Residual Gas Pressure Research Articles

High efficient removal of tin from lead bullion based on the oxygen-controlling method under vacuum

Conventional detinning process of lead bullion usually includes the following problems: the oxidizing refining process takes a long time to finish the oxidation of tin and products mass slag, while the basic refining process consumes large reagent, and the labor condition is poor. Therefore, a novel technique with oxygen controlled under vacuum condition for removing tin in crude lead was investigated, which shows characters such as, low-energy consumption, less metal wastage and environmental friendly. During this process, tin was removed from lead bullion by converting to tin oxide and concentrating in the dross. The experimental results showed that the residual Sn-concentration in detinned lead was about 2 ppm corresponding to the lead loss ratio about 2–3 wt% under the following experimental conditions: temperature of 750 °C, oxidation time of 80 min, agitation speed of 100 rpm and air flow rate of 60 mL/min corresponding to the residual gas pressure of 57 KPa.

Laser-induced damage threshold tests of ultrafast multilayer dielectric coatings in various environmental conditions relevant for operation of ELI beamlines laser systems

Increasing the laser-induced damage resistance of optical components is one of the major challenges in the development of Peta-watt (PW) class laser systems. The extreme light infrastructure (ELI) beamlines project will provide ultrafast laser systems with peak powers up to 10 PW available every minute and PW class beams at 10 Hz complemented by a 5-TW, 1-kHz beamline. Sustainable performance of PW class laser systems relies on the durability of the employed optical components. As part of an effort to evaluate the damage resistance of components utilized in ELI beamlines systems, damage thresholds of several optical multilayer dielectric coatings were measured with different laser parameters and in different environments. Three coatings were tested with 10 Hz and 1 kHz pulse repetition rates, and the effect of a cleaning treatment on their damage resistance was examined. To explore the damage threshold behavior at different vacuum levels, one coating was subject to tests at various residual gas pressures. No change of damage threshold in a high vacuum with respect to ambient pressure was recorded. The effect of the cleaning treatment was found to be inconsistent, suggesting that development of the optimal cleaning treatment for a given coating requires consideration of its specific properties.

GEANT4 models for the secondary radiation flux in the collimation system of a 300 MeV proton microbeam

In Harbin, we are developing a 300MeV proton microbeam for many applications in space science including upset studies in microelectronic devices, radiation hardness of materials for satellites and radiation effects in human tissues. There are also applications of this facility proposed for proton therapy. The microbeam system will employ a purpose-built proton synchrotron to provide the beam. However there are many challenges to be addressed in the design, construction and operation of this facility. Here we address two important design aspects for which we apply GEANT4 modeling. First, the high energy proton beam interacts strongly with beam line materials, especially the collimation slits, to produce showers of secondary particles which could introduce significant background signals and degrade the resolution of the proton microbeam. Second, the beam transport within the residual vacuum of the beam line may also introduce undesirable background radiation. In both cases mitigation strategies need to be incorporated during the design phase of the new system. We study the use of a dipole magnet following the aperture collimator to reduce the flux of secondary particles incident on the analysis chamber. Monte Carlo simulations are performed using GEANT4 and SRIM. By inserting the dipole magnet, we find as expected a significant reduction in the scattering of protons and other particles, such as neutrons and gamma rays, at the collimation system exit position. Secondary radiation from the residual gas pressure within the beam line vacuum system are also modelled and found to be negligible under the standard operating conditions.

Axial heating and temperature of RF-excited non-neutral plasmas in Penning-Malmberg traps

Electro-magnetostatic traps have been used for decades to provide long-term storage of charged particle samples or non-neutral plasmas. The dynamics and equilibrium states of these ideally simple systems can be strongly diverted from the usual working conditions (i.e. single-species, quiescent samples) in the presence of oppositely charged particles or external electric field perturbations. Both these conditions occur when the plasma is generated by means of a radio-frequency (RF) excitation continuously applied on a trap electrode. The application of RF drives of some volts over periods larger than typical collisional time scales leads to residual-gas ionization and to the accumulation of an electron plasma, a process that has previously been exploited as an alternative to thermionic or photoemission electron sources. The analysis of the axial energy distribution shows a deviation of the continuously excited final state from maxwellianity dependent on the radial position and the subsequent relaxation to equilibrium after the interruption of the drive. Systematic measurements also indicate the high sensitivity to the residual gas pressure of both the total confined charge and of the attainable densities and plasma profiles. The results are compared to the information obtained from a very simple one-dimensional electron heating model and show the validity of its most basic features together with its shortcomings.

Density and surface tension of diluted Sn–In alloys

The results from measuring the density and surface tension of Sn–In melts via the sessile drop method in a helium atmosphere and at a residual gas pressure of 0.01 Pa are presented. The density polytherms of all samples are linear with negative temperature coefficients. In the range of 550–750°C, the surface tension falls linearly as the temperature rises.

