Omegatron Mass Spectrometer Research Articles

エネルギーフィルターを備えたオメガトロン型質量分析器による水素シートプラズマ中での負イオン温度計測

We succeeded in measuring the negative hydrogen ions temperature TH- in the sheet plasma by using an omegatron mass spectrometer. The TH- was determined by measuring the ion current as a function of the ion repeller voltage VG2 using the omegatron mass spectrometer. Calculated using an energy distribution function, TH- was approximately 0.27 eV in the sheet plasma.

Analysis of Hydrocarbons of the JET Divertor Cryogenic Pump at the End of the Carbon Wall Campaign Using a Micro Gas Chromatograph

The JET Active Gas Handling System (AGHS) analytical glovebox contains a custom built Gas Chromatography (GC) system and an Omegatron Mass Spectrometer. The equipment is primarily used to determine the purity of the hydrogen isotopes recovered and separated by the AGHS.Another application is to analyse the composition of the torus exhaust gas to identify and quantify all compounds including hydrocarbons generated during plasma operation. The installed GC system could only measure hydrocarbons up to propane, hence a new system was added: a Micro Gas Chromatograph, capable of analysing mixtures of hydrocarbons up to decane.Results of the analyses of hydrocarbons at the end of the carbon wall campaign with the new Micro GC are presented in this paper.

Spectroscopic determination of the singly ionized helium density in low electron temperature plasmas mixed with helium in a linear divertor plasma simulator

The spectroscopic method is developed to obtain the He+ ion density nHe+ in low electron temperature, Te=5–20eV, plasmas mixed with He. Plasmas were produced in the PISCES-B linear divertor plasma simulator [R. P. Doerner et al., Phys. Scr. T111, 75 (2004)] where the electron densities are ne=(1−15)×1018m−3 and the ionization degree is ∼1–10%. In the method, the He I line intensity IHeI at λ=447.1nm is used, instead of the He II line intensity in the conventional method. The radial confinement time of He+ ions is requisite, and is measured to be at a level of the Bohm confinement time. The He+ ion concentration, nHe+∕ne, is found to be proportional to IHeI, and to weakly depend on ne and Te. Because of the higher ionization energy of He than other species (D2, Ne, and Ar), the measured nHe+∕ne becomes systematically lower than the He gas pressure fraction, and agrees with data from an omegatron mass spectrometer. The omegatron measurement and estimates of the He+ ion loss rates indicate that the influences of vibrationally excited deuterium molecules on the particle balance of He+ ions are small at Te⩾10eV.

Evaluation of an Omegatron mass spectrometer for use in the plasma exhaust processing of a fusion reactor

The plasma exhaust processing plant of fusion reactors require on-line analysis of gas streams to monitor various gas compositions. The resolution of an Omegatron increases with decreasing mass and it can easily discriminate between all the 20+ species of ions between masses 1 and 9, except between T + and He 3 + ions. The Omegatron is a candidate device for gas analysis, it is small, simple to operate and relatively inexpensive. The disadvantages are the upper pressure limit of about 1.0E−6 mbar and low output currents, typically less than 1.0E−11 A, which give slow response times. The Omegatron at the Tritium Laboratory Karlsruhe is well established and has been used successfully for qualitative analyses of tritiated gas mixtures. Quantitative measurements on known gas mixtures up to mass 28 have revealed several anomalies, particularly when helium is present. Work to explain this effect is reported. The gas in the mass spectrometer has to be a representative sample and be introduced in a reasonable timescale. A potential pumping and expansion arrangement is described. The Omegatron is highly suited to computer control as the cyclotron frequencies of the various ions are precisely known and techniques to control the Omegatron and evaluate the results are proposed.

