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
A 1 m vacuum ultraviolet （VUV） spectrometer with temporal and spatial resolution was developed for impurity study of HL-2A tokamak. The instrument is equipped with two concave gratings blazed at 80 nm and 150 nm, re...A 1 m vacuum ultraviolet （VUV） spectrometer with temporal and spatial resolution was developed for impurity study of HL-2A tokamak. The instrument is equipped with two concave gratings blazed at 80 nm and 150 nm, respectively, and a windowless back-illuminated charge coupled device （CCD） detector of 256 × 1024 pixels. Tile total wavelength coverage of spectrometer is 30～ 320 nm with a spectral resolution of 0.015 nm at a width of entrance slit of 10 μm. A portion of this range is observed during a plasma discharge with a spectral range of 20 nm. The minimum integration time of the detector system is about 6.7 ms for each frame in a full binning mode. Using a space-resolved slit located between the entrance slit and the grating a radial profile on the vertical direction with a range of 400 mm can be obtained. The primary results were successfully obtained with high signal-to-noise ratio and good spectral resolution, which demonstrated the instrument functions very well.展开更多
The ultra-low-frequency （ULF） electromagnetic emission is recently recognized as one of the most promising candidates for short-term earthquake （EQ） prediction. This paper reviews previous convincing evidence on t...The ultra-low-frequency （ULF） electromagnetic emission is recently recognized as one of the most promising candidates for short-term earthquake （EQ） prediction. This paper reviews previous convincing evidence on the presence of ULF emissions before three major EQs. Then, we present further statistical study on the ULF occurrence, our networks of ULF monitoring in different spatial scales in Japan and finally we present several signal processings to identify the seismogenic emissions by showing latest results for recent large EQs.展开更多
MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear...MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear density ramp experiment, interchange-like MHD modes whoserational surface is located very close to the last closed flux surface are strongly excited in acertain discharge condition and affect the plasma transport appreciably. In NBI-heated plasmasproduced at low toroidal field, various Alfven eigenmodes are often excited. Bursting toroidalAlfven egenmodes excited by the presence of energetic ions induce appreciable amount of energeticion loss, but also trigger the formation of internal and edge transport barriers.展开更多
The deposition profile of the impurity pellet is measured by a two-dimensional fast- framing vacuum ultraviolet （VUV） camera system in the large helical device （LHD）. The fast framing camera selectively measures t...The deposition profile of the impurity pellet is measured by a two-dimensional fast- framing vacuum ultraviolet （VUV） camera system in the large helical device （LHD）. The fast framing camera selectively measures the emission from the hydrogen-like ions of carbon （C VI） with a frame rate of several kHz. From the emission profile of the hydrogen-like carbon ions, which are in the process of ionization, the initial deposition profile of the carbon is estimated using a simple one-dimensional transport model.展开更多
OBJECTIVE:Admission hyperglycemia in acute myocardial infarction (MI) is related with increased in-hospital and long term mortality and major cardiac adverse events。 We aimed to investigate how admission hyperglycemi...OBJECTIVE:Admission hyperglycemia in acute myocardial infarction (MI) is related with increased in-hospital and long term mortality and major cardiac adverse events。 We aimed to investigate how admission hyperglycemia affects the short and long term outcomes in elderly patients >65 years) after primary percutaneous coronary intervention for ST elevation myocardial infarction。 METHODS:We retrospectively analyzed 677 consecutive elderly patients (mean age 72.2 ±5.4)。 Patients were divided into two groups according to admission blood glucose levels。 Group : low glucose group (LLG), glucose < 168 mg/dL; and Group 2: high glucose group (HGG), glucose >168 mg/dL。 RESULTS:In-hospital, long term mortality and in-hospital major adverse cardiac events were higher in the high admission blood glucose group (P <0.001)。 Multivariate regression analysis showed: Killip > 1, post-thrombolysis in MI <3 and admission blood glucose levels were independent predictors of in-hospital adverse cardiac events (P <0.001)。 CONCLUSIONS:Admission hyperglycemia in elderly patients presented with ST elevation myocardial infarction is an independent predictor of in-hospital major adverse cardiac events and is associated with in-hospital and long term mortality。展开更多
