Magnetic Confinement Devices Research Articles

Eigenvalue Solver for Fluid and Kinetic Plasma Models in Arbitrary Magnetic Topology

AbstractArbiTER (Arbitrary Topology Equation Reader) is a new code for solving linear eigenvalue problems arising from a broad range of physics and geometry models. The primary application area envisioned is boundary plasma physics in magnetic confinement devices; however ArbiTER should be applicable to other science and engineering fields as well. The code permits a variable numbers of dimensions, making possible application to both fluid and kinetic models. The use of specialized equation and topology parsers permits a high degree of flexibility in specifying the physics and geometry.

The implementation of a data acquisition and service system based on HDF5

A data acquisition and service system based on HDF5 has been designed. It includes four components: data acquisition console, data acquisition subsystem, data archive system and data service. The data acquisition console manages all DAQ information and controls the acquisition process. The data acquisition subsystem supports continuous data acquisition with different sampling rates which can be divided into low, medium and high level. All experimental data will be remotely transferred to the data archive system. It adopts HDF5 as its low-level data storage format. The hierarchical data structure of HDF5 is useful for efficiently managing the experimental data and allows users to define special data types and compression filter which can be useful to deal with special signals. Several data service tools have also been developed so that users can get data service via Client/Server or Brower/Server. The system will be demonstrated on Keda Torus eXperiment (KTX) device, which is a new Reversed Field Pinch (RFP) magnetic confinement device. The details are presented in the paper.

会切磁瓶探析—磁场位形为磁阱的新型磁约束装置

会切磁瓶是由布置在正多面体各顶点的磁体，构成的磁约束装置。其内部的磁场位形，是底部磁感应强度为零的理想磁阱，已达到了阱深定义的极限值。磁感应强度变化曲线显示，在相同容积下，正12面体会切磁瓶的磁感应强度落差，是垒球缝线圈的磁感应强度落差的20多倍，且会切磁瓶还有着极大的可扩展性。会切磁瓶对等离子体的约束原理是依靠磁阱，磁约束理论表明，只有磁阱位形磁场，才能真正做到等离子体的稳定约束。而Tokamak或磁镜，是依靠磁力线对电粒子的粘连，理论和实践都表明，其存在着各种宏观和微观不稳定性。而在会切磁瓶中，这些不稳定性都将不复存在。从会切磁瓶的构成看，无论是材料、运行、扩展性等方面，会切磁瓶都有着传统磁约束装置不可比拟优势。 The cusp magnetic bottle is a magnetic confinement device constituted by magnets on each vertex of the regular polyhedron. The internal magnetic field configuration is an ideal magnetic trap with the bottom magnetic induction intensity of zero, which could reach up to the limit value defined by the trap depth. The changing curve of magnetic induction intensity has indicated that, the magnetic induction intensity difference for cusp magnetic bottle of regular dodecahedron is over 20 times greater than that for softball seal coil of same volume and that the cusp magnetic bottle has a larger space to expand. The constraint theory of plasma by the cusp magnetic bottle is to rely on the magnetic trap and magnetic confinement theory indicates that, only magnetic trap configuration can truly achieve the stable confinement of plasma. Tokamak or magnetic mirror is to rely on the adhesion of particles of electricity on magnetic line of force. However, it has all kinds of macroscopic and microcosmic instabilities from both theoretically and practically. These instabilities would no long exist in the cusp magnetic bottle. From the constitution of cusp magnetic bottle, the materials, operation, structure, flexibility, expansibility and other aspects all indicate that the cusp magnetic bottle is far superior to traditional magnetic confinement devices.

Magnetic Field Analysis of Plasma Guide in Galathea Trimyx

You Galathea Trimyx is a kind of small size, multipole magnetic confinement devices in controlled thermonuclear fusion. Plasma guide is one of important part in Galathea Trimyx which is responsible for transporting fast and slow plasma bunches ejected from plasma gun. The distribution and uniformity of magnetic field in completed plasma guide is analyzed in detail, including in x -axis direction and in z-axis direction. On the basis, the motion of plasma in the guide is discussed.

Determination of broken KAM surfaces for particle orbits in toroidal confinement systems

The destruction of Kolmogorov–Arnold–Moser surfaces in a Hamiltonian system is an important topic in nonlinear dynamics, and in particular in the theory of particle orbits in toroidal magnetic confinement systems. Analytic models for transport due to mode-particle resonances are not sufficiently correct to give the effect of these resonances on transport. In this paper we compare three different methods for the detection of the loss of stability of orbits in the dynamics of charged particles in a toroidal magnetic confinement device in the presence of time dependent magnetic perturbations.

