A novel method for trace tritium transport studies

Abstract

A new method combining a free-form solution for the neutron emissivity and the ratio method (Bonheure et al 2006 Nucl. Fusion 46 725–40) is applied to the investigation of tritium particle transport in JET plasmas. The 2D neutron emissivity is calculated using the minimum Fisher regularization method (MFR) (Anton et al 1996 Plasma Phys. Control. Fusion 38 1849, Mlynar et al 2003 Plasma Phys. Control. Fusion 45 169). This method is being developed and studied alongside other methods at JET. The 2D neutron emissivity was significantly improved compared with the first MFR results by constraining the emissivity along the magnetic flux surfaces. 1D profiles suitable for transport analysis are then obtained by subsequent poloidal integration.In methods on which previous JET publications are based (Stork et al 2005 Nucl. Fusion 45 S181, JET Team (prepared by Zastrow) 1999 Nucl. Fusion 39 1891, Zastrow et al 2004 Plasma Phys. Control. Fusion 46 B255, Adams et al 1993 Nucl. Instrum. Methods A 329 277, Jarvis et al 1997 Fusion Eng. Des. 34–35 59, Jarvis et al 1994 Plasma Phys. Control. Fusion 36 219), the 14.07 MeV D–T neutron line integrals measurements were simulated and the transport coefficients varied until good fits were obtained. In this novel approach, direct knowledge of tritium concentration or the fuel ratio nT/nD is obtained using all available neutron profile information, e.g both 2.45 MeV D–D neutron profiles and 14.07 MeV D–T neutron profiles (Bonheure et al 2006 Nucl.Fusion 46 725–40). Tritium particle transport coefficients are then determined using a linear regression from the dynamic response of the tritium concentration nT/nD profile.The temporal and spatial evolution of tritium particle concentration was studied for a set of JET discharges with tritium gas puffs from the JET trace tritium experiments. Local tritium transport coefficients were derived from the particle flux equation Γ = −D∇nT + VnT, where D is the particle diffusivity and V the convection velocity.Tritium transport in the plasma core approaches the neoclassical level in some cases. For the set of plasmas analysed and within the uncertainty, tritium particle confinement follows the ITER IPB98(y,2) particle scaling confinement.