Low-pressure Helium Gas Research Articles

Transport measurement of MgB2 wire under the sub-cooled water ice compared to other cooling conditions

The standard DC transport measurements of MgB2 composite conductors were done in vacuum, low-pressure helium gas, sub-cooled solid nitrogen and water ice. The effect of these coolants on electro-thermal behaviour was studied at self-field and temperature range from 32 K to 36.5 K. The obtained results show that even small volume of Helium gas enhances the sample thermal stability during the I–V measurement in comparison to those obtained in vacuum. The cooling by solid nitrogen improves the sample stability in contrast to helium gas. The measurements performed inn water ice exhibits an excellent and stable behavior of superconducting wire carrying high transport current below and above the quench as well. Consequently, water ice shows simple, safe, and promising He-free mode of cooling for future superconducting systems.

Emission Spectrochemical Analysis of Soft Samples Including Raw Fish by Employing Laser-Induced Breakdown Spectroscopy with a Subtarget at Low-Pressure Helium Gas.

Laser-induced breakdown spectroscopy (LIBS) to detect the light elements such as lithium (Li) and boron (B) and heavy elements such as copper (Cu) and lead (Pb) in raw fish samples is reported in this work. This is made possible by understanding that the soft target absorbs recoil energy and as a result, the ablated atoms gushing from the soft target do not acquire sufficient speed to form a shock wave. In order to overcome this problem, we set a subtarget on the back of the soft target so as to produce the repulsion force by which the gushing speed of the ablated atoms is increased, yielding a sufficiently high plasma temperature or sufficiently large thermal energy needed for the excitation of the ablated atoms. Excellent spectral qualities of various soft samples such as margarine, butter, peanut butter, strawberry jam, raw tuna, raw gindara, and raw salmon are presented. Furthermore, a linear calibration curve with a zero intercept is also obtained for Li, Cu, and Pb. The detection limit of Li, Cu, and Pb is found to be around 0.1 mg/L. This modification of LIBS for soft samples by using a subtarget effect clearly promises a rapid and in situ soft sample analysis since there is practically no sample digestion in the analysis.

Effect of anode material on the breakdown in low-pressure helium gas

An experimental study of the electric breakdown in helium gas for the plane–parallel electrode configuration has been conducted using a copper cathode and a variety of anode materials: copper, aluminum, stainless steel, graphite, platinum-plated aluminum and goldplated aluminum. According to the Paschen law for studied electrode configuration, the breakdown voltage is a function of the product of gas pressure and inter-electrode gap. The breakdown processes on the left, lower pressure side of the Paschen curve have been the subject of this investigation. For those pressures, the Paschen curve may become multi-valued, where any given pressure corresponds to three breakdown voltage values. It was experimentally demonstrated that the form of the Paschen curve might strongly depend on the material of the anode and the cleanness of the anode surface. A possible explanation for this phenomenon is that electrons streaming from the cathode are reflected by the surface of the anode.

Slow Current Discharges and Quenching of the MSU Superconducting Cyclotron Gas-Stopper Magnet

The Michigan State University cyclotron gas-stopper magnet generates a strong focusing cyclotron magnetic field that permits an ion beam of up to 100 MeV/u to enter the magnet and have most of its energy reduced by low-pressure helium gas. The magnet has two superconducting coil cryostats mounted within warm iron poles and a warm split iron return yoke. The coils are connected in series using room temperature cables. The peak magnet stored energy is 3.5 MJ. The magnet has been tested to its full operating current of 180 A. During tests, the magnet discharged inadvertently three times. Two low-current discharges caused the magnet current to decay through the power supply system. A discharge at 180 A quenched the magnet, because the quench protection system caused the magnet to discharge across a 1.25-Ω resistor. This fired the cold quench protection diodes within the cryostat, quenching both coils. The magnetic field in the gap was measured as the magnet discharged. For the two low-current discharges, the magnetic field followed the current in the external magnet circuit. During a quench, the magnetic field decay rate was much slower than the external circuit current decay rate.

