Effect Of Toroidal Field Ripple Research Articles

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

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

Alpha particle ripple loss in CFETR steady-state scenario

Confinement of alpha particles is one of the key issues of burning plasma in tokamaks. Due to the discreteness of the toroidal field (TF) coils, the loss alpha particles induced by TF ripple can cause a strong heat load on the first wall. In this work, by using the guiding center code ORBIT, we investigated alpha particle TF ripple loss in Chinese Fusion Engineering Test Reactor (CFETR) steady-state scenario (v20190422), in which both the initial distribution and classical steady-state slowing down distribution of alpha particles are considered. Effects of TF ripple on three particle loss mechanisms, namely prompt loss, ripple well trapping loss and stochastic diffusion loss, are analyzed in detail. Through comparison, it is found that the stochastic diffusion is the main mechanism of alpha particle ripple loss. Moreover, the toroidal and poloidal profiles of the heat load on the first wall are calculated and compared with the safety threshold of CFETR. In addition, a comparison study of alpha particle ripple loss in the hybrid scenario (v20190422) has been carried out. It is found that both total particle loss fraction and maximum heat load in the steady-state scenario are approximately 50% larger than those in the hybrid scenario.

Fast Ion Trajectory Calculations in Tokamak Magnetic Configuration Using Symplectic Integration Algorithm

A numerical scheme based on Symplectic Integration Algorithm (SIA) has been used to develop an orbit following code to calculate fast ion trajectories in tokamak magnetic configuration. For the purpose of demonstrating the expediency of symplectic schemes, the algorithm has been applied to the H´enon-Heiles system and compared with non- symplectic Runge–Kutta Algorithm (RKA) for numerically integrating the Hamiltonian equations. In contrast to RKA, the long-time stability of SIA has been highlighted. Furthermore, the SIA has been used to find the exact trajectories of, trapped and passing, fast ions in tokamak. In particular, the effect of an intrinsic magnetic field perturbation has been investigated, i.e. toroidal field ripples. This perturbation is toroidal field ripple (TFR) which are there due the discrete number to toroidal coils around the torus. The numerical scheme used shows excellent conservation of particle energy as well as of angular momentum (in axi-symmetric case). The effect of TFR on these trajectories has been simulated and it is shown that the resonance between toroidal precession of bananas and the field ripples results in spread of the trajectories for banana particles, whereas the passing fast ions are unaffected.

Theoretical and Experimental Investigation of Effects of Toroidal Field Ripple on Poloidal Beta, Internal Inductance and Shafranov Shift in IR-T1 Tokamak

<b> </b><b> </b>In this paper we presented an investigation of effects of the toroidal field ripple (TF ripple) (due to finite number of the toroidal field coils) on the poloidal beta, internal inductance, and Shafranov shift in IR-T1 Tokamak. For these purposes, array of magnetic probes and also a diamagnetic loop with its compensation coil were designed, constructed and installed on outer surface of the IR-T1. Amplitude of the TF ripple is obtained 0.01, and also the effects of TF ripple on the poloidal beta, internal inductance, and Shafranov shift were discussed. In the high field side region of tokamak chamber, the TF ripple effects is the decreasing and increasing of the poloidal beta and internal inductance, respectively, whereas the low field side have inverse situations. Also no sensible variation observed in the Shafranov shift due to TF ripple on IR-T1 plasma.

Edge pedestal characteristics in JET and JT-60U tokamaks under variable toroidal field ripple

The effects of toroidal field (TF) ripple on the edge pedestal characteristics were examined in the TF ripple scan experiments at the plasma current Ip of 1.1 MA in JET and JT-60U. The TF ripple amplitude δR was defined as a value averaged over the existing ripple wells at the separatrix on the outer midplane. By the installation of ferritic inserts (FIs), δR was reduced from 1% to 0.6% at 3.2T (0.5% at 2.2 T) in JT-60U. In JET, δR was varied from 0.08% to 1% by feeding different currents to the odd and even set of coils out of 32 TF coils. The pedestal pressure pped was similar for the cases before and after the installation of FIs in JT-60U. Similarly, no clear difference in pped was also observed in the variation of δR in JET. The core and edge toroidal rotation clearly shifted in the counter-direction by increased δR. However, there were no changes in the spatial profiles of electron density, electron temperature and ion temperature. By the installation of FIs in JT-60U, the ELM frequency fELM decreased by ∼20%, while the ELM energy loss increased by 50–150%. The increased ELM loss power by 30% suggests a reduction of inter-ELM transport with the reduced δR. In JET, fELM increased only slightly with increased δR while the edge toroidal rotation frequency decreased as δR increased. From the inter-machine similarity experiment at 1.1 MA, TF ripple less than 1% does not strongly affect the pedestal pressure. However, in the single TF ripple scan at the higher Ip of 2.6 MA in JET, it clearly decreases with the increased δR, accompanying with a strong density pump out at large TF ripple. These results suggests that the effect of TF ripple on H-mode properties becomes stronger in the plasmas with higher Ip or lower edge collisionality of ripple diffusion.

