An ion gun with relatively high yield at low pressure (<10−3 Pa)

An ultrahigh‐vacuum ion gun is described which is designed specifically for operation at pressures ?1.0×10−3 Pa. It produces mass analyzed ion beams at voltages 100 V to 10 kV and currents up to ∠1×10−7 A. For pressures ?1×10−5 Pa, 0.2 A Torr−1 of argon ions can be focused onto a 0.4‐cm‐diameter target 45 cm from the source. The gun operates without differential pumping in a system having a background pressure of 4.0×10−9 Pa. With the source in continuous operation at 30 mA electron emission, the partial pressures of H2 and CO within the source are each ∠1×10−9 Pa, and the total apparent source pressure is 11×10−9 Pa (equiv.N2). At a beam energy of 1 keV,ion energy spread (FWHM) is 0.6 eV and the beam divergence half‐angle at the source is 0.4°.