Evaluation of the remote lower protective seam mining for coal mine gas control: A typical case study from the Zhuxianzhuang Coal Mine, Huaibei Coalfield, China

The protective seam mining technology is the most effective and economical method in realizing the safe mining of outburst-prone coal seams. To study the effects of remote lower protective seam mining on coal mine gas control, a typical case (average layer spacing: 78 m) taken from the Zhuxianzhuang Coal Mine was investigated by a comprehensive evaluation through numerical simulation, gas extraction data statistics, residual gas pressure/content measurements and recovering gas emission analysis. The results indicate that after the recovery of the protective seam, the unloading effects could lead to a maximum expansion deformation rate of the protected seam by 33.4‰, which remarkably increases the permeability of the coal seam by 4320 times. Combining with the pressure-relief gas extraction methods, considerable amount of the gas (about 78.58%) was extracted from the protected seam, resulting in the maximum residual gas pressure and content of 0.26 MPa and 4.29 m3/t respectively, which indicate that the outburst risk has been completely eliminated. Additionally, among the gas extraction methods, the penetrating borehole extraction presents the best drainage effect, accounting for 42.58%–55.09% of the total extracted pressure-relief gas. The effect of the surface wells extraction is closely related to the number of wells and whether the wells can work properly or not. However, the effect of interception boreholes extraction is poor and the extracted amount is almost negligible. Moreover, a protected range extension phenomenon is noticed, which demonstrate that the protected area generated by the protective seam mining is larger than that of the theoretical predicted one, and thus a further study is needed.

Effect of the ion background on the spectral and amplitude characteristics of the output signal from the oscillator with the turbulent electron beam

The effect of the residual gas pressure on the spectral and amplitude characteristics of the output signal from the oscillator with the turbulent electron beam is examined. It is shown that ions resulting from gas ionization in the drift region promote formation of denser and more compact space charge bunches. Denser bunches increase the output signal power and aid in appearance of higher-order components in the spectrum, thus extending the working range to a higher-frequency region. When the device operates in the regime of noiselike signal generation, ions contribute to a decrease in the irregularity of the output power spectrum to about 0.3 dB in the working frequency range up to two octaves.

Thermal evaporated hyperbranched Ag nanostructure as an effective secondary-electron trapping surface coating

We study secondary electron yield (SEY) suppression of silver using a hyperbranched nanostructure obtained by thermal evaporation. First, we perform thermal evaporation at different residual gas pressures for studying the influence of pressure on surface morphologies. A self-assembled hyperbranched Ag nanostructure has been achieved at 100 Pa. Then, we further investigate the detailed formation process of the self-assembled hyperbranched Ag nanostructure qualitatively and find it to be dominated by “screening effect”. Finally, we study the obvious SEY suppression effect of this special structure. We show that 100 Pa is the best process condition within our experimental scope from the SEY suppression point of view. It exhibits maximum SEY (δmax) of ∼0.9. We also show that the combining of this nanostructure with the micro-porous surface we developed before can further improve its SEY suppression effect which leading to a δmax of ∼0.8. We propose a novel 2D rectangular-hemisphere hybrid trap model to perform numerical simulation of secondary electron dynamics for interpretation of the experimental results. In total, this work provides guidance to controllable preparation of low SEY metallic surfaces for potential applications in particle accelerators, RF microwave components and satellite systems.

Beam transport and space charge compensation strategies (invited).

The transport of intense ion beams is affected by the collective behavior of this kind of multi-particle and multi-species system. The space charge expressed by the generalized perveance dominates the dynamical process of thermalisation, which leads to emittance growth. To prevent changes of intrinsic beam properties and to reduce the intensity dependent focusing forces, space charge compensation seems to be an adequate solution. In the case of positively charged ion beams, electrons produced by residual gas ionization and secondary electrons provide the space charge compensation. The influence of the compensation particles on the beam transport and the local degree of space charge compensation is given by different beam properties as well as the ion beam optics. Especially for highly charged ion beams, space charge compensation in combination with poor vacuum conditions leads to recombination processes and therefore increased beam losses. Strategies for providing a compensation-electron reservoir at very low residual gas pressures will be discussed.

Pyroelectric neutron generator for calibration of neutrino and dark matter detectors

Pyroelectric crystals, such as LiNbO3 or LiTaO3 being under influence of a temperature gradient can produce an electric field up to 105 kV/cm. It was experimentally confirmed that a crystal installed in a chamber with a residual gas pressure of about 1 mTorr could be used to generate X-Ray radiation with an energy up to 100 keV The same setup could be used to generate s 2.45 MeV neutrons if the target is deuterated and residual gas is D2. Due to such properties as On/Off mode of operation and the absence of radioactive materials, pyroelectric neutron generators seem to be a promising tool for calibration of neutrino and dark matter and other low background detectors. We propose the application of the controlled pyroelectric neutron generator for calibration of such detectors.

