Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device

Abstract

The progress of physical understanding as well as parameter improvement of net-current-free helical plasma is reported for the Large Helical Device since the last Fusion Energy Conference in Daejeon in 2010. The second low-energy neutral beam line was installed, and the central ion temperature has exceeded 7 keV, which was obtained by carbon pellet injection. Transport analysis of the high-Ti plasmas shows that the ion-thermal conductivity and viscosity decreased after the pellet injection although the improvement does not last long. The effort has been focused on the optimization of plasma edge conditions to extend the operation regime towards higher ion temperature and more stable high density and high beta. For this purpose a portion of the open helical divertors are being modified to the baffle-structured closed ones aimed at active control of the edge plasma. It is compared with the open case that the neutral pressure in the closed helical divertor increased by ten times as predicted by modelling. Studies of physics in a three-dimensional geometry are highlighted in the topics related to the response to a resonant magnetic perturbation at the plasma periphery such as edge-localized-mode mitigation and divertor detachment. Novel approaches of non-local and non-diffusive transport have also been advanced.

ICRF Heating Experiment on LHD in Foreseeing a Future Fusion Device

“…Ion cyclotron range of frequencies (ICRF) heating is one of the important tools for the Large Helical Device (LHD) [1,2] and future fusion devices. On the other hand, there are many technical and engineering problems in the ICRF antennas in considering the application to the fusion devices.…”

Creation of Impurity Source inside Plasmas with Various Types of Tracer-Encapsulated Solid Pellet

“…In this situation, a Tracer-Encapsulated Solid Pellet (TESPEL) [1,2] was developed to promote the impurity transport study in the magnetically-confined plasma. The impurity transport study with the TESPEL technology has been performed mainly in the Large Helical Device (LHD) [3,4] at the National Institute for Fusion Science (NIFS) in Japan, and is currently planned in the TJ-II stellarator [5] at the National Fusion Laboratory in the Research Center for Energy, Environment and Technology (CIEMAT) in Spain [6]. The TESPEL is a double-layered impurity pellet.…”

Direct measurement of refracted trajectory of transmitting electron cyclotron beam through plasma on the Large Helical Device

“…The LHD [17,18] is a suitable machine for direct measurement of transmitted-EC beam and for the validation of the EC-beam refraction because the LHD has many ports for installing the beam target and is equipped with the high-power ECRH system [19][20][21].…”