Thermonuclear Fusion Plasmas Research Articles

Quantum-mechanical four-body versus semi-classical three-body theories for double charge exchange in collisions of fast alpha particles with helium targets

AbstractWithin the two-channel distorted wave second-order perturbative theoretical formalism, we study capture of both electrons from helium-like targets by heavy nuclei as projectiles at intermediate and high impact energies. The emphasis is on the four-body single-double scattering (SDS-4B) method and the three-body continuum distorted wave impact parameter method (CDW-3B-IPM). The SDS-4B method deals with the full quantum-mechanical correlative dynamics of all the four interactively participating particles (two electrons, two nuclei). The CDW-3B-IPM is a semi-classical three-body independent particle model (one electron, two nuclei), using a combinatorial calculus to describe double capture by a product of two uncorrelated probabilities, integrated over impact parameters. Both theories share a common feature in having altogether two electronic full Coulomb continuum wave functions. One such function is centered on the projectile nucleus in the entrance channel, whereas the other is centered on the target nucleus in the exit channel. These two methods satisfy the correct initial and final Coulomb boundary conditions in the asymptotic region of scattering, at infinitely large inter-particle separations. Yet, it is presently demonstrated that most of the available experimental data on total cross sections for the double capture from helium by alpha particles distinctly favor the SDS-4B method. This is especially true at intermediate energies. Such energies are critically important in versatile applications under the general umbrella of ion transport in matter, including thermonuclear fusion (plasma physics) and ion therapy (medicine).

Evidence of Electron Heating by Alpha Particles in JET Deuterium-Tritium Plasmas.

The fusion-born alpha particle heating in magnetically confined fusion machines is a high priority subject for studies. The self-heating of thermonuclear fusion plasma by alpha particles was observed in recent deuterium-tritium (D-T) experiments on the joint European torus. This observation was possible by conducting so-called "afterglow" experiments where transient high fusion yield was achieved with neutral beam injection as the only external heating source, and then termination of the heating at peak performance. This allowed the first direct evidence for electron heating of plasmas by fusion-born alphas to be obtained. Interpretive transport modeling of the relevant D-T and reference deuterium discharges is consistent with the alpha particle heating observation.

Hygienic assessment of electromagnetic fields generated by promising models of power plants

Introduction. The analyses of staff occupationally connected with maintenance and operation of plants included in the Federal Project “Development of technologies for Controlled Thermonuclear Fusion (CTF) and innovative plasma technologies” electromagnetic safety problems required full-scale measurements of the electromagnetic fields (EMF) and hygienic assessment in personnel workplaces. Materials and methods. Measurements of EMF frequency and intensity-time parameters and preliminary hygienic assessment in workplaces of Tokamaks MEFIST-0, T-11M, TUMAN-3M, FT-2, magnetic trap MK-200M were carried out. Results. The studies showed very high levels of pulsed magnetic fields (MF) (up to 433 mT), despite of official regulatory values absence, according to magnetic component effects mechanisms can be assessed as human health risk factor. Radio frequency EMF levels, despite the short-term exposure, can have the adverse effect on human health, because in all points of possible employees’ location there were exceeding the maximum permissible values (up to 170 fold). 1 Hz-1 kHz frequency range EMF electric and magnetic components amplitude-frequency characteristics peaks may be risk factor for human health too (despite the lack of this frequency range hygienic standards in Russia). Limitations. The limitations of the study are determined by the lack of generated by new CTF samples EMF frequency and intensity-time parameters objective data. Conclusion. EMF assessment in examined CTF staff work places pilot study showed that pulsed MF, radio frequency EMF, 1 Hz-1 kHz frequency range EMF both components levels reach very high values and, despite the absence of officially valid regulatory values, according to factor action mechanisms, can be risk factor for personnel health.

