During the past two years at JET under EFDA three promising H-mode operational scenarios have been further developed. The results were the simultaneous realization of high density and confinement as required for ITER.

A first method showed that by increasing the plasma triangularity, strong gas puffing does not deteriorate confinement in these plasmas, providedsufficient heating is applied. Thus, high density values can be obtained without confinement loss, resulting in addition to plasmas with very low dilution. The additional 7.5 MW of Neutral Beam power, available in campaign C7, will allow to extend the studies to ELMs mitigation effects to plasmas at higher absolute densities.

Another means of increasing the density without confinement deterioration is high field side pellet fuelling with a well chosen repetition rate, as demonstrated in C4. A new high field side pellet track (fig. left) , due to be available in campaign C6, enabling to launch pellets into the plasma with up to three times higher velocities, will allow a further optimization of the promising results of C4. A third method consists in seeding the plasma with impurities. Those plasmas not only show high confinement and densities as needed for ITER. Promising indications have been found that the enhanced radiation from the seeded impurity also results in a reduced heat load to the divertor. The studies started in campaigns C1-C4 will be further extended this year in all three regimes. The removal of the septum in the divertor (fig. left) will allow an assessment of its contribution in establishing the excellent results of the 2000-2001 campaigns. The final aim is to obtain an integrated operational scenario combining the necessary conditions for use on ITER : high confinement, high density and an acceptable power and particle exhaust.

High confinement regime, observed in tokamak plasmas

Neutral Beam power:
Injection of a beam of fast neutral particles which become ionised in the plasma and heat it as they slow down

Plugged In Neutral Injector

Edge Localised Mode is an instability which appears when the plasma is in the high-confinement H-mode configuration as it depends on the pressure profile at the plasma edge

JET – C(ampaign)1:
31 March – 28 July 2000

4 Sept. – 27 Oct. 2000

6 Nov. – 8 Dec. 2000

8 Jan. – 30 March 2001

18 March – 31 May 2002

16 Sept. – 11 Oct. 2002

21 Oct. – 13 Dec. 2002