Control of hot-filament ionization gauge emission current: mathematical model and model-based controller

Abstract

The lack of adequate models for feedback-controlled emission current in hot-filament cathode ionization gauges (IGs) makes it difficult to achieve precision control over a wide range of emission currents (0.01-10 mA). A nonlinear mathematical model for transforming the filament heating power into emission current is developed. Experimental and theoretical results are shown. An electron emission regulator is described which was designed for use in the calibration of IGs, mass spectrometers and vapour rate measurements with IGs.

Thermionic Electron Beam Current and Accelerating Voltage Controller for Gas Ion Sources

“…The thermionic electron source is described by nonlinear static characteristics [ 26 ], and its dynamic properties can be expressed by first-order inertia with delay [ 17 ]. For this reason, a modified three-input and two-output signal transfer function equation of the thermionic electron source can be written as follows: where K(I e ) is the gain, T(I e ) is the time constant, and T 0 (I e ) is the time delay dependent on the output value I e [ 26 ].…”

“…Many control systems of thermionic electron sources established upon analogue [11][12][13][14][15][16][17][18][19] or digital [20,21] technology provide only emission or the trap current stabilization. The electron accelerating voltage is dependent on the cathode heating voltage and the voltage drop across the emission current sensing resistor (see Equation ( 3)).…”

Recommended Practice for Pressure Measurement and Calculation of Effective Pumping Speed in Electric Propulsion Testing

“…The filament current supply should be dc. The controller should control bias voltages within a few volts directly at the gauge head, and emission currents should be controlled to within a few percent [14,15]. If the bias voltage is controlled within the gauge controller, the voltage can vary with heating current due to resistive voltage drop across the cable and vary with cable length.…”

“…For VF-7, the ISO speeds are rated for air at 23;000 l∕s mounted according to ISO 1608; therefore, the equivalent speed at the pump entrance is given by Eq. (15): P Eq P S ∕a 23;000 l∕s∕0.672 34;230 l∕s (15) It is also common practice for the baffle manufacturers to provide a pumping speed reduction factor k. For VF-7, the chevron manufacturer provided a correction factor of 50%. This can be used to determine the conductance of the baffle: P Eff kP Eq (16) 1∕kP Eq 1∕P Eq 1∕C Baffle (17) Therefore,…”

A LabView‐based hot cathode electron source simulator with no‐boundary condition computation method

“…Such distribution for long filaments and high temperatures has been calculated [1]. Some analytic methods have been presented in [2], but only for the part near the centre of the filament and with a large error. More accurate calculations have been done in [3], but without calculations of the electron emission current.…”