Thermonuclear Fusion Reactors Research Articles

Role of energetic tritium chemistry on developing thermonuclear fusion reactors

The reaction kinetics of the two conversion processes for the chemical state of tritium in neutron irradiated Li 2O during the thermal annealing was investigated. The chemical states of tritium were T − state and T + state. The abundance of T − state was increased in the temperature region of 400–500 K (Conversion I) and it was decreased above 500 K (Conversion II). These kinetic constants were determined. The kinetics of Conversion I and Conversion II was determined to be 7.79 exp(0.45 ± 0.04 eV/ kT) s −1 and 8.53 × 10 4 exp(0.90 ± 0.08 eV/ kT) s −1, respectively. The annealing kinetics of irradiation defects of F-centers (oxygen vacancy occupied by one electron), which was a major defect in neutron-irradiated Li 2O, was also studied. Based on those experimental results, a comprehensive migration model for energetic tritium produced in lithium oxides including the dynamics of irradiation defects was proposed.

Thermomechanical processes in an inertial thermonuclear fusion reactor blanket under cyclic exposure to neutron fluence

The thermomechanical processes occurring in the blanket of a heavy-ion inertial thermonuclear fusion reactor are analyzed. The heat-release density in the structural materials and the blanket coolant is calculated on the basis of prescribed characteristics of the neutron pulse from a ~1 GJ microexplosion of a target. Calculations of the nonstationary thermoelastic stress and pressure fields as well the temperature of the wall and blanket coolant are performed using simple one-dimensional models. The amplitude and frequency characteristics of the stress and pressure waves generated by the energy released in the microexplosion are obtained. The thermal relaxation processes occurring in the elements of the blanket between successive microexplosions are analyzed.

Double polarized dd-fusion experiment

We present an experiment to measure the spin-correlation coefficients for double-polarized deuteron-fusion in the energy range of 10–100 keV to determine the quintet suppression factor. The experiment setup and the future upgrade plans are described. The possible gain for future thermonuclear fusion reactors is discussed as well.

ON PERFORMANCE OF HIGH ENERGY PARTICLE COLLIDERS AND OTHER COMPLEX SCIENTIFIC SYSTEMS

Many complex scientific and technical systems demonstrate exponential performance progress with time ∝ e+t/C. The characteristic progress time C, a measure of empirical difficulty and complexity, is analyzed for high energy elementary particle colliders, astrophysical searches for galaxies and exoplanets, protein structure determination, and compared with computers and thermonuclear fusion reactors. An explanation of the characteristic exponential progress is offered.

A Time Decay Vacuum is a New Era of Space Science with Reference to Magnetohydrodynamic Flows

A controlled thermonuclear fusion reaction of the Sun is the heart of the space craft propulsion system. A band of ultraviolet radiation and X-ray emission of shorter wave length permeated by a magnetic mirror in the presence of a radiofrequency accelerator with the Sun at the resonant level is to produce hydrogen fusion laser due to a driving force to act as a laser fusion thruster. A superfluid helium (4He2) of burning with the Sun is a fifth state of matter. A higher state of matter is confined to a typical helical line which corresponds to the existence of outer universe.

Modeling of dust formation in a DC discharge

Nanostructured dust particles are often found in thermonuclear fusion reactors with carbon plasma-facing components [1]. Parasitic plasmas in remote locations of fusion devices may contribute to the formation of this dust. Particle formation in these conditions is investigated here using a simple laboratory DC electrical discharge. We make use of a numerical model to analyze the formation of dust through cathode sputtering and subsequent molecular growth.The model developed for this study includes three modules. The first one describes the DC discharge in a dust-free plasma with a Monte-Carlo simulation combined with an analytical discharge model. In the second module we perform the computation of growth and transport of carbon clusters and particles in the discharge column [2]. The largest molecular edifice (C15) is assumed to give rise to spontaneous nucleation of solid particles. The third plasma module solves for the total dust density, average mass and average charge.