A long-pulse plasma discharge for more than 30 min. was achieved on the Large Helical Device （LHD）. A plasma of ne = 0.8 × 10^19 m^-3 and T10 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and avera...A long-pulse plasma discharge for more than 30 min. was achieved on the Large Helical Device （LHD）. A plasma of ne = 0.8 × 10^19 m^-3 and T10 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and averaged PNBI = 0.067 MW. Total injected heating energy was 1.3 G J, which was a quarter of the prepared RF heating energy. One of the keys to the success of the experiment was a dispersion of the local plasma heat load to divertors, accomplished by shifting the magnetic axis inward and outward.展开更多
This paper shows that the standing, backward- and forward-accelerated large amplitude relativistic electromagnetic solitons induced by intense laser pulse in long underdense collisionless homogeneous plasmas can be ob...This paper shows that the standing, backward- and forward-accelerated large amplitude relativistic electromagnetic solitons induced by intense laser pulse in long underdense collisionless homogeneous plasmas can be observed by particle simulations. In addition to the inhomogeneity of the plasma density, the acceleration of the solitons also depends upon not only the laser amplitude but also the plasma length. The electromagnetic frequency of the solitons is between about half and one of the unperturbed electron plasma frequency. The electrostatic field inside the soliton has a one-cycle structure in space, while the transverse electric and magnetic fields have half-cycle and one-cycle structure respectively. Analytical estimates for the existence of the solitons and their electromagnetic frequencies qualitatively coincide with our simulation results.展开更多
Artificial neural networks are trained to forecast the plasma disruption in HL-2A tokamak. Optimized network architecture is obtained. Saliency analysis is made to assess the relative importance of different diagnosti...Artificial neural networks are trained to forecast the plasma disruption in HL-2A tokamak. Optimized network architecture is obtained. Saliency analysis is made to assess the relative importance of different diagnostic signals as network input. The trained networks can successfully detect the disruptive pulses of HL-2A tokamak. The results obtained show the possibility of developing a neural network predictor that intervenes well in advance for avoiding plasma disruption or mitigating its effects.展开更多
This paper summarizes recent achievements in the characterization ofcandidate vanadium alloys obtained for fusion in the framework of the Japan-China Core UniversityProgram. National Institute for Fusion Science (NIFS...This paper summarizes recent achievements in the characterization ofcandidate vanadium alloys obtained for fusion in the framework of the Japan-China Core UniversityProgram. National Institute for Fusion Science (NIFS) has a program of fabricating high-purityV-4Cr-4Ti alloys. The resulting products (NIFS-HEAT-1,2), were characterized by various researchgroups in the world including Chinese partners. South Western Institute of Physics (SWIP) fabricateda new V-4Cr-4Ti alloy (SWIP-Heat), and carried out a comparative evaluation of hydrogenembrittlement of NIFS-HEATs and SWIP-Heat. The tensile test of hydrogen-doped alloys showed that theNIFS-HEAT maintained the ductility to relatively high hydrogen levels. The comparison of the datawith those of previous studies suggested that the reduced oxygen level in the NIFS-HEATs should beresponsible for the increased resistance to hydrogen embrittlement. Based on the chemical analysisdata of NIFS-HEATs and SWIP-Heats, neutron-induced activation was analyzed in Institute of PlasmaPhysics (IPP-CAS) as a function of cooling time after the use in the fusion first wall. The resultsshowed that the low level of Co dominates the activity up to 50 years followed by a domination of Nbor Nb and Al in the respective alloys. It was suggested that reduction of Co and Nb, both of whichare thought to have been introduced via cross-contamination into the alloys from the molds usedshould be crucial for reducing further the activation.展开更多
In the large helical device （LHD） having three dimensional configuration, Alfven eigenmodes （AEs） destabilized by energetic ions are widely investigated using neutral beam heated plasmas with monotonic and non-mon...In the large helical device （LHD） having three dimensional configuration, Alfven eigenmodes （AEs） destabilized by energetic ions are widely investigated using neutral beam heated plasmas with monotonic and non-monotonic rotational transform （l/2π） profiles. In a plasma with monotonic l/2π-profile, core-localized toroidicity-induced Alfven eigenmode （TAE） as well as global one are often observed. With the increase in the averaged toroidal beta value, defined as the ratio of total plasma pressure to toroidal magnetic pressure, core-localized TAE with low toroidal mode number becomes global. In a relatively high beta plasma with monotonic l/2π-profile, two TAEs with different toroidal mode number often interact nonlinearly and generate another modes through three wave coupling. In a plasma with non-monotonic l/2π-profile generated by intense counter neutral beam current drive, reversed shear Alfven eigenmode （RSAE） and geodesic acoustic mode （CAM） excited by energetic ions were observed for the first time in a helical plasma. Nonlinear coupling was also observed between RSAE and GAM.展开更多
