Investigation of Effects of Toroidal Field Ripple on Plasma Poloidal Beta in IR-T1 Tokamak

We present an investigation of effect of Toroidal Field (TF) ripple (due to finite number of the toroidal field coils) on the plasma poloidal Beta in IR-T1 Tokamak. For this purpose, array of magnetic probes and also a diamagnetic loop with its compensation coil were designed, constructed, and installed on the outer surface of IR-T1. Amplitude of the TF ripple is obtained 0.01, and also the effect of the TF ripple on the poloidal Beta discussed. In the high field side region of tokamak chamber, the TF ripple effect is decreasing of the poloidal Beta, whereas the low field side has inverse situation.     

Measurement of the Shafranov Parameter in Presence of the Toroidal Field Ripple in IR-T1 Tokamak

In this paper we present an investigation of the effects of Toroidal Field ripple (TF ripple) on the Shafranov parameter in IR-T1 Tokamak. For this purpose, a diamagnetic loop with its compensation coil were designed and installed on outer surface of the IR-T1 Tokamak. Amplitude of the TF ripple is obtained 0.01, and also the effect of TF ripple on the Shafranov parameter discussed. In presence of the TF ripple and in low field side of the IR-T1 Tokamak chamber (θ = 0), the local value of Shafranov parameter increased, whereas in the high field side (θ = 180) the Shafranov parameter decreased.     

The Behavior of Radial Electric Field and Toroidal Rotation in the Edge Plasma of Divertor Tokamak

A new method for describing the nature of radial electric field and its relation with toroidal rotation in edge plasma of small size divertor tokamak is proposed in this work. The expression of radial electric field in the edge plasma of small size divertor tokamak can be divided into two parts. The first part E _r ⁽⁰⁾ is related to electrostatic potential of plasma in edge plasma of this tokamak. The second part E _r ⁽¹⁾ is related to contribution of toroidal rotation of radial current in edge plasma of this tokamak. The results of this work provide the following: (1) A new one-dimensional ordinary differential equation for toroidal velocity is obtained. The one-dimensional ordinary differential equation suggest new tool to explaining tokamak experiments involving measurements of plasma rotation and radial electric field. (2) Also the results of this work shows that, the main contribution to the radial electric field inside separatrix (plasma core) gives the term E _r ⁽¹⁾.     

TF Ripple Effects on Plasma Energy Confinement Time in IR-T1 Tokamak

In this paper we present analysis of the effects of Toroidal Field ripple (TF ripple) on the plasma energy confinement time in IR-T1 Tokamak. For this purpose, a diamagnetic loop with its compensation coil were designed and installed on outer surface of the IR-T1 tokamak. Amplitude of the TF ripple is obtained 0.01, and also the effects of TF ripple on the plasma energy confinement time discussed. In presence of the TF ripple and in low field side of the IR-T1 tokamak chamber (θ = 0), the local value of energy confinement time increased, whereas in the high field side (θ = 180), the energy confinement time decreased.     

Effects of Resonant Helical Field on Plasma Internal Inductance in IR-T1 Tokamak

Measurement of plasma internal inductance is important in tokamak plasma experiments (plasma internal inductance relates to the plasma current profile). In this paper we present an experimental investigation of effects of Resonant Helical Field (RHF) on the plasma internal inductance in IR-T1 tokamak. For this purpose, four magnetic probes and also a diamagnetic loop with its compensation coil were constructed and installed on outer surface of the IR-T1 tokamak, and Shafranov parameter, poloidal Beta, and then the internal inductance determined. In order to investigate the effects of RHF on internal inductance, we measured it in presence and also in absence of different modes of the RHF (L = 2, L = 3, L = 2&3). Experimental results show that L = 3 mode can flat the plasma current and increase the plasma internal inductance.     

Effects of ferromagnetic components on energetic ion confinement in ITER

By using a fully three dimensional magnetic field orbit-following Monte-Carlo code, the energetic ion confinement was investigated for the current conceptual design of the ferromagnetic components in ITER which will be employed for reducing the toroidal magnetic field (TF) ripple. The ferromagnetic insert is effective in the reference standard scenario with Q = 10 (Scenario No. 2) and steady state scenario with Q = 5 (Scenario No. 4) to improve the energetic ion confinement. Over-compensation appears at half of the full toroidal magnetic field and its effect becomes stronger when the quantity of the ferromagnetic insert is increased in order to more reduce the TF ripple at the full toroidal magnetic field. Though the current design is acceptable, whether to increase the ferromagnetic insert to achieve lower TF ripple amplitude at the full field operation depends on how prospected are possibilities of lower field operations. Planned test blanket modules do not induce large loss (<1%) at the full field in Scenario No. 4. At the half field, however, the loss reaches ∼10% for the alpha particles due to localized large TF ripple.     