Fokker-Planck multi-species equations in the adiabatic asymptotics

The main concern of the present paper is the study of the multi-scale dynamics of thermonuclear fusion plasmas via a multi-species Fokker-Planck kinetic model. One of the goals is the generalization of the standard Fokker-Planck collision operator to a multi-species one, conserving mass, total momentum and energy, as well as satisfying Boltzmann's H-theorem. Secondly, we perform on one hand a mathematical asymptotic limit, letting the electron/ion mass ratio converging towards zero, to obtain a thermodynamic equilibrium state for the electrons (adiabatic regime), whereas the ions are kept kinetic. On the other hand, we develop a first numerical scheme, based on a Hermite spectral method, and perform numerical simulations to investigate in more details this asymptotic limit.

Study of solid molecular deuterium D2 growth under gas pressure

The injection of high-speed cryogenic pellets made of frozen hydrogen-isotopes, represents to date the most effective method to fuel magnetically confined thermonuclear fusion plasmas. Moreover, the injection of very large pellets composed of cryogenic solid of some suitable impurity (typically a noble-gas such as H2, Ne, or H2/Ne, D2/Ne mixtures), shattered in relatively small fragments just before entering the plasma, seems to be the most promising method to reduce the damage risks for the plasma-facing components in case of a plasma disruption. This technology, known as "Shattered Pellet Injection" (SPI), allows to spread out the plasma energy and mitigate possible damage to the in-vessel components, as well as to densify the plasma to suppress the formation of runaway electrons, and/or dissipate their energy. Several techniques to produce and launch cryogenic pellets have been investigated in the past decades. "Pipe gun" injectors are reliable and relatively simple devices are still commonly used today. They make use of single- or two-stage pneumatic light-gas guns to accelerate the pellet at high speeds. In these injectors, the cryogenic pellets are formed “in situ” (i.e., inside the launching barrel), by de-sublimating them directly from the gas phase, i.e., at temperatures and pressures below those of the triple point. The simplest case is pure deuterium pellets (T < 18.7 K, P < 171.3 hPa). The production of good quality solid deuterium, capable of withstanding the mechanical stress during the acceleration of the pellets, is a key issue. To this end the phase transition of deuterium from gas to solid (and vice versa) is modeled with extensive molecular-dynamics (MD) simulations. Moreover, the solid growth from the gas phase is simulated in an ample range of temperatures and pressures, to find the best compromise between growth velocity and mechanical properties of the resulting solid system.

Multiphysics Modeling of Insert Cooling System for a 170-GHz, 2-MW Long-Pulse Coaxial-Cavity Gyrotron

High-power, high-frequency gyrotrons are the only promising sources for the electron cyclotron resonance heating and current drive (ECRH&CD) in the present thermonuclear fusion plasma experiments and in future power plants. Compared to the hollow-cavity gyrotron design, the coaxial cavity gyrotron design facilitates improved mode competition control, which eventually increases the output power per tube. At KIT-IHM, the successful operation of a 170-GHz gyrotron has been demonstrated in the short-pulse regime, and the ongoing research activities are aiming to upgrade the existing coaxial cavity gyrotron from short-pulse (1–10 ms) to long-pulse (~ 1s) operation. In this paper, with the help of multiphysics simulations, the performance of the insert cooling system is verified for the continuous wave (CW) operation and the operating limits of the insert cooling systems are determined. The perfectly aligned coaxial Glidcop insert will be able to withstand operating conditions leading to a maximal heat flux of about 0.39 kW/cm2. The influence of insert misalignment on insert loading is also studied systematically in this paper.

Electron capture, ionization and excitation cross sections for keV collisions between fully stripped ions and atomic hydrogen in ground and excited states

Using a semiclassical close-coupling approach, we have calculated electron capture, excitation and ionization cross sections for collisions of fully stripped hydrogen, helium and lithium ions with atomic hydrogen in the ground state and in all excited states up to n=3. The cross sections for collision energies between 1 and 100 keV/u are given in table form. Furthermore, we provide estimates of the accuracy of the cross sections. The set of data presented in this work represent the first complete and consistent quantum study of these collision systems and will find use in the modeling and diagnosis of thermonuclear fusion plasma reactors.

