Thermonuclear Fusion Devices Research Articles

Simulation of disruptions on coatings and bulk materials

An important issue for the next step thermonuclear fusion devices is the development of a reliable engineering solution for the first wall and in particular for the divertor. Besides severe mechanical loads, these plasma facing components (PFC) will be subjected to energetic pulses during plasma disruptions. To evaluate the performance of plasma facing materials and thus to predict the lifetime of the PFCs, simulation experiments have been performed in the JAERI electron beam irradiation stand (JEBIS). Here different candidate plasma facing materials were evaluated in short beam pulses (1.2–10 ms) with an energy deposition of 2–9 MJ m −2 . The response of the individual materials to single and multiple shot beam pulses was investigated, and in these analyses special attention was given to the material erosion (melting, sublimation, particle emission). The quantification of these effects was done by weight loss measurements and by optical profilometry on the ablation craters. In addition, microstructural and morphological changes in the loaded surface were investigated.

Fundamental aspects of high-energy ion-beam simulation techniques and their relevance to fusion materials studies

This paper surveys and discusses the fundamental aspects of employing ion beams for simulating radiation damage phenomena, particularly those effects which will influence the performance of materials in controlled thermonuclear fusion devices. A wide spectrum of ion beams having a range of energies has been progressively developed and deployed over the past thirty years for fission- and fusion-reactor materials studies. Some of the ways in which ion beams have been used to study fusion materials problems are considered, e.g. microstructural stability, cavity formation and growth, helium and hydrogen gas behaviour, plasma-materials interactions such as sputtering and blistering and the effects of damage and transmutation products on mechanical properties. A large body of data has been obtained and the greater control of experimental parameters that can be obtained using ion beams has enabled a detailed understanding to be obtained of fundamental damage processes and material behaviour under simulated fusion-reactor conditions. The main deficiency in understanding still lies in the inter-correlation of damage between ion and neutron conditions. It is concluded that the technique is still a useful complement to fission-reactor irradiation methods and is likely to have a continuing role to play, particularly in the plasma-materials interaction area, until such time as high-fluence 14 MeV neutron irradiation facilities become available.

Anomalous transport arising from nonlinear resistive pressure-driven modes in a plasma

Anomalous transport caused by fluctuations of resistive pressure-driven modes is discussed within the framework of magnetohydrodynamics (MHD). The nonlinear-reduced equations describing fluctuations localized near a particular magnetic field line are derived for tokamak and reversed-field-pinch (RFP) plasmas, taking into account nonzero viscosity and heat conductivity. For an ideally stable but resistively slightly unstable plasma, the anomalous transport is caused particularly by convective motions. The convection is studied as bifurcation from the linearly unstable equilibrium and the expression of the anomalous transport in a tokamak plasma is obtained as a function of the mean pressure gradient near the critical point. In order to evaluate the effects of the convection on the anomalous transport under various conditions, the reduced equations are also solved numerically. It is found that Nusselt number, that is, the ratio of the total heat conductivity including the anomalous heat transport to the classical collisional heat conductivity, is significantly large under some conditions. This partially accounts for the large heat losses in controlled thermonuclear fusion devices.

Local Wall Power Loading Variations in Thermonuclear Fusion Devices

A 2½-dimensional geometric model is presented that allows calculation of power loadings at various points on the first wall of a thermonuclear fusion device. Given average wall power loadings for b...

In-situ measurement of tritium partial pressure by bremsstrahlung counting method

To measure tritium pressure in fuel processing systems in DT burning fusion devices, the applicability of a bremsstrahlung counting method was examined by using an apparatus for supply and recovery of highly concentrated tritium gas. For the measurement of bremsstrahlung, a newly designed proportional counter showed a considerably high sensitivity to the measurement of bremsstrahlung. In addition, the bremsstrahlung counting rate showed excellent linearity to tritium partial pressure when the total pressure was below 100 Torr. Above this upper pressure limit, the counting rate deviated downward from the linear relation. The deviation, however, could be represented quite well by a simple exponential function of pressure. It was shown that the tritium partial pressure in the hydrogen isotope gases could be determined in the range from 5 × 10−2 to 760 Torr. Consequently, the present methods is quite useful for in-situ and non-destructive measurements of tritium partial pressure in the fuel processing systems of thermo-nuclear fusion devices.

