V.I. Pistunovich

Development of a liquid-metal fusion reactor divertor with a capillary-pore system

Abstract The absence of a satisfactorily developed fusion reactor (FR) divertor approach (having no lost layers of sputtered plate materials and/or replaceable blocks) has become the reason for the development of the new concept of liquid-metal divertor (LMD) with a capillary-pore (CP) lithium protection system. Creative and novel design and material solutions, combined with unique natural thermophysical properties of Li working in a gas target evaporation—radiation mode, ensures the prolonged and steady performance of a FR divertor (D).

Superpermeability: Critical points for applications in fusion

Abstract One of key points for the applications of superpermeable membranes in fusion is the question of the upper limit of the permeation flux density. Theoretical estimates give the maximum fluxes of ∼ 10 19 cm −2 s −1 for the V group metal membranes. The permeation fluxes of up to 3 × 10 16 and 4 × 10 17 cm −2 s −1 were achieved using Nb and thermal atomic hydrogen in the direct membrane experiments and in simulation absorption experiments respectively. Achievement of higher fluxes has been limited by the experimental equipment opportunities. Another important point is the reliability of membrane operation in the presence of chemically active gases. No negative effects of CH 4 , CO and O 2 specially introduced on a superpermeable Nb membrane were detected during 3000 h of operation. Such membranes coupled with special hydrogen atomizers can be easily incorporated into the up-to-date ITER design concept. The membranes installed in every of the 24 ducts might isolate > 90% of D/T with the flux densities already reached.

Russian DEMO plant study

Abstract A conceptual design study of the DEMO reactor is being carried out in Russia. The main efforts are concentrated on the study of steady state reactor DEMO-S. This reactor will be operated with an advanced plasma regime involving a high fraction of bootstrap current. A divertor concept with open liquid lithium as a plasma facing material was chosen. Two extreme approaches were analyzed: the first assumes that liquid lithium is loaded with direct heat flux from 100 to 150 MW m −2 ; the consumption of liquid lithium and a form of lithium surface are defined; in the second approach lithium plasma dynamics in the divertor is analysed using the 2-D MHD divertor code. With this approach heat loads are considerably decreased by the radiation. Some additional issues connected with utilization of vanadium alloys in the DEMO reactor, including environmental and safety aspects, material activation and refabrication were also analyzed.

Experimental and calculated basis of the lithium capillary system as divertor material

First results as experimental and calculated basis of a new concept are described in the paper. Experimental models of liquid lithium capillary structure have been tested at long-pulse high heat loads. The power loads on the capillary target up to 50 MW/m2 were provided by an electron beam with electron energy ≤ 9 ke V in a longitudinal magnetic field of 0.25 T. Seven experiments were performed with the different capillary targets. The effects of disruption discharges in tokamaks have been simulated by means of magnetized plasma flows with pulse length of 0.2 ms, electron density of 1022 m3 and energy density up to 4 MJ/m2. The plasma flow was generated by a quasistationary plasma accelerator and interacted with a lithium capillary structure. 2D modelling of the ITER divertor with a lithium target is presented as the first step in the validation of a new divertor concept. A lithium radiative divertor scenario has been examined for the ITER using DDIC95 code. First calculations have shown that thermal loads on the divertor plates are reduced down to 1.3 MW/m2. The main power is radiated in the divertor.

Bulk retention of deuterium in graphites exposed to deuterium plasma at high temperature

Abstract A highly ionized deuterium plasma with a low residual gas pressure and a high intensity D2+-ion beam were used for the study of deuterium retention in RG-Ti-91 and POCO AXF-5Q graphites. Deuterium retention in the samples was estimated by TDS during heating to 2000 K. Mechanical removal of a surface layer 100 μm thick was used to distinguish bulk and surface fractions of retained deuterium. The samples of RG-Ti and POCO graphites were exposed to a plasma with an ion flux of 3 × 1017 D/cm2 · s in the ‘Lenta’ plasma device for 10 to 104 s at residual deuterium pressure of 0.04 Pa at 1400 K. Under plasma exposure deuterium capture in RG-Ti graphite reached the saturation level at a fluence of 4 × 1020 D/cm2 while the bulk inventory was negligible. As for POCO graphite, deuterium retention increased with fluence and was equal to 18 appm in the bulk for a fluence of 7 × 1021 D/cm2. The same amount of deuterium in the bulk was obtained after gas exposure of POCO at an effective pressure of 0.8 Pa (1400 K, 6 h). With this result, the tritium concentration in the plasma-facing graphite materials can reach 1500 appm or 380 grams of tritium per ton of graphite. To understand the role of ion flux in generation of effective pressure, POCO was irradiated with 16 keV D2+-ions at 1400 K for 4 h to 8 × 1020 D/cm2 (ion flux was 6 × 1016 D/cm2 · s, residual deuterium pressure was 0.004 Pa). The results are discussed on the basis of structural differences for POCO and RG-Ti graphites.