Mechanical testing of the IFMIF HFTM-DC prototype during operation in the HELOKA-LP helium loop

The so called High Flux Test Module (HFTM) represents the component of IFMIF (International Fusion Irradiation Facility) in which material specimens are being placed that accumulate high neutron induced damage rates (≥20dpa/fpy). Damage rates of this magnitude are limited to a volume of ∼500cm3 (attenuation in beam direction) behind a beam footprint of 20×5cm2, so the high flux region of the module is contained in a flat faced, cuboid volume of 5.6cm depth. Efforts for a high spatial utilisation and the demand for a high neutron transmission lead to a thin-walled container design. As an efficient, space-saving method to cool the container and the material specimens, an array of mini-channels (1mm gaps) through which low pressure (0.3MPa) helium gas is flowing is established. Installed closely to the target and due to space constraints by other irradiation modules, the HFTM is implemented as a slender and tall construction with features that are challenging for pressure equipment. Experimental studies on a 1:1 prototype of the HFTM-DC (double compartment) have been made in the Helium Loop Karlsruhe – Low Pressure (HELOKA-LP) during 2015. The experiments also included intensive testing to demonstrate the mechanical reliability of the HFTM under IFMIF relevant operation conditions. Therefore, the module was instrumented with numerous sensors which measure displacement, deformation and mechanical strain. The reactions on temperature and pressure loads were studied. In this paper the experimental results will be presented and compared to the numerical (FEM) simulation studies.

Practical and highly sensitive elemental analysis for aqueous samples containing metal impurities employing electrodeposition on indium-tin oxide film samples and laser-induced shock wave plasma in low-pressure helium gas.

We have conducted an experimental study exploring the possible application of laser-induced breakdown spectroscopy (LIBS) for practical and highly sensitive detection of metal impurities in water. The spectrochemical measurements were carried out by means of a 355nm Nd-YAG laser within N2 and He gas at atmospheric pressures as high as 2kPa. The aqueous samples were prepared as thin films deposited on indium-tin oxide (ITO) glass by an electrolysis process. The resulting emission spectra suggest that concentrations at parts per billion levels may be achieved for a variety of metal impurities, and it is hence potentially feasible for rapid inspection of water quality in the semiconductor and pharmaceutical industries, as well as for cooling water inspection for possible leakage of radioactivity in nuclear power plants. In view of its relative simplicity, this LIBS equipment offers a practical and less costly alternative to the standard use of inductively coupled plasma-mass spectrometry (ICP-MS) for water samples, and its further potential for in situ and mobile applications.

Postcompression of high-energy terawatt-level femtosecond pulses and application to high-order harmonic generation

We perform a post-compression of high energy pulses by using optical-field ionization of low pressure helium gas in a guided geometry. We apply this approach to a TW chirped-pulse-amplification based Ti:Sapphire laser chain and show that spectral broadening can be controlled both with the input pulse energy and gas pressure. Under optimized conditions, we generate 10 fs pulses at TW level directly under vacuum and demonstrate a high stability of the post compressed pulse duration. These high energy post-compressed pulses are thereafter used to perform high harmonic generation in a loose focusing geometry. The XUV beam is characterized both spatially and spectrally on a single shot basis and structured continuous XUV spectra are observed.

Production of metastable 23S1 helium in a laser produced plasma at low pressures

We used cavity ringdown spectroscopy to study how the laser ablation of various materials (graphite, aluminum and iron) influences production of 23S1 metastable helium in the regime of low pressure helium gas. Plasma was produced by nanosecond Nd:YAG laser at 1064nm with irradiance from 0.8 to 10.9×109W/cm2. Helium pressure ranged from 0.03 to 0.2mbar. It was found that at higher irradiances, metastable production for all materials reaches saturation due to plasma shielding and is more pronounced for graphite. The highest yield of metastables was found in the case of aluminum target (0.05%). For metals, production rate is discussed in terms of work function and ionization potential.

Application of optical-field-ionization-induced spectral broadening in helium gas to the postcompression of high-energy femtosecond laser pulses

We report a detailed numerical study on the postcompression of high-energy (∼30 mJ) femtosecond laser pulses (∼40 fs), using the spectral broadening induced by optical-field ionization of a low-pressure helium gas in a capillary. Our numerical results are in very good agreement with previously published experimental data on spectral shapes, transmitted energies and recompressed pulse durations in the full range of laser energies and gas pressures investigated. Then, we calculate the performances of the method with shorter input pulses (∼20 fs) and demonstrate that few optical cycles recompressed pulses with 5 to 8.5 mJ energy could then be achieved.