Depth Profiling of Tritium in Materials for Fusion Technology

The paper outlines recent progress in depth profiling of tritium distribution near the surface of materials by two ion beam techniques; elastic recoil detection (ERD) and T(d,/alpha/)n nuclear reaction analysis (NRA). The sensitivity and depth-resolution of both methods are examined for a series of tritiated titanium films. Calculated depth profiles and ranges of implanted tritium ions in selected candidate materials for thermonuclear fusion devices are also given. Depth profiles of tritium implanted into specimens of graphite and lithium oxides as a function of temperature are discussed as the examples of applications.

Proposal for a sensitive leak test telescope

A proposal for an in-vessel movable leak sensor, called a leak test telescope, is described for leak localization inside two of the largest thermonuclear fusion devices (TFTR and JET). To improve sensitivity and source identification beyond the present state of the art, a differential sensor head employing two actively pumping collimators, a continuously rotating shutter, and a quadrupole mass spectrometer as sensor is proposed. With the use of phase-lock signal processing this detector should be capable of detecting a leak of 1×10−6 Torr l/s from a distance of 0.5 m in a typical fusion environment with backgrounds >1×10−7 Torr deuterium–tritium.

Relative sensitivities of Bayard–Alpert gauges and a quadrupole mass spectrometer for hydrogen isotope molecules

To apply mass spectrometers and ionization gauges to thermonuclear fusion devices such as pressure gauges, we measured the relative sensitivities (normalized to H2) of Bayard–Alpert (B–A) gauges (UGD‐1S and UGS‐1A, ANELVA Co.) and a quadrupole mass spectrometer (MSQ‐150A, ULVAC Co.) for hydrogen isotopes. In the case of the B–A gauges, the relative sensitivities were determined as RHDB=1.07, RD2B=0.99, RHTB=1.03, RDTB=0.97, and RT2B =0.95. In the case of the quadrupole mass spectrometer, they were RHDM =1.09, RD2M =0.99, RHTM =1.06, RDTM =0.96, and RT2M =0.88. These values agreed quite well with those observed by Dibeler et al. for the mass spectrometer of the magnetic deflection type. It was revealed that the relative sensitivities of the quadrupole mass spectrometer were essentially the same as those for the B–A gauges except T2.

Tritium problems in a thermonuclear fusion device

Works under way in CEA Saclay on a fusion reactor tritium system are described. Areas covered are large components for the torus vacuum system, fuel clean-up processes, electrolytic cell, atmosphere clean-up and tritium recovery from solid wastes. All these tasks are covered theoretically and experimentally.

High-power millimetre-wave mode converters in overmoded circular waveguides using periodic wall perturbations

Abstract This work reports on measurements and calculations (coupled mode equations) on the conversion of circular electric TE0n gyrotron mode compositions (TE01 to TE04) at 28 and 70 GHz to the linearly polarized TE11 mode by means of mode converter systems using periodic waveguide wall perturbations. Mode transducers with axisymmetric radius perturbations transform the TE0n gyrotron mode mixture to the more convenient TE01 mode for long-distance transmission through overmoded waveguides. Proper matching of the phase differences between the TE0n modes and of lengths and perturbation amplitudes of the several converter sections is required. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TE01 mode into the TE11 mode which produces an almost linearly polarized millimetre-wave beam needed for efficient electron cyclotron resonance heating (ECRH) of plasmas in thermonuclear fusion devices. The experimentally determined TE0n -to-TE01 conversion efficiency is (98 ± 1)% at 28 and 70 GHz (99% predicted) while the TE01-to-TE,, converter has a (96 ± 2)% conversion efficiency at 28 GHz (95% predicted) and (94 ± 2)% at 70 GHz (93% predicted) with ohmic losses included in each case. This paper also presents theoretical and experimental results on the two-step TE16-to-TE12-to-TE11 mode conversion at 28 GHz by means of two periodically rippled-wall mode converters. The conversion efficiencies achieved are almost 92% and 95%, respectively. Similar converters might be used for transformation of the output modes of future high-frequency TE1n gyromonotrons or 10 GHz gyro-klystron amplifiers into the TE11 mode, which in turn can then be transformed by circumferentially corrugated or dielectrically coated mode transducers into the perfectly linearly polarized quasi-optical HE11 hybrid mode. The efficiency of periodically modulated wall mode-converters can be considerably improved by proper re-matching of the phase difference between the two converted modes within the converter.

