Measurement of spatial distributions of fusion reactions in an inertial electrostatic confinement fusion device driven by a ring-shaped magnetron ion source

Abstract

Summary form only given. In an inertial electrostatic confinement (IEC) fusion device, the so-called `beam-beam' reactions are preferable as they occur between accelerated ions at the center of the device with a rate proportional to the square of cathode current. A newly developed -IEC device aims to enhance the beam-beam reactions by the use of a magnetron ion source at low pressure (several mPa D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). In previous experiments with this new IEC device, we observed neutron production rate which was proportional to the 1.7th power of the IEC current for the first time in the world. It is necessary to be clear if the non-linear dependence was from beam-beam reactions or not. Measurement of spatial distribution of proton production by DD fusion reactions should be an effective means of determining the contribution of beambeam reactions. This is because beam-beam reactions are expected to occur at the cathode center, unlike other reactions that occur on the cathode surface or in the plasma volume. A system which mainly consists of a movable detector and a movable collimator has been used for the measurement in the previous IEC. With this new low pressure IEC, however, a larger bore collimator is needed in order to detect ample proton count rate because the current of the new IEC is much smaller than the previous one, limiting x-ray flux on the detector by the collimator at the same time to separate proton signals from pileup x-ray noise. Additionally, spatial resolution is required to be higher than the previous system because we have to distinguish the contribution of the central gridded cathode space from the cathode surface. We have thus designed a new measurement system. The distance between a movable detector and a movable collimator is 426mm, and the collimator which is 20mm in diameter is arranged in the vicinity of the IEC anode. The spatial resolution is expected to be high enough to distinguish the central cathode space from the cathode surface. At this moment, we succeeded in separating proton signals from x-ray noise when IEC voltage was 40kV and current was 0.2mA in 5.7mPa D2 gas with the new collimation system. We will measure protons with different parameters, and will discuss the spatial distribution of fusion reactions.