MHD beta limits for advanced scenarios on JET


Bondeson, A., Liu, D.-H., Söldner, F.X., Persson, M., Baranov, Y.F. & Huysmans, G.T.A. (1999). MHD beta limits for advanced scenarios on JET. Nuclear Fusion, 39(11), 1523-1533. In Scopus Cited 23 times.

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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 simeq 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 simeq 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 simeq 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%.