Optical oscillator strengths of the vibronic excitations of molecular deuterium determined by the dipole ( γ , γ ) method

Absolute optical oscillator strengths of the Lyman and Werner bands of molecular deuterium are determined by a $\mathrm{dipole}(\ensuremath{\gamma},\ensuremath{\gamma}$) method with the high energy resolution of 25 meV. A comprehensive comparison shows that an excellent agreement between the present experimental results and the earlier theoretical calculations is achieved for both Lyman and Werner bands. In addition, the electronic transition dipole moments of ${\mathrm{D}}_{2}$ are derived. The absolute optical oscillator strengths of the Lyman and Werner bands of ${\mathrm{D}}_{2}$ reported in this work can serve as the benchmark to test calculations with different theoretical models and calculational codes and, also, be used in thermonuclear fusion plasma and other fields.

From Electrojet to ITER: India's Journey in Experimental Plasma Physics

India has an international presence in Plasma Physics and its diverse applications such as thermonuclear fusion, material processing, strategic and environmental applications and plasma devices. From a modest start in the early 1970s, we have made great strides in the field of experimental plasma physics. Capacity building in techniques relevant to plasma production, manipulation and parameter control, pulsed power, creation of magnetic fields of complex geometries, clean vacuum and pumping systems, development and deployment of diagnostics to enable understanding of fundamental processes in plasmas and computer simulation to model plasma phenomena have been truly remarkable. Parallel to this, a community of physicists, engineers and computer experts has grown and matured. Funding mechanisms and financial support essential to broad base the research and development activity by drawing in Universities and education institutes have been nucleated. It is through these activities that the human resource and technology development essential to sustain India's ambitious forays into magnetic confinement fusion and industrial and strategic plasma applications has taken place. This paper is an attempt to give a historical perspective to this journey, which started at the Physical Research Laboratory, Ahmedabad and later, involved the Institute for Plasma Research at Gandhinagar, many DAE Institutions, IITs and Universities.

Performance study of the neutron-TPC**Supported by National Natural Science Foundation of China (11275109)

Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics, nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM (Gas Electron Multiplier amplification)-TPC (Time Projection Chamber), named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution, high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution (FWHM) of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10−5 for 1.2 MeV, 1.81 MeV and 2.5 MeV neutrons respectively.

Energies and transition rates in Ge-like ions between In XVIII and Ce XXVII

The energy levels, wavelengths, oscillator strengths, and radiative electric dipole (E1), magnetic quadrupole (M2) transition probabilities for Ge-like ions (49≤Z≤58) among the lowest 88 fine-structure levels belonging to the ([Ar] 3d10)4s24p2, ([Ar] 3d10)4s24p4d, ([Ar] 3d10)4s4p3, ([Ar] 3d10)4s4p24d, ([Ar] 3d10)4s24d2, and ([Ar] 3d10)4p4 configurations are calculated using the fully relativistic multiconfiguration Dirac–Fock (MCDF) approach including the correlations within the n=7 complex, Breit interaction (BI) and quantum electrodynamics (QED) effects. For comparison, an independent calculation using the many-body perturbation theory (MBPT) method is also carried out to confirm the present energy levels accuracy, taking Xe XXIII as an example. The present results are compared with available experimental and theoretical results and good agreement is obtained. These accurate theoretical data are useful for controlled thermonuclear fusion research, plasma physics, and astrophysical applications.

Design of a neutron-TPC prototype and its performance evaluation based on an alpha-particle test

A neutron-TPC (nTPC) is being developed for use as a fast neutron spectrometer in the fields of nuclear physics, nuclear reactor operation monitoring, and thermo-nuclear fusion plasma diagnostics. An nTPC prototype based on a GEM-TPC (Time Projection Chamber with Gas Electron Multiplier amplification) has been assembled and tested using argon-hydrocarbon mixture as the working gas. By measuring the energy deposition of the recoil proton in the sensitive volume and the angle of the proton track, the incident neutron energy can be deduced. A Monte Carlo simulation was carried out to analyze the parameters affecting the energy resolution of the nTPC, and gave an optimized resolution under ideal conditions. An alpha particle experiment was performed to verify its feasibility, and to characterize its performance, including energy resolution and spatial resolution. Based on the experimental measurement and analysis, the energy resolution (FWHM) of the nTPC prototype is predicted to be better than 3.2% for 5 MeV incident neutrons, meeting the performance requirement (FWHM<5%) for the nTPC prototype.

