Bar Helium Research Articles

Quenching for the Future—In Memoriam of Sören Segerberg

Sören Segerberg passed away on July 27, 2021 at the age of 78. Born in 1943 he graduated from Materials Science and Engineering at KTH Royal Institute of Technology in Stockholm, Sweden, in 1968 with a degree in metallurgical science. Sören Segerberg was a leading expert in the quenching area. From 1979 on and the next 25 years, he worked in research and development at the Institute for Engineering Technology Research (IVF, today RISE) in Gothenburg, Sweden. He was one of the initiators of the development and sale of IVF’s Quenchotest/ivf SmartQuench, an equipment for quality control of cooling curve measurement. He was also a contributor in the development of ASTM D6200 and ISO 9950.During his time at RISE, many projects in the field of quenching were carried out involving cooling characteristics of quenchants, classification of quench oils and polymers as well as correlation between quenching characteristics of quenching media and hardness. In the early 90s, one focus lay on environmental adapted quenchants and methods. The work included spray-quenching with e.g. water/air-mixtures, fluidized bed and, of course, cooling in gas. The latter was an extensive part of the work, also including an equipment with an atmospheric furnace connected to a cold high-pressure gas cooling chamber.Pressures up to 40 bar helium and up to 10 bar with nitrogen could be used. The aim was to study whether gas cooling could be used as an environmental adapted replacement for oil or salt cooling. Today the use of cooling in gas has substantially increased and has proven to be a sustainable alternative to liquid quenching, especially oils.

Development of a beta‐type Stirling heat pump with rhombic drive mechanism by a modified non‐ideal adiabatic model

In this paper, a thermodynamic model is developed for predicting the performance of a beta-type Stirling heat pump with rhombic drive mechanism for water heater and the model is validated by a 1-kW class prototype Stirling heat pump. In the present model, the working space is divided into expansion space, heat absorber, regenerator, heat rejecter and compression space. The pressure, mass and temperature variations of working fluid in each working space are predicted. The temperature variation of wall boundary is also taken into consideration. The temperature of working fluid in each working space and the temperature of wall boundary are obtained by solving energy equations simultaneously. Eventually, the pressure of working fluid in each working space can be corrected by using empirical formula of pressure drop. All the thermal properties of working fluid and wall boundary in each working space at each time step can be obtained by repeating the above process. Then, the performance of heat pump such as absorbing heat, rejecting heat, indicated power and COP can be calculated. A series of experimental measurements and comparisons are also conducted for validating present model. The results show that the prototype heat pump can produce 904 W heating power and 38°C hot water under 1 LPM water flow rate with 5 bar helium at 1000 rpm.

Design of a Continuous Pellet Fueling System for Wendelstein 7-X

A continuous pellet fueling system (CPFS) is currently being designed at the Oak Ridge National Laboratory (ORNL) for the long pulse operation of the Wendelstein 7-X (W7-X) stellarator. The purpose of the CPFS is to provide deep continuous fueling for feedback-controlled high-density operation and mitigation of predicted hollow density profiles. The system will provide the capability to inject cylindrical pellets of solid hydrogen or deuterium into the plasma core, with flexibility to vary the pellet size, velocity, and injection frequency. Pellets are nominally of 3 mm in diameter and have a length between 1 and 4 mm. The heart of the CPFS is a vertically oriented, twin-screw extruder, cooled by three Gifford-McMahon cryocoolers in parallel, designed to form a continuous filament of hydrogen or deuterium. The filament width, which determines the pellet length, can be adjusted by means of a variable nozzle driven by a linear actuator at the base of the extruder. Coupled to the nozzle is a solenoid-operated gas gun and cutter assembly. A pneumatic propellant valve pulses a burst of ~60 bar helium to accelerate the cut pellet into W7-X. Three gaps in the guide tubes provide pumping locations to remove the helium propellant before it reaches the plasma. The maximum velocity of the pellet is limited by its ability to survive navigating the guide tube trajectory intact. A microwave cavity located within the guide tube provides the capability to measure the pellet size and velocity. The mechanical and thermal designs of the W7-X extruder, adjustable nozzle, and gun and cutter assembly design are described. A guide tube design and experimental pellet survivability test results are presented.

Batch chemical microreactors: Reversible, in situ UHV sealing of a microcavity

We propose a new type of microreactor to study heterogeneous catalytic systems. The proposed device operates using a batch reactor scheme, in which catalyst and reactant are introduced in one step and analyzed in a subsequent step. This differs from a flow microreactor in which reaction and analysis take place continuously. A batch microreactor could evaluate the products from a very small amount of catalyst – possibly <100 nanoparticles – but requires a microcavity which can be hermetically and reversibly sealed. Using UV lithography and a combination of standard and deep reactive ion etching, we fabricated a microcavity with a sealing scheme that mimics the knife edge seal employed in macro-metal gasket sealing schemes. The volume of the microcavity is 2.5 × 10 - 9 liters. To test the sealing performance of the device, the microcavity is loaded and sealed with 1 Bar of helium in an ultra-high vacuum (UHV) environment. Mass spectrometry is used to probe the amount of gas remaining. From these tests, the leak rate is < 2 × 10 - 16 Bar L/s. Furthermore, we demonstrate that the device is reusable, and there is no performance degradation after several sealing cycles.

