Soft X-ray spectrum measurement of the ultralong discharge in the TRIAM-1M tokamak

In order to evaluate the electron temperature and the effective charge number ( Z eff ) of the ultralong discharge by a lower hybrid current drive in the TRIAM-1M tokamak, the soft X-ray energy spectrum is measured by the pulse height analysis system. The accuracy of the electron temperatures determined by the soft X-ray spectrum measurements is confirmed by comparing with the temperature obtained by the Thomson scattering system for OH plasmas. We obtained a bulk electron temperature of about 1.5 keV and a Z eff value of about 2 during the long-term discharge. It was found that the impurities observed in the spectrum were K α -lines of Fe, Cr and Ni originating from the stainless-steel limiter and they did not increase during the long-term discharge. Thus we obtained clean plasmas with relatively high temperature by a lower hybrid current drive.