Surface Ionization Detector Research Articles

Characterization of in situ work function and cesium flux measurement setup suitable for cesium seeded negative ion source applications

A proof of principle experiment has been performed for the in situ measurement of the work function in vacuum conditions (~10−7 torr) relevant to cesium-seeded negative ion sources for fusion applications. The work function is measured using the principle of the photoelectric effect. The performance of the work function measurement setup and temperature-controlled cesium (Cs) oven has been characterized using various diagnostics such as a quartz crystal microbalance, a surface ionization detector and pressure measurements. The background impurities responsible for work function degradation are detected using the residual gas analyzer. The work function (⩽3.06 eV) and Cs flux (~1012 atoms s−1) have been measured directly at the sample surface during controlled Cs evaporation using a novel, inexpensive and portable design of the cathode–anode assembly.

Characterization of the SPIDER Cs oven prototype in the CAesium Test Stand for the ITER HNB negative ion sources

The ITER Heating Neutral Beam (HNB) injector is required to deliver 16.7 MW of power to the plasma from a neutralized beam of H−/D− negative ions, produced by an RF source and accelerated up to 1 MeV. To enhance the H−/D− production, Cs will be routinely evaporated in the source by means of specific ovens embedded in the source, to reduce its work function. Controlling and monitoring the evaporation rate of Cs inside the source will be fundamental to achieve the desired performance for the ITER HNB.The prototype RF negative ion source SPIDER has been developed and built in the Neutral Beam Test Facility at Consorzio RFX. In SPIDER, liquid Cs based ovens will be used to inject Cs vapors inside the source. The CAesium Test Stand (CATS) has been specifically designed and set up for testing, commissioning, and characterizing Cs ovens in vacuum, but also to study the Cs evaporation and deposition onto surfaces. A SPIDER Cs oven prototype has been manufactured and tested in CATS in order to characterize its thermal behavior, by means of thermocouples and thermal camera, and its Cs flux, by means of Surface Ionization Detectors and Laser Absorption Spectroscopy.

Electron-Stimulated Desorption of Cesium Atoms from Graphene-Covered Iridium

Electron-stimulated desorption (ESD) of cesium atoms from graphene on a metal (iridium) substrate has been directly observed for the first time using the time-of-flight technique with a surface-ionization detector. The appearance threshold of the yield of Cs atoms from the sample surface at 160 K was 20 eV. An additional ESD peak of Cs atoms was observed at an electron energy of 56 eV. The observed ESD of Cs atoms from graphene is related to the nonmetal nature of this carbon film on the metal substrate surface.

Influence of Bed Material, Additives, and Operational Conditions on Alkali Metal and Tar Concentrations in Fluidized Bed Gasification of Biomass

Gasification of biomass results in release of tar and alkali metal compounds that constitute a significant challenge to the optimization of the gasification process. Here we describe on-line measurements of alkali, condensable tar, and particle concentrations in product gas from a 2–4 MWth dual fluidized bed gasifier, with the aims to characterize typical concentrations and contribute to the understanding of alkali–tar interactions. The influence of bed material, additives, and operational parameters on the concentrations is investigated. Alkali concentrations are measured with a surface ionization detector, and particle and tar concentrations are determined using aerosol measurement techniques. The gasification of wood chips using quartz or olivine as bed material results in an alkali concentration of 30–250 mg m–3, and the observed alkali levels are consistent with a significant release of the fuel alkali content. Addition of ilmenite to a quartz bed and additions of K2SO4 and K2CO3 to an olivine bed in...

Электронно-стимулированная десорбция атомов цезия с графена на иридии

AbstractElectron-stimulated desorption (ESD) of cesium atoms from graphene on a metal (iridium) substrate has been directly observed for the first time using the time-of-flight technique with a surface-ionization detector. The appearance threshold of the yield of Cs atoms from the sample surface at 160 K was 20 eV. An additional ESD peak of Cs atoms was observed at an electron energy of 56 eV. The observed ESD of Cs atoms from graphene is related to the nonmetal nature of this carbon film on the metal substrate surface.

Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant

Alkali metal compounds may have positive influences on biomass gasification by affecting char reactivity and tar reforming, but may also disturb the process by formation of deposits and agglomerates. We herein present results from online measurements of alkali compounds and particle concentrations in a dual fluidized bed gasifier with an input of 32 MWth. A surface ionization detector was used to measure alkali concentrations in the product gas, and aerosol particle measurement techniques were employed to study concentrations and properties of condensable components in the gas. Measurements were performed during start-up and steady-state operation of the gasifier. The alkali concentration increased to approximately 200 mg m-3 when fuel was fed to the gasifier and continued to rise during activation of the olivine bed by addition of potassium carbonate, while the alkali concentration was in the range from 20 to 60 mg m-3 during steady-state operation. Addition of fresh bed material and recirculated ash had...