The results on high power injection with the ueutral bean, injection （NBI） system for the Large Helical Device （LHD） are reported. The system consists of three beam-lines with two hydrogen negative ion （H^- ion）...The results on high power injection with the ueutral bean, injection （NBI） system for the Large Helical Device （LHD） are reported. The system consists of three beam-lines with two hydrogen negative ion （H^- ion） sources installed in each beam-line. In order to improve the injection power, a new beam accelerator with a multi-slot grounded grid （MSGG） has been developed and applied to one beam-line. Using the accelerator, a maximum power of 5.7 MW was achieved in 2003 and 2004, and the maximum energy of 189 keV was reached. The power and energy exceeded the design values of the individual beam-line for LHD. The other beam-lines also increased their injection power up to about 4 MW, and the total injection power of 13.1 MW was achieved with three beam-llnes in 2003. Although the accelerator had an advantage in high power beam injection, extracted beams expand in the short side direction of the ground-grid slot. The disadvantage has been resolved by modifying the aperture shapes of the steering grid.展开更多
Density modulation experiments are powerful experimental schemes for the study of particle transport. The diffusion coefficients （D） and convection velocity （V）, which cannot be evaluated from the particle balance...Density modulation experiments are powerful experimental schemes for the study of particle transport. The diffusion coefficients （D） and convection velocity （V）, which cannot be evaluated from the particle balance in the equilibrium state, can be obtained separately. Further, the estimated values of D and V are determined independent of the absolute value of the particle source rate, which is difficult to obtain experimentally. However, the sensitivities and interpretation of D and V from the modulation experiments need to be considered. This paper describes numerical techniques for solving the particle balance equation of the modulation components. Examples of the analysis are shown regarding the data of LHD experiments, and the results of the modulation experiments are discussed.展开更多
The efficiency of energetic ion confinement is reduced in a tokamak plasma by the non-axisymmetric field, namely the ripple field. The ripple field is produced by a finite number of toroidal field coils. It is affecte...The efficiency of energetic ion confinement is reduced in a tokamak plasma by the non-axisymmetric field, namely the ripple field. The ripple field is produced by a finite number of toroidal field coils. It is affected by the non-axisymmetric finite beta effect. The three-dimensional MHD equilibrium calculation code VMEC is used to analyze the non-axisymmetric finite beta effect in a ripple tokamak. In the VMEC code, the flux coordinates are used, so the calculation region is limited to the area of plasma. To calculate the orbit outside the plasma, we develop a field calculation code, which is based on the Biot-Savart law. The details of the method and results are described in this paper.展开更多
A simple Core-SOL-Divertor （C-S-D） model has been developed to investigate qualitatively the overall features of the operational space for the integrated core and edge plasma. To construct the simple C-S-D model, a ...A simple Core-SOL-Divertor （C-S-D） model has been developed to investigate qualitatively the overall features of the operational space for the integrated core and edge plasma. To construct the simple C-S-D model, a simple core plasma model of ITER physics guidelines and a two-point SOL-divertor model are used. The simple C-S-D model is applied to the study of the EAST operational space with lower hybrid current drive experiments under various kinds of trade-off for the basic plasma parameters. Effective methods for extending the operational space are also presented, From this study for the EAST operational space, it is evident that the C-S-D model is a useful tool for understanding qualitatively the overall features of the plasma operational space.展开更多
