Agilent 4UHV Ion Pump Controller Design to Optimize Pump Performance

Ion pump controllers are often considered just accessories needed to power ion pumps. Only basic parameters such as the maximum power and the communication interface are considered relevant, with the power usually being overspecified, resulting in needlessly expensive controllers. However, a properly designed controller can substantially improve the ion pump performance. A controller with variable voltage as a function of the pump operating pressure maximizes the pumping speed in the entire operating range. This is because the energy with which the ions inside the pump bombard the cathodes is the nominal applied high voltage (multiplied by the electrical charge), reduced by the space charge effect due to the electron cloud present in the ion pump cell1. Since the space charge effect is pressure-related, a variable high voltage should be applied to maintain optimum bombardment energy, resulting in the best possible pumping performance at any pressure. Additionally, reducing the applied voltage at low pressure enables use of the ion pump as a reliable pressure gauge down to the 1 × 10–10 mbar range2. Furthermore, a properly designed voltage-versus-current controller curve can start even a large ion pump at relatively high pressure (1 × 10–4 mbar) with limited power, and with negligible aging of the pump.