An ultrabright and monochromatic electron point source made of a LaB6 nanowire.

Electron sources in the form of one-dimensional nanotubes and nanowires are an essential tool for investigations in a variety of fields, such as X-ray computed tomography, flexible displays, chemical sensors and electron optics applications. However, field emission instability and the need to work under high-vacuum or high-temperature conditions have imposed stringent requirements that are currently limiting the range of application of electron sources. Here we report the fabrication of a LaB6 nanowire with only a few La atoms bonded on the tip that emits collimated electrons from a single point with high monochromaticity. The nanostructured tip has a low work function of 2.07 eV (lower than that of Cs) while remaining chemically inert, two properties usually regarded as mutually exclusive. Installed in a scanning electron microscope (SEM) field emission gun, our tip shows a current density gain that is about 1,000 times greater than that achievable with W(310) tips, and no emission decay for tens of hours of operation. Using this new SEM, we acquired very low-noise, high-resolution images together with rapid chemical compositional mapping using a tip operated at room temperature and at 10-times higher residual gas pressure than that required for W tips.

New measurements of multilayer insulation at variable cold temperature and elevated residual gas pressure

New MLI measurements at the TU Dresden flow type calorimeter have been carried out. Specimens of 20 layer double side aluminized polyester film were tested. A cylindrical cold surface of 0.9 m2 is held at the desired cold boundary temperature between approximately 30 K and 300 K. The heat transfer through the MLI is measured by recording the mass flow as well as the inlet and the outlet temperature of the cooling fluid. Measurements at varied cold boundary temperatures have been performed. Moreover the effect of an additional vacuum degradation - as it might occur by decreasing getter material performance in real systems at elevated temperatures - is studied by a controlled inlet of nitrogen gas. Thus the vacuum pressure was varied over a range of 10-7 mbar to 10-2 mbar. Different cold boundary temperatures between 35 K and 110 K were investigated. Test results for 20 layer MLI are presented.

Microdischarges in diodes with small gaps and field emission glassy carbon cathodes

We report on the results of experimental investigation of microdischarges in diodes with small gaps and glassy carbon field-emission cathodes. It is shown that microdischarges in diodes with multipoint cathodes are initiated and evolve at the tips of micropoints when the field-emission current density attains the critical values in accordance with the Dyke theory. The field-emission current density in diodes with a developed surface without micropoints does not attain critical values and does not trigger microdischarges. It has been established experimentally that for diode gaps smaller than 100 µm, the change in the residual gas pressure from 1 × 10–7 to 1 × 10–5 Torr does not affect the emissivity and stability of field emission from glassy carbon cathodes. The threshold field strength at which microdischarges are initiated in diodes with glassy carbon cathodes remains unchanged in the residual gas pressure range from 1 × 10–7 to 1 × 10–5 Torr.

Vacuum lifetime and residual gas analysis of parabolic trough receiver

The vacuum characteristics and lifetime are the key problems of parabolic trough receiver. Heat loss of the receiver will greatly increase when the vacuum has been lost. Especially, if hydrogen is inside the annulus space of the receiver, heat loss at a level is approximately a factor of four higher than the loss for a receiver with good vacuum. Suitable vacuum levels and residual gases should be maintained in the receiver to ensure performances during its projected lifetime. In this paper, the variations of composition and partial pressure of residual gases with temperature in the receiver were measured by a high sensitivity quadrupole mass spectrometer gas analyzer. The effects of residual gas and getter on the vacuum lifetime of receiver were analyzed. The results showed that hydrogen was the main residual gas in the annular space of receiver without getter, and the nitrogen was the main gas released in the receiver with getter. It can be confirmed that the residual gas analysis was a very effective way to predict and evaluate the vacuum lifetime of the receiver.

Cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outbursts during coal roadway excavation

Coal and gas outbursts comprise the predominant hazards in Chinese coal mines. A large number of accidents have occurred during coal roadway excavation. In this study, we propose the application of a cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outburst disasters during coal roadway excavations. In this technique, a high-pressure water jet is applied in a coal body to cut a slot. This helps to increase the permeability of the coal seam, improve the gas-extraction efficiency of the borehole, and prevent and control coal and gas outburst disasters during excavations. In the field test in which hydraulic slotting was employed, the average mass of coal that was discharged from a slotted borehole is 8.2 t; the weight of the largest discharged mass is 16 t. The diameter of the slotted borehole is 12.87 times the diameter of a conventional borehole, which effectively improves the borehole's influence range. After half a month of gas extraction, the average gas-extraction concentration for the slotted borehole is 26%, whereas the average gas-extraction concentration of the conventional borehole is 7%, that is, the gas-extraction concentration for the slotted borehole is approximately 3.7 times the gas-extraction concentration of the conventional borehole. After four months of gas extraction, the residual gas content and gas pressure for the 11091 transportation roadway satisfy the requirement of the State Administration of Work Safety. A conventional borehole requires a minimum period of six months to prevent and control outbursts, whereas a slotted borehole requires a minimum period of four months. These results suggest that the technology can improve the efficiency of gas drainage, reduce the gas drainage time, and is a potential application for preventing and controlling future gas disasters.