V-4Cr-4Ti is the leading candidate vanadium alloy as structural material of a V-Li blanket. Due to the interaction between Ti and interstitial solutes of C, N, and O, precipitation occurs at 600--700℃, increases the ...V-4Cr-4Ti is the leading candidate vanadium alloy as structural material of a V-Li blanket. Due to the interaction between Ti and interstitial solutes of C, N, and O, precipitation occurs at 600--700℃, increases the alloy strength significantly but reduce its ductility. As the ductility reduction is in an acceptable level, the strengthening might be utilized for the components that are subjected to high stress levels. Although cold work （CW） is known as an effective way to strengthen an alloy, so far few reports were found on strengthening a vanadium alloy by cold rolling.展开更多
Theoretical and experimental studies associated with electric field effectson the stability and transport are briefly surveyed. The effects of radial electric field on thesuppression and/or enhancement of various micr...Theoretical and experimental studies associated with electric field effectson the stability and transport are briefly surveyed. The effects of radial electric field on thesuppression and/or enhancement of various microinstabilities such as drift waves, flute mode andtemperature gradient modes are discussed. The suppression of flow shear on the electron temperaturegradient mode in plasmas with slightly hollow density profiles is investigated by solving thegyrokinetic integral eigenvalue equation. Comparison between theoretical predictions andexperimental observations based on the HIBP measurements with high temporal and spatial resolutionsis made in bumpy tori and heliotron (CHS) devices.展开更多
The preparation for an experimental soft x-ray tomography study on the Heliotron J (H-J) machine is carried out,with the objectives of evaluating the capability of the current soft x-ray tomographic system in terms of...The preparation for an experimental soft x-ray tomography study on the Heliotron J (H-J) machine is carried out,with the objectives of evaluating the capability of the current soft x-ray tomographic system in terms of the identification of different mode structures and their poloidal rotation,and the axis shift with different plasma and machine parameters,and fixing the physics goals for the experimental study.These preparations were carried out via a simulated soft x-ray data set arising from different plasma conditions,such as magnetic islands,low beta and high beta.Soft x-ray tomography (SXT) is performed by the discrete pixel method including singular value decomposition and Phillips-Tikhonov regularization,to obtain clear and smooth images.The H-J soft x-ray tomography results from simulated soft x-rays for the equilibrium H-J plasma sensed the magnetic axis shift clearly and an estimate was also achieved.Successful reconstruction for mode structure m =1/n =1 was obtained along with the realization of the poloidal rotation of the structure.The reconstruction for the m =2/n =1 mode was not very clear for the current soft x-ray diagnostic design.Effective mode identification was not possible due to the lack of measurements.The SXT from the current soft x-ray diagnostic on H-J,the magnetic axis shift can be estimated and the m =1/n =1 mode can be studied.Study of higher poloidal modes is difficult with the current design.展开更多
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.
基金National Natural Science Foundation of China(No.10475022)
文摘A 1 m vacuum ultraviolet （VUV） spectrometer with temporal and spatial resolution was developed for impurity study of HL-2A tokamak. The instrument is equipped with two concave gratings blazed at 80 nm and 150 nm, respectively, and a windowless back-illuminated charge coupled device （CCD） detector of 256 × 1024 pixels. Tile total wavelength coverage of spectrometer is 30～ 320 nm with a spectral resolution of 0.015 nm at a width of entrance slit of 10 μm. A portion of this range is observed during a plasma discharge with a spectral range of 20 nm. The minimum integration time of the detector system is about 6.7 ms for each frame in a full binning mode. Using a space-resolved slit located between the entrance slit and the grating a radial profile on the vertical direction with a range of 400 mm can be obtained. The primary results were successfully obtained with high signal-to-noise ratio and good spectral resolution, which demonstrated the instrument functions very well.
基金A considerable part of the works was carried out in the frameworks of Frontier Projects by NASDA and RIKENNICT(National Institute of Information and Communications Technology) (R and D promotion scheme funding international joint research) for its financial support
文摘The ultra-low-frequency （ULF） electromagnetic emission is recently recognized as one of the most promising candidates for short-term earthquake （EQ） prediction. This paper reviews previous convincing evidence on the presence of ULF emissions before three major EQs. Then, we present further statistical study on the ULF occurrence, our networks of ULF monitoring in different spatial scales in Japan and finally we present several signal processings to identify the seismogenic emissions by showing latest results for recent large EQs.
