Abstract: A filament assembly includes a core and a filament. At least a central portion of the filament is disposed on the core. At least the central portion may be straight or may have a high-resistance configuration such as one in which the filament follows a path that changes direction. A thermionically emissive layer may be disposed on the core so as to encapsulate at least the central portion. The filament assembly may be utilized in any application requiring the production of electrons.

Abstract: Tracer gas leak detection is provided by a calibration system with a gas leak detector having a test port for receiving a sample containing a tracer gas and coupled to a vacuum pump; a calibrated leak for a calibration sample containing the tracer gas; a mass filter coupled to the test port for receiving the test sample in an operating mode, coupled to the calibrated leak through a calibrated leak valve for receiving the calibration sample in a calibration mode, having controllable transmission of the tracer gas and providing a filtered sample; detector detecting the tracer gas in the filtered sample; a programmable gain element providing a measured value of leak rate in response to the detector signal; and a controller configured, in response to a mode control signal, to operate the leak detector in the calibration mode over two or more working ranges using the calibrated leak.

Abstract: A trace gas sensing apparatus includes a cathode, an anode, a vacuum enclosure, and a membrane. The anode coaxially surrounds the cathode, wherein the cathode and the anode define an annular ionization chamber. The vacuum enclosure surrounds the cathode and the anode and includes a gas inlet fluidly communicating with the ionization chamber. The membrane is coupled to the gas inlet in a sealed manner and is permselective to trace gas. The apparatus may further include circuitry for applying a negative voltage potential to the cathode and for measuring an ion current signal generated by the cathode, and a magnet assembly for generating a magnetic field in the ionization chamber. The cathode may include an elongated member located along a longitudinal axis, and first and second end plates orthogonal to the longitudinal axis.

Abstract: A trace gas sensing apparatus includes a cathode, an anode, a vacuum enclosure, and a membrane. The anode coaxially surrounds the cathode, wherein the cathode and the anode define an annular ionization chamber. The vacuum enclosure surrounds the cathode and the anode and includes a gas inlet fluidly communicating with the ionization chamber. The membrane is coupled to the gas inlet in a sealed manner and is permselective to trace gas. The apparatus may further include circuitry for applying a negative voltage potential to the cathode and for measuring an ion current signal generated by the cathode, and a magnet assembly for generating a magnetic field in the ionization chamber. The cathode may include an elongated member located along a longitudinal axis, and first and second end plates orthogonal to the longitudinal axis.

Abstract: Tracer gas leak detection is provided by a calibration system with a gas leak detector having a test port for receiving a sample containing a tracer gas and coupled to a vacuum pump; a calibrated leak for a calibration sample containing the tracer gas; a mass filter coupled to the test port for receiving the test sample in an operating mode, coupled to the calibrated leak through a calibrated leak valve for receiving the calibration sample in a calibration mode, having controllable transmission of the tracer gas and providing a filtered sample; detector detecting the tracer gas in the filtered sample; a programmable gain element providing a measured value of leak rate in response to the detector signal; and a controller configured, in response to a mode control signal, to operate the leak detector in the calibration mode over two or more working ranges using the calibrated leak.

Abstract: Mass spectrometers for trace gas leak detection and methods for operating mass spectrometers are provided. The mass spectrometer includes an ion source to ionize trace gases, such as helium, a magnet to deflect the ions and a detector to detect the deflected ions. The ion source includes an electron source, such a filament. The method includes operating the electron source at an electron accelerating potential relative to an ionization chamber sufficient to ionize the trace gas but insufficient to form undesired ions, such as triply charged carbon.

Abstract: A mass spectrometer includes a main magnet having spaced-apart polepieces which define a gap, the main magnet producing a magnetic field in the gap, an ion source to generate ions and to accelerate the ions into the magnetic field in the gap, the ion source located outside the gap, and an ion detector to detect a selected species of the ions generated by the ion source and deflected by the magnetic field. The ion detector is located in the gap at a natural focus point of the selected species of ions. The mass spectrometer may be used in a trace gas leak detector.