Doping He droplets by laser ablation with a pulsed supersonic jet source.

Laser ablation offers the possibility to study a rich number of atoms, molecules, and clusters in the gas phase. By attaching laser ablated materials to helium nanodroplets, one can gain highly resolved spectra of isolated species in a cold, weakly perturbed system. Here, we present a new setup for doping pulsed helium nanodroplet beams by means of laser ablation. In comparison to more well-established techniques using a continuous nozzle, pulsed nozzles show significant differences in the doping efficiency depending on certain experimental parameters (e.g., position of the ablation plume with respect to the droplet formation, nozzle design, and expansion conditions). In particular, we demonstrate that when the ablation region overlaps with the droplet formation region, one also creates a supersonic beam of helium atoms seeded with the sample material. The processes are characterized using a surface ionization detector. The overall doping signal is compared to that of conventional oven cell doping showing very similar dependence on helium stagnation conditions, indicating a comparable doping process. Finally, the ablated material was spectroscopically studied via laser induced fluorescence.

Surface Ionization Detector for High-Performance Liquid Chromatography

Here is reported the combination of microcolumn high-performance liquid chromatography with an on-line surface ionization detector (HPLC-SID). This device was developed using commercial gas chromatography instrumentation and an interface to vaporize the chromatographic effluent. Addition of air at a flow rate of at least 50 mL/min to the effluent enhanced sensitivity and reduced baseline noise. Tributylamine was detected by the device with a minimum detectable amount of 3.0 × 10−12 g/sec at a signal-to-noise ratio of three in a mobile phase composed of acetonitrile/water at a flow rate of 6 µL/min. The signal was linear with concentration for at least 3 orders of magnitude. Preliminary results for effluents of aromatic hydrocarbons are presented as an example of the capabilities of the HPLC-SID system.

Effect of deposition of samarium atoms on the electron-stimulated desorption of cesium and samarium atoms from the surface of tungsten coated by gold and cesium

It has been shown that deposition of Sm atoms on W(100) surface coated by several monolayers of gold and cesium affects noticeably the yield of Cs atoms in electron-stimulated desorption (ESD) from this surface. The measurements have been performed by the time-of-flight method with a surface-ionization detector. The paper reports on the first observation of ESD of Sm atoms from the tungsten surface coated by layers of gold and cesium. The ESD threshold for Sm atoms, E e = 57 eV, coincides with that for Cs atoms and corresponds to the energy of the Au 5p 3/2 core level. The dependence of the ESD yield of Sm atoms on the bombarding electron energy E e follows a resonance pattern in the form of a narrow peak located in the range 57 ≤ E e ≤ 66 eV. Deposition of Sm atoms at room temperature (∼300 K) reduces (by a factor of about two) the ESD yield of Cs atoms for 600 s, and deposition of Sm atoms at 160 K reduces the ESD of Cs atoms down to zero already for 270 s. This difference finds explanation in the study of the change the structure of the top layer of the (Au + Cs)/W surface coating undergoes under cooling of the surface from 300 to 160 K.

Controllable evaporation of cesium from a dispenser oven

This instrument allows controlled evaporation of the alkali metal cesium over a wide range of evaporation rates. The oven has three unique features. The first is an alkali metal reservoir that uses a dispenser as a cesium source. The heating current of the dispenser controls the evaporation rate allowing generation of an adjustable and stable flow of pure cesium. The second is a blocking valve, which is fully metallic as is the body of the oven. This construction both reduces contamination of the dispenser and enables the oven to be operated up to 300 °C, with only small temperature variations (<5 °C). By minimizing the temperature variation, the built up of the alkali metal at a cold spot is significantly hindered. The last feature is an integral surface ionization detector for measuring and controlling the evaporation rate. The dispenser oven can be easily transferred to the other alkali-metals.

Surface ionization detection of amine containing drugs

We report on the development of miniaturized detection systems for amine containing illicit drugs. The present investigation builds on our previous work, which has shown that surface ionization (SI) gas detection is very sensitive and selective towards molecules with amine functional groups and insensitive towards water vapour and methanol, i.e. two chemicals often used to prepare liquid solutions of illicit drug samples. Here we firstly demonstrate that amine-containing illicit drugs can be sensitively detected using flash evaporation directly into the air gap of a SI detector. We also demonstrate that this kind of straight-forward detection is insensitive to most additives present in street samples. Secondly, we demonstrate that SI vapour detectors can easily be interfaced to gas-chromatographic columns, which provides selectivity options beyond the intrinsic amine selectivity of SI detectors. Furthermore, the use of a GC-SI set-up with a split/splitless injection system has allowed us to precisely evaluate the SI detection limit.