Start-up phase of the HELOKA-LP low pressure helium test facility for IFMIF irradiation modules

As part of the Engineering Validation and Engineering Design Activities (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF) [1], it is foreseen to design and test a 1:1 scale prototype of the IFMIF High Flux Test Module (HFTM) [2]. The module has been designed to be cooled by a low pressure helium gas flowing through minichannels to remove the nuclear heat.The Helium Loop Karlsruhe-Low Pressure (HELOKA-LP) has been designed to provide coolant at 1:1 HFTM operational conditions: massflow 12–120g/s, inlet pressure 0.3–0.6MPa, inlet temperature RT – 250°C. A secondary objective is to use the experience gained with HELOKA-LP for the planning of the IFMIF helium cooling system.The facility has been put into operation in 2009, and has since then been in a test and optimization phase. It was proven, that the above mentioned requirements for the facility are achieved. The paper describes the process layout and components of the facility. The performance is characterized by the results of several steady state and transient benchmark tests. Typical start-up and transition times relevant for the operation mode in the IFMIF irradiation campaigns are obtained. Additionally first results on the impurity ingress and the cooling gas chemistry are described.

8 T cryogen free magnet with variable temperature space

A conduction cooled 8 T superconducting magnetic system with variable temperature insert is developed and tested. The cryomagnetic system is based on a commercial two-stage pulse tube cryocooler with cooling power of 1W at 4.2 K. The compact superconducting magnet is manufactured from NbTi wire and impregnated with epoxy resin by "wet" technology. The clear diameter of variable temperature space is 20 mm. The system provides temperature range of 5.5-300 K. The variable temperature space is filled by low pressure helium gas. To eliminate the overheating of the magnet at high temperatures the heat switch is used in thermal coupling between variable temperature space and the 4K stage. The system design, manufacturing and test results are presented.

Quenching of He-induced intensity enhancement effect in H and D emission produced by Nd-doped yttrium aluminum garnet laser irradiation on solid targets in low pressure helium gas

An experimental study was performed on the N2-induced quenching of He-induced intensity enhancement effect in reduced-pressure plasma emission produced by Nd-YAG irradiation on solid zircaloy and porous fossil samples. The spatial distributions and temporal variations in the emission intensities show pronounced intensity quenching effects on the He I 667.9 nm, H I 656.2 nm, and D I 656.1 nm emission lines in both samples when a tiny amount (5% by volume) of nitrogen was added to helium gas, while leaving the spatial and temporal intensity profiles of the heavier Zr and Ca atoms virtually unaffected. In both cases of different ambient gases, the spatial and temporal variations in the He, H, and D emission intensities exhibit distinct features and changes, which are clearly distinguishable from those observed on the Zr and Ca emission lines, which were mainly produced by the shock-wave induced thermal excitation process. The analysis of these data unambiguously revealed the presence of an additional and distinct “He-assisted” excitation mechanism in the He plasma, which was further suggested to be related to the He metastable excited state. The quenching effect was therefore explained as a consequence of energy depletion of the He metastable excited state triggered by the Penning ionization process induced by the presence of nitrogen. This also explains the relatively insensitive response of the Zr and Ca emission intensity profiles to nitrogen addition despite the increased plasma electron density resulting from the ionization process.

Limiting the permeability of composites for cryogenic applications

The correlation between thermal fatigue-generated networks of transverse micro-cracks and the permeability of carbon fiber polymer matrix composites (PMCs) was the focal point of this effort. Epoxy and bismaleimide matrix PMCs were cycled between liquid nitrogen temperature (−196 °C) and elevated temperature. The samples were then optically examined for micro-cracks and evaluated for their tendency for leakage in a fluid containment application. Composite coupons were tested for the rate of flow of low-pressure helium gas in the through-thickness direction at room temperature (RT) and liquid nitrogen (LN 2) temperature as a function of the applied cycles. The choice of lay-up drastically influenced the permeability. Samples with [0/90] 2S and [0/90/45/−45] S lay-ups resisted leakage at least 100 cycles more than the [0/45/−45/90] S samples. The temperature of the elevated portion of the thermal cycle also had a large impact on the initiation and propagation of transverse cracks and the eventual creation of complete through-thickness gas flow paths that were the source of permeability. For example, for the [0/45/−45/90] S lay-up of IM7/5250-4 a relatively moderate 57 °C reduction in the elevated hold temperature decreased permeability by up to 100 times.

227: A Series of 285 Patients, with a 12-Month Follow-Up, Treated with “Helica” For Endometriosis: A New and Safe Thermo Coagulation Energy

The helica thermal coagulator is a new instrument that combines low pressure helium gas with electrical power and is used for the treatment of endometriosis. The device is very simple to use and is able to rapidly treat large areas of endometriosis or surrounding peritoneum.

