Development of Advanced Pellet Injector Systems for Plasma Fueling

Abstract

Two types of solid hydrogen pellet injection systems have been developed, and plasma refueling experiments have been performed using these pellet injectors. One is an in-situ pipe-gun type pellet injector, which has the simplest design of all pellet injectors. This in-situ pipe-gun injector has 10 injection barrels, each of which can independently inject cylindrical solid hydrogen pellets (3.4 and 3.8 mm in diameter and length, respectively) at velocities up to 1,200 m/s. The other is a repetitive pellet injector with a screw extruder, which can form a 3.0 mmφ solid hydrogen rod continuously at extrusion rates up to 55 mm/s. This extruder allows consecutive pellet injection up to 11 Hz without time limit. Both of these pellet injectors employ compact cryo-coolers to solidify hydrogen; therefore, they can be operated using only electrical input instead of a complicated liquid helium supply system. In particular, using a combination of the repetitive pellet injector with cryo-coolers provides a steady-state capability with minimum maintenance.

Twenty barrel in situ pipe gun type solid hydrogen pellet injector for the Large Helical Device

“…A fully remote control capability is secured by employing GM (Gifford-McMahon) cycle compact cryo-coolers as with the previous pellet injectors which are developed for the LHD experiments. 8,11 Since the pellet injector can be operated by using only electric power, which is the most fundamental facility in a laboratory, without a liquid helium supply system; it is possible to operate the pellet injector remotely without accessing it for a long time. The cabling distance between the LHD main control room and the LHD experimental hall is about 400 m. In order to minimize the cabling, the remote control of the pellet injector has been built on an Ethernet connection with the fiber optics between the control computers in the LHD main control room and the PLC (Programmable Logic Controllers) located near the pellet injector in the LHD experimental hall.…”

“…Already we had developed a repetitive pellet injector with a screw type solid hydrogen extruder which can inject pellets continuously a) Electronic mail: sakamoto@LHD.nifs.ac.jp at a frequency of up to 11 Hz. 8 However, its core fueling capabilities are far from adequate to build up the highly peaked IDB plasmas due to deficiencies in maximum pellet velocity and minimum pellet injection interval. From the view point of the core fueling capabilities, a simple in situ pipe gun type solid hydrogen pellet injector is preferable although the possible number of pellet injections is exactly restricted by the installed number of pellet injection barrels.…”

Design activities on helical DEMO reactor FFHR-d1

“…In order to secure a reliability of the pellet injection, pneumatic pellet acceleration is assumed as in ITER pellet injectors. This choice leads to a disadvantage due to propellant gas consumption which requires about three times larger than a injected pellet mass [29]. It is reasonable to use a fuel gas as a propellant gas to prevent an impurity mixing and then the pumped propellant gas at a differential pumping system is directly reusable as the propellant gas and/or fuel gas as shown by broken line in Fig.…”

FEM Simulation of Axisymmetric Pellet Injection System Using HTS Linear Acceleration

“…As the fuel supply to the nuclear fusion reactor, a pellet injection system by using solid hydrogen pellets made of the frozen hydrogen/deuterium has been developed [1,2]. The solid hydrogen pellets are accelerated such as the air gun using the helium gas and driven into a hightemperature plasma.…”