Effect of Fuelling Depth on the Fusion Performance and Particle Confinement of a Fusion Reactor

The fusion performance and particle confinement of an international thermonuclear experimental reactor(ITER)-like fusion device have been modeled by numerically solving the energy transport equation and the particle transport equation. The effect of fuelling depth has been investigated. The plasma is primarily heated by the fusion produced alpha particles and the loss process of particles and energy in the scrape-off layer has been taken into account. To study the effect of fuelling depth on fusion performance, the ITERH-98P(y,2) scaling law has been used to evaluate the transport coefficients. It is shown that the particle confinement and fusion performance are significantly dependent on the fuelling depth. Deviation of 10% of the minor radius on fuelling depth can make the particle confinement change by ~ 61% and the fusion performance change by ~ 108%. The enhancement of fusion performance is due to the better particle confinement induced by deeper particle fuelling.     

Simulation of Toroidal Rotation Effect on Heat Flux Transport in the Edge Plasma of Small Size Divertor Tokamak

The effect of toroidal rotation on heat flux transport in the edge plasma of small size divertor was simulated by B2SOLP0.5.2D transport code. The main results of simulation shows that, the following: (1) the radial heat flux is strongly influenced by toroidal rotation. (2) The amplification of conduction part of radial heat flux imposes nonresilient profile of ion temperature, under which the effect of toroidal rotation on ion temperature profile is strong. (3) The ion distribution and its gradients are lower for counter-injection neutral beam than for co-injection neutral beam. (4) Reversal of toroidal rotation during using neutral beam injection result in reverses of radial electric field and E × B drift velocity. (5) The toroidal rotation strong influence on the ion temperature scale length of the ion temperature gradient (ITG). (6) Switch on and off all drifts leads to higher change in the ion density distribution in edge plasma of small size divertor tokamak when the unbalance neutral beam injection are considered (7) the comparison between radial heat flux at different momentum input shows that, the radial ion heat flux with larger ion temperature scale length in the case of co-injection neutral beam is larger than the ion heat flux with smaller ion temperature scale length in the case of counter-injection neutral beam.     

Effects of Particle Confinement and Recycling on Thermally Stable Regions in D-T Tokamak Plasma

The water accumulation phenomena in the upper plenum of a PWR was investigated by using the data of the Cylindrical Core Test Facility (CCTF) test.

When the liquid inventory in the upper plenum is small, the liquid carryover rate from the upper plenum was governed by the liquid inlet flow rate. After some amount of the water was accumulated in the upper plenum, the liquid carryover rate was governed by the steam up-flow rate and the liquid inventory in the upper plenum. The liquid carryover rate was higher with the higher steam up-flow rate and the larger liquid inventory. This trend on the liquid carryover rate was also observed in small scale model test.

Based on the CCTF data, the empirical correlation on the liquid carryover rate was obtained.     

Effects of Alfvenic Poloidal Flow and External Vertical Field on Plasma Position in IR-T1 Tokamak

We analyzed dynamic equilibrium properties of a large aspect ratio and low Beta tokamaks, in particular deriving a modified relation for the Shafranov shift in the presence of poloidal flow and external vertical field, and demonstrate it experimentally on the IR-T1 tokamak. Poloidal flow can produce modifications in the equilibrium properties. By increasing Alfvenic Mach number from zero, flow produce outward force, and plasma shifted in outward direction. If the poloidal Alfvenic Mach number equal to one, singularity will observe in the solution of generalized Grad–Shafranov equation. Also inversion of Shafranov shift in the transition of flow speed between sub-Alfvenic to super-Alfvenic speeds can be observed due to inward force produced by flow.     

The Effects on the Plasma Poloidal Velocity and Electrical Field Distribution with NBI and ICRH on HL-1M Tokamak

It is an important subject to improve the plasma confinement for fusion plasmas. The plasma confinement is sensitive to the plasma edge conditions. The L-H mode transition is related to the edge radial electrical field E_r, the gradient of E_r and the poloidal rotation velocity. In the meantime, the edge plasma radial transport is relates also to the change of poloidal electrical field E_θ. The first L-H mode transition was observed on ASDEX with NBI. This result indicated that the edge fluctuations, the radial transport and the interaction between the wall and the limiters were all reduced and the plasma confinement was improved. NBI and ICRH ex     

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.     

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.     

An Analysis of Ripple and Error Fields Induced by a Blanket in the CFETR

The Chinese Fusion Engineering Tokamak Reactor(CFETR) is an important intermediate device between ITER and DEMO. The Water Cooled Ceramic Breeder(WCCB)blanket whose structural material is mainly made of Reduced Activation Ferritic/Martensitic(RAFM) steel, is one of the candidate conceptual blanket design. An analysis of ripple and error field induced by RAFM steel in WCCB is evaluated with the method of static magnetic analysis in the ANSYS code. Significant additional magnetic field is produced by blanket and it leads to an increased ripple field. Maximum ripple along the separatrix line reaches 0.53% which is higher than 0.5% of the acceptable design value. Simultaneously, one blanket module is taken out for heating purpose and the resulting error field is calculated to be seriously against the requirement.     

