Numerical study of fast ion behavior in the presence of magnetic islands and toroidal field ripple in the EAST tokamak

A peculiar first orbit loss type was found apart from the normal ones when we use ORBIT code to simulate fast ion orbits in the EAST tokamak. Fast ion orbits were studied in the presence of toroidal field （TF） ripple and magnetohydro- dynamic （MHD） perturbations. We analyzed the properties of the drifted orbits in detail and compared their differences, finding that the combined effects of ripple and magnetic islands are much greater than the effects of either one of them alone. Then we investigated the orbitdeviations as a function of pitch angle in different radial positions. The modeling results demonstrate that the loss of trapped particles is mainly caused by the ripple, while MHD＇perturbation mainly plays an important role in the passing particles. Furthermore we modeled the loss rate using different equilibriums. Results prove that a higher beta can indeed improve the confinement of fast ions, while a little change in the q profile can make the topologies of magnetic islands become quite different and results in quite different total particle losses.

Preliminary Engineering Design of Toroidal Field Magnet System for Superconducting Tokamak HT-7U

HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating tokama-k fusion reactor. This paper describes only a toroidal field (TF) superconducting magnet system of HT7U. In this paper, design criteria of conductor and stability analysis, coil winding and support structure design of magnet system, mechanical calculation and stress analysis, heat load evaluation are given.

Design of a Wedge-Shaped Toroidal Field Winding for KTX Device

The KTX device is a reversed field pinch （RFP） device currently under construction. Its maximum plasma current is designed as 1 MA with a discharge time longer than 100 ms. Its major radius is 1.4 m and its minor radius is 0.55 m. One of the most important problems in the magnet system design is how to reduce the TF magnetic field ripple and error field. A new wedge- shaped TF coil is put forward for the KTX device and its electromagnetic properties are compared with those of rectangular-shaped TF coils. The error field B,I/Bt of wedge-shaped TF coils with 6.4 degrees is about 6% as compared with 8% in the case of a rectangular-shaped TF coil. Besides, the wedge-shaped TF coils have a lower magnetic field ripple at the edge of the plasma region, which is smaller than 7.5% at R=1.83 m and 2% at R=l.07 m. This means that the tokamak operation mode may be feasible for this device when the plasma area becomes smaller, because the maximum ripple in the plasma area of the tokamak model is always required to be smaller than 0.4%. Detailed analysis of the results shows that the structure of the wedged-shape TF coil is reliable. It can serve as a reference for TF coil design of small aspect ratio RFPs or similar torus devices.

Simulations of energetic alpha particle loss in the presence of toroidal field ripple in the CFETR tokamak

Energetic alpha particle losses with the toroidal field ripple and the Coulomb collision in the CFETR tokamak have been simulated by using the orbit-following code GYCAVA for the steady-state and hybrid scenarios.The effects of the outer boundary and the ripple amplitude on alpha particle losses have been investigated.The loss fractions and heat loads of alpha particles in the hybrid scenario are much smaller than those in the steady-state scenario for a significant ripple amplitude.Some alpha particles in the plasma core are lost due to the ripple stochastic transport for a large ripple amplitude parameter.The heat loads with the last closed flux surface boundary are different from those with the wall boundary for the CFETR tokamak,which can be explained by typical alpha particle orbits.Discrete heat load spots have been observed in alpha particle loss simulations,which is due to the ripple well loss.The transition of the lost alpha particle behavior from the ripple stochastic diffusion to the ripple well trapping has been identified in our CFETR simulations.The Coulomb collision effect is responsible for this transition.

The effect of toroidal field on the rotating magnetic field current drive in rotamak plasmas

A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field （RMF）. The driven current can reverse the original equilibrium field and generate a field-reversed-configuration. In a conventional rotamak, a toroidal field （TF） is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail. The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when Bv and radio frequency generator power are fixed. Besides driving current, the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.

