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Highlights • Thermal shock behavior of samples was characterized after helium irradiation. • Combined helium irradiation and thermal shock has significant influence on crack propagation. • Observing fuzz was more likely to converge densely at the phase interface. • Y 2 O 3 doping can improve thermal shock resistance of the W-Y 2 O 3 composite. Abstract Tungsten can be the preferred plasma-facing material for nuclear fusion reaction. In this work, W-Y 2 O 3 composite powder was successfully fabricated through the wet chemical method, and bulk materials were obtained by rolling and high temperature annealing. W-2 vol% Y 2 O 3 was exposed to 80 eV helium ion irradiation with a flux of 1.5 × 1022 ions/(m2·s) at 1503–1553 K to assess its thermal shock resistance and helium ion irradiation damage behavior. The thermal shock behaviors of samples were studied under a laser beam. The energy densities of the laser thermal shock were 0.32, 0.48, and 0.64 GW/m2. W-Y 2 O 3 was compared with commercial pure tungsten. The hardness of pure tungsten and W-Y 2 O 3 before and after helium irradiation was measured by using a micro-hardness tester. The surface micrograph after helium ion irradiation and thermal shock was observed through scanning electron microscopy. Results show that W-Y 2 O 3 composite materials have better resistance to laser thermal shock than pure tungsten. [ABSTRACT FROM AUTHOR]

Tungsten is a primary material in plasma-facing components (PFCs), but several disadvantages limit its application in fusion reactors. This work examined tungsten–niobium (W–Nb) alloys as potential PFC materials and investigated their response to low-energy helium ion irradiation. W–Nb powders were milled for 25 and 36 h, and the W–Nb samples were exposed to 50 and 80 eV helium ion irradiation with a flux of 1.5 × 10 22 ions/m 2  s at 1230 °C. The sample with a dense structure and obtained after a 25-h milling exhibited enhanced anti-irradiation performance. Sufficient energy can be provided to promote helium ion migration in the matrix, resulting in the formation of nanotendrils. Furthermore, in W–Nb alloys, the Nb-rich regions are more attractive to helium ions and thus provide protection to the tungsten matrix. [ABSTRACT FROM AUTHOR]

In tokamaks, the temperature of the plasma-facing wall is an important parameter for achieving particle balance and therefore steady-state operation. QUEST, which is a middle-sized spherical tokamak, has hot walls that act as plasma-facing walls. They can be actively heated with sheath heaters and actively cooled with water. To control the wall temperature, heating and cooling systems have been developed. These systems adjust the power of the sheath heaters and the motor valves of the cooling system, respectively. The two systems communicate via Ethernet through UDP and control the hot-wall temperature cooperatively. The plasma control system (PCS) in QUEST has also been modified, especially with respect to gas fueling, in order to enable long-duration plasma sustainment. A feedback controller has been installed in the PCS, together with a mass flow controller, allowing Hα emission from the plasma which is used as a reference signal, to be well controlled. Plasma density calculations using a field-programmable gate array are proposed for the feedback control system. [ABSTRACT FROM AUTHOR]

The plasma control system (PCS) of QUEST is developed according to the progress of QUEST project. Since one of the critical goals of the project is to achieve the steady-state operation with high temperature vacuum vessel wall, the PCS is also required to have the capability to control the plasma for a long period. For the increase of the loads to processing power of the PCS, the PCS is decentralized with the use of reflective memories (RFMs). The PCS controls the plasma edge position with the real-time identification of plasma current and its position. This identification is done with not only flux loops but also hall sensors. The gas fueling method by piezo valve with monitoring the Hα signal filtered by a digital low-pass filter are proposed and suitable for the steady-state operation on QUEST. The present status and prospect of the PCS are presented with recent topics. [ABSTRACT FROM AUTHOR]

In the present RF-driven divertor plasma of QUEST, it has been observed that orbit-driven current flows in the open magnetic surfaces outside of the closed magnetic surfaces. To observe this phenomenon and the characteristics of the orbit-driven current, current density profiles have been calculated on two different equilibrium conditions. We calculated current density profiles from particle guiding center orbits both for the fundamental and the second harmonic resonances for the 8.2 GHz electron cyclotron current drive. From this calculation, hollow current density profiles have been obtained with significant characteristics on both conditions. Only positive current distribution has been observed in the open magnetic surfaces outside of the closed magnetic surfaces. [ABSTRACT FROM AUTHOR]

The plasma control system (PCS) of QUEST was a centralized system, which lost its scalability because of the overload imposed on its central processing unit (CPU) of the PCS, making it impossible to add new functions. Thus, the PCS is distributed into a main workstation (WS) and subsystem (SS) with a reflective memory (RFM) in order to share data between these systems so as to mitigate the load on each system. As a result, 128 double-precision floating-point numbers (DBLs) can be transferred from the SS to the WS with a maximum latency of 250 μs. The WS and the SS each have quad-core CPUs, and tasks are executed in parallel. Although one of the four cores is intermittently occupied by up to 90% by this transaction, the occupation is normally 60%. A time correction procedure is used to map the recorded data sets on the WS and the SS to a common time base by referring to the time difference between two systems. [ABSTRACT FROM AUTHOR]

W-2vol.%TiC composites were prepared through wet-chemical method combined with sintering and hot-rolling process. In this work, the evolution of damage micrograph in W-2vol.%TiC was studied by SEM in situ observation as functions of annealing temperature and implantation fluence. The results show that the surface morphology of the W matrix was slightly affected after D ions irradiation, while the dispersively distributed TiC particles were damaged severely. After annealing at 1173 K and 1573 K, the irradiation damage structure was repaired. [ABSTRACT FROM AUTHOR]