托卡马克等离子体中快粒子触发的高频鱼骨模不稳定性研究

本文考虑托卡马克等离子体中快粒子的空间密度分布剖面,在中性束及电子回旋共振加热的条件下,建立了研究鱼骨模的色散关系并对鱼骨模作了数值研究。结果表明:快粒子对内扭曲模有致稳作用,且在近轴加热条件下可激发高频鱼骨模,其频率与快粒子的环向进动频率一致。鱼骨模的增长率与快粒子的密度梯度有关,一般随密度梯度的增加而增大。在高比压区间,勉强通行快粒子可驱动鱼骨模进入第二稳定区,在该区域鱼骨模是稳定的。     

Determination of the Plasma Internal Inductance and Evaluation of its Effects on Plasma Horizontal Displacement in IR-T1 Tokamak

We analyzed dynamic equilibrium properties of a large aspect ratio and low Beta tokamaks, in particular deriving a modified relation for the Shafranov shift in the presence of poloidal flow and external vertical field, and demonstrate it experimentally on the IR-T1 tokamak. Poloidal flow can produce modifications in the equilibrium properties. By increasing Alfvenic Mach number from zero, flow produce outward force, and plasma shifted in outward direction. If the poloidal Alfvenic Mach number equal to one, singularity will observe in the solution of generalized Grad–Shafranov equation. Also inversion of Shafranov shift in the transition of flow speed between sub-Alfvenic to super-Alfvenic speeds can be observed due to inward force produced by flow.     

The Effect of Trapped Particles on Gradient Drift Instabilities in Finite Pressure Plasma with a Longitudinally Nonuniform Magnetic Field

Gradient drift instabilities are considered on the basis of local dispersion relation developed for the case of longitudinally nonuniform magnetic field. Such a field allows simulating the effect of trapped particles in tokamak geometry separately from other effects. Completely electromagnetic approach is developed to take into account finite pressure. Trapped particles and magnetic field nonuniformity are taken into account by the frequency of the magnetic drift of the particle. Modes propagating perpendicularly to the magnetic field lines are typical from the viewpoint of effect of trapped electrons. In finite pressure plasma (ratio of the plasma pressure to the magnetic pressure β ~ 0.1), growth rate decrease is significant, as compared with electrostatic limit (β → 0).     

Effects of the Hot Electron Interchange Instability on Plasma Confined in a Dipolar Magnetic Field

The Levitated Dipole Experiment (LDX) explores confinement and stability of plasma created within the dipole field of a strong superconducting magnet. During initial experiments, long-pulse, quasi-steady state discharges that last more than 10 s and have peak beta of more than 20% are studied. The plasma is created by multi-frequency electron cyclotron resonance heating (ECRH) at 2.45 and 6.4 GHz. A population of energetic electrons, with mean energies above 50 keV, dominates the plasma pressure. Creation of high pressure, high beta plasma is possible only when intense hot electron interchange (HEI) instabilities are stabilized by sufficient neutral gas fueling. The instabilities resonate with the magnetic drift motion of the energetic electrons and can cause rapid radial transport. Measurements of the electrostatic and magnetic fluctuations of the HEI instability are described along with observations of the instability’s spectral characteristics. Fluctuations of the outer poloidal field induced by the HEI show a rapid evolution of the perturbed pressure profile.      

The Influence of the Negative Radial Electric Field on the Orbit of Banana Particles in Tokamak

This paper explores the patterns of influence of the negative radial electric field on the drift displacement and trajectory of charged particles, for it is essential for further investigation into the transitional mechanism of L-H Mode. In the light of superposition between the poloidal velocity of charged particles and the E ×B drift caused by the negative radial electric field, the paper offers a theoretical analysis and value simulations. Under the action of different radial electric fields, results have been obtained in regard to changes in the velocity of charged particles (mainly ions), patterns of changes in drift displacement, regional change of banana particles, and features of transition and change between trajectories of transiting particles and banana particles.     

The Influence of Resonance Helical Field on the Z eff and Impurity Radiation in IR-T1 Tokamak

The influence of resonant helical field, RHF, on effective ion charge, Z _eff, and impurity radiations on IR-T1 tokamak discharges was studied. The theoretical calculation of Z _eff with RHF indicated that the Z _eff decreased. To observe the effects of reduced Z _eff on impurity radiation, two important parts of plasma were investigated, equilibrium region of plasma and disruptive plasma. The results obtained from previous experiments on equilibrium plasma showed the increased radiation of impurities, in comparison with preceding and next regions, whereas the new results indicate that the impurities radiation decreases remarkably in disruptive part of plasma.