Sampling and Online Analysis of Alkalis in Thermal Process Gases with a Novel Surface Ionization Detector

When using biomass or waste as a feedstock for power production, alkalis are a major concern because of their negative effects on equipment. To investigate the release behavior of alkalis and the effectiveness of countermeasures, it is indispensable to quantify alkali emissions with a high time resolution (less than 1 min). This paper presents a newly developed alkali detector based on the principle of surface ionization. The detector includes a number of improvements compared to previous designs that enable a reproducible measurement of alkalis in heavily tar- and particle-laden product gases. Our redesigned alkali detector has demonstrated high sensitivity and improved characteristics for making measurements of tar- and particle-laden process gases. Using an ultrasonic nebulizer as a source for alkali aerosols, we could conduct a calibration of the alkali detector over 4 orders of magnitude. In combination with a dilution setup and a sampling lance, we could take online measurements of gasifier producer gas with a high degree of reproducibility and a high time resolution of 1 s. The measurements of product gas have proven the feasibility of using the detector for field measurements.

Study of the surface ionization detector for gas chromatography

The structure of the surface ionization detector (SID) and the operation parameters of GC–SID were investigated to reduce peak tailing and to enhance sensitivity. The performances of the GC–SID, including its repeatability, linearity, sensitivity, selectivity, and tolerance towards water vapor, were evaluated systematically. Compared with nitrogen–phosphorus detector (NPD), the SID was able to detect fg level triethylamine, and selectively respond to alkylamines, some anilines, and some nitrogen heterocyclic compounds. Among alkylamines, the SID sensitivity to diisobutylamine was rather small. Even so, it was also still 10 times higher than that on NPD. The SID selectivity, defined as the sensitivity ratio between triethylamine and various tested non-nitrogen compounds, was higher than 10 6. It was found that the SID is highly tolerant towards water vapor, allowing direct injection of water sample. Finally, the GC–SID was applied to directly measure trace amines in headspace gases of rotted meat and trace simazine in tap water. The SID sensitivity to simazine was proven to be 5 times higher than that on flame ionization detector (FID). This study suggests that the SID is a promising GC detector.

A surface ionization detector for capillary gas chromatography

A novel surface ionization detector using a reducing quartz liner and a Mo emitter with a quartz enclosed internal heater for selective measurement of alkylamines by gas chromatography is designed and evaluated.

Transmission of Alkali Aerosols through Sampling Systems

AbstractIn biomass gasification, particles such as condensed alkali salts pose a threat on equipment. Due to high loads of condensable tars in the gases, sampling of these particles to liquids and subsequent analysis of the liquid is frequently the method of choice for measuring the alkali concentration in the gas. However, little is known about the collection efficiency of liquid sampling devices. By measuring the aerosol transmission using a surface ionization detector, two continuous sampling systems are compared with conventional impinger bottles. A low collection efficiency for the latter was found, but down to nearly zero transmission for the continuous sampling systems. The main mechanisms for mass transfer from gas to liquid are discussed with emphasis on particle removal in gas slugs in two‐phase flow inside tubes of the sampling system.

Electron-stimulated desorption of cesium atoms from cesium layers adsorbed ongold-covered tungsten

The electron-stimulated desorption (ESD) yields and energy distributions (ED) for neutralcesium atoms have been measured from cesium layers adsorbed on a gold-covered tungstensurface as a function of electron energy, gold film thickness, cesium coverage andsubstrate temperature. The measurements have been carried out using a time-of-flightmethod and surface ionization detector in the temperature range 160–300 K. Ameasurable ESD yield for Cs atoms is observed only after deposition of morethan one monolayer of gold and cesium on a tungsten surface at a temperatureT = 300 K, which is accompanied by the formation of a CsAu semiconductor film covered with a cesiumatom monolayer. The Cs atom ESD yield as a function of incident electron energy has aresonant character and consists of two peaks, the appearance of which depends on bothelectron energy and substrate temperature. The first peak has an appearance threshold atan electron energy of 57 eV and a substrate temperature of 300 K that is due to Au5p3/2 core level excitation in the substrate. The second peak appears at an electronenergy of 24 eV and a substrate temperature of 160 K. It is associatedwith a Cs 5s core level excitation in the Cs adsorbed layer. The Au5p3/2 level excitation corresponds to a single broad peak in the ED with amaximum at a kinetic energy of 0.45 eV at a substrate temperatureT = 300 K, which is split into two peaks with maxima at kinetic energies of 0.36 and 0.45 eV at asubstrate temperature of 160 K, associated with different Cs atom ESD channels. The Cs 5slevel excitation leads to an ED for Cs atoms with a maximum at a kinetic energy of ∼ 0.57 eV whichexists only at T < 240 K and low Cs concentrations. The mechanisms for all the Cs atom ESD channels areproposed and compared with the Na atom ESD channels in the Na–Au–W system.