Analysis of the ITER low field side reflectometer employing the Beam Tracing Method

The Beam Tracing Method, which describes electromagnetic wave propagation in the short wavelength limit including diffraction effects, is applied to microwave reflectometry. The torbeam code has been augmented with relativistic corrections to the electron mass – which are necessary for a reliable description in high temperature plasmas such as in ITER, and a beam coupling model for the receiving antenna coupling. The propagation and reception behaviour of reflectometer probe beams in the ITER geometry is computed. The received power is affected by the intensity of the beams, the offset of the beams respectively to the receiver antenna and the angle of incidence. Using a magnetic field derived from a 3D equilibrium it is shown that the effects of toroidal field ripple in ITER on the beam propagation are negligible. Various antenna configurations for the ITER low field side reflectometer are proposed and analyzed, particularly their sensitivity to plasma height variations.

RETRACTED ARTICLE: 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.

RETRACTED ARTICLE: 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.

RETRACTED ARTICLE: 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.

Principal physics developments evaluated in the ITER design review

As part of the ITER Design Review and in response to the issues identified by the Science and Technology Advisory Committee, the ITER physics requirements were reviewed and as appropriate updated. The focus of this paper will be on recent work affecting the ITER design with special emphasis on topics affecting near-term procurement arrangements. This paper will describe results on: design sensitivity studies, poloidal field coil requirements, vertical stability, effect of toroidal field ripple on thermal confinement, material choice and heat load requirements for plasma-facing components, edge localized modes control, resistive wall mode control, disruptions and disruption mitigation.

Effect of toroidal field ripple and toroidal rotation on H-mode performance and ELM characteristics in JET/JT-60U similarity experiments

The effect of the toroidal field (TF) ripple and edge toroidal rotation (VT) on H-mode and pedestal performance as well as on ELM characteristics are investigated both in JET and JT-60U using matched plasma shape. In JT-60U, the amplitude of TF ripple (δr) was reduced from ∼1.2% to ∼0.5% (averaged value at BT = 2.2 T) after the installation of ferritic steel tiles (FSTs). In addition with FSTs, δr can also be varied by changing the toroidal magnetic field for a given separatrix position. In JET, the TF system can be configured to feed different currents to the odd and even coil sets out of 32 TF coils. In this operation mode, δr can actively be varied by selecting the appropriate differential current between each coil set. In both devices, it is observed that the edge VT, which was in the same direction as the plasma current (co-VT), reduced with increasing δr. Even at the same δr of 0.5%, the achievable edge VT in JT-60U was still lower than that in JET due to higher neutral beam fast ion losses in JT-60U. A series of power and density scans performed at several δr indicated that plasmas with smaller ripple amplitude and/or larger co-VT are favourable to achieve higher pped and HH factor in both devices. As for ELM characteristics, larger co-VT seems to increase the ELM energy loss together with the reduction of the ELM frequency.

Effect of toroidal field ripple on the formation of internal transport barriers

The effect of a toroidal field (TF) ripple on the formation and performance of internal transport barriers (ITBs) has been studied in JET. It was found that the TF ripple had a profound effect on the toroidal plasma rotation. An increased TF ripple up to δ = 1% led to a lower rotation and reduced the rotational shear in the region where the ITBs were formed. ITB triggering events were observed in all cases and it is thought that the rotational shear may be less important for this process than, for example, the q-profile. However, the increase in the pressure gradient following the ITB trigger was reduced in discharges with a larger TF ripple and consequently a lower rotational shear. This suggests that toroidal rotation and its shear play a role in the growth of the ITB once it has been triggered.

Effect of toroidal field ripple on plasma rotation in JET

Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (δ) from an average value of M = 0.40–0.55 for operations at the standard JET ripple of δ = 0.08% to M = 0.25–0.40 for δ = 0.5% and M = 0.1–0.3 for δ = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (δ ∼ 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect.