Plasma confinement by magnetic field with convex-concave field lines

It has been found that plasma confinement by the magnetic field of alternating-sign curvature with convex–concave field lines results in a strong stabilizing action against convective (flute-interchange) perturbations. For simple combinations of axisymmetric mirrors and cusps the calculations according to the kinetic stability criterion give strongly, centrally peaked stable plasma pressure profiles instead of shallow ones. For the experimental research of this effect, a compact magnetic confinement device has been modified by adding of the external current coil to fulfil the field-line curvature requirements. The critical convectively-stable plasma pressure profiles calculation in this experimental geometry and the probe measurements of the spatial plasma distribution in the new magnetic configuration of alternating-sign curvature have been performed. The experimental results give some support for a conclusion that there is an increase in the ion saturation current at the region near the minimum of the specific volume min ∫dl/B. This region corresponds to the average minimum in the second adiabatic invariant, and the kinetic description predicts the stable pressure profile peaking here due to reduction of charge separation by particle drift in alternating-sign curvature.

Addressing the Challenges of Plasma-Surface Interactions in NSTX-U

The importance of conditioning plasma-facing components (PFCs) has long been recognized as a critical element in obtaining high-performance plasmas in magnetic confinement devices. Lithium coatings, for example, have been used for decades for conditioning PFCs. Since the initial studies on the Tokamak Fusion Test Reactor (TFTR), experiments on devices with different aspect ratios and magnetic geometries like the National Spherical Torus Experiment (NSTX) continue to show the relationship between the lithium PFCs and good confinement and stability. While such results are promising, their empirical nature do not reflect the detailed relationship between the PFCs and the dynamic conditions that occur in the tokamak environment. A first step developing an understanding such complexity will be taken in the upgrade to NSTX, or the National Spherical Torus Experiment-Upgrade (NSTX-U) that is nearing completion. New measurement capabilities include the materials analysis and particle probe for in situ surface analysis of samples exposed to tokamak plasmas. The onion-skin modeling for edge analysis (OEDGE) suite of codes, for example, will be used to model the underlying mechanisms for such material migration in NSTX-U. This will lead to a better understanding of how plasma-facing surfaces evolve during a shot, and how the composition of the plasma-facing surface influences the discharge performance we observe. This paper will provide an overview of these capabilities, and highlight their importance for NSTX-U plans to transition from carbon to high- ${Z}$ PFCs.

A Spectrally Resolved Motional Stark Effect Diagnostic for the TJ‐II Stellarator

AbstractA spectrally resolved motional stark effect (MSE) diagnostic has been implemented for the TJ‐II stellarator to quantify the magnitude and pitch of components of the magnetic field created in this magnetic confinement device. The system includes a compact diagnostic neutral beam injector (DNBI) that provides a short pulse of accelerated neutral hydrogen atoms with an e–1 beam radius of 2.1 cm to stimulate the Doppler‐displaced Balmer Hαs emissions, which are the basis for this diagnostic. Measurement of the wavelength separation of the Stark splitting of the Hα spectrum, as well as of the relative line intensities of its components, allow the local magnitude and direction of the internal magnetic field components to be measured at 10 positions across the plasma. The use of a DNBI extends such measurements to the electron cyclotron resonance (ECR) heated phases of plasmas while also overcoming the need for the complicated inversion techniques that are required when such measurements are performed with a heating neutral beam injector (NBI). Moreover, the use of the shot‐to‐shot technique with reproducible discharges further simplifies fits to the MSE spectra as nearby impurity spectral emission lines can be eliminated or significantly reduced. After outlining the principles of this technique and the diagnostic set‐up, magnetic field measurements made during ECR or NBI heating phases are reported for a range of magnetic configurations and are compared with vacuum magnetic field estimates in order to evaluate the capabilities and limitations of this diagnostic for the TJ‐II. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

