Fusion reactors will exhaust large volumes of hydrogen species and helium, and cryopumps can satisfy the pumping needs. Two programs described here were undertaken to develop the high performance, continuous operation required. The capability of charcoal as a cryogenic sorbent was optimized and improved by use of specific charcoal types and grades, and by use of thermally conductive bonds for attaching the charcoal to the cryogenically cooled substrate. A 30% demonstrated pumping speed improvement is significant for a system in which the pump dimensions are measured in tens of square meters. An automatically controlled continuous duty cryopump system was developed, fabricated and demonstrated. The system pumps deuterium, and can be readily modified to pump helium by addition of a sorbent such as charcoal. This two-unit system has one unit being regenerated while the other unit is pumping. It is prototypical of a fusion reactor pump in which five units would be pumping for each unit that is being regenerated. Low tritium holdup is projected for an operational installation.
The FTU tokamak will have to operate steadily at high magnetic fields in order to reach the expected performance. Its magnet and vacuum chamber, due to thermal and electromagnetic loads, will undergo very high stresses for a large number of shots. In order to assess the feasibility of the components, numerical codes to compute current, magnetic field and temperature distributions, and extensive three dimensional finite element stress analysis have been developed. The main results obtained are illustrated.
Atmospheric molecular hydrogen (H2) mole fractions have been continuously measured at the Shangdianzi regional station in China. In this study, we present the atmospheric H2 time series from January 2015 to April 2016, and investigate the diurnal and seasonal cycles, and the impact of meteorological factors on the observed values. Atmospheric H2 mole fractions at Shangdianzi vary from a minimum of 381 ppb (parts per billion, 10−9 dry air mole fraction) to a maximum of 1535 ppb, with a median of 510 ppb and a mean (± standard deviation) of 555 ± 113 ppb during the observation period. The results indicate that H2 mole fractions at Shangdianzi are frequently influenced by local sources and sinks. Regionally representative conditions account for 44.7% of the total records with a mean mole fraction of 488 ± 20 ppb. The highest regionally representative H2 mole fraction is observed in July, while the lowest is observed in October. Peak-to-trough amplitude in the seasonal cycle is 63 ± 3 ppb. H2 mole fractions show nighttime depletion in all seasons, with the lowest values in the morning (7:00–10:00 local time). The H2 mole fractions are also influenced by local surface wind direction at Shangdianzi. Winds from NW-NNW-N-NNE-NE-ENE-E directions are always associated with negative contribution to atmospheric H2 loading, whereas winds from SSW-SW-WSW-W directions generally enhance the H2 values. The results of trajectory clustering analysis demonstrate that air masses from a southerly direction induce high H2 mole fractions. Conversely, mean H2 mole fractions are low when air masses are from the north, northwest, and east directions.
A medium-sized DT burning tokamak has been designed with low-activation Al-alloys. We can obtain a large plasma current up to 4.5 MA with an elongation of 2.3, by taking advantage of the good shell effect of Al-alloy vessel and by applying the appropriate feedback control system. Such a large current is effective for the improvement of confinement and high β-value. To obtain these plasma parameters, PF coils are placed inside TFC. Single pancake windings and their connection by welding remove complexity originated from this configuration. By the use of keys in the extended wedge region and large shear panels the displacement of TFC caused by large overturning moment is suppressed to be less than 1 mm. For reduction of induced activity, almost all the components have been designed with Al-alloys except TFC and inboard PFC conductors. The newly developed Al-alloy has been applied to the vacuum vessel, where the new structure of one-turn break is adopted using Al2O3 ceramic spraying. Gamma-rays from activated copper conductor in TFC and inboard PFC are shielded by a lead plate located between the vacuum vessel and PFC. This concept would be extended to devices which aim at Q ⪢ 1 and much longer burning time, if all the coils are made of Al-alloy of which contents of impurity and alloying element are well-controlled.