A Consideration on Increasing Current Density in Normal Conducting Toroidal Field Coil for Spherical Tokamak Power Plant

The center post is the most critical component as an inboard part of the toroidal field coil for the low aspect ratio tokamak. During the discharge it endures not only a tremendous ohmic heating owing to its carrying a rather high current but also a large nuclear heating and irradiation owing to the plasma operation. All the severe operating conditions, including the structure stress intensity and the stability of the structure, largely limit the maximum allowable current density. But in order to contain a very high dense plasma, it is hoped that the fusion power plant system can operate with a much high maximum magnetic field BT ≥12 T-15 T in the center post. A new method is presented in this paper to improve the maximum magnetic field up to 17 T and to investigate the possibility of the normal conducting center post to be used in the future fusion tokamak power plant.

FE Stress Analysis of the Toroidal Field Magnets of HT-7U

In this paper, the mechanical strength of the toroidal field (TF) magnets of HT-7U with the electromagnetic force in different magnetic fields is emphatically analyzed by means of finite element method. The model and feasible method of computation are put forward. Some important conclusions are made available for reference in the design and construction of TF for HT-7U.

Feasibility Study on Welding Structure of the HT-7U Toroidal Field Coil Case

The Toroidal Field (TF) coil case of the HT-7U superconducting tokamak device is made of austenitic stainless steel 316LN and is designed to operate at cryogenic temperature (4 K). 316LN can retain high strength and fracture toughness at 4 K. Feasibility study on technical process of welding has been experimentally considered as a hopeful joint method for suppression of post-welding deformation and reduction of over-heating. Meanwhile the final range of stress intensity and the stress intensity factor (K) for pre-cracks of welding structure have been determined by using J-integral. These related results are optimistic and have shown that there's no problem in strength and fracture toughness at the vicinity of the pre-crack tip. This paper introduces the welding structure of TF coil case in detail.

The Analysis and Calculation for the Toroidal Magnetic Field of HT-7U

The HT-7U super-conducting tokamak is a full super-conducting magnetically confined fusion device, It mainly consists of super-conducting toroidal field (TF) coils and super conducting poloidal field (PF) coils. This paper describes the distribution of magnetic field, ripple and electromagnetic loads of TF system, some results are necessary to analyze and calculate the stresses and deformation on TF system by a finite element method. Meanwhile, in this paper, the main scope of the calculation is carried out for the case of constant magnetic field on conductor of the TF coil winding in order to provide electromagnet parameters for the quench analysis of Cable-in-Conduit Conductor (CICC) of TF system in HT-7U.

Radial magnetic field in magnetic confinement device

The intrinsic radial magnetic field（B r） in a tokamak is explored by the solution of the Grad–Shafranov equation in axisymmetric configurations through an expansion of the four terms of the magnetic surfaces. It can be inferred from the simulation results that at the core of the device, the tokamak should possess a three-dimensional magnetic field configuration, which could be reduced to a two-dimensional one when the radial position is greater than 0.6a. The radial magnetic field and the amzimuthal magnetic field have the same order of magnitude at the core of the device. These results can offer a reference for the analysis of the plasma instability, the property of the core plasma, and the magnetic field measurement.

The Implementation of Magnetic Islands in Gyrokinetic Toroidal Code

The implementation of magnetic islands in gyrokinetic simulation has been verified in the gyrokinetic toroidal code（GTC）.The ion and electron density profiles become partially flattened inside the islands.The density profile at the low field side is less flattened than that at the high field side due to toroidally trapped particles in the low field side,which do not move along the perturbed magnetic field lines.When the fraction of trapped particles decreases,the density profile at the low field becomes more flattened.

Buckling Analysis of TF Coil Inner Leg for Central Solenoidless Tokamak

The central post is one of the critical components for the low aspect ratio tokamak, which endures not only a tremendous ohmic heating because it carries a rather high current, but also a large neutron heating and irradiation owing to the plasma operation. The DS copper alloy Glidcop AL-25[8] was chosen as the conductor material for its adequate mechanical properties and physics properties. The central post has a cylindrical structure with lots of cooling channels. The length of the central post for the next generation of nuclear fusion spherical tokamaks will be more than 10 m or 20 m. The structural stability is very crucial. When the applied load is larger than the structure critical buckling load, the device will lose its stability and collapse. In order to calculate the critical buckling load, a 1/6-segment finite element model was used and the force acting on the central post was simulated. The results showed that the vertical compressive stresses mainly affect the stability of the central post. The linear buckling analysis results with finite element method based on small deformation theory were given in this paper. The relation curves and functions for buckling factor, depending on the different lengths and the radius of the central post, the diameter of cooling channel and the maximum allowable current density, were also shown.

