Effect of Vacuum Condition on Thermionic Emission of Tungsten Filaments with Low Voltage DC

The photon source (proton) for cyclotron is using electrons to ionize hydrogen gas to release proton particle. The main aim of this research is to produce electrons that have sufficient energy to ionize hydrogen gas to form proton for small scale cyclotron. There are several methods to generate electrons, (i) Thermionic emission (ii) Photoelectric emission (iii) Secondary emission, and (iv) Field emission. In this research, thermionic emission was used to generate electrons. To achieve thermionic emission for this research, the filament temperature must be approximately 1000 K and this temperature was achieved when approximately DC 10 volts was applied across the filament. In this paper, variation of vacuum pressure on thermionic emission of the filament was studied. Testing the filament for thermionic emission, firstly, glass vacuum tube with electrical feed throughs and outlet terminal for vacuum pump and vacuum gauge, the length of the glass tube is 16 cm, bottom end of the glass tube diameter is 8 cm and 0.3 cm thickness and the other small end is 2.6 cm diameter in which silicon rubber gasket was constructed. Vacuum chamber can be consistently pumped down to approximately 210-3 mmHg. Vacuum chamber must be withstanding the pressure and completely seal is important so vacuum test for vacuum chamber is the important first step for entire research. Results show the suitable vacuum condition was achieved approximately about -746 mmHg to -752mmHg. The temperature is enough to reach good thermionic emission and emission current from filament is about (73 to 99.67 mA). However, some impurities due to tungsten filament and housing materials are the challenges to get stable vacuum condition.