A Multichannel Nanoparticle Scintillation Microdevice With Integrated Waveguides for Alpha, Beta, Gamma, X-Ray, and Neutron Detection

This paper reports on a glass microdevice with a new patterned nanoparticle composite resin that detects and discriminates all species of radiation emitted from fissionable bombmaking materials. Tailored charge conversion nanoparticles doped into a fast-electron scintillating resin produce different optical pulses specific to the radiation species. These pulses exit since the nanoparticles are appreciably smaller than the wavelength of light. The resins are integrated into a glass substrate where deep cavities are made using microsandblasting, forming independent optical paths leading to fiber-optic attachments. Separate off-the-shelf photomultiplier tubes measure the light pulses. The beta detector was tested with a 90Sr source which produced 1470 cpm with the doped scintillator, while the same source produced 1500 cpm with an off-the-shelf Geiger counter. An Am/Be neutron source was used to test Gd-loaded detectors which exhibited an increase in count rates with an increase in Gd loading. The different nanoparticles used convert differing radiation species into electrons through independent physical mechanisms, including charge conversion (alpha), secondary electron (beta), photoelectron (gamma/X-rays), and an on-chip thermonuclear fusion reaction (neutron) to evaluate the specific isotope radiation signature. The four different detectors use four different methods to convert four different types of radiation into electrons; as a consequence, the measured pulses are characteristic to the radiation, allowing pulse height spectroscopy to be used.

Modelling of dust grain formation in a low-temperature plasma reactor used for simulating parasitic discharges expected under tokamak divertor domes

The presence of nanostructured dust particles has been reported in thermonuclear fusion reactors with carbon plasma-facing components. These particles contribute to tritium retention and pollution of the edge plasma. Understanding the way these particles can grow in the plasma phase is necessary for designing engineering solutions that avoid or at least limit their formation. As a first step towards this goal, this paper presents a numerical study of the formation of dust in a simple model laboratory electrical discharge: a dc discharge generated in argon with a graphite electrode. The aim here is to investigate whether carbon sputtering through ion and fast neutral bombardment of the cathode and subsequent molecular growth of carbon clusters and particle nucleation and development can explain dust formation in this model discharge. Results show that field reversal effects and negative cluster formation and trapping can fully explain dust formation in such a dc discharge.

Study of the ignition requirements and burn characteristics of DTx pellets for Inertial Confinement Fusion

The ignition temperature of a thermonuclear fusion reaction is found to decrease on adding a small amount of tritium (x ~ 0.0112) to deuterium fusion pellet. In this paper the catalytic regime for tritium has been analyzed by changing the fraction of tritium (x). The initial density and temperature of the pellet are also found to influence the ignition conditions in a major way. A zero dimensional three temperature model which includes the energy deposition of charged particles via small and large angle Coulomb scattering, nuclear scattering and collective plasma effects has been used. A density-temperature regime is found where internal tritium breeding occurs even on including all the radiative loss mechanisms like bremsstrahlung and inverse Compton scattering.

Design of a GEM-based detector for the measurement of fast neutrons

A novel neutron detector has been developed and tested in collaboration between LNF-INFN and ENEA-Frascati. The aim is to obtain a versatile system that can be employed for the simultaneous measurement of the neutron flux in various energy bands from 1 to 20 MeV. The main drive for this development is the need of neutron detectors with low sensitivity to γ -rays and high count rate capability for operation in the neutron flux environment ~ 3 × 10 8 n / cm 2 s expected in future controlled thermonuclear fusion reactors. In these devices the fusion power is assessed through the measurement of the 2.5 and 14 MeV neutrons emitted by the plasma. A multilayer detector architecture, including a proton recoil converter, a proton absorber and a triple Gas Electron Multiplier (GEM), has been adopted. The detector read-out system consists of 128 pads ( 12.3 × 6 mm 2 ) in a 8 × 16 matrix. The work on the detector design and optimization carried out with the MCNPX code and the experimental tests at the Frascati Neutron Generator (FNG) on a detector prototype for 2.5 and 14 MeV measurements are presented.

A broad chemical and structural characterization of the damaged region of carbon implanted alumina