Destabilized LiBH4−NaAlH4 Mixtures Doped with Titanium Based Catalysts

We investigate the hydrogen storage properties of the mixed complex hydride LiBH4−NaAlH4 system, both undoped and doped with a TiCl3 additive. The mixed system is found to initiate a transformation to LiBH4−NaAlH4 after ball-milling, and the doped system is found to have a significant lower hydrogen release temperature compared to the undoped system and that of titanium doped LiAlH4 and NaAlH4 systems. Three dehydrogenation steps with a total of 3.5 wt % released hydrogen are observed for samples with a 2:3 molar ratio, when heated to ∼210 °C under a constant heating ramp in a 1 bar helium atmosphere. A slow hydrogen release is also observed at room temperature in the freshly ball-milled powders due to decomposition of the formed LiAlH4. X-ray powder diffraction spectra shows that the first dehydrogenation step is completed after a couple of days at room temperature. LiNa2AlH6 is found in NaAlH4 rich mixtures at higher temperature, and this phase is found to reversibly discharge and recharge hydrogen at 80 bar and 180 °C.

Behaviour of Various Glass Seal for Planar Solid Oxide Fuel Cell

One of the critical issues in designing a planar solid oxide fuel cell (SOFC) is the development of materials to hermetically seal the metal (430 series stainless steel) or ceramic interconnector with the ceramic electrolyte of the cell. The main objective of this sealing material is to achieve a low leak rate, long-term stability at operating temperature and chemical compatibility with other components. One of the compositions has been operated in an SOFC in excess of 30 minutes over the range of 600, 700, 800, and 900°C. The seal is a composition of polymer blend and glass of 1:3, 1:1 and 3:1 by weight. The leakage rate of each seal was measured simultaneously under the compressive force of 100 N, 2 bar Helium. The seal was characterized using a thermogravimetric analysis. The effect of glass composition on operating temperature and compressive forces on the leakage rate have been discussed and correlated.

Miniaturation of thermoacoustic refrigerators

The possibility to miniature thermoacoustic refrigerators is theoretically investigated. Both standing-wave and traveling-wave systems are considered. In the consideration of standing-wave refrigerators, a system consisting of a resonator tube (50 cm) with a closed end and a PVC stack (length 5 cm) is taken as a reference. Helium is used at a mean pressure of 10 bars and an amplitude of 1 bar. The operating frequency is 1 kHz. The variation of the performance of the refrigerator when scaled down in size is computed under the prerequisites that the temperature difference over the stack or the energy flux or energy flux density are fixed. The analytical results show, as expected, that there is a limitation for scaling-down of a standing-wave thermoacoustic refrigerator due to heat conduction. Similar scaling trends are also shown in traveling-wave refrigerators. The traveling-wave reference system consists of a feedback inertance tube of 0.567 m long, inside diameter 78 mm, a compliance volume of 2830 cm3 and a 24 cm thermal buffer tube. The regenerator is sandwiched between two heat exchangers. The system is operated at 125 Hz and filled with 30 bar helium gas. Again, the thermal conductance forms a practical limitation in down-scaling.

Synthesis of Biodiesel via Deoxygenation of Stearic Acid over Supported Pd/C Catalyst

High catalytic activity was achieved in the deoxygenation of stearic acid in dodecane in a temperature range of 270–300 °C under 17 bar helium over palladium on nanocomposite carbon Sibunit. Besides n-heptadecane, which was obtained previously in this reaction with palladium on activated carbon, n-pentadecane was also formed in significant amounts.

Efficient and fast thermalization of Rare Isotope Beam from projectile fragmentation

Gas stopping is the method of choice for converting rare isotope beams obtained via projectile fragmentation and in-flight separation into low-energy beams. Current gas stopper systems for high-energy beams are based on linear gas cells filled with 0.1–1 bar of helium. While successful for a number of experiments, they are limited in the maximum beam rates that can be used and exhibit long extraction times that can lead to decay losses for very short-lived isotopes. To avoid these limitations, a new type of gas stopper is being developed at the NSCL/MSU based on a cyclotron-type magnet with a stopping chamber filled with helium buffer gas at low pressure. RF-guiding techniques are used to extract the thermalized ions from the central region.