The effect of toroidal field ripple on confined alphas in TFTR DT plasmas

The pellet charge exchange (PCX) diagnostic on the Tokamak Fusion Test Reactor (TFTR) presently measures trapped alpha distribution functions with very small pitch angles ( nu ||/ nu ~0.05) at the midplane. The measured PCX alpha signal exhibits a depletion region near the outboard region. Results of the alpha energy spectra and radial profile suggest that stochastic ripple diffusion is the cause of the depletion. Comparison of the ripple stochastization boundary with Goldston-White-Boozer theory also shows the correct functional dependence on alpha energy and q profile

Transport in tokamaks – a review of experiment

The main experimental results on confinement and transport processes in tokamaks are summarised. It is difficult to draw definite conclusions from measurements of the global energy containment time even in the quasi-steady phase of those ohmically heated discharges, which do not exhibit gross instability or appreciable effects due to runaway electrons. However, comparison of particle and energy confinement suggests that the loss process is mainly conduction rather than convection. In order to separate the various energy input and loss mechanisms the assumptions of classical ohmic heating and equipartition are made. The experimental evidence for these assumptions is presented. The dominant energy transport process is electron thermal conduction, for which a formalism is suggested for comparing experimental data with various theoretical models. Particle and iimpurity transport appears to require the neoclassical pinch tenn in addition to anomalous particle diffusion at a significantly lower rate than electron conduction. The contribution of the sawtooth instability to transport can be measured in principle and is only important in certain conditions. 1-D models of the discharge are quite successful provided empirical forms of the electron conduction and particle diffusion are used. Partial dat a exists on various related topics: plasma rotation, radial electri c fields, the boundary layer, the effects of toroidal field ripple and low frequency instabilities. This material is summarised.

α-particle ripple losses during slow down in a tokamak reactor

An investigation is made of the effect of toroidal field ripple mirrors on the confinement of α particles. It is found that the diffusion of α particles into the loss regions of the ripple mirrors during slow down gives rise to significant particle and energy losses.

Nonadiabatic effects of field ripple on energetic ions in Tokamaks

Some effects of toroidal field ripple on energetic ion orbits in Tokamaks are considered. A finite gyroradius generalization of the adiabatic orbit theory condition for ripple trapping is derived. Resonances between the cyclotron motion and the motion through the field ripple are discussed. Conditions on the magnitude of the field ripple and the gyroradius are derived, such that the phase space islands corresponding to the cyclotron resonances overlap the ripple-trapping region. The intrinsic orbit stochasticity resulting from island overlap may be described as pitch-angle scattering. The diffusion coefficient is obtained from a mapping which is derived from the equations of motion. After scattering into the ripple-trapping region of phase space, particles are lost due to guiding drifts in the toroidal field. Applications to ions in reactor-size Tokamaks are discussed.

Effects of toroidal field ripple on suprathermal ions in tokamak plasmas

Analytic calculations of three important effects of toroidal field ripple on suprathermal ions in tokamak plasmas are presented. In the first process, collisional ripple-trapping, ions become trapped in local magnetic wells near their banana tips owing to pitch-angle scattering as they traverse the ripple on barely unripple-trapped orbits. In the second process, collisionless ripple-trapping, ions are captured (again near a banana tip) owing to their finite orbits, which carry them out into regions of higher ripple. In the third process, banana-drift diffusion, fast-ion banana orbits fail to close precisely, due to a ripple-induced ‘variable lingering period’ near the banana tips. These three mechanisms lead to substantial radial transport of banana-trapped, neutral-beam-injected ions when the quantity α*≡ε|τ|/Nqδ is of order unity or smaller.

Effects of Toroidal Field Ripple on the Loss of Energetic Injected Ions and Toroidal Coil Configuration in a Tokamak Reactor

Effects of Toroidal Field Ripple on the Loss of Energetic Injected Ions and Toroidal Coil Configuration in a Tokamak Reactor

Effect of Toroidal Field Ripple on Fast Ion Behavior in a Tokamak

Computational studies have been performed for fast ion behavior in a Tokamak with toroidal field ripple. Collisionless behavior of fast ions relating to rippletrapping, ripple-detrapping and banana drift is of essential importance in fast ion loss processes in case of quasi-perpendicular neutral beam injection. The collisionless ripple trapping and ripple-enhanced banana drift produce a large number of loss bands in velocity space and enhance the loss of fast ions. The fast ion loss associated with ripple can be categorized into two groups; ripple-trapped loss and banana-drift loss. The amount of loss particles due to the respective loss process is significantly influenced by the effect of finite banana size of fast ions. The ripple-trapped loss particles are localized in a specific region on the first wall surface.