A long-pulse plasma discharge for more than 30 min.was achieved on the LargeHelical Device(LHD).A plasma of n_e=0.8×10^(19)m^(-3)and T_(iO)=2.0 keV was sustained withP_(ICH)=0.52 MW,P_(ECH)=0.1 MW and averaged P_...A long-pulse plasma discharge for more than 30 min.was achieved on the LargeHelical Device(LHD).A plasma of n_e=0.8×10^(19)m^(-3)and T_(iO)=2.0 keV was sustained withP_(ICH)=0.52 MW,P_(ECH)=0.1 MW and averaged P_(NBI)=0.067 MW.Total injected heatingenergy was 1.3 GJ,which was a quarter of the prepared RF heating energy.One of the keys to thesuccess of the experiment was a dispersion of the local plasma heat load to divertors,accomplishedby shifting the magnetic axis inward and outward.展开更多
On the Large Helical Device (LHD) where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier (ETB) was produced in neutral-beam-injection (NBI) heated plasmas through transi...On the Large Helical Device (LHD) where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier (ETB) was produced in neutral-beam-injection (NBI) heated plasmas through transition and non-transition processes. The former case is the ETB formation by L-Htransition, where characteristics of L-H transition observed in a tokamak plasma are clearly recognized. The confinement improvement is the modest (- 10%), compared with the ISS95 international stellarator scaling. The threshold power for the transition is comparable or slightly lower than the ITER scaling law established by tokamaks and compact tori. The ETB is formed inside the ergodic field layer of the vacuum field. The ETB formation destabilizes edge coherent modes such as m/n = 1/1, 2/3 and 1/2, of which rational surfaces are in the magnetic hill. The formed ETB is partially and transiently destroyed by these coherent edge MHD modes and edge localized modes (ELMs) typically observed in Ha signals. The latter ETB is observed in a plasma with large reversed NBI-driven current more than 100 kA at Bt = 1 T. In these plasmas, the edge magnetic shear is enhanced by the current and the rotational transform in the core region is expected to be appreciably reduced. Thus reduced rotational transform in the plasma central region will enhance outward heat and particle fluxes toward ergodic edge layer. The ETB with steep electron temperature gradient up to - 5 keV/m is formed by blocking enhanced outward heat flux.展开更多
In the Large Helical Device (LHD), two different divertor configurations, i.e. helical divertor (HD) and local island divertor (LID), are utilized to control the edge plasma. The HD with two X-points is an intri...In the Large Helical Device (LHD), two different divertor configurations, i.e. helical divertor (HD) and local island divertor (LID), are utilized to control the edge plasma. The HD with two X-points is an intrinsic divertor for heliotron devices, accompanied with a relatively thick ergodic layer outside the confinement region. Edge and divertor plasma behavior from low density to high density regimes is presented, referring to the divertor detachment. The effect of the ergodic layer on the edge transport is also discussed. On the other hand, the LID is an advanced divertor concept which realizes a high pumping efficiency by the combination of an externally induced magnetic island and a closed pumping system. Experimental results to confirm the fundamental divertor performance of the LID are presented.展开更多
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘A long-pulse plasma discharge for more than 30 min.was achieved on the LargeHelical Device(LHD).A plasma of n_e=0.8×10^(19)m^(-3)and T_(iO)=2.0 keV was sustained withP_(ICH)=0.52 MW,P_(ECH)=0.1 MW and averaged P_(NBI)=0.067 MW.Total injected heatingenergy was 1.3 GJ,which was a quarter of the prepared RF heating energy.One of the keys to thesuccess of the experiment was a dispersion of the local plasma heat load to divertors,accomplishedby shifting the magnetic axis inward and outward.
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion and the JSPS Grant-in-Aid for Exploratory Research(No.6656287)
文摘On the Large Helical Device (LHD) where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier (ETB) was produced in neutral-beam-injection (NBI) heated plasmas through transition and non-transition processes. The former case is the ETB formation by L-Htransition, where characteristics of L-H transition observed in a tokamak plasma are clearly recognized. The confinement improvement is the modest (- 10%), compared with the ISS95 international stellarator scaling. The threshold power for the transition is comparable or slightly lower than the ITER scaling law established by tokamaks and compact tori. The ETB is formed inside the ergodic field layer of the vacuum field. The ETB formation destabilizes edge coherent modes such as m/n = 1/1, 2/3 and 1/2, of which rational surfaces are in the magnetic hill. The formed ETB is partially and transiently destroyed by these coherent edge MHD modes and edge localized modes (ELMs) typically observed in Ha signals. The latter ETB is observed in a plasma with large reversed NBI-driven current more than 100 kA at Bt = 1 T. In these plasmas, the edge magnetic shear is enhanced by the current and the rotational transform in the core region is expected to be appreciably reduced. Thus reduced rotational transform in the plasma central region will enhance outward heat and particle fluxes toward ergodic edge layer. The ETB with steep electron temperature gradient up to - 5 keV/m is formed by blocking enhanced outward heat flux.
基金supported by NIFS under Grant(No.NIFS05ULPP506)in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘In the Large Helical Device (LHD), two different divertor configurations, i.e. helical divertor (HD) and local island divertor (LID), are utilized to control the edge plasma. The HD with two X-points is an intrinsic divertor for heliotron devices, accompanied with a relatively thick ergodic layer outside the confinement region. Edge and divertor plasma behavior from low density to high density regimes is presented, referring to the divertor detachment. The effect of the ergodic layer on the edge transport is also discussed. On the other hand, the LID is an advanced divertor concept which realizes a high pumping efficiency by the combination of an externally induced magnetic island and a closed pumping system. Experimental results to confirm the fundamental divertor performance of the LID are presented.