Variational principle for the neoclassical theory has been developed by including a momentum restoring term in the electron-electron collisional operator, which gives an additional free parameter maximizing the heat p...Variational principle for the neoclassical theory has been developed by including a momentum restoring term in the electron-electron collisional operator, which gives an additional free parameter maximizing the heat production rate. All transport coefficients are obtained including the bootstrap current. The essential feature of the study is that the aspect ratio affects the function of the electron-electron collision operator through a geometrical factor. When the aspect ratio approaches to unity, the fraction of circulating particles goes to zero and the contribution to particle flux from the electron-electron collision vanishes. The resulting diffusion coefficient is in rough agreement with Hazeltine. When the aspect ratio approaches to infinity, the results are in agreement with Rosenbluth. The formalism gives the two extreme cases a connection. The theory is particularly important for the calculation of bootstrap current in spherical tokamaks and the present tokamaks, in which the square root of the inverse aspect ratio, in general, is not small.展开更多
Preionization has been widely employed to create initial plasma and help the toroidal plasma current formation.This research focuses on implementing a simple,economical and practical electron cyclotron resonance(ECR)p...Preionization has been widely employed to create initial plasma and help the toroidal plasma current formation.This research focuses on implementing a simple,economical and practical electron cyclotron resonance(ECR)preionization technique on the newly constructed EXL-50 spherical tokamak,and evaluating the effectiveness on improving the plasma current startup.Two types ECR microwave preionization experiments for the plasma initialization without the central solenoid are reported:(1)2.45 GHz microwave preionization and current startup with2.45 GHz ECR source;(2)2.45 GHz microwave preionization and current startup with 28 GHz ECR source.Application of the 2.45 GHz ECR microwave preionization to the experiments has contributed to(1)getting rid of the plasma breakdown delay;(2)the significant improvement of the discharge quality:the discharge is much longer and more stable while the driven plasma current is larger,compared to the discharge without preionization.展开更多
A cylindrical model of linear MHD instabilities in tokamaks is presented. In the model, the cylindrical plasma is surrounded by a vacuum which is divided into inner and outer vacuum areas by a conducting wall. Lineari...A cylindrical model of linear MHD instabilities in tokamaks is presented. In the model, the cylindrical plasma is surrounded by a vacuum which is divided into inner and outer vacuum areas by a conducting wall. Linearized resistivity MHD equations with plasma viscosity are adopted to describe our model, and the equations are solved numerically as an initial value problem. Some of the results are used as benchmark tests for the code, and then a series of equilibrium current profiles are used to simulate the bootstrap current profiles in actual experiments with a bump on tail. Thus the effects of these kinds of profiles on MHD instabilities in tokamaks are revealed. From the analysis of the numerical results, it is found that more plasma can be confined when the center of the current bump is closer to the plasma surface, and a higher and narrower current bump has a better stabilizing effect on the MHD instabilities.展开更多
Two-dimensional structure of density fluctuations is examined during the current jump phase, indicating a change from the open magnetic fields to the closed ones. During the smooth current ramp-up phase the two-dimens...Two-dimensional structure of density fluctuations is examined during the current jump phase, indicating a change from the open magnetic fields to the closed ones. During the smooth current ramp-up phase the two-dimensional contour of the LiI intensity shows vertically alignment, consistent with the magnetic surfaces. At the inflection point in Ip ramp-up the LiI intensity contour becomes flat in the observation regime and then suddenly a steep gradient and higher intensity regime are formed in the vertical direction. This higher intensity corresponds to a burst of LiI waveform. According to these changes in the contour, it is found that, within ~1 ms around the burst of LiI, a low frequency coherent wave with a long wavelength rapidly grows. The relations with other signals （magnetic flux and microwave stray power） are discussed with respect to the topological change in the magnetic configuration and mode conversion of the incident electromagnetic waves.展开更多
A method for the reconstruction of the plasma boundary in the sino-united spherical tokamak （SUNIST） based on the outer plasma magnetic diagnostics is reported. In SUNIST, the magnetic flux loop integral signals wer...A method for the reconstruction of the plasma boundary in the sino-united spherical tokamak （SUNIST） based on the outer plasma magnetic diagnostics is reported. In SUNIST, the magnetic flux loop integral signals were measured recently and the plasma boundary could be reconstructed well with a current filament （CF） model by setting 2 to 8 current filaments. There are three additional filament positional parameters in addition to the filament current to minimize the square root error in the CF model. The plasma configuration obtained with the CF method is consistent with the visible plasma image from the CCD camera. The average difference in the minor radii for the plasma boundary, by applying the CF model and EFIT code, is below 6 mm.展开更多
Both start-up and sustainment of plasma were successfully achieved by fully non- inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface ...Both start-up and sustainment of plasma were successfully achieved by fully non- inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launched microwave power and vertical magnetic field, while not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray （HXR） emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 keV to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed.展开更多
Experiments on the start-up and formation of spherical tokamak plasmas by electron cyclotron heating alone without ohmic heating and electrode discharge assisted electron cyclotron wave current start-up will be carrie...Experiments on the start-up and formation of spherical tokamak plasmas by electron cyclotron heating alone without ohmic heating and electrode discharge assisted electron cyclotron wave current start-up will be carried out on the SUNIST (Sino United Spherical Tokamak) device. The 2.45 GHz/100 kW/30 ms microwave power system and 1000 V/50 A power supply for electrode discharge are ready for experiments with non-inductive current drive.展开更多
基金The project supported by the National Nature Science Fundation of China(No.19885006 and No.10175020)
文摘Variational principle for the neoclassical theory has been developed by including a momentum restoring term in the electron-electron collisional operator, which gives an additional free parameter maximizing the heat production rate. All transport coefficients are obtained including the bootstrap current. The essential feature of the study is that the aspect ratio affects the function of the electron-electron collision operator through a geometrical factor. When the aspect ratio approaches to unity, the fraction of circulating particles goes to zero and the contribution to particle flux from the electron-electron collision vanishes. The resulting diffusion coefficient is in rough agreement with Hazeltine. When the aspect ratio approaches to infinity, the results are in agreement with Rosenbluth. The formalism gives the two extreme cases a connection. The theory is particularly important for the calculation of bootstrap current in spherical tokamaks and the present tokamaks, in which the square root of the inverse aspect ratio, in general, is not small.
