Kameel Arshad

Development and Optimization of STEP—A Linear Plasma Device for Plasma-Material Interaction Studies

The linear plasma device Simulator for Tokamak Edge Plasma (STEP) has been constructed at Beihang University, Beijing, to study plasma-material interactions (PMIs) for fusion reactor applications. The device can produce versatile low-energy and high flux plasma in laboratory experiments and is highly cost-effective to replicate the fusion-relevant plasma environment to study PMI processes. The attractive feature of the device is its compact design with a main body dimension of 1.5 × 1.5 × 0.8 m3 including the plasma source, vacuum chamber, magnetic coils, and diagnostics. A longitudinal magnetic field of up to 0.26 T is used to confine the plasma onto the target in an ∼1-m-long vacuum tube. It can produce a steady-state plasma of low impinging ion energy of <100 eV, ion flux up to 1022 m−2 · s−1, and fluence of >1026 m−2 per exposure. Various plasma species such as hydrogen, deuterium, helium, and nitrogen can be produced to manipulate PMI processes for different target grades. The STEP device provides an experimental platform to improve the understanding of PMIs, validate computational simulation results, and build a database of fusion material performance and lifetime.

Effects of consolidation conditions on microstructures and properties of tungsten-vanadium alloy

To face the harsh environment of intense irradiations, tungsten vanadium alloys (W-5wt.% V) were fabricated by spark plasma sintering (SPS) of mechanical alloying powder under different consolidation conditions. X-ray diffraction (XRD) was used to study the phase structures of the alloy powder and the sintered material. To investigate the improvements in mechanical properties and microstructures, the sintering temperatures and dwell times were taken into account for similar composition of tungsten vanadium alloy. The mechanical properties were estimated using micro-hardness and bending strain tests. The detail morphology analysis of the polished cross sectional surface and fracture surface of the samples were performed by scanning electron microscopy (SEM) and quadrant back scattering detector (QBSD). A highest relative density was achieved by alloy material sintered at 1600 °C for 5 min. The two alloy specimens, one sintered at 1100 °C for 2 min and then at 1600 °C for 3 min and the other sintered at 1600 °C for 3 min, have relatively low density but show better mechanical properties. The grain growth of tungsten and vanadium was influenced by consolidation temperature and not much by the difference in dwell time at same peak temperature.

Thermal stability evaluation of microstructures and mechanical properties of tungsten vanadium alloys

The thermal stability is important for tungsten based alloys as plasma facing materials to survive against high heat flux in fusion reactors. In this work, the thermal stability of W-5%V alloy fabricated following a powder metallurgy route by spark plasma sintering technique has been studied. To investigate the impact of temperature on the mechanical properties and microstructures, the alloy was subjected to heat treatment for 2 h over the temperature range 900–1500°C in a pure argon furnace. The micro-hardness values of the heat treated alloys were highly stable as compared to pure tungsten. A slight decrease flexural strength was observed with increasing annealing temperature. The maximum change flexural strength at the highest treated temperature was noted about 14% lower. The morphology analyses of the crack surfaces by scanning electron microscopy did not identify a drastic change in tungsten grain size, after heat treatment. The results indicate that the addition of vanadium in tungsten improves the overall thermal stability of microstructures and mechanical properties.

Effects of vanadium alloying on the microstructures and mechanical properties of hot-pressed tungsten material

Tungsten and vanadium (W–V) alloys (with 1, 5 and 10 wt.% V) are fabricated by hot pressing (HP) at 1800∘C under 20 MPa for 2 h. The effects of V content on the microstructures and mechanical properties of W–V alloy are investigated. The results indicate that with increasing V content, (i) the formation of W–V alloying phase is enhanced and the grain size of W-matrix is significantly refined; (ii) the relative density gradually increases from 92.16% to 97.72% in the case of pure W to W-10 wt.% V; (iii) the hardness rises linearly while the bending strength decreases, which is related to the enhanced alloy phase formation.

The role of vanadium additive in the activated sintering and shrinkage rate of tungsten–vanadium alloys

Spark plasma sintering (SPS) is a common and effective way to fabricate tungsten-based materials for preliminary investigations of their application in fusion reactor. The selection of doping materials and their appropriate concentration in tungsten is important for activated consolidation and to improve the shrinkage rate during the sintering process. The impact of vanadium concentration on the shrinkage rate of tungsten–vanadium (W–V) alloys has been studied in this work. Improvement in the shrinkage rate and mechanical strength of W–V alloys has been achieved by increasing the V concentration. The residual porosity was gradually decreased and the activated sintering conditions got better with the increase of V concentration. The saturation of shrinkage rate has been found at 1550°C for W-10 wt.%V.