Residual Gas Adsorption and Desorption in the Field Emission of Titanium-Coated Carbon Nanotubes

Titanium (Ti)-coated multiwall carbon nanotubes (CNTs) emitters based on the magnetronsputtering process are demonstrated, and the influences of modification to CNTs on the residual gasadsorption, gas desorption, and their field emission characteristic are discussed. Experimental resultsshow that Ti nanoparticles are easily adsorbed on the surface of CNTs due to the “defects” producedby Ar+irradiation pretreatment. X-ray photoelectron spectroscopy (XPS) characterization showedthat Ti nanoparticles contribute to the adsorption of ambient molecules by changing the chemicalbonding between C, Ti, and O. Field emission of CNTs coated with Ti nanoparticles agree well withthe Fowler–Nordheim theory. The deviation of emission current under constant voltage is 6.3% and8.6% for Ti-CNTs and pristine CNTs, respectively. The mass spectrometry analysis illustrated thatTi-coated CNTs have a better adsorption capacity at room temperature, as well as a lower outgassingeffect than pristine CNTs after degassing in the process of field emission

Performance of a Low Energy Ion Source with Carbon Nanotube Electron Emitters under the Influence of Various Operating Gases

Low energy ion measurements in the vicinity of a comet have provided us with important information about the planet’s evolution. The calibration of instruments for thermal ions in the laboratory plays a crucial role when analysing data from in-situ measurements in space. A new low energy ion source based on carbon nanotube electron emitters was developed for calibrating the ion-mode of mass spectrometers or other ion detectors. The electron field emission (FE) properties of carbon nanotubes (CNTs) for H2, He, Ar, O2, and CO2 gases were tested in the experiments. H2, He, Ar, and CO2 adsorbates could change the FE temporarily at pressures from10−6 Pa to10−4 Pa. The FE of CNT remains stable in Ar and increases in H2, but degrades in He, O2, and CO2. All gas adsorbates lead to temporary degradation after working for prolonged periods. The ion current of the ion source is measured by using a Faraday cup and the sensitivity is derived from this measurement. The ion currents for the different gases were around 10 pA (corresponding to 200 ions/cm3 s) and an energy of ~28 eV could be observed

Performance of a Low Energy Ion Source with Carbon Nanotube Electron Emitters under the Influence of Various Operating Gases

Low energy ion measurements in the vicinity of a comet have provided us with importantinformation about the planet’s evolution. The calibration of instruments for thermal ions in thelaboratory plays a crucial role when analysing data from in-situ measurements in space. A new lowenergy ion source based on carbon nanotube electron emitters was developed for calibrating theion-mode of mass spectrometers or other ion detectors. The electron field emission (FE) properties ofcarbon nanotubes (CNTs) for H2, He, Ar, O2, and CO2gases were tested in the experiments. H2, He,Ar, and CO2adsorbates could change the FE temporarily at pressures from10−6Pa to10−4Pa. The FEof CNT remains stable in Ar and increases in H2, but degrades in He, O2, and CO2. All gas adsorbateslead to temporary degradation after working for prolonged periods. The ion current of the ion sourceis measured by using a Faraday cup and the sensitivity is derived from this measurement. The ioncurrents for the different gases were around 10 pA (corresponding to 200 ions/cm3s) and an energy of~28 eV could be observed

Research on control strategy for AC side asymmetric fault of MMC-HVDC transmission system

When the Modular Multilevel Converter (MMC) fails on the AC side, the operating characteristics of MMC will be damaged. If the system wants to retain stable for a long time in the process of operation, it is obliged to design the control strategy in case of asymmetric fault. In this article, the control strategy based on feedback linearization principle is adopted to diminish the negative sequence current caused by breakdown, and a DC voltage controller is devised to suppress the fluctuation of the double frequency component under asymmetric fault conditions. The validity of the control strategy requires to be verified, the running results on PSCAD platform indicate this method is effective and feasible

A Cylindrical Triode Ultrahigh Vacuum Ionization Gauge with a Carbon Nanotube Cathode

In this study, a cylindrical triode ultrahigh vacuum ionization gauge with a screen-printed carbon nanotube (CNT) electron source was developed, and its metrological performance in different gases was systematically investigated using an ultrahigh vacuum system. The resulting ionization gauge with a CNT cathode responded linearly to nitrogen, argon, and air pressures in the range from ~4.0 ± 1.0 × 10−7 to 6 × 10−4 Pa, which is the first reported CNT emitter-based ionization gauge whose lower limit of pressure measurement is lower than its hot cathode counterpart. In addition, the sensitivities of this novel gauge were ~0.05 Pa−1 for nitrogen, ~0.06 Pa−1 for argon, and ~0.04 Pa−1 for air, respectively. The trend of sensitivity with anode voltage, obtained by the experimental method, was roughly consistent with that gained through theoretical simulation. The advantages of the present sensor (including low power consumption for electron emissions, invisible to infrared light radiation and thermal radiation, high stability, etc.) mean that it has potential applications in space exploration

Applications of Vacuum Measurement Technology in China’s Space Programs

The significance of vacuum measurement technology is increasingly prominent in China’s thriving space industry. Lanzhou Institute of Physics (LIP) has been dedicated to the development of payloads and space-related vacuum technology for decades, and widely participated in China’s space programs. In this paper, we present several payloads carried on satellites, spaceships, and space stations; the methodologies of which covered the fields of total and partial pressure measurement, vacuum and pressure leak detection, and standard gas inlet technology. Then, we introduce the corresponding calibration standards developed in LIP, which guaranteed the detection precision of these payloads. This review also provides some suggestions and expectations for the future development and application of vacuum measurement technology in space exploration

Development of an CNT field emission UHV ionization gauge with customized electronics

An ionization vacuum gauge with carbon nanotube (CNT) cathode was designed for measurement of ultra high vacuum (UHV). The sensor was constructed based on Bayard-Alpert type gauge. The key index of the control unit is determined by theoretical analysis and experimental results. A customized detection circuit was designed considering the characteristics of the output ion current of the sensor, the performance of which, such as linearity, noise, bandwidth and gain, were determined by a series of tests and calibrations. At last, the vacuum measurement range and uncertainty of this gauge were determined. The test results showed that the lower limit of the CNT-cathode ionization vacuum gauge enters 10-8Pa, The measurement uncertainty is about 4.0% in the pressure range of 10-4Pa-10-7Pa. This work can provide a new solution for UHV measurement

Study of a low-energy collimated beam electron source and its application in a stable ionisation gauge

Stable ionisation vacuum gauges obtain stable sensitivity by controlling both the well-defined electron trajectory and electron energy in the ionisation volume. To achieve this goal, a collimated electron beam and large ion- isation cross-section are required as the electrons enter the ionisation volume. In this paper, a low-energy electron source based on carbon nanotubes is designed to realise a collimated electron beam by the addition of specialised deceleration and focus electrodes. The experimental transmission is approximately 25%, which is in good agreement with the simulation results. Furthermore, a simulation study is carried out combining the electron source with the components of a novel stable ionisation gauge. The numerical simulation results show a sensitivity of 0.250 Pa-1. It provides an important reference for the development of stable ionisation gauge based on the field emission cathode