Helium-neon Mixtures Research Articles

Experimental evaluation of heat transfer effect on turbocompressor performance operating with helium-neon gas mixtures

Within the framework of the Future Circular Collider (FCC) currently being investigated at CERN, the entire cryogenic cycle had to be revised with respect to the existing Large Hadron Collider (LHC). In particular, a novel pre-cooling cycle had to be developed for this purpose. This led to a closed-loop cryogenic cycle operating with a mixture of helium and neon, also called Nelium. To better understand the challenges and opportunities associated with the design and operation of radial compressors with such light gases, a closed loop test facility has been designed, built and commissioned at the ITSM (University of Stuttgart). The test facility has been developed to operate with air as well as with helium-neon gas mixtures of varying mixing ratios ranging from pure neon to pure helium. In this paper, the test facility architecture and operation procedure are briefly introduced together with a description of the newly installed compressor stage. Experimental performance measurements are then compared to adiabatic and diabatic numerical simulation validating respectively the pressure rise and diabatic stage efficiency for various gases. The heat transfer effect on compressor stage performance is then described and the respective contribution of the influencing factors are quantified.

Improved Technology for Obtaining Enriched Neon-Helium Mixtures

A novel technology for the production of high concentration neon-helium mixtures on different air separation units (including units without fraction separators) is presented. It is proposed to complete the ASU with pressure swing adsorption (PSA) devices for obtaining a neon-helium mixture. The PSA unit enriches the neon-helium mixture due to the energy of compressed gases taken from the ASU condenser-evaporator. The calculations of the PSA technology was performed using the wave approach. The implementation of this approach takes unsteady transient mass transfer processes into account both in the layers of the adsorbent and inside of the grains. It is shown that the proposed technique makes it possible to obtain an enriched neon-helium mixture with a total concentration of neon and helium to 90 and with a recovery ratio of 40–50 %.

Innovative neon refrigeration unit operating down to 30 K

A new compact, low-cost, economically competitive and environmentally friendly cryogenic system for cooling a continuous gas flow down to about 30 K is under developing at the ILK Dresden, reported in this paper. The paper shows thermodynamic calculations of cycles on neon and neon-helium mixtures. The assessment of the degree of thermodynamic perfection of the neon cycles in comparison of neon-helium cycles is provided. The use of neon and neon-helium mixture in cryogenic cycles for cryostatting at a temperature level of 27…63 K will increase the thermodynamic efficiency of the cryogenic system and reduce the energy costs of obtaining cold at this temperature level. A technological chain/process, as well as the main economic indicators of the system under development are presented. The availability of such an innovative refrigeration system can be used in a wide range of cryogenic and cooling applications.

An integrated mixed refrigeration cycle for pre-cooling of refrigeration below 25 K

Two trends can be found in current large-scale cryogenic projects. The first is the ever-increasing capacity requirements, while also a shift towards cooling demands at higher temperatures is observed. Conventional helium cycles require the use of oil flooded screw compressors, which are limited in efficiency, capacity, and reliability. Reverse-Brayton cycles with neon-helium mixtures deliver efficient refrigeration at a temperature above the dew point of neon, but cannot be applied to the cooling of conventional superconductors. This paper describes an approach where oxygen as a heavier gas allows the use of turbo-compressors viable. The oxygen is separated and used for providing refrigeration at higher temperature levels.

Transport coefficients of helium-neon mixtures at low density computed from ab initio potentials.

The viscosity, thermal conductivity, diffusion coefficient, and thermal diffusion factor of helium-neon mixtures at low density are calculated for a wide range of temperature and for various molar fractions. The Chapman-Enskog method is employed considering the 10th order of the Sonine polynomial expansion. Ab initio potentials for intermolecular interactions are used to calculate the omega-integrals. The relative numerical error of the present results obtained for the potentials used here is less than 7 × 10-5 for the thermal diffusion factor and 2 × 10-5 for all the other coefficients. Since each employed potential has a different accuracy, the uncertainty related to such accuracies was analyzed, considering the contribution of each potential uncertainty. It was found that the total uncertainty due to the potentials is larger than the numerical error and it varies depending on the temperature and molar fraction. A comparison of the calculated transport coefficients with those available in the open literature shows that the present calculations provide the most accurate values currently available for the transport coefficients of helium-neon binary mixtures at low density.

