Simulation study of the ionization gauge with carbon nanotube cathode

Study of the ionization gauge with carbon nanotube cathode for carbon nanotube (CNT) field emission cathode, a high gate electrode voltage, as high as several hundred volts, is required to generate high emission field current. However, high gate potentials could affect the electric field distribution in the ionization space significantly, and the electron energies endowed by gate potential are relatively high for the gas ionization. Both of them have negative impacts on the ionizatio Simulation n probability. In this work, the structure of the ionization gauge with CNT cathode was optimized from the simulation study. The results show that electron trajectory in the ionization space vary with the change of the voltage ratio between the anode and the gate (V_grid/V_gate). For extractor gauge, the longest effective electron trajectory could be achieved when the ratio of V_grid/V_gate reaches 1.6. The sensitivity decreases with increasing the anode potential, which is due to the drop of the ionization probability caused by the high anode potential. Accordingly, a new cathode structure is proposed with adding a suppressor electrode between the gate and the anode. The suppressor electrode is help to decrease the electron energy, leading the increase of the sensitivity. This design provides a new approach to extend the measurement lower limit for CNT field emission based ionization gauge.