2016 年 14 巻 ists30 号 p. Pb_149-Pb_156
Research on a debris removal system that uses an electrodynamic tether (EDT) system has been conducted in JAXA. The EDT system requires an active electron emission device to drive a large electric current through the tether for obtaining adequate de-orbit thrust. A field emission cathode (FEC) is one good option for the electron emitter owing to its simplicity and potential performance. The FEC used in this study is comprises an emitter electrode with a carbon nanotube (CNT) coating and a gate electrode as the extraction electrode. In these EDT systems, it is expected that several FEC units will operate in parallel to fulfill the redundancy requirement. Since interactions between cathode units may cause instability or performance degradation, parallel operation experiments must be performed on the FECs prior to practical on-orbit operation. We conducted experiments on FEC parallel and single operations in both vacuum and plasma environments. Consequently, we found that the following control method for the FEC is effective for obtaining a maximum emission current and minimizing the gate current; the gate voltage is controlled in response to the change in the emitter potential by configuring the upper limit of the emission and gate currents. However, the emission currents during parallel operations of the FECs were still lower than those during operations of single FECs. The electron current passing through the gate in the plasma environment was found to be lower than that in the vacuum as the positive potential of the gate attracts electrons from the plasma.