Evidence for the importance of radial transport in plasma detachment in the Nagoya University Divertor Simulator (NAGDIS-II)

Measurements of ion and electron temperatures have been performed in detaching helium–hydrogen plasmas in a linear divertor simulator experiment using spectroscopy, a Langmuir probe, and an omegatron mass spectrometer. Detachment in these plasmas is characterized by a significant (≈20×) reduction in the central plasma flux at the target plate as the target region neutral pressure is increased from 2 to 12 mTorr. The data indicate that partially detached gas-target plasmas consist of a hot (Te≈5 eV) core region along the axis of the plasma column, surrounded by a cold (Te≈0.1 eV) halo region of recombining plasma. At Te=5 eV, plasma recombination is negligible compared with ionization; these experiments therefore provide evidence that detachment is primarily caused by radial transport and by a gradual drop in the ionization source as the temperature of the core region drops below 5 eV.

Design and operation of an Omegatron mass spectrometer for measurements of positive and negative ion species in electron cyclotron resonance plasmas

The Omegatron mass spectrometer, originally developed for measuring atomic constants, was employed for measuring both positive ions and negative ions in high density, electron cyclotron resonance etching plasmas. The main disadvantages of the conventional design of the Omegatron include the observation of resonance frequency shifts and poor mass resolution in a relatively weak magnetic field. Based on 2D numerical analysis, several modifications were carried out to overcome these limitations: the (±) ion collector, differential pumping, different RF excitation methods, an additional magnet for uniform magnetic field, etc. Experimental results indicated the presence of H- and H-2 in H2 plasmas, and F- and CF- in CF4 plasmas.

Ion-cyclotron-resonance mass spectrometry with a microwave plasma source

The feasibility of coupling an electron-cyclotron-resonance (ECR) plasma-processing reactor directly to an omegatron mass spectrometer is demonstrated. The ECR plasma is created in a chamber that is coupled to the omegatron through a small, grounded orifice. Ions created in the ECR chamber flow along the magnetic field into the omegatron analysis cell, and the mass spectrum of these ions is recovered. Using this technique the mass spectra of both single-component (He) and two-component (N/sub 2/ and N) ECR plasmas were measured. The mass resolution as a function of the omegatron excitation voltage for He and N/sub 2/ plasmas was obtained and found to compare well to theoretical calculations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An omegatron mass spectrometer for plasma ion species analysis

An omegatron mass spectrometer which can be used to measure the ion species and charge state distribution in a magnetized plasma is described. In the conventional omegatron, ions are formed as the result of gas ionization by a fine electron beam passing through the center of the analyzer along the magnetic field. In the plasma omegatron, the plasma ions are entering the analyzer through a small floating aperture. We employ a biasing technique to reduce the ion velocity along the magnetic field and, thus, achieve improved ion collection and sensitivity. Experiments have been performed to demonstrate the instrument’s operation in the PISCES-A linear plasma device, at a magnetic field B=1.3 kG. Mass spectra have been obtained in hydrogen, helium, and nitrogen plasmas, and typical results are presented.

Helium leak detection in JET in the presence of high deuterium partial pressure

Leak detection in JET (∼200 m3 volume, ∼8000 m length of welds, ∼300 bolted vacuum connections, base pressure at room temperature 2×10−9 mbar) had originally been based on the use of helium (4He) as a tracer gas. Later, high deuterium (D2) partial pressures due to D2 plasma operation made high-sensitivity leak testing by standard methods with 4He impossible; hence, alternative methods had to be developed. This eventually led to the use of a high-resolution Omegatron mass spectrometer able to separate D2 and 4He. Additional compression and selective pumping provides a sensitivity of 10−9 mbar l s−1. The advantages of the Omegatron system compared with other alternative methods will be presented. The use of a fully tritium compatible Omegatron in conjunction with ∼400 tracer gas tubes during the active phase leak detection will be discussed.

The Catalytic Exchange of Hydrogen-Deuterium on Copper-Nickel Alloy Plates after Various Surface Treatments

Abstract The catalytic activities of nine copper-nickel alloys (5 cm2 in area) in hydrogen-deuterium exchange were examined at 1.5 Torr partial pressures of hydrogen and deuterium, using an ultra-high vacuum apparatus incorporated with an omegatron mass spectrometer for continuous gas analysis. Without any surface treatment, the activity was greatest on pure nickel, decreased gradually as the content of copper in the alloys increased and virturally vanished in the alloys containing copper more than 70%. The activity of each alloy sample was observed to be extremely enhanced by a slight surface treatment of oxidation-reduction (Po2=2.3 Torr at 500°C for 1 min, PH2=16 Torr at 300°C for 2 hr). The activity of the 85% copper alloy after the oxidation-reduction treatment was greatest, one hundred times that of pure nickel. Annealing for a short time in an ultra-high vacuum subsequent to the oxidation-reduction treatment caused the catalytic activity to decrease abruptly at a critical temperature (425°C). On the bases of the electron microscopic observations and the measurement of the surface roughness changed by the pre-treatments, the nature of active sites on copper-nickel alloys was discussed.

