“…In a previous study, high-density H − ion sheet plasmas were generated using TPDsheet-U, and H − ion current densities of over 20 mA cm −2 were obtained under the following conditions: a gas pressure of 0.3 Pa, a discharge current of 80 A, an external magnetic field of ∼40 mT, and an extraction voltage of 10 kV. However, the co-extracted electron current is ∼10 times the negative-ion current, and the thermal damage caused by this electron poses a problem in the long-operation of the negative-ion source TPDsheet-U [12,13]. An electron fence (EF) was installed on the extraction grid (PG).…”