Fundamental experiments on evaporation of cesium in ion sources

Basic experiments are carried out to study the cesium evaporation and desorption from surfaces at different temperatures in an environment, which is very close to the conditions of negative hydrogen ion sources for fusion applications: in a vacuum base pressure of 10(-5) mbar and in a hydrogen plasma in the Pa-range. Several diagnostic techniques such as emission and absorption spectroscopy, a surface ionization detector, and a quartz-microbalance have been utilized to determine the cesium densities, evaporation and desorption rates. The work function of a cesiated surface measured by the photoelectric effect degrades with increasing plasma-off time. Impurities and cesium compounds are detected by a residual mass analyzer.

Gas chromatography with surface ionization detection of nitro pesticides

AbstractA surface ionization gas chromatographic detector, based upon positive surface ionization, was used in capillary gas chromatography to sensitively and selectively detect nitro pesticides: pendimethalin, trifluralin, flumetralin. Higher sensitivity (better detection limit), substance specificity, and advantageous applicability are reported. Sensitivity to pendimethalin, trifluralin, and flumetralin was 1.4 C g−1, 1.1 C g−1, and 1.0 C g−1, respectively, with the linear range of operation greater than 1 × 105 for these compounds. The minimum detectable level was in the range of 10−13 g s−1. Compared with an atomic emission detector, SID provided a 110 times better detection limit for trifluralin.

Qualitative Evaluation of Alkali Release during the Pyrolysis of Biomass

The thermochemical emission of alkali metals from biomass samples and two organic salts was investigated for the first time using a novel combination of a thermogravimetric analyzer with a jet flow condenser attached to a surface ionization detector. This equipment allows the identification and comparison of the main alkali release temperatures of various kinds of biomass during pyrolysis. It has also been used to test the release patterns of two organic salts, which are present in various kinds of biomass, with low decomposition temperatures.

Resonances in electron stimulated desorption yield of cesium atoms from germanium monolayer-covered tungsten

The electron-stimulated desorption (ESD) yields and energy distributions for Cs atoms from a cesium layer adsorbed on germanium monolayer-covered tungsten surfaces have been measured as a function of electron energy, cesium coverage Θ, and substrate temperature. Cs is adsorbed at low temperature, 160K. The measurements have been carried out using a time-of-flight method and surface ionization detector. The Cs atom appearance threshold is about 24eV at Θ 0.15 ML which can be associated with the Ge 3d level excitation energy; a resonantlike peak with a maximum at Ee about 38eV that can be associated with the W 5p3∕2 level excitation energy also appears. This peak is seen only at Θ 0.3 and at Ee about 50eV. A third resonantlike peak is observed at Θ>0.5 ML, at Ee about 80eV. The positions of these two peaks can be associated with W 5p1∕2 and W 5s level excitation energies, respectively. The intensities of all resonant features pass through maxima at Θ=1 as the cesium coverage increases and are almost independent of the substrate temperature. The energy distribution for Cs atoms consists of a bell-shaped peak with a maximum at a kinetic energy of 0.55eV at Θ 0.15: a wide one with a maximum at a kinetic energy of 0.5eV and a narrow one with a maximum at a kinetic energy of 0.35eV. The results are interpreted to arise from three ESD channels for Cs atoms associated with excitations of Cs, Ge, and W core levels, respectively.The electron-stimulated desorption (ESD) yields and energy distributions for Cs atoms from a cesium layer adsorbed on germanium monolayer-covered tungsten surfaces have been measured as a function of electron energy, cesium coverage Θ, and substrate temperature. Cs is adsorbed at low temperature, 160K. The measurements have been carried out using a time-of-flight method and surface ionization detector. The Cs atom appearance threshold is about 24eV at Θ 0.15 ML which can be associated with the Ge 3d level excitation energy; a resonantlike peak with a maximum at Ee about 38eV that can be associated with the W 5p3∕2 level excitation energy also appears. This peak is seen only at Θ 0.3 and at Ee about 50eV. A third resonantlike peak is observed at Θ>0.5 ML, at Ee about 80eV. The positions of th...