基金The project supported by the Core-University Program between Japan and China on Plasmas and Nuclear Fusion, and a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science
文摘MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear density ramp experiment, interchange-like MHD modes whoserational surface is located very close to the last closed flux surface are strongly excited in acertain discharge condition and affect the plasma transport appreciably. In NBI-heated plasmasproduced at low toroidal field, various Alfven eigenmodes are often excited. Bursting toroidalAlfven egenmodes excited by the presence of energetic ions induce appreciable amount of energeticion loss, but also trigger the formation of internal and edge transport barriers.
基金supported by the NIFS budget code ULPP021,the Ministry of Education Science,Sports and CultureGrant-in-Aid for Scientific Research(B)23340184partially supported by the JSPS-NRF-NSFC A3 Foresight Program in the field of Plasma Physics(No.11261140328)
文摘The deposition profile of the impurity pellet is measured by a two-dimensional fast- framing vacuum ultraviolet （VUV） camera system in the large helical device （LHD）. The fast framing camera selectively measures the emission from the hydrogen-like ions of carbon （C VI） with a frame rate of several kHz. From the emission profile of the hydrogen-like carbon ions, which are in the process of ionization, the initial deposition profile of the carbon is estimated using a simple one-dimensional transport model.
文摘OBJECTIVE:Admission hyperglycemia in acute myocardial infarction (MI) is related with increased in-hospital and long term mortality and major cardiac adverse events。 We aimed to investigate how admission hyperglycemia affects the short and long term outcomes in elderly patients >65 years) after primary percutaneous coronary intervention for ST elevation myocardial infarction。 METHODS:We retrospectively analyzed 677 consecutive elderly patients (mean age 72.2 ±5.4)。 Patients were divided into two groups according to admission blood glucose levels。 Group : low glucose group (LLG), glucose < 168 mg/dL; and Group 2: high glucose group (HGG), glucose >168 mg/dL。 RESULTS:In-hospital, long term mortality and in-hospital major adverse cardiac events were higher in the high admission blood glucose group (P <0.001)。 Multivariate regression analysis showed: Killip > 1, post-thrombolysis in MI <3 and admission blood glucose levels were independent predictors of in-hospital adverse cardiac events (P <0.001)。 CONCLUSIONS:Admission hyperglycemia in elderly patients presented with ST elevation myocardial infarction is an independent predictor of in-hospital major adverse cardiac events and is associated with in-hospital and long term mortality。
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 Large Helical Device （LHD）. A plasma of ne = 0.8 × 10^19 m^-3 and T10 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and averaged PNBI = 0.067 MW. Total injected heating energy was 1.3 G J, which was a quarter of the prepared RF heating energy. One of the keys to the success of the experiment was a dispersion of the local plasma heat load to divertors, accomplished by shifting the magnetic axis inward and outward.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10575015, 10445003, 10335020 and 10375011）, the National Key Laboratory of Laser Fusion, China （Grant No 51480010205ZW0901）, the Scientific Research Foundation for Returned 0verseas Chinese Scholars, State Education Ministry and the Foundation of China Academy of Engineering Physics （Grant No 20060217）.
文摘This paper shows that the standing, backward- and forward-accelerated large amplitude relativistic electromagnetic solitons induced by intense laser pulse in long underdense collisionless homogeneous plasmas can be observed by particle simulations. In addition to the inhomogeneity of the plasma density, the acceleration of the solitons also depends upon not only the laser amplitude but also the plasma length. The electromagnetic frequency of the solitons is between about half and one of the unperturbed electron plasma frequency. The electrostatic field inside the soliton has a one-cycle structure in space, while the transverse electric and magnetic fields have half-cycle and one-cycle structure respectively. Analytical estimates for the existence of the solitons and their electromagnetic frequencies qualitatively coincide with our simulation results.
基金Project supported by the National Natural Science Foundations of China （Grant No 10775040） and partially by JSPS-CAS Core University Program on Plasma and Nuclear Fusion.Acknowledgments The authors take this opportunity to express their sincere thanks to Q. D. Gao for his continuing encouragement and support. They gratefully acknowledge Y. Liu, B. B. Feng and F. Z. Li for fruitful discussions. Finally, the authors thank the entire HL-2A team for supplying the experimental data.
