Contour plots of the normalized pellet penetration depth: λ/a for each pellet size, cylindrical shape with (a) 3.0 mm, (b) 3.4 mm, and (c) 3.8 mm in diameter and length, predicted by NGS pellet ablation model. Flat density profile: m−3 and parabolic temperature profile: keV, where T e(0) = 0–4 keV, are assumed. λ/a = 1 represents that the pellet penetrates to the plasma center: ρ = 0.
Schematic view of the 20 barrel in situ pipe gun type solid hydrogen pellet injector and the LHD plasma. The pellet injector is installed at the vicinity of horizontally elongated poloidal cross section on the outboard side mid-plane.
Schematic view of the pellet formation part in the cryogenic chamber. (a) The enlarged illustration of the pellet formation part in the barrel. The barrel which is made of bright annealing 316 austenite stainless steel pipe is brazed with the oxygen-free copper block. (b) Arrangement of four sets of heat sinks viewed from the rear face. Five barrels are mechanically connected by M16 threads to a heat sink which is cooled by the exclusive compact cryo-cooler. (c) Side view of the cryogenic chamber and valve set.
Typical cooling down characteristics of the cryogenic heat sinks. The enlarged plot around the completion of the cooling down that is indicated by colored band is also plotted.
Predicted pellet velocity by the ideal gun theory. Lines and colored bands denote the calculated values and semi-empirically predicted ranges of the pellet velocity, respectively. (a) Barrel length dependence for 5 MPa He propellant gas. (b) Propellant gas pressure dependence at the barrel length of L barrel = 0.97 m. Hydrogen and helium are considered as propellant gases.
Exhaust performance of the differential pumping system. (a) Conceptual diagram of the three-stage differential pumping system and the representative parameter of the system. (b) Comparison between the calculation results and measurements. Chain line, broken line, and solid line denote the calculated pressure change at the first, second, and final expansion chambers, respectively. Filled triangle, open square, and filled circle denote the measured pressure change at the first, second, and final expansion chambers, respectively.
Schematic diagram of the pellet injection control system which consists of three sections, (1) man-machine interface, (2) operation and monitoring, and (3) injection control. Each section is connected to the others through an Ethernet LAN connection.
Waveform of the pellet fueled discharge with real-time injection timing control to maintain m−2 referring to a line density signal.
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