Research of the capillary structure heat removal efficiency under divertor conditions

Abstract Experimental models of capillary structure for liquid metal fusion reactor divertor simulation have been designed, manufactured and tested in order to estimate the behaviour and possibilities of plasma-facing components based on lithium capillary system at long-pulse high heat load. The power load on the capillary target structures up to 50 MW/m 2 was provided by electron beam with electron energy ≤ 10 keV. The exposition-time was up to several minutes and was limited by the lithium quantity in the supply vessel. The operation parameters of the models determined in the experiments are in accordance with there design estimations. The tests of various model constructions at the divertor relevant power loads have shown promise for the new concept of a divertor taking into account long life and reliability.

Reflection and retention of low energy light ions during bombardment of fusion materials

Experimental and computational data on light ions reflection and retention for energy below hundreds of eV are presented. Mass spectrometric method is used to measure particle reflection R N and particle retention coefficients for different angles of incidence of D ions on different targets. Strong influence of surface oxidation for Be is observed. Results are compared with the binary collision computer simulations. R N as a function of primary energy reveals the maximum with amplitude and energy depending on the angle of incidence, attractive potential E s and atomic number of target. Strong isotopic effect in hydrogen backscattering from Be is observed. The regular relief influence on hydrogen ions backscattering from Be and C target was computer simulated and it is shown that considerable increase in R N (R N max /R N (0)=1.85 for proton normal incidence on Be target) is noticed

Impurity production and transport processes in divertor regions

Abstract 2D modelling of the ITER divertor with a lithium target are presented as the first step in the validation of a new divertor concept, based on the capillary structure applied for the cooling of the divertor plates by the evaporation of lithium. The lithium radiative divertor scenario has been examined for the ITER using the DDIC95 code. This code has been specially produced to simulate the behavior of the main plasma and that of impurities, at their arbitrary densities in a real divertor geometry. The self-consistent simulation of a background plasma, neutral gas and impurities is a specific feature of this code. First calculations have shown that the thermal loads on the divertor plates are reduced to 1 MW/m2. The main power entering the divertor is radiated on the baffles in the divertor. The longitudinal and radial distributions of lithium neutral and ion density are presented in this paper. The lithium flux through the magnetic line near the separatrix and Zeff in the main plasma are estimated. On the basis of the 1D code the fusion plasma parameters inside the separatrix and the values of lithium flow through the separatrix at which the self-sustaining D-T reaction takes place have been calculated.

Tungsten erosion at low energy impact under steady state plasma conditions

Abstract Tungsten in considered as one of the candidate materials for application infuture fusion devices for plasma facing components. The calculated threshold energy of deuterium for physical sputtering of tungsten is rather high [3] (341 eV). Thus one could expect that tungsten surface sputtering would be absent in pure hydrogen edge plasma with low temperature. Continuous deuterium plasma conditions were used in these experiments to investigate the tungsten erosion characteristics.

Membrane pumping technology for helium and hydrogen isotope separation in the fusion reactor

Abstract A gas pumping system for ITER, improved by implementation of superpermeable membranes for selective hydrogen isotope exhaust, is considered. A study of the pumping capability of a niobium membrane for a hydrogen-helium mixture has been performed. Monte Carlo simulations of gas behaviour for the experimental facility and fusion reactor have been done. The scheme of the ITER pumping system with the membranes and membrane pumping technology was considered. The conceptual study the membrane pump for the ITER was done. This work gives good prospects for the membrane pumping use in ITER to reduce the total inventory of tritium necessary for reactor operation.