Thermal Decompsition of Ammonium Salts of Transition Metal Oxyacids. IV. Determination of Constituents of Gases Evolved in Decomposition of Ammonium Chromate

Abstract Constituents of gases evolved in thermal decomposition of ammonium chromate and ammonium dichromate have been studied by an omegatron mass spectrometer. From the data of gas analysis, the following conclusions have been obtained. The decomposition of the first step started with proton transfer mechanism and the ratio of NH3 to H2O was not 2 : 1 at the beginning. The second step corresponded to the formation of N2, N2O, and H2O through oxidation of NH3 by the chromate anion. The decomposition in the third step was accompanied by the evolution of oxygen molecules. The production of CrO3 was confirmed by comparing the dissociation pressure of CrO3 produced in AC decomposition with that of pure CrO3. The decomposition in the last step corresponded to the process from CrO2 to Cr2O3, with the evolution of O2, CO2, and CO.

Thermal Decomposition of Ammonium Salts of Transition Metal Oxyacids. II. The Determination of the Gas Constituents Evolved by Ammonium Paramolybdate Decomposition

Abstract Gases evolved by the decomposition of ammonium paramolybdate tetrahydrate have been analyzed by means of an omegatron mass spectrometer. Only water molecules of the hydration were eliminated during the first stage of decomposition, and the final stage was not the elimination reaction of ammonia but the oxidation reaction of ammonia by Mo(VI) oxide. Between 150 and 250°C, ammonia and water were evolved in a mole ratio of roughly 2:1, corresponding to the elimination of (NH4)2O. However, the range is not clear because of the overlap of the elimination of water at the lower limit and that of nitrogen at the upper limit. At higher temperatures, a small amount of NO was observed.

An Atomic Oxygen Beam System for the Investigation of Mass Spectrometer Response in the Upper Atmosphere

An atomic oxygen beam system has been designed and tested for the laboratory evaluation of mass spectrometers used in upper atmospheric measurements. The atomic oxygen is generated by thermal dissociation of molecular oxygen on the surface of a tungsten filament heated to 2800 K. A symmetrical bidirectional beam is produced to permit simultaneous monitoring of the particle flux in the beam while target experiments are being conducted. Flux levels of 5×1014 particles cm−2 sec−1 over a cross-sectional area of 1 cm2 have been produced with a relative atomic oxygen concentration of 70%. At flux levels below 1013 particles cm−2 sec−1, relative atomic oxygen concentrations of more than 90% were obtained. The oxygen beam is of high purity and free from chemically active contaminants. Strong chemical and low temperature pumping are used to reduce background gas contributions to less than 1%. Measurements of the relative atomic concentration in the beam were made with a quadrupole spectrometer using an open flowthrough ion source. The absolute flux of molecular oxygen was determined with the aid of an enclosed omegatron mass spectrometer. The combined use of both instruments permitted a determination of the magnitude of the atomic oxygen flux in the beam.