Organic coolants offer a unique set of characteristics for fusion applications. Their main advantages include high temperature (670 K) but low pressure (2 MPa) operation, limited reactivity with lithium and lithium—lead, reduced corrosion and activation, good heat transfer capabilities, no MHD effects, and an operating temperature range that extends to room temperature. The major disadvantages are decomposition and flammability. The organic fluid characteristics are described in sufficient detail to allow fusion system designers to evaluate organic coolants for specific applications. Analyses are presented for organic-cooled blankets, first walls, high heat flux components and thermal power cycles. Designs are identified that take advantage of organic coolant features, yet have fluid decomposition related costs that are a small fraction of the overall cost of electricity. Particularly interesting applications include organic-cooled high heat flux components (up to about 8 MW/m2) for use with liquid metal cooled blankets.
A bucket plasma source for the 10 MW neutral beam test stand has been constructed by using aluminium-alloy which is a material of low density and low neutron induced radioactivity. In order to improve heat removal which is mainly generated along the cusp line in the bucket plasma source, a magnet arrangement1 of the dislocated cusp line (DCL) type similar to that of the CORDIS2 ion source was applied. Simultaneously a chamber structure was fabricated featuring good heat transfer through the use of corrugated fins. The characteristics of this source in pulsed operation for the DCL have been investigated and compared with those in the normal cusp line (NCL). Cooling was efficient and metal arcing has not occurred in the DCL arrangement. However, the arc power efficiency in the case of the DCL was decreased by a factor of 1.2 ∼ 1.6 compared with that in the NCL. The plasma potential in the DCL is positive and higher than that in the NCL. The ion current density of about 0.2 A cm−2 in the hydrogen plasma was achieved across an area of 16×66 cm2 with density uniformity of better than 10% at about 120 kW of arc power for a pulsed period of 1 s.
Ion implantation driven permeation (IDP) behavior has been investigated for deuterium implanted with low energy (100–1800 eV) into aluminium-lithium alloys (Al-0.89wt.%Li and Al-2.22wt.Li alloys) to stimulate the behavior of tritium. The experimental results showed that the steady state IDP behavior for AlLi alloys was divided into two temperature regions around 620 K for 0.89wt.%-Li alloy and 700 K for 2.22wt.%-Li alloy. In the high temperature regions, the IDP fluxes through both alloys depended significantly on the temperature, while the IDP fluxes were almost constant in the low temperature regions. This fact would suggest that the change in the above temperature dependencies are attributed to the change of the chemical trap site in alloys, because the temperatures at the turning point of the temperature dependencies coincide with those at the phase transition from α to α + δ phase.
An approximate analytical solution of the problem of melting and evaporation during disruptions in magnetic fusion reactors is developed via a technique known as the heat balance integral method. The heat balance integral method has been used successfully in the past in analyzing a variety of heat transfer problems, and is particularly well suited to handle nonlinear boundary value problems such as the one considered in this paper. The results obtained with this approach are then compared with results generated via a numerical techniques based computer code developed elsewhere. It is found that the results obtained via this method are quite reasonable in view of the assumptions made in developing the solution. In addition, some tentative approximate scaling laws are derived.
Some stainless steels have wavy resolidification surface after a simulated plasma disruption. The rough surface is considered to be formed bym ovement of the melt layer, which is driven by imbalance of the surface tension. The effect occurs when the temperature coefficient of the surface tension is positive. The temperature of the melt of an elevated part is high, hence its high surface tension draws melted material away from other locations resulting in growth of the swell. A computer code was developed for simulating the phenomenon. The heat-conduction equation was solved to obtained the position of the liquid-solid interface, and the velocity profile was calculated from equilibrium of the surface tension and the viscous resistance, neglecting inertial force. The mass transfer in the direction parallel to the surface was computed and then the changes of the shape of the surface was calculated using the mass conservation law. The calculational result for the roughness, the dominant wavelength of undulation and their dependence on the heat load agreed well with the experimental result, which indicates the validity of the above mechanism of rough-surface formation.
The environmental issues in the R-project are mainly considered from radiological safety point of view. Supposing a new experimental site for the program to be constructed in Toki Area, land and water surveys have been made since 1982 on the background radiation levels and radioactive material concentrations. Results of in-situ observations using instruments of various types are given and compared, such as TLD's (exposed for every three months), a pressurized ionization chamber, a NaI(Tl) detector in DBM mode, and a portable Ge detector. Also shown are the data from laboratory analyses of sampled materials in α- and γ-spectrometries, and neutron activation method. Tritium concentrations in river water samples have been quarterly measured with a liquid scintillation counter. These kinds of data will further be compiled to define the regional characteristics of the site environments. In relating to the expected radiation yields in the R-project, the importance of monitoring methods effective to pulsed radiation components is particularly emphasized. Possible use of ionization chamber and TLD's for this purpose is discussed in some detail with the preliminary application to the existing tokamak experiments on JIPP T-IIU.