核聚变理论再探及聚变堆的自持燃烧

根据修正后的狭义相对论，得出通电流等离子体的箍缩效应，本质上是尺缩效应，其并不能对聚变反应起促进作用。对电磁辐射理论的质疑，指出目前的电磁辐射理论并不符合麦克斯韦方程组，再结合聚变实验结果，推测目前的电磁辐射理论低估了聚变堆的辐射能。以上两点揭示了目前核聚变理论与实验形成巨大差异的原因，并得出目前的聚变装置不能实现聚变堆自持燃烧的结论。由此提出了对目前磁约束聚变装置在功能上的改进，将聚变堆包层第一壁设计为具有反射镜的功能，使辐射能重新返回，以达到聚变堆的自加热目的。最后探讨了磁镜与环流器相组合的聚变装置新型，阐述了该装置具有其它磁约束装置不可比拟的优势。 Based on the corrected special theory of relativity, the pinch effect has been proved to be length contraction effects for plasma like galvanization. It will not accelerate the fusion reaction. By questioning the electromagnetic radiation theory, the current theory has been approved that it does not fit the Maxwell’s equation. Combined with the testing results of the fusion reaction, the current electromagnetic radiation theory underestimated the radiation power of the fusion reactor. As mentioned above, it revealed the reasons causing the great difference between the current fusion theory and the testing results, and concluded that the current fusion reactor cannot achieve self-sustained combustion. So the improvements on the magnetic confinement devices have been suggested. For achieving self-heating of the fusion reactor, the first wall of the fusion reactor must be designed to reflect the radiation. At last, the new device which combined magnetic mirror and Tokamak has been discussed and its superiority has been approved over the rest of magnetic con-finement devices.

A new method of measuring the poloidal magnetic and radial electric fields in a tokamak using a laser-accelerated ion-beam trace probe.

Both the poloidal magnetic field (Bp) and radial electric field (Er) are significant in magnetic confinement devices. In this paper, a new method was proposed to diagnose both Bp and Er at the same time, which was named Laser-accelerated Ion-beam Trace Probe (LITP). This method based on the laser-accelerated ion beam, which has three properties: large energy spread, short pulse lengths, and multiple charge states. LITP can provide the 1D profiles, or 2D images of both Bp and Er. In this paper, we present the basic principle and some preliminary theoretical results.

Physical aspects of divertor Thomson scattering implementation on ITER

This paper describes the challenges of Thomson Scattering implementation in the ITER divertor and evaluates the capability to satisfy project requirements related to the range of the measured electron temperature and density. A number of aspects of data interpretation are also discussed. Although this assessment and the proposed solutions are considered in terms of ITER compatibility, they may also be of some use in currently operating magnetic confinement devices.

Fast wave evanescence in filamentary boundary plasmas

Radio frequency waves for heating and current drive of plasmas in tokamaks and other magnetic confinement devices must first traverse the scrape-off-layer (SOL) before they can be put to their intended use. The SOL plasma is strongly turbulent and intermittent in space and time. These turbulent properties of the SOL, which are not routinely taken into account in wave propagation codes, can have an important effect on the coupling of waves through an evanescent SOL or edge plasma region. The effective scale length for fast wave (FW) evanescence in the presence of short-scale field-aligned filamentary plasma turbulence is addressed in this paper. It is shown that although the FW wavelength or evanescent scale length is long compared with the dimensions of the turbulence, the FW does not simply average over the turbulent density; rather, the average is over the exponentiation rate. Implications for practical situations are discussed.

A new class of magnetic confinement device in the shape of a knot

We describe a new class of magnetic confinement device, with the magnetic axis in the shape of a knot. We call such devices “knotatrons.” An example is given that has a large volume filled with magnetic surfaces, with significant rotational-transform, and with the magnetic field produced entirely by external circular coils.

On the electrostatic potential in the scrape-off layer of magnetic confinement devices

The mechanism regulating the equilibrium electrostatic potential in the scrape-off layer (SOL) of magnetic confinement devices is elucidated. Based on a generalized Ohm's law and the boundary conditions at the magnetic presheath entrance, an analytical expression for the equilibrium electrostatic potential is derived. Results imply that the relative importance of the plasma dynamics at the sheath and far away from the wall in setting the value of the electrostatic potential depends on the density and temperature drops that are established between the two regions. Global, three-dimensional fluid simulations of tokamak SOL turbulence in a simple configuration are performed, confirming the validity of our predictions. The results presented here are general and can be applied to other open-field-line configurations, including linear devices and simple magnetized toroidal devices.