The cyclotron gas stopper project at the NSCL

Gas stopping is becoming the method of choice for converting beams of rare isotopes obtained via projectile fragmentation and in-flight separation into low-energy beams. These beams allow ISOL-type experiments, such as mass measurements with traps or laser spectroscopy, to be performed with projectile fragmentation products. Current gas stopper systems for high-energy beams are based on linear gas cells filled with 0.1–1 bar of helium. While already used successfully for experiments, it was found that space charge effects induced by the ionization of the helium atoms during the stopping process pose a limit on the maximum beam rate that can be used. Furthermore, the extraction time of stopped ions from these devices can exceed 100 ms causing substantial decay losses for very short-lived isotopes. To avoid these limitations, a new type of gas stopper is being developed at the NSCL/MSU. The new system is based on a cyclotron-type magnet with a stopping chamber filled with Helium buffer gas at low pressure. RF-guiding techniques are used to extract the ions. The space charge effects are considerably reduced by the large volume and due to a separation between the stopping region and the region of highest ionization. Cyclotron gas stopper systems of different sizes and with different magnetic field strengths and field shapes are presently investigated.

Manufacturing and testing of a gamma type Stirling engine

In this study, a gamma type Stirling engine with 276 cc swept volume was designed and manufactured. The engine was tested with air and helium by using an electrical furnace as heat source. Working characteristics of the engine were obtained within the range of heat source temperature 700–1000 °C and range of charge pressure 1–4.5 bar. Maximum power output was obtained with helium at 1000 °C heat source temperature and 4 bar charge pressure as 128.3 W. The maximum torque was obtained as 2 N m at 1000 °C heat source temperature and 4 bar helium charge pressure. Results were found to be encouraging to initiate a Stirling engine project for 1 kW power output.

Rate constants for the decomposition of 2-butoxy radicals and their reaction with NO and O2

The reactivity of 2-butoxy radicals has been investigated using the laser photolysis/laser induced fluorescence technique. Three reactions have been studied: (i) The rate constants for the reaction with NO have been measured by the same technique at total pressures between 0.03 < p < 0.4 bar of helium and at five temperatures between 295–348 K. No pressure dependence has been found within the experimental error, and a small negative temperature dependence has been found, in agreement with earlier studies: k1 = (4.4 ± 0.6) × 10−12 exp((4.9 ± 0.3) kJ mol−1/RT) cm3 s−1. (ii) The rate constant with O2 has been measured at room temperature and 0.131 bar of helium: k2 = (9 ± 2) × 10−15 cm3 s−1. Significant quenching of 2-butoxy fluorescence by O2 prevented experiments in a larger temperature range: kq,O2 = (4 ± 1) × 10−11 cm3 s−1. (iii) The temperature and pressure dependence of the unimolecular decomposition at total pressures between 0.01 < p < 0.8 bar of helium and at four temperatures between 291–348 K. The low and the high pressure limiting rate constants as well as the broadening factor Fcent have been extracted from a falloff analysis of the experimental results: k3,0,He = 3.2 × 10−8 exp(−35.9 kJ mol−1/RT) cm3 s−1, k3,∞ = 1.1 × 1014 exp(−53.6 kJ mol−1/RT) s−1, and F3,c = 0.87 − T/870 K. We anticipate an uncertainty of ±30% for these rate constants. These results are in excellent agreement with earlier predictions (C. Fittschen, H. Hippler and B. Viskolcz, Phys. Chem. Chem. Phys., 2000, 2, 1677–1683 (); R. Mereau, M.-T. Rayez, F. Caralp and J.-C. Rayez, Phys. Chem. Chem. Phys., 2000, 2, 3765 ()) .

A detailed experimental and theoretical study on the decomposition of methoxy radicals

We present a detailed experimental and theoretical study on the pressure and temperature dependence of the rate constant for the thermal unimolecular decomposition of methoxy radicals, according to CH3O + M → CH2O + H + M. Experimentally, we studied the decomposition of the methoxy radical at temperatures between 680 and 810 K and pressures ranging from 1 to 90 bar helium. The methoxy radicals have been generated by laser flash photolysis of methylbenzoate [C6H5C(O)OCH3] at 193 nm and detected by laser-induced fluorescence. Additionally, we characterized the important features of the potential energy surface by ab initio calculations. The results of these calculations were used to analyze the thermal rate constant applying both the Troe formalism as well as a master equation approach. The following falloff parameters have been extracted: k1,∞ = 6.8 × 1013 exp(−109.5 kJ mol−1/RT) s−1, k1,0 = [He] 1.9 × 10−8(T/1000 K)−2.4 exp(−101.7 kJ mol−1/RT) cm3 s−1 and FC(He) = 0.715–T/4340 K. Additionally, we reanalyzed the literature data for N2 as bath gas and we recommend the following falloff parameters for this: k1,0 = [N2] 3.1 × 10−8(T/1000 K)−3.0 exp(−101.7 kJ mol−1/RT) cm3 s−1 and FC(N2) = 0.97–T/1950 K. In contradiction to earlier studies we did not find any indications that tunneling markedly contributes to the thermal rate constant under our experimental conditions. We calculated the specific and the high-pressure limiting rate constants using RRKM theory and obtained satisfactory agreement with experimental results. We attribute the strong fluctuations of the specific rate constants to be essentially caused by the properties of the density of states. For the β C–H scission reactions in alkoxy radicals we suggest for the high-pressure limiting rate constants a common A factor and activation energy of A = 1013.8 ± 0.3 s−1 and Ea = 94 ± 6 kJ mol−1. Consequently, the reverse reactions, i.e. the H-atom additions to the carbon site of the CO π bond in aldehydes and ketones, always compete with the direct H-atom abstraction.