Absorption and desorption of hydrogen, deuterium, and tritium for Zr–V–Fe getter

Nonevaporable getters have wide applicability for developing the tritium handling techniques for thermonuclear fusion devices. From this viewpoint, mechanisms of the absorption and desorption of hydrogen isotopes and the isotope effects were investigated for a Zr–V–Fe alloy (St-707) by means of the mass analyzed thermal desorption spectroscopy. It was observed that the absorption rate was proportional to the first power of the pressure, indicating that the rate limiting step is the dissociative adsorption of hydrogen isotopes on the surface. The activation energy was very small, in the order of magnitude of a few tens of calories per mole in a temperature range from −196 to 200 °C. The desorption rate was proportional to the square of the amount of absorption, indicating that the rate limiting step is the associative desorption reaction of hydrogen atoms or ions diffused to the surface from the bulk. The rate constants for hydrogen and deuterium were determined as kd(H2)=(5.3+2.6−1.7)exp[−(28.0±0.7)×103/RT] and kd(D2)=(5.0+2.7−1.7)exp[−(28.6±0.8)×103/RT] in [1/Pa 1 s], respectively, where R is in [cal/mol deg]. With regard to tritium, the rate constant was evaluated as kd(T2)=(5.0+20−4.0)exp[−(29.3±3)×103/RT], however, the frequency factor will have to be corrected by knowing the relative sensitivity factor of the mass spectrometer for tritium (T2).

Thermonuclear fusion product diagnostics by nuclear track detectors

The nuclear track detector materials CR-39 and PM-355 are capable of proton and alpha particle track recording and thus well suited to charged particle diagnostics in thermonuclear fusion devices. In a study to determine the respective absolute recording efficiencies and energy resolutions for protons and alpha particles in real diagnostics situations, a series of experiments with monoenergetic particles of known energies and angles of incidence were performed. Alpha particles could be quantitatively detected for angles of incidence of up to 70°, and their etch pit depth rather than the diameter for defined etching conditions gave satisfying information on the alpha particle energy. Contrary to other investigators, however, we found a monotonically decreasing detection probability for protons already above 3 MeV and no proton track could be developed above incident energies of 7 to 8 MeV. The proton detection depends more strongly on the angle of incidence; only tracks of protons with angles of incidence smaller than 30° could be made visible by etching. The proton energy could be derived from track diameter measurements better than from etch pit depths.

Trapped states of deuterium implanted into graphite and the thermal desorption

Chemical sputtering of graphite and the retention of hydrogen are important subjects for thermonuclear fusion devices. We measured thermal desorption processes of deuterium implanted into graphite at room temperature by means of the flash desorption spectroscopy along with surface characterization by XPS and SIMS. Chemical shift of the Cls peak was observed by XPS due to the deuterium-ion implantation. In SIMS spectra, CD ± and C 2D − signals appeared after the implantation. Based on these observations, it was concluded that C-D and/or C 2-D species were formed on the surface due to the implantation. The implanted deuterium desorbed as D 2 and CD 4 by flashing the sample above 500°C. The fraction of the desorbed amount of CD 4 strongly depended on the flashing mode. Moreover, no methane appeared after the irradiated sample was annealed above 500°C. It was concluded that a part of the C-D and/or C 2-D species associated each other in the graphite during the flash desorption to form molecular deuterium which presumably adsorbed on carbon atoms.