文摘Artificial neural networks are trained to forecast the plasma disruption in HL-2A tokamak. Optimized network architecture is obtained. Saliency analysis is made to assess the relative importance of different diagnostic signals as network input. The trained networks can successfully detect the disruptive pulses of HL-2A tokamak. The results obtained show the possibility of developing a neural network predictor that intervenes well in advance for avoiding plasma disruption or mitigating its effects.
基金The project supported by The Core-University Program on Plasma and Nuclear Fusion sponsored by JSPS(Japan)and CAS (China)
文摘This paper summarizes recent achievements in the characterization ofcandidate vanadium alloys obtained for fusion in the framework of the Japan-China Core UniversityProgram. National Institute for Fusion Science (NIFS) has a program of fabricating high-purityV-4Cr-4Ti alloys. The resulting products (NIFS-HEAT-1,2), were characterized by various researchgroups in the world including Chinese partners. South Western Institute of Physics (SWIP) fabricateda new V-4Cr-4Ti alloy (SWIP-Heat), and carried out a comparative evaluation of hydrogenembrittlement of NIFS-HEATs and SWIP-Heat. The tensile test of hydrogen-doped alloys showed that theNIFS-HEAT maintained the ductility to relatively high hydrogen levels. The comparison of the datawith those of previous studies suggested that the reduced oxygen level in the NIFS-HEATs should beresponsible for the increased resistance to hydrogen embrittlement. Based on the chemical analysisdata of NIFS-HEATs and SWIP-Heats, neutron-induced activation was analyzed in Institute of PlasmaPhysics (IPP-CAS) as a function of cooling time after the use in the fusion first wall. The resultsshowed that the low level of Co dominates the activity up to 50 years followed by a domination of Nbor Nb and Al in the respective alloys. It was suggested that reduction of Co and Nb, both of whichare thought to have been introduced via cross-contamination into the alloys from the molds usedshould be crucial for reducing further the activation.
基金LHD project budget of Japan (NIFS08ULHH508)the Grant-in-aid for Scientific Research from MEST of Japan (No.16082209)the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘In the large helical device （LHD） having three dimensional configuration, Alfven eigenmodes （AEs） destabilized by energetic ions are widely investigated using neutral beam heated plasmas with monotonic and non-monotonic rotational transform （l/2π） profiles. In a plasma with monotonic l/2π-profile, core-localized toroidicity-induced Alfven eigenmode （TAE） as well as global one are often observed. With the increase in the averaged toroidal beta value, defined as the ratio of total plasma pressure to toroidal magnetic pressure, core-localized TAE with low toroidal mode number becomes global. In a relatively high beta plasma with monotonic l/2π-profile, two TAEs with different toroidal mode number often interact nonlinearly and generate another modes through three wave coupling. In a plasma with non-monotonic l/2π-profile generated by intense counter neutral beam current drive, reversed shear Alfven eigenmode （RSAE） and geodesic acoustic mode （CAM） excited by energetic ions were observed for the first time in a helical plasma. Nonlinear coupling was also observed between RSAE and GAM.
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘The results on high power injection with the ueutral bean, injection （NBI） system for the Large Helical Device （LHD） are reported. The system consists of three beam-lines with two hydrogen negative ion （H^- ion） sources installed in each beam-line. In order to improve the injection power, a new beam accelerator with a multi-slot grounded grid （MSGG） has been developed and applied to one beam-line. Using the accelerator, a maximum power of 5.7 MW was achieved in 2003 and 2004, and the maximum energy of 189 keV was reached. The power and energy exceeded the design values of the individual beam-line for LHD. The other beam-lines also increased their injection power up to about 4 MW, and the total injection power of 13.1 MW was achieved with three beam-llnes in 2003. Although the accelerator had an advantage in high power beam injection, extracted beams expand in the short side direction of the ground-grid slot. The disadvantage has been resolved by modifying the aperture shapes of the steering grid.