Heavy-ion-induced production and physical preseparation of short-lived isotopes for chemistry experiments

Physical separation of short-lived isotopes produced in heavy-ion-induced fusion reactions is a powerful and well-known method and often applied in investigations of the heaviest elements, called the transactinides ( Z ⩾ 104 ). By extracting these isotopes from a recoil separator, they can be made available for transport to setups located outside the heavily shielded irradiation position such as chemistry setups. This physical preseparation technique overcomes many limitations currently faced in the chemical investigation of transactinides. Here we describe the basic principle using relatively short-lived isotopes of the lighter group 4 elements zirconium (Zr) and hafnium (Hf) used as analogs of the lightest transactinide element, rutherfordium (Rf, element 104). The Zr and Hf isotopes were produced at the LBNL 88-Inch Cyclotron using a cocktail of 18O and 50Ti beams and the appropriate targets. Subsequently, the isotopes were physically separated in the Berkeley Gas-filled Separator (BGS) and guided to a Recoil Transfer Chamber (RTC) to transfer them to chemistry setups. The magnetic rigidities of the reaction products in low-pressure helium gas were measured and their identities determined with γ-spectroscopy. Using preseparated isotopes has the advantages of low background and beam plasma free environment for chemistry experiments. The new possibilities that open up for chemical investigations of transactinide elements are described. The method can readily be applied to homologous elements within other groups in the periodic table.

Antiproton slowing down, capture, and decay in low-pressure helium gas

Data on p slowing down and capture in helium at 1 and 0.2 mb at room temperature are presented and compared to the corresponding previously publicated data in molecular hydrogen and deuterium. A Monte Carlo simulation containing a low-energy extrapolation of measured p electronic stopping power in helium gas, screened Rutherford collisions, and simple cascade mechanisms is able to reproduce the gross features of the data, but cannot explain some nontrivial details of the measured distributions.

New optical absorption spectra of Cu2 molecules produced by the gas evaporation technique

A study was conducted on the optical absorption spectra ranging from 233 to 285 nm, which were taken in a region close to the source of evaporation of Cu, in low-pressure helium gas of 100 Torr. Eight band systems for Cu2 dimers designated as system 1 through 8 were identified. The spectroscopic constants for the band origins were derived as follows: ṽ ≈ 42 200 cm−1 for system 1, ṽ00 = 41 604.74cm−1 for system ṽ00 = 39 606.70cm−1 for system ṽ00 = 38 124.32cm−1 for system 4, ṽ00 = 38 048.65 cm−1 for system 5, 98, ṽ00 = 36 834.22cm−1 for system 6, ṽ00 = 36 341.55 cm−1 for system 7 and ṽ00 = 36 174.99cm−1 for system 8. For all cases in which vibrational constants of the lower state could be determined, it was found that the transition originated from the ground state of Cu2.

Effect of different elementary processes on the breakdown in low-pressure helium gas

We investigated the breakdown in low-pressure helium gas both experimentally and by computer simulations. At low breakdown voltages (VBR1000 V) the experimental and simulation results show a good agreement (differences are within 20%), while at higher voltages the simulations and experiments agree qualitatively. Our simulations indicate that several processes contribute to the particular shape of the Paschen curve in helium at low pressures. These processes are: (1) the dependence of the (ion-induced) secondary electron emission yield on the ion energy, (2) the appearance of ion impact ionization of the gas at high electric fields and (3) the secondary electron emission from the cathode due to fast neutral atoms.

A New Emission Spectrum of Au2 in the Gas Evaporation Technique: 761–809 nm

A study was conducted on the optical emission spectrum of Au2, in the range of 761 to 809 nm, at a region close to the source of evaporation of Au in low pressure helium gas (100 Torr). A new band system of Au2 dimers in the gas phase was identified. The derived spectroscopic constants on the basis of a vibrational analysis are listed as follows: νe=12845.98+0.29 cm-1, ωe'=89.58±0.37 cm-1, ωexe'=0.20±0.06 cm-1, ωe''=95.80±0.31 cm-1, ωexe''=0.21±0.10 cm-1.

Optical emission spectra of Ag3 molecules in the gas evaporation technique

A study was conducted of optical emission spectra, taken at a region near the source of the evaporation of Ag in a low pressure helium gas (100 Torr). A new Ag3 emission band system was identified. Spectroscopic constants for an excited and a lower state (the ground state) in the gas phase were derived as follows: ν00=19 809.4±2.0 cm−1, ω′1=106.8±1.0 cm−1, x′11=−0.2±0.5 cm−1, ω″1=129.0±1.0 cm−1, and x″11=−0.1±0.5 cm−1 for the 107Ag2109Ag trimers. Spectroscopic constants for three other isotope species were also derived. The lower state was the 2B2 ground state.