Pixelated Single-crystal Diamond Detector for fast neutron measurements

Single-crystal Diamond Detectors (SDDs), due to their high radiation hardness, fast response time and small size, are good candidates as fast neutron detectors in those environments where the high neutron flux is an issue, such as spallation neutron sources and the next generation thermonuclear fusion plasmas, i.e. the ITER experiment. Neutron detection in SDDs is based on the collection of electron-hole pairs produced by charged particles generated by neutron interactions with 12C. Recent measurements have demonstrated the SDD capability of measuring the neutron flux with a good energy resolution and at high rates. In this work a novel detector based on a 12-pixels SDD matrix will be presented. Each pixel is equipped with an independent electronic chain: the fast shaping preamplifier coupled to a digitizer is able to combine the high rate capability and the good energy resolution. Two CAEN digitizers are compared and the possibility of performing good energy resolution measurements (<2%) and at high rates (>1 MHz per channel) is described. Each pixel was characterized and calibrated using an 241Am source: the energy resolution was evaluated and gives a mean value of 1.73% at 5.5 MeV. The good energy resolution achieved and its uniformity between pixels are the demonstration of the capability of this novel detector as a spectrometer. This system will be installed during the next Deuterium-Tritium campaign on a collimated vertical line of sight at JET for 14 MeV neutron measurements.

Classical transport equations for burning gas-metal plasmas

Thermonuclear inertial confinement fusion plasmas confined by a heavy metal shell may be subject to the mixing of metal into the gas with a resulting degradation of fusion yield. Classical plasma diffusion driven by a number of gradients can provide a physical mechanism to produce atomic mix, possibly in concert with complex hydrodynamic structures and/or turbulence. This paper gives a derivation of the complete dissipative plasma hydrodynamics equations from kinetic theory, for a binary ionic mixture plasma consisting of electrons, e, a light (hydrogenic gas) ion species, i, and a heavy, high ZI plasma metal species, I. A single mean ionization state for the heavy metal, ZI, is assumed to be provided by some independent thermodynamic model of the heavy metal ZI=ZI(ni,nI,Te). The kinetic equations are solved by a generalized Chapman-Enskog expansion that assumes small Knudsen numbers for all species: NKe≡λe/L≪1,NKi≡λi/L≪1. The small electron to ion mass ratio, me/mi≪1, is utilized to account for electron-ion temperature separation, Te≠Ti, and to decouple the electron and ion transport coefficient calculations. This produces a well ordered perturbation theory for the electrons, resulting in the well known “Spitzer” problem of Spitzer and collaborators and solved independently by Braginskii. The formulation in this paper makes clear the inherent symmetry of the transport and gives an analytic solution for all values of the effective charge Zeff, including Zeff&amp;lt;1. The electron problem also determines the ambipolar electric field and the “thermal forces” on both ion species that are needed for the ion kinetic solution. The ion transport problem makes use of the small mass ratio between ion species, mi/mI≪1, to identify an “ion Spitzer problem” that is mathematically identical to that for the electrons but with different thermodynamic forces. The ionic scattering parameter, ΔI≡nIZI2/ni, replaces the Zeff of the electron problem, but has an extended domain, 0≤ΔI&amp;lt;∞, to cover all mixture fractions from the pure gas to the pure metal plasma. The extension of the Spitzer problem to include this extended domain is given in this work. The resulting transport equations for the binary gas-metal plasma mixture are complete and accurate through second order. All transport coefficients are provided in analytic form.

Effective Cavity Length of Gyrotrons

Megawatt-class gyrotron oscillators for electron cyclotron heating and non-inductive current drive (ECH&CD) in magnetically confined thermonuclear fusion plasmas have relatively low cavity quality factors in the range of 1000 to 2000. The effective length of their cavities cannot be simply deduced from the cavity electric field profile, since this has by far not a Gaussian shape. The present paper presents a novel method to estimate the effective length of a gyrotron cavity just from the eigenvalue of the operating TEm,n mode, the cavity radius and the exact oscillation frequency which may be numerically computed or precisely measured. This effective cavity length then can be taken to calculate the Fresnel parameter in order to confirm that the cavity is not too short so that the transverse structure of any mode in the cavity is the same as that of the corresponding mode in a long circular waveguide with the same diameter.