As candidate materials for future thermonuclear fusion reactors, isolating ceramics will be submitted to high energy gamma and neutron radiation fluxes together with an intense particle flux. Amorphization cannot be tolerated in ceramics for fusion applications, due to the associated volume change and the deterioration of mechanical properties. Therefore, a comprehensive study was carried out to examine the effects of carbon beam irradiation on polycrystalline aluminium oxide (Al2O3), a ceramic component of some diagnostic and plasma heating systems. Complementary techniques have allowed a complete chemical and structural surface analysis of the implanted alumina. Implantation with 75keV, mono-energetic carbon ions at doses of 1×1017 and 5×1017ions/cm2 was performed on polished and thermally treated ceramic discs. The alumina targets were kept below 120°C. The structural modifications induced during ion irradiation were studied by the GXRD and TEM techniques. Under these conditions, alumina is readily amorphized by carbon ions, the thickness of the ion-beam induced disordered area increasing with the ion dose. Matrix elements and ion implanted profiles were followed as a function of depth by using ToF-SIMS, indicating the maximum concentration of implanted ions to be in the deeper half of the amorphous region. Ion distribution and chemical modifications caused in the Al2O3 substrate by carbon irradiation were corroborated with XPS. The amount of oxygen in the vicinity of the implanted alumina surface was reduced, suggesting that this element was selectively sputtered during carbon irradiation. The intensity of those peaks referring to Al–O bonds diminishes, while contributions of reduced aluminium and metal carbides are found at the maximum of the carbon distribution. TEM observations on low temperature thermally annealed specimens indicate partial recovery of the initial crystalline structure.

Bonding and Interfaces and their Thermo-Mechanical Performance on the Example of Plasma Facing Divertor Components for Thermo-Nuclear Fusion Reactors

The optimization of CFC/Cu-interfaces for plasma facing divertor components in thermo-nuclear fusion reactors is proposed and demonstrated via an integrative numerical-experimental approach mainly comprising a macro-scale to micro-scale finite element modeling technique together with fracture mechanics tests. Results obtained by finite element analyses of real-scale CFC flat tile divertor components under high heat flux loading conditions are verified by the findings of tests in an ion beam high heat flux facility. From the macro-scale FE models of the full component the loading conditions are derived for micro-scale FE models that incorporate principal details of the micro-structured CFC/Cu-interface thus allowing to capture explicitly locally acting dissipative mechanisms which in turn at the macro-scale in fracture mechanics experiments increase the fracture toughness of the CFC/Cu-interface.

High Heat Flux Testing of TiC-Doped Isotropic Graphite for Plasma Facing Components

The technical design solution for the future thermonuclear fusion reactor, ITER, must guarantee a reasonable lifetime from a safety and economical point of view. Carbon fibre reinforced carbon (CFC) is envisaged as a corrective material solution for the strike point area of ITER divertor due to its high thermal shock resistance necessary to withstand excessive heat loads during transient thermal loads; in particular plasma disruptions that can deposit energy densities of several ten MJm-2 with a typical timescale in the order of milliseconds. In this work, as potential alternative to CFCs new finely dispersed TiC-doped isotropic graphites with high thermal conductivity and mechanical strength, manufactured using synthetic mesophase pitch “AR” as raw material, have been evaluated under typical disruption conditions using an energetic electron beam at the JUDITH facility.

Setting up and managing a remote maintenance operation for fusion

Trying to set up and manage a remote maintenance operation for a thermonuclear fusion reactor is a complex undertaking. There are many problems and challenges which need addressing. This paper tries to guide the reader through this process by composing a list of generic problems and by analysing possible solutions. The first challenge before setting up a remote maintenance operation for a fusion reactor is the systematic analysis of all the remote handling requirements. Based upon this the remote handling concept, including facility layout and equipment, can be defined. The following aspects have to be considered and incorporated into the remote handling concept: • Remote handling task development. • Remote handling task logistics and resource management. • Command, control and human–machine interface system. • Viewing and camera systems. • Virtual reality and Augmented Reality software. • Automatic path planning and collision avoidance. • Remote transfer of heavy loads. • Maintainability of RH equipment. • Reliability, redundant systems and safety. • Rationalisation and modularity in both hardware and software. • Recovery from failure modes. • Condition monitoring and fault detection/prediction. • Ability to deal with unforeseen problems. Oxford Technologies Ltd. has a proven track record in setting up and running the Remote Handling group at the JET Joint Undertaking in Culham, UK. Based on the unique experience gained at JET, Oxford Technologies Ltd. also developed the current design and remote handling concept of the ITER Hot Cell during a study in 2004. Examples of both the JET remote handling experience and the ITER Hot Cell design and layout are given throughout this paper.

Joining of machined SiC/SiC composites for thermonuclear fusion reactors

A low-activation glass–ceramic based on silica, alumina and yttria has been designed and tested as joining material for 2D fusion grade SiC/SiC. Neutron-induced radioactivity of elements present in the glass has been simulated by European Activation System EASY-2007 code package. The mechanical strength of the joined SiC/SiC has been tested by 4-point bending on three different kinds of joined samples. Bending strength higher than 120 MPa has been measured at room temperature, with composite failure in most cases.

