On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

VISCOSITY OF NORMAL AND SUPERFLUID HELIUM THREE

Nous avons mesuré la viscosité de la composante normale de l'3He dans les phases A et B, et dans le liquide de Fermi normal. Près de Tc, nous pouvons décrire la viscosité réduite avec l'équation (1 - η/ ηc) = A(l - T/Tc)1/2 - B(l - T/Tc). A l'aide des résultats applicables au liquide normal, nous avons calculé le temps de relaxation τ(0)T2 d'une quasi-particule dans l'état normal.The normal fluid viscosity has been measured in the A and B phases of 3He, as well as in the normal Fermi liquid. Near Tc we find that the reduced viscosity can be written in the form (1 - η/ ηc) = A(l - T/Tc)1/2 - B(1 - T/Tc) . Using the normal liquid results we have calculated the normal state quasiparticle relaxation time τ(0)T2

DIRECT OBSERVATION OF ORBITAL DISSIPATION AND SUPERFLOW COLLAPSE IN 3He-A

Des expériences de pendule de torsion dans lesquelles le temps de relaxation orbitale est comparable à la période d 'oscillation montrent une atténuation fortement dépendante de l'amplitude dans 3He-A qui est absente dans 3He-B A forte amplitude, la densité superfluide apparente tend vers zéro, suggérant l'effondrement du courant superfluide comme l 'ont décrit Bhattacharyya, Ho et Mermin.Torsion pendulum experiments in which the orbital relaxation time is comparable with the oscillation period show strong amplitude dependent damping in 3He-A that is absent in 3He-B. At large amplitudes the apparent superfluid density decreases towards zero, suggesting collapse of superflow as described by Bhattacharyya, Ho and Mermin