7% without. The corresponding bootstrap fractions are about 46 and 38%, respectively. A third type of equilibrium that is interesting for steady state operation has qmin 2.1 and low inductance. Here the β * limits are lower, 4.9 and 3.4%, but the bootstrap fractions are higher, 77 and 60%.

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