Lifetime measurement of the 5d2 D 5/2 state in Ba+

The lifetime of the metastable 5d2 D 5/2 state has been measured for a single trapped Ba+ ion in a Paul trap in Ultra High Vacuum (UHV) in the 10−10 mbar pressure range. A total of 5046 individual periods when the ion was shelved in this state have been recorded. A preliminary value $\tau _{D_{5/2}} = 26.4(1.7)$ s is obtained through extrapolation to zero residual gas pressure.

Storing keV negative ions for an hour: the lifetime of the metastable ^(2)P((1/2)^(o)) level in ^(32)S^(-).

We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p^{5} ^{2}P_{1/2}^{o}→3p^{5} ^{2}P_{3/2}^{o} spontaneous radiative decay in ^{32}S^{-} to be 503±54 sec. This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10^{-14} mbar at 13K and storage of 10keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ from the only available theoretical prediction [P. Andersson etal., Phys. Rev. A 73, 032705 (2006)].

Conceptual design of a novel pressure swing CO2 adsorption process based on self-heat recuperation technology

CO2 capture and storage (CCS) technology has attracted attention for the mitigation of CO2 emissions. Among the dominant CO2 capture technologies, pressure swing adsorption (PSA) is a promising alternative to amine-based absorption. However, its capture cost should be further decreased to facilitate its commercial implementation in industry. In this study, a novel low-cost PSA CO2 capture process based on self-heat recuperation technology is discussed. An energy balance of the conventional process and the proposed process is simulated and compared using a commercial process simulator (PRO/II ver. 9.1, Invensys). In the proposed PSA process, the exothermic heat of adsorption is recuperated using a reaction heat transformer (RHT) and is recirculated for adsorbent regeneration. The waste residual gas pressure can also be recovered by an expander at the top of an adsorption tower. The simulation results indicate that the energy consumption of the proposed PSA process is 40% that of the conventional process.

Electron-Impact Excitation of Gas-Phase Sulfur

Herein we present results from a study of optical emission in the range 270–550 nm that was stimulated in collisions of low-energy electrons (2–50 eV) with gas-phase S. Experimental. Excitation of S was studied using an optical method with an MDR-2 high-aperture diffraction monochromator in the range 270–550 nm on an automated apparatus. The apparatus and procedures for measuring and calibrating the beam energy of exciting electrons were described in detail [7]. The beam diameter was 1.5 mm for electrons emitted by an oxide cathode. The beam was formed by a four-electrode electron gun, passed through a gas-fi lled cell 12 mm high and 10 mm in diameter, and was detected by a deep Faraday cup. The energy of electrons in the beam (full width at half-height of the distribution maximum of differentiated voltammetric characteristics) was ~0.5 eV at 20 ��A. Gas-phase S was fed into the collision cell from a separate resistance-heated reservoir loaded with S (~5 g) through a thin-walled tube 4 mm in diameter and 60 mm long. This enabled the temperatures of the collision cell, electron beam, and Faraday cup, which had their own independent resistance heaters, to be maintained 20–30 K above the temperature of the S reservoir. Thus, condensation of gas-phase S on the components of the aforementioned electron-optical system was avoided. The S reservoir temperature for all measurements was maintained within 335 ± 2 K. The vacuum chamber was evacuated using an oil pump at 500 L/s. The residual gas pressure in the vacuum chamber during the measurements was <10 –6 Torr. Emission resulting from collisions of electrons and gas-phase S passed through quartz windows of the collision cell and vacuum chamber, was focused using a dual-lens condenser onto the input slit of the MDR-2 diffraction monochromator (grating 1200 lines/mm, reverse dispersion 2 nm/mm), and was detected by an FEU-106 photoelectron multiplier. Single FEU photoelectron pulses were pre-amplifi ed, shaped by a broad-band amplifi er-discriminator, fed through an interface card into a pulse counter, and stored in a PC. The signal at each measurement point was accumulated for 10–60 s of exposure depending on the intensity of the emitted spectral lines or molecular bands in order to ensure that the measurement accuracy was better than 5–10% at the emission maximum.

热应力和残余气压对光纤法布里-珀罗压力传感器温度性能的影响

热应力和残余气压对光纤法布里-珀罗压力传感器温度性能的影响