Numerical analysis of MD events and preliminary thermal calculation for KTX vacuum vessel

KTX is a new reversed field pinch (RFP) magnetic confinement device which is under design in ASIPP and USTC. Major disruption (MD) events may occur in future operating process, which is simulated with the finite element (FE) method. The results present that the peaks of eddy currents on vessel and conductor shell are respectively 11.791kA and 68.637kA with maximum stress 67.1MPa due to high transient electromagnetic (EM) force. It is confirmed that the structure is still strong enough to bear the electromagnetic loads even if the worst case. Besides, as KTX vacuum vessel will take the method of natural cooling for heat dissipation during plasma discharge (0.5–1.0MA), a preliminary thermal calculation was implemented in normal condition to decide suitable time parameters such as duration and interval. It is suggested that the discharge interval should be no less than 5min for the complete 1MA plasma with 100ms duration, which can guarantee the temperature of vacuum vessel below 200°C.

Structure of C Deposition Layers under Various Deposition Conditions

The structure of deposited carbon layers formed under various conditions ranging from small scale laboratory to large scale magnetic confinement devices was characterized using Raman spectroscopy. By comparing ion beam and TEXTOR experiments, the deposition temperature is found to be the dominant factor in three dimensional disorder of sp2 sites and sp3 ratio at T>493 K. While, no clear temperature dependence on properties of aromatic rings was observed, indicating other parameters responsible for the aromatic rings present in carbon deposition layers. The carbon layers from JET differed significantly, indicating influence of Be compound formation on Raman parameters.

Review and limitations of 3D plasma blob modeling with reduced collisional fluid equations

Recent 3D studies on plasma blobs (coherent structures found in the edge region of magnetic confinement devices) have demonstrated that the drift wave instability can strongly limit the blob’s coherency and cross field convective nature that is predicted by 2D theory. However, the dominant unstable drift wave modes that effect plasma blobs were found to exist in parameter regimes that only marginally satisfied several of the major assumptions considered for the validity of the reduced collisional fluid equations used in the study. Namely, the neglect of electron heat flow, finite electron mean free path effects, and thermal ions. A follow up study demonstrated how the drift wave instability might change if a set of equations that does not suffer from the limitations mentioned above were considered. In the present paper, the results of this later work are used to discuss the limitations on using the collisional fluid equations for 3D studies of plasma blobs.

Intermittent transport in edge plasma with a 3-D magnetic geometry in the Large Helical Device

Blobby plasma transport is a universally observed phenomenon in magnetic confinement devices, and it is considered to be closely related to edge plasma physics. We have investigated such an intermittent event observed inside the divertor region of the Large Helical Device by using a fast-scanning Langmuir probe with two electrodes. Ion saturation current fluctuations showed negative spikes in the divertor leg and positive spikes in the private region. Further, the time delay between the two fluctuations followed a unique trajectory in the positive-skewness region. We found common as well as different fluctuation characteristics between the LHD and tokamaks. We discuss the analysis results in relation to the blob-generation and propagation behaviors in the three-dimensional magnetic geometry around the divertor leg. In addition, we quantitatively estimated the blob propagation velocity and size based on a theoretical assumption.

New Thermodynamical Force in Plasma Phase Space that Controls Turbulence and Turbulent Transport

Physics of turbulence and turbulent transport has been developed on the central dogma that spatial gradients constitute the controlling parameters, such as Reynolds number and Rayleigh number. Recent experiments with the nonequilibrium plasmas in magnetic confinement devices, however, have shown that the turbulence and transport change much faster than global parameters, after an abrupt change of heating power. Here we propose a theory of turbulence in inhomogeneous magnetized plasmas, showing that the heating power directly influences the turbulence. New mechanism, that an external source couples with plasma fluctuations in phase space so as to affect turbulence, is investigated. A new thermodynamical force in phase-space, i.e., the derivative of heating power by plasma pressure, plays the role of new control parameter, in addition to spatial gradients. Following the change of turbulence, turbulent transport is modified accordingly. The condition under which this new effect can be observed is also evaluated.

Helium effects on tungsten surface morphology and deuterium retention

Recent experimental results on tungsten surface morphology, especially nano-structure (fuzz), induced by helium plasma exposure at temperatures between 1000K and 2000K are reviewed. This structure was firstly reported in 2006. In this review, most of experimental results reported so far including characteristics and formation conditions of the nano-structure in both linear plasma devices and magnetic confinement devices, erosion and arcing by steady-state plasma exposure and ELM-like pulsed heat or pulsed plasma exposure by a laser and a plasma gun are summarized. In addition, He effects on D retention under simultaneous D/He irradiation on tungsten are presented.