Nonlinear free thermal convection in a spherical shell:A variable viscosity model

In mantle convection models, the mantle viscosity is generally assumed constant or dependent on depth. In this paper, a laterally variable viscosity is introduced into mantle convection model in which the mantle viscosity consists of a constant background and latitude-dependent viscosity with small fluctuations. The features of toroidal field dependent on depth and Rayleigh number are discussed under two boundary conditions, i.e., the top rigid and bottom stress-free boundaries (R-F boundary for short) and both rigid ones (R-R boundary for short), respectively. The results show that the energy of toroidal field mainly concentrates in the middle and upper parts of a spherical shell, and the ratio of toroidal to total velocities amounts to only a few percents and hardly depends on Rayleigh number, while the convection patterns of toroidal field have been strongly affected by Rayleigh number. It is found that the convection patterns and velocities of toroidal field have obvious differences in latitudinal direction, which clearly reflects the effects of lateral mantle viscosity variations on the convection patterns. These preliminary results give us a possible hint to study some global tectonic phenomena, e.g. the asymmetry of the southern and northern hemispheres and the Earth's differential rotation.

Finite Element Analyses and Instrumentation Layout for Single Coil Testing of TF Coils in HT-7U

The HT-7U tokamak is a magnetically-confined full superconducting fusion device, consisting of superconducting toroidal field (TF) coils and superconducting poloidal field (PF) coils. These coils are wound with cable-in-conductor (CICC) which is based on UNK NbTi wires made in Russian '. A single D-shaped toroidal field magnet coil will be tested for large and expensive magnets systems before assembling them in the toroidal configuration. This paper describes the layout of the instrumentation for a superconducting test facility based on the results of a finite element modeling of the single coil of toroidal magnetic field (TF) coils in HT-7U tokamak device. At the same time, the design of coil support structure in the test facility is particularly discussed in some detail.

Terrestrial ground temperature variations in relation to solar magnetic variability,including the present Schwabe cycle

We study the influence of solar activity on climate by investigating the relation between the long-term components of the total magnetic fluxes of both the equatorial and polar fields of the sun and the average terrestrial ground temperature. This is done for the period 1610 (beginning of systematic sunspot observations) till present with an extrapolation to 2015. It is found that from 1610 till about the first half of the 20th century the variation of the long-term average terrestrial ground temperatures is chiefly due to the variation of solar activity, with seemingly random, non-solar residuals. Around 2007, after the Grand Maximum of the 20th century, solar activity, after having gone through a remarkable transition period (~2005 to ~2010), entered into another Grand Episode. That Episode started with the present solar cycle, in shape comparable to the equally weak Schwabe cycle #14. The transition period, in combination with the present low Schwabe cycle causes that the solar contribution to the total terrestrial temperature variation is small during the on-going decade. It results in a slowing down of the rise of temperature after ~2005.

Investigation of electron cyclotron current drive efficiency on the J-TEXT tokamak

Electron cyclotron current drive(ECCD) efficiency research is of great importance for the neoclassical tearing mode(NTM) stabilization.Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD power threshold reduction.ECCD efficiency has been investigated on the J-TEXT tokamak.The electron cyclotron wave(ECW) power scan was performed to obtain the current drive efficiency.The current drive efficiency is derived to be approximately η_(0)=(0.06-0.16)×10^(19)A m^(-2)W^(-1)on the J-TEXT tokamak.The effect of the residual toroidal electric field has been included in the determination of the current drive efficiency,which will enhance the ECCD efficiency.At the plasma current of I_(p)=100 kA and electron density of n_(e)=1.5×10^(19)m^(-3),the ratio of Spitzer conductivity between omhic(OH)and ECCD phases is considered and the experimental data have been corrected.The correction results show that the current drive efficiency η_(1)caused by the fast electron hot conductivity decreases by approximately 79%.It can be estimated that the driven current is approximately 24 kA at 300 kW ECW power.