Ohmic heating coil power supply using thyristor circuit breaker in a thermonuclear fusion device

Ohmic heating coil power supply using thyristor circuit breaker in a thermonuclear fusion device

Energy and mass distributions of sputtered particles

For surfaces exposed to the plasma of a magnetic-confinement thermonuclear fusion device, it is expected that sputtering will not only determine useful materials lifetimes, but will also result in the introduction of plasma impurities, thereby limiting the performance of the device. Even in present devices however, only a relatively small proportion of the eroded material is actually found in the plasma. Consequently, plasma transport processes play an extremely important role in determining plasma impurity levels. The efficiency of these transport processes depends on the kinetic energy and charge state (11,220) angle of emission (12) and possibly on the molecular structure of the sputtered materials (11). It is the purpose of this review to summarize the current data base with regard to the kinetic energy and mass distribution of the sputtered atoms and molecules. Although there is a relative abundance of data f dr high energy (> 1 keV) sputtering by Ar +, Kr + and Xe +, there is extremely little data for low energy H +, D +, He + or even Ne +; i.e. there is almost no data in the region of greatest interest. Some general trends can be inferred from the heavier ion data, but only with a limited degree of confidence. The reason for this limited confidence is explained and an evaluation is made of the extent to which different properties of the sputtered material are expected to affect plasma impurity levels.

Mass spectrometric studies of alloys proposed for high temperature reactor systems: II. Inconel alloy 617 and nimonic alloy PE 13

The vaporization of the alloys inconel 617 and nimonic PE 13 was studied by high-temperature mass spcctromctry. This is of particular interest for the use of these alloys in advanced gas-cooled high temperature reactors and thermonuclear fusion devices. Therefore, the partial pressures of nickel, chromium (1355–1527 K) and cobalt (1214–1517 K) over inconel 617 as well as of nickel, chromium, iron (1349 to 1493 K) and cobalt (1279 to 1500 K) over nimonic PE 13 were determined in the given temperature ranges. Chemical activities, partial free energies of mixing and excess partial free energies of the alloy components were computed from the partial pressures. The thermodynamic functions obtained are discussed.

Possibility of palladium-alloy membrane pumps for thermonuclear fusion devices

Possibility of palladium-alloy membrane pumps for thermonuclear fusion devices

Radiation blistering of structural materials for fusion devices and reactors

Radiation blistering can be an important erosion process when the structural components of controlled thermonuclear fusion devices or reactors are exposed to the impact of energetic particles leaving the plasma region. A brief review of some of the important parameters governing the radiation blistering process is given. Erosion rates associated with helium blistering in V, Nb and Type 304 stainless steel are reported for different irradiation temperatures and different projectile energies.

Magnetically Insulated Transformer for Attaining Ultrahigh Voltages

A high voltage transformer in which a high magnetic field inside a hard vacuum insulates against breakdown is proposed. The magnetic field is generated by electric currents in high field superconductors. Voltages up to 109 V may be attainable with such a system. A rectifier using high magnetic fields can transform the end voltage from ac to dc. The energy output at the terminal of the secondary coil can be extracted in the form of either an electron or an ion beam through the use of the field emission process. Potential applications include (1) high energy particle accelerators with beam intensities many orders of magnitude larger than in conventional accelerators or meson factories, (2) use in controlled thermonuclear fusion devices, and (3) continuous pumping of powerful lasers. The feasibility of the system will depend upon depressing the breakdown perpendicular to the direction of the high magnetic field.

Levitation of Current Carrying Hoops of Quadrupole Magnetic Field for Thermonuclear Fusion Device

A simple and reliable method of levitating current-carrying hoops of a quadrupole magnetic field for thermonuclear fusion devices is presented. The hoops are initially posed on three supports, which are then propelled downward by repulsive force generated in a magnetic coil fed from a capacitor bank, leaving the current carrying hoops gravitating in space for more than 10 msec. The reproducibility is perfect and no damage nor deformation has been sustained by the components even after repeated use. Some preliminary experiments on plasma injection with this device are described. A suggestion is also presented on another possible method of levitation which should permit weightless suspension in space for longer periods as required in thermo-nuclear reactors.