Deuterium inventory in plasma facing materials by means of NRA: A microbeam probe approach

Particle retention in tokamak walls is a key issue for long time discharges in future thermonuclear fusion reactors. Plasma wall interactions drive the fuel retention through two major mechanisms: co-deposition with carbon produced by wall erosion and particle retention in wall materials. In this study, we report results obtained from the tokamak Tore Supra, from which two types of samples were analyzed by means of micro-NRA: (i) small pieces of deposited carbon layers were collected after cumulative discharges and deuterium contents were measured; (ii) carbon fiber composite (CFC) samples, immersed in the plasma during an experimental campaign were also analyzed. 3D deuterium elemental mapping demonstrated that deuterium can be trapped at depths much higher than usual implantation depths and deep local retention sites have been evidenced and localized.This study demonstrates that μNRA can be used for assessment of deuterium post-mortem inventory in tokamaks, both by measuring uniformly distributed deuterium in small fragments of deposited carbon layers and by locally describing deuterium 2D and 3D distributions in complex structures.

Real-time fibre optic radiation dosimeters for nuclear environment monitoring around thermonuclear reactors

The ability of fibre optic sensors to operate in hazardous nuclear environments and their intrinsic immunity to electro-magnetic interference make fibre optic sensing a very promising technology for the future ITER thermonuclear fusion reactor. In this paper, we evaluate fibre optic sensing technology for monitoring radiation dose in the vicinity of ITER during its operation and during the maintenance periods. First, the performance of an OSL dosimeter interrogated remotely using radiation tolerant optical fibres is evaluated both for real-time and integrating measurements for doses exceeding 100 Gy. We demonstrate its satisfactory operation in a mixed gamma neutron field. Second, we discuss the successful calibration of a new scintillating fibre optic radiation probe based on CsI(TI) crystals for operation in the dose-rate range 0.3–3000 mGy/h. The CsI(TI) crystal scintillator is mounted at the end of a 10-m long multimode fibre transceiver link to allow for remote deployment. The probes can detect and measure gamma dose rates ranging from 1 to 1000 mGy/h. Finally, we investigate the possible use of commercially available PMMA plastic optical fibres as on-line dosimeters up to 34 kGy. The dose measurement is derived from the radiation-induced attenuation in the optical fibre itself. A novel interrogation scheme based on a ratiometric technique is proposed for real-time dosimetry.

Investigation of phase transition in Li 2TiO 3 by high temperature X-ray diffraction

Li 2TiO 3, one of the promising candidates for tritium breeding in a thermonuclear fusion reactor, has been investigated by X-ray diffraction at high temperatures. It was found that the crystal system of Li 2TiO 3 is monoclinic at 30–900 °C with a higher order structural phase transition at about 450 °C, showing agreement with dependence of thermal conductivity on temperature. This phase transition involved variation of the thermal expansion coefficient, which could also be observed by dilatometry.

Chinese scientists conduct more tests on thermonuclear fusion reactor

Chinese scientists conduct more tests on thermonuclear fusion reactor

Computer simulations of cavitation collapses at high static pressure using hydrocode HYADES: Plasma conditions and shock waves in the liquid

Previously (JASA 121 pt.2, p. 3181) transient cavitation in high pressure spherical resonators was described. The phenomenon is characterized by cavitation events lasting a few ms (100 s acoustic cycles) in which a cavity (or cavities) collapse violently, emitting flashes of light of widths ∼1–40 nsec and spherical shock waves with amplitudes ∼1–100 bars (depending on the static pressure) at a distance of 10 cm from the collapse. Both SL and shock amplitudes are proportional to the static pressure. The goal of these experiments is to investigate how the static pressure increases the intensity of acoustic cavitation collapse and whether thermonuclear fusion reactions are possible this way. The determination of plasma temperatures, pressures, and densities is therefore critical in making progress. Furthermore, the amplitude and velocity of the shock waves can be used to determine the conditions at stagnation (end of collapse), assuming the cavity size at that time is known. To this end, results of numerical simulations using HYADES plasma physics hydrocode will be presented, with emphasis on the plasma conditions versus the amount of gas in the cavity and the static pressure, as well as the amplitude and velocity of the outgoing shock waves generated after the collapse [Work supported by SMDC Contract No. W9113M‐07‐C‐0178.]