Introduction of Ion Source

The ion source is the "heart" of the helium mass spectrometer leak detector (i.e., the mass spectrometer component). Its function is to convert helium gas molecules entering the instrument into ions that can be detected and measured. It is typically constructed from special metals resistant to high temperatures with excellent electron emission properties, and features a compact design, making it an internal core component of the instrument.

Function of Ion Source

The ion source is the first and most critical step in enabling the detection function of a mass spectrometer. Its core role is to "create" and "shape" ions, with the specific process as follows:
Electron Emission:
The filament is electrically heated to incandescence (approximately 2000°C), causing it to emit thermal electrons.
Electron Acceleration and Confinement:
An acceleration voltage (e.g., 100-200V) is applied between the ionization chamber (anode) and the filament (cathode), causing the emitted electrons to be accelerated toward the ionization chamber.
Simultaneously, a weak magnetic field (generated by permanent magnets) perpendicular to the electron beam path forces the electrons to travel in a spiral trajectory, significantly increasing their flight path and thus the probability of collision with gas molecules.
Gas Molecule Ionization:
When high-energy electrons collide with helium (and other) gas molecules entering the ionization chamber, energy is transferred to the molecules, causing them to lose an electron and form positively charged helium ions.
This process can be represented as: He + e⁻ → He⁺ + 2e⁻
Ion Extraction and Focusing:
At the opposite end of the ionization chamber, a repeller electrode with a high negative voltage pushes the positively charged helium ions out of the chamber.
Subsequently, a set of focus electrodes (Einzel lenses) use precise electric fields to converge the scattered ions into a narrow ion beam and direct it toward the subsequent mass analyzer.