Analysis of indefinite divertor footprint with proper orthogonal decomposition in hydrogen/deuterium plasmas in LHD

Abstract Divertorparticle flux signals on divertorplates were analyzed with the multivariable analysis technique, namely, proper orthogonal decomposition (POD), to characterize the indefinite divertor footprintin the Large Helical Device. To verify whether isotope effects exist in relation to the divertorplasmas, the POD outputs in hydrogen (H) and deuterium (D) plasmas were first compared by analyzing a number of discharges. It was found that the dominant components of the divertorparticle flux profiles in H and D plasmas were similar, indicating no isotope effect. In addition, total reconstructed divertorparticle fluxes in H plasmas were higher than those in D plasmas, suggesting an isotope effect. Furthermore, the footprint-profile modification with from the SOL-side to the private-side peak due to the edge electron pressure gradient in H and D plasmas were slightly different, relating to an isotope effect.