Operation Characteristics of the Bennett-Type Radio-Frequency Mass Spectrometer

Operation characteristics of the7-5-3-1cycle5-stage Bennett-type radio-frequency mass spectrometer(Bennett-type MS)with the secondary electron multiplier, designed for the square wave operation, was investigated in the pressure range from10-5to10-9Torr, simultaneously using the omegatron mass spectrometer as a reference. As the Bennett-type MS has many electrodes, the determination of relative electrode potentials for nice operation has been said difficult. In this investigation, however, getting the reference data with the omegatron mass spectrometer made it easy to determine the relative electrode potentials for obtaining good operation characteristics. The important factors of the Bennett-type MS operation are the voltage and the wave form of the applied radio-frequency, the drift voltages and the stability of the barrier voltage. As a result of the ion accelerating-voltage scanning method at a fixed radio-frequency, the ion background current wasincreased gradually in the high mass range. The reproducibility of the mass spectra obtained with the Bennett-type MS was satisfactory under the same conditions throughout the experiment. Even in the ultra-high vacuum conditions(-10-9Torr), Bennett-type MS can be used in the low mass range(1-10)without any significant ghost peaks though the operation in this mass range was difficult in the past, and can also be used up to the high mass range(-200). The minimum detectable partial pres sure was about10-13Torr and obtaining the resolution of50was relatively easy. The mass spectrum was also observed on the synchroscope screen in the range from10-5to10-9Torr. A so-called broad surface peak appeared around M=15was gradually predominant in the ultra-high vacuum region, and this peak could probably be due to the O ions produced from adsorbed CO on the tungsten grid surface under electron bombardment because of the inadequate structure of the ion source.

A Mass Spectrometer without Memory Effect for Gas Analysis in Ultrahigh Vacuum

The described Omegatron mass-spectrometer is equipped with an internal heating device. All inner metal parts of the Omegatron gauge axe made of noble metal and can be held during the measurements at a maximum temperature of ≈ 500 °C. For cleaning and degassing the gauge the temperature of the metal parts can be increased up to 900 °C. All parts of the gauge made of base metals are enamelled. The fact that the memory effect can be held down by the entirely heatable Omegatron is a new and important criterion for measurements of partial pressures in the ultrahigh vacuum range. A further advantage of the heatable Omegatron-box is the remarkable constancy of ion transmission which is obtained at constant electrode-potentials even after many heating-cycles.

Dissociation Pressures of Various Metallic Oxides

Abstract Gases evolved during a vacuum heat treatment of various oxides were analyzed by means of an omegatron mass spectrometer. Carbon dioxide, carbon monoxide and water were detected as main gases evolved at lower temperatures. Oxygen due to thermal dissociation of ZnO, CdO, NiO, CuO, Cu2O, and WO3 was found at high temperatures. In the case of MoO3, however, evolution of oxygen was not observed. The equilibrium pressures of the evolved gases over these oxides have been measured with a McLeod gauge and a Knudsen gauge. The oxygen dissociation pressures of ZnO, CdO, NiO, CuO, and Cu2O were measured and compared with the calculated values.

548. Omegatron mass spectrometer with high resolution. (Germany): E P T M Suurmeyer and J C Francken, Vakuum-TEchnik, 17 (1), Jan 1968, 1–7 ( in German)

548. Omegatron mass spectrometer with high resolution. (Germany): E P T M Suurmeyer and J C Francken, Vakuum-TEchnik, 17 (1), Jan 1968, 1–7 ( in German)

70. Operating parameters of the omegatron mass spectrometer in ultrahigh vacuum: J M Bradford, Rep NASA-TN-3129, Dec 1965, NASA Langley Res Center, Va.

Operating parameters of omegatron mass spectrometer in ultrahigh vacuum determined for helium, nitrogen, argon, and carbon dioxide to give maximum sensitivity

Omegatron Mass Spectrometer for Partial Pressure Measurements in Upper Atmosphere

A simple Omegatron mass analyzer used for measuring density and temperature of nitrogen in the 100 to 350 km region of the upper atmosphere has been developed. The mechanical and electrical configurations have been designed for rocket flight application, and the operating parameters optimized for the upper atmosphere measurement. This Omegatron is calibrated and flown as part of a sounding rocket experiment known as the Thermosphere Probe, which also contains an electron temperature probe for determining electron temperature and density. Several successful flights have shown that the Omegatron is a reliable device for this application.

False peaks in the omegatron mass-spectrometer: A P Averin,Pribory i Tekh Eksper, 5, 1965, 174–177.

False peaks in the omegatron mass-spectrometer: A P Averin,Pribory i Tekh Eksper, 5, 1965, 174–177.