Current state, problems, and prospects of thermonuclear facilities based on the magneto-inertial confinement of hot plasma

Magneto-inertial fusion (MIF) is an original technique of inertial thermonuclear fusion, where spherical and cylindrical gas or plasma configurations are compressed under the action of an external magnetic field. We present a brief review of recent data on laser- and plasma jet-driven MIF systems and possible ways they can be applied. This work also presents problems of and prospects for the application of such approaches.

The Gyrotron at 50: Historical Overview

Gyrotrons form a specific group of devices in the class of fast-wave vacuum electronic sources of coherent electromagnetic wave radiation known as electron cyclotron masers (ECMs) or cyclotron resonance masers (CRMs). The operation of CRMs is based on the cyclotron maser instability which originates from the relativistic dependence of the electron cyclotron frequency on the electron energy. This relativistic effect can be pronounced even at low voltages when the electron kinetic energy is small in comparison with the rest energy. The free energy for generation of electromagnetic (EM) waves is the energy of electron gyration in an external magnetic field. As in any fast-wave device, the EM field in a gyrotron interaction space is not localized near a circuit wall (like in slow-wave devices), but can occupy large volumes. Due to possibilities of using various methods of mode selection (electrodynamical and electronic ones), gyrotrons can operate in very high order modes. Since the use of large, oversized cavities and waveguides reduces the role of ohmic wall losses and breakdown limitations, gyrotrons are capable of producing very high power radiation at millimeter and submillimeter wavelengths. The present review is restricted primarily by the description of the development and the present state-of-the-art of gyrotrons for controlled thermonuclear fusion plasma applications. The first gyrotron was invented, designed and tested in Gorky, USSR (now Nizhny Novgorod, Russia), in 1964.

Relativistic plasma nanophotonics for ultrahigh energy density physics

Femtosecond laser pulses were used to heat dense matter, converting it into an extremely hot plasma. 52-times ionized gold was achieved as well as gigabar pressures, which can be exceeded only in the central hot spots of thermonuclear fusion plasmas.

Thermonuclear Fusion Reactivities for Drifting Tri-Maxwellian Ion Velocity Distributions

The presence of strong magnetic fields in magnetically confined thermonuclear fusion plasmas introduces a considerable anisotropy in the ion velocity distributions. Drifting or streaming of ionic species is another source of anisotropy in fusion plasmas. To account for these anisotropies, we consider in the present work a generalization of the equilibrium Maxwellian distribution in the form of a drifting tri-Maxwellian distribution function. It is shown that the calculation of thermonuclear reactivities for these distributions is best carried out in a transformed velocity space. Computational results for gyrotropic velocity distributions with drifts parallel and perpendicular to the magnetic field are presented.

Lithium-based surfaces controlling fusion plasma behavior at the plasma-material interface

The plasma-material interface and its impact on the performance of magnetically confined thermonuclear fusion plasmas are considered to be one of the key scientific gaps in the realization of nuclear fusion power. At this interface, high particle and heat flux from the fusion plasma can limit the material’s lifetime and reliability and therefore hinder operation of the fusion device. Lithium-based surfaces are now being used in major magnetic confinement fusion devices and have observed profound effects on plasma performance including enhanced confinement, suppression and control of edge localized modes (ELM), lower hydrogen recycling and impurity suppression. The critical spatial scale length of deuterium and helium particle interactions in lithium ranges between 5–100 nm depending on the incident particle energies at the edge and magnetic configuration. Lithium-based surfaces also range from liquid state to solid lithium coatings on a variety of substrates (e.g., graphite, stainless steel, refractory metal W/Mo/etc., or porous metal structures). Temperature-dependent effects from lithium-based surfaces as plasma facing components (PFC) include magnetohydrodynamic (MHD) instability issues related to liquid lithium, surface impurity, and deuterium retention issues, and anomalous physical sputtering increase at temperatures above lithium’s melting point. The paper discusses the viability of lithium-based surfaces in future burning-plasma environments such as those found in ITER and DEMO-like fusion reactor devices.