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘Density modulation experiments are powerful experimental schemes for the study of particle transport. The diffusion coefficients （D） and convection velocity （V）, which cannot be evaluated from the particle balance in the equilibrium state, can be obtained separately. Further, the estimated values of D and V are determined independent of the absolute value of the particle source rate, which is difficult to obtain experimentally. However, the sensitivities and interpretation of D and V from the modulation experiments need to be considered. This paper describes numerical techniques for solving the particle balance equation of the modulation components. Examples of the analysis are shown regarding the data of LHD experiments, and the results of the modulation experiments are discussed.
基金performed with the support and backing of the NIFS Collaborative Research Program
文摘The efficiency of energetic ion confinement is reduced in a tokamak plasma by the non-axisymmetric field, namely the ripple field. The ripple field is produced by a finite number of toroidal field coils. It is affected by the non-axisymmetric finite beta effect. The three-dimensional MHD equilibrium calculation code VMEC is used to analyze the non-axisymmetric finite beta effect in a ripple tokamak. In the VMEC code, the flux coordinates are used, so the calculation region is limited to the area of plasma. To calculate the orbit outside the plasma, we develop a field calculation code, which is based on the Biot-Savart law. The details of the method and results are described in this paper.
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusionalso carried out as a joint project under the Facility Utilization Program of JAERI.
文摘A simple Core-SOL-Divertor （C-S-D） model has been developed to investigate qualitatively the overall features of the operational space for the integrated core and edge plasma. To construct the simple C-S-D model, a simple core plasma model of ITER physics guidelines and a two-point SOL-divertor model are used. The simple C-S-D model is applied to the study of the EAST operational space with lower hybrid current drive experiments under various kinds of trade-off for the basic plasma parameters. Effective methods for extending the operational space are also presented, From this study for the EAST operational space, it is evident that the C-S-D model is a useful tool for understanding qualitatively the overall features of the plasma operational space.
基金Supported by the Core University Program （CUP） between Japan and China and the National Natural Science Foundation of China （50271025）
文摘V-4Cr-4Ti is the leading candidate vanadium alloy as structural material of a V-Li blanket. Due to the interaction between Ti and interstitial solutes of C, N, and O, precipitation occurs at 600--700℃, increases the alloy strength significantly but reduce its ductility. As the ductility reduction is in an acceptable level, the strengthening might be utilized for the components that are subjected to high stress levels. Although cold work （CW） is known as an effective way to strengthen an alloy, so far few reports were found on strengthening a vanadium alloy by cold rolling.
文摘Theoretical and experimental studies associated with electric field effectson the stability and transport are briefly surveyed. The effects of radial electric field on thesuppression and/or enhancement of various microinstabilities such as drift waves, flute mode andtemperature gradient modes are discussed. The suppression of flow shear on the electron temperaturegradient mode in plasmas with slightly hollow density profiles is investigated by solving thegyrokinetic integral eigenvalue equation. Comparison between theoretical predictions andexperimental observations based on the HIBP measurements with high temporal and spatial resolutionsis made in bumpy tori and heliotron (CHS) devices.
文摘The preparation for an experimental soft x-ray tomography study on the Heliotron J (H-J) machine is carried out,with the objectives of evaluating the capability of the current soft x-ray tomographic system in terms of the identification of different mode structures and their poloidal rotation,and the axis shift with different plasma and machine parameters,and fixing the physics goals for the experimental study.These preparations were carried out via a simulated soft x-ray data set arising from different plasma conditions,such as magnetic islands,low beta and high beta.Soft x-ray tomography (SXT) is performed by the discrete pixel method including singular value decomposition and Phillips-Tikhonov regularization,to obtain clear and smooth images.The H-J soft x-ray tomography results from simulated soft x-rays for the equilibrium H-J plasma sensed the magnetic axis shift clearly and an estimate was also achieved.Successful reconstruction for mode structure m =1/n =1 was obtained along with the realization of the poloidal rotation of the structure.The reconstruction for the m =2/n =1 mode was not very clear for the current soft x-ray diagnostic design.Effective mode identification was not possible due to the lack of measurements.The SXT from the current soft x-ray diagnostic on H-J,the magnetic axis shift can be estimated and the m =1/n =1 mode can be studied.Study of higher poloidal modes is difficult with the current design.