The OH-yield in the reaction of O(1D) + CH4 under high pressure conditions up to 560 bar helium

The pressure dependence of the OH yield in the reaction O(

The high-pressure range of the reaction CH(2Π)+CO+M⇒HCCO+M

The pulsed laser photolysis (PLP), time-resolved saturated laser-induced fluorescence (SLIF) technique has been used to study the reaction CH+CO+M⇒HCCO+M (1) in the temperature range between 300–800 K and at total pressures between 4 and 160 bar helium. The CH radicals have been generated using UV-multiphoton dissociation of CHBr3 at 248 nm. In the investigated temperature and pressure range, the usual falloff behavior of the reaction has been found. Falloff curves have been constructed and a high-pressure limiting rate constant with a weak negative temperature dependence of k1,∞=1.7×10−10(T/300 K)−0.4 cm3 molecule−1 s−1 has been extracted. This high-pressure limiting rate constant has been treated in terms of the statistical adiabatic channel model. Isobar Arrhenius curves have been constructed for pressures between 0.01 and 100 bar, including the formation of C2O+H at high temperatures.

Parity nonconservation in elastic p alpha scattering.

Parity nonconservation in the hadronic interaction was studied by elastic scattering of 46 MeV longitudinally polarized protons on $^{4}\mathrm{He}$. The scattering chamber consisted of a 110 bar helium gas target, surrounded by a cylindrical ionization chamber in an axially symmetric arrangement, and a Faraday cup. The relative cross sections, ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\mathrm{\ensuremath{-}}}$, for positive and negative helicity of the incident beam were measured by integrating the currents from the Faraday cup and from the ionization chamber during 20 ms intervals, and digitizing the charges. The angular acceptance function of the ionization chamber extends from ${\mathrm{theta}}_{\mathrm{lab}=31}$\ifmmode^\circ\else\textdegree\fi{} to approximately 80\ifmmode^\circ\else\textdegree\fi{}, with maximum weight at 41\ifmmode^\circ\else\textdegree\fi{}. The parity nonconserving longitudinal analyzing power ${A}_{z}$=(${\ensuremath{\sigma}}^{+}$-${\ensuremath{\sigma}}^{\mathrm{\ensuremath{-}}}$)/(${\ensuremath{\sigma}}^{+}$+\ensuremath{\sigma} $^{\mathrm{\ensuremath{-}}}$) was deduced from 2.3\ifmmode\times\else\texttimes\fi{}${10}^{6}$ individual measurements of ${p}_{z}$${A}_{z}$. The magnitude of the beam polarization was \ensuremath{\Vert}${p}_{z}$\ensuremath{\Vert}\ensuremath{\simeq}0.83. The emphasis is on quantitative treatments of instrumental effects, the most important of which is caused by the nonuniform distribution of residual transverse polarization components of the beam. The final result for the longitudinal analyzing power at a mean laboratory energy of 46 MeV is ${A}_{z}$=-(3.3\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$. The uncertainty includes the statistical error as well as the systematic uncertainties from transverse polarization, modulation of intensity, position, emittance, and energy of the beam associated with helicity reversal, double scattering, asymmetry from \ensuremath{\beta} decay, and electronic cross talk. The result is compared to theoretical predictions and to related experiments.

Magnetic hyperfine interaction of swift43 K ions recoiling in helium and xenon

The 738 keV 7/2− isomeric state in43K (Τ=292 ± 5 ns,g=1.266 ± 0.015) was produced in the reaction4He(40Ar,p) using the 185 MeV pulsed40Ar beam of VICKSI and a 2–7 bar helium target cell. The suitability of this isomeric state for hyperfine studies during recoil in gases and after implantation into solids was investigated via the TDPAD technique. The hyperfine deorientation of highly stripped43K ions in He and Xe was investigated and interpreted with the AbragamPound model. When adding up to 15% Xe to the He target gas, a near-exponential loss of alignment with the Xe partial pressure was observed. This effect can be explained by K-hole production in43K in the Xe-K collision for which a cross section ofσ=5 · 10−18 cm2 was estimated.