基金funded by the compact fusion project in the ENN group。
文摘Preionization has been widely employed to create initial plasma and help the toroidal plasma current formation.This research focuses on implementing a simple,economical and practical electron cyclotron resonance(ECR)preionization technique on the newly constructed EXL-50 spherical tokamak,and evaluating the effectiveness on improving the plasma current startup.Two types ECR microwave preionization experiments for the plasma initialization without the central solenoid are reported:(1)2.45 GHz microwave preionization and current startup with2.45 GHz ECR source;(2)2.45 GHz microwave preionization and current startup with 28 GHz ECR source.Application of the 2.45 GHz ECR microwave preionization to the experiments has contributed to(1)getting rid of the plasma breakdown delay;(2)the significant improvement of the discharge quality:the discharge is much longer and more stable while the driven plasma current is larger,compared to the discharge without preionization.
基金supported by National Natural Science Foundation of China(No.10675029)National Basic Research Program of China(Nos.2008CB717801,2008CB787103,2009GB105004,2010GB106002)
文摘A cylindrical model of linear MHD instabilities in tokamaks is presented. In the model, the cylindrical plasma is surrounded by a vacuum which is divided into inner and outer vacuum areas by a conducting wall. Linearized resistivity MHD equations with plasma viscosity are adopted to describe our model, and the equations are solved numerically as an initial value problem. Some of the results are used as benchmark tests for the code, and then a series of equilibrium current profiles are used to simulate the bootstrap current profiles in actual experiments with a bump on tail. Thus the effects of these kinds of profiles on MHD instabilities in tokamaks are revealed. From the analysis of the numerical results, it is found that more plasma can be confined when the center of the current bump is closer to the plasma surface, and a higher and narrower current bump has a better stabilizing effect on the MHD instabilities.
基金the NIFS Collaboration Research Program (NIFS07KOAR009,NIFS05KUTR012)the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘Two-dimensional structure of density fluctuations is examined during the current jump phase, indicating a change from the open magnetic fields to the closed ones. During the smooth current ramp-up phase the two-dimensional contour of the LiI intensity shows vertically alignment, consistent with the magnetic surfaces. At the inflection point in Ip ramp-up the LiI intensity contour becomes flat in the observation regime and then suddenly a steep gradient and higher intensity regime are formed in the vertical direction. This higher intensity corresponds to a burst of LiI waveform. According to these changes in the contour, it is found that, within ~1 ms around the burst of LiI, a low frequency coherent wave with a long wavelength rapidly grows. The relations with other signals （magnetic flux and microwave stray power） are discussed with respect to the topological change in the magnetic configuration and mode conversion of the incident electromagnetic waves.
基金supported by National Natural Science Foundation of China (Nos.10775177, 10535020)the Major State Basic Research Development Program of China (Program 973) (No.2008CB717804)
文摘A method for the reconstruction of the plasma boundary in the sino-united spherical tokamak （SUNIST） based on the outer plasma magnetic diagnostics is reported. In SUNIST, the magnetic flux loop integral signals were measured recently and the plasma boundary could be reconstructed well with a current filament （CF） model by setting 2 to 8 current filaments. There are three additional filament positional parameters in addition to the filament current to minimize the square root error in the CF model. The plasma configuration obtained with the CF method is consistent with the visible plasma image from the CCD camera. The average difference in the minor radii for the plasma boundary, by applying the CF model and EFIT code, is below 6 mm.
文摘Both start-up and sustainment of plasma were successfully achieved by fully non- inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launched microwave power and vertical magnetic field, while not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray （HXR） emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 keV to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed.
基金The project supported by National Natural Science Foundation of China (Nos. 10275041, 10375089)
文摘Experiments on the start-up and formation of spherical tokamak plasmas by electron cyclotron heating alone without ohmic heating and electrode discharge assisted electron cyclotron wave current start-up will be carried out on the SUNIST (Sino United Spherical Tokamak) device. The 2.45 GHz/100 kW/30 ms microwave power system and 1000 V/50 A power supply for electrode discharge are ready for experiments with non-inductive current drive.