In parallel to the conceptual design of the R-tokamak, research and development efforts on the systems and the components have been carried out to obtain scopes to realize the device. Because we intended to introduce DT fuels into the device, the items of research and development works are quite different to that of non-burning machines. Alminium alloy developments to avoid activations by 14 MeV neutron irradiations, tritium safe handling and vacuum system with tritium are examples of this category. Beside specific requirement directly caused by DT introduction, highly reliable operation of the machine is strongly requested, because it is the necessary condition to perform experiments safely. However, these efforts are still in an early stage of investigation and many efforts are needed to prepare a rigid data base tokamak operation with reacting plasma.
Optimal Control Theory is used to analyze the laser-heating of plasmas confined in strong solenoidal magnetic fields. Heating strategies that minimize a linear combination of heating time and total energy spent by the laser system are found. A numerical example is used to illustrate the theory. Results of this example show that by an appropriate modulation of the laser intensity, significant savings in the laser energy are possible with only slight increases in the heating time. However, results may depend strongly on the initial state of the plasma and on the final ion temperature.
Scoping studies for NET using the SUPERCOIL system code are described. Capital cost optimized devices satisfying constraints imposed on stresses/strains, fields, access, etc. are compared. The main objectives are to determine what impact the main design characteristics, performance objectives and underlying plasma physics assumptions have on the parameters and cost of NET. A complete picture for choosing the main parameters of NET is developed and illustrated by the main NET study points used during the conceptual design phase.
A major issue in the design of fusion reactor blankets is the trade-off between tritium breeding and other blanket design requirements. While net breeding is required, the blanket design should also ensure adequate heat removal, efficient power production and sufficient shielding. A novel aqueous self-cooled blanket concept (ASCB) based on lithium compounds dissolved in water has been proposed and analyzed using one-dimensional neutronics calculations. This concept utilizes zircaloy for the structural material and a vanadium alloy for the first wall. Light water as well as heavy water systems lead to an acceptable design with respect to tritium breeding. One-dimensional tritium breeding ratios in the range 1.1–1.2 seem feasible for the proposed concept. Contrary to conventional blanket designs, the 3-D tritium breeding ratio is expected to be comparable to the 1-D performance because of the additional breeding in water cooled duct shields and high heat-flux components. The resulting design is simple, utilizes materials with a large data base, does not require additional neutron multiplying materials, and satisfies the commonly proposed criteria for a fusion blanket.
For the study of the alpha particles behavior in DT plasma the ‘Reacting Plasma Project’ (R-project in short) was initiated in 1981. The design study of the ‘R-tokamak’ was performed from 1981 to 1985, and evolved through three versions. The first version is based upon the usual tokamak and is similar to TFTR. The remote maintenance and dismantling however is considered very difficult. For the reduction of the residual radiation level the design of DT tokamak with aluminum alloy was conducted. It was found that hand-on maintenance after 1000 DT shots was feasible. Another effect of the aluminum alloy is the increase of the shell effect and stabilization of the variously shaped tokamak. The 3rd version tokamak with the extremely shaped cross-section (the crescent tokamak) is proposed for tokamak improvement (higher beta, better confinement and low radioactivity).
Of the many components and systems comprising a fusion reactor like the Tokamak Fusion Test Reactor (TFTR), few, if any, are subjected to more extreme and severe conditions than the protective armor for the interior vacuum vessel wall. The primary TFTR limiter, referred to as the Phase II bumper limiter, provides protection of the inner vacuum vessel wall from neutral beam shine through, normal plamsa loads, and major disruptive instabilities. The highly transient nature of forces and temperatures induced by these conditions produces significant dynamic responses in various parts of the bumper limiter structural system. This paper addresses the incorporation of a finite element dynamic analysis in the study of bumper limiter behavior when subjected to several electromagnetic load scenarios. These loads, due to a variety of realistic plasma conditions, were used in the interactive design and optimization of limiter components and support locations and flexibilities which enable the structure to perform within established criteria.