Neon helium mixtures as a refrigerant for the FCC beam screen cooling: comparison of cycle design options

In the course of the studies for the next generation particle accelerators, in this case the Future Circular Collider for hadron-hadron interaction (FCC-hh), different aspects are being investigated. One of these is the heat load on the beam screen, which results mainly from the synchrotron radiation. In case of the FCC-hh, a heat load of 6 MW is expected. The heat has to be absorbed at 40 to 60 K due to vacuum restrictions. In this range, refrigeration is possible with both helium and neon. Our investigations are focused on a mixed refrigerant of these two components, which combines the advantages of both. Especially promising is the possible substitution of the oil flooded screw compressors by more efficient turbo compressors. This paper investigates different flow schemes and mixture compositions with respect to complexity and efficiency. Furthermore, thermodynamic aspects, e.g. whether to use cold or warm secondary cycle compressors are discussed. Additionally, parameters of the main compressor are established.

Gain measurements at 543 nm in helium neon laser discharges

A single-mode frequency stable helium neon laser operating on the 543 nm neon transition was used to probe an electrical discharge in helium neon mixtures. Values for the optical gain at this wavelength were obtained. A comparison with the widely documented behaviour of the 633 nm transition, which shares the same upper state as the 543 nm transition, shows a marked difference in the variation of the optical gain with discharge pressure. This is shown to occur due to the differing behaviour of the lower laser state population densities with pressure. It is proposed that this could be due to the resonance peak in the electron excitation cross section from the ground state to the 2 level. Variation of gain with discharge current is also presented.

Some Remarks on Pressure Effects on 2p53p-2p5ns (n=5, 6, 7) Transitions in Neon

The collisional broadening and shift of 494.5 nm spectral line of neon arising from 2p 5 3p-2p 5 7s transition, emitted from a low-pressure glow dis- charge in pure neon and neon-helium mixtures have been measured. The values of pressure broadening and shift coefficients were determined. Exper- imental data of 494.5 nm line as well as our earlier results for spectral lines originating from the 2p 5 3p-2p 5 ns (n = 5, 6) transitions are compared with those resulting from the Kaulakys and Ueda theories of pressure effects on Rydberg states.

Pressure effects on 2p53p-2p55d and 2p53p-2p56d transitions in neon

The collisional broadening and shift of three spectral lines 486.3, 515.8 and 520.3 nm of neon emitted from a low-pressure glow discharge in pure neon and neon-helium mixtures have been measured. The values of pressure broadening and shift coefficients were determined. The authors' experimental data disagree with those resulting from the Kaulakys (1984) and Ueda (1985) theories of pressure effects on Rydberg states.

Dissociative recombination measurements at elevated temperatures in helium-neon mixtures

The temperature dependence of the electron-ion dissociative recombination (DR) rate of neon dimer ions has been measured in mixtures of helium and neon using the shock tube technique. The temperature range 500-3000 K was examined and the temperature dependence of the observed recombination was found to be independent of the composition of the helium-neon mixture and the different dimer ion formation mechanisms involved. The results obtained confirm earlier arguments about the fall-off in efficiency of DR for vibrationally excited rare-gas ions.

Reactions of excited neon atoms in neon-helium afterglows. I. Rate data

The de-excitation of excited-neon-atom populations in the afterglow period of pulsed discharges in neon-helium mixtures has been examined at 300 and 400K. The importance of two- and three-body processes involving collisions with ground-state neon and helium atoms was confirmed and rate data were obtained for the important reaction channels.

Four-body conversion of atomic helium ions

The conversion of atomic helium ions into molecular ions was studied in pure helium and in helium-neon mixtures containing between 0.1 at.% and 50 at.% neon. The experiments showed that the termolecular conversion reaction, ${\mathrm{He}}^{+}+2\mathrm{He}\ensuremath{\rightarrow}\mathrm{He}_{2}^{}{}_{}{}^{+}+\mathrm{He}$, is augmented by the four-body conversion reaction ${\mathrm{He}}^{+}+3\mathrm{He}\ensuremath{\rightarrow}\mathrm{products}$, where the products could include either $\mathrm{He}_{2}^{}{}_{}{}^{+}$ or $\mathrm{He}_{3}^{}{}_{}{}^{+}$ ions. Conversion rate coefficients of (5.7 \ifmmode\pm\else\textpm\fi{} 0.8) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and (2.6 \ifmmode\pm\else\textpm\fi{} 0.4) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}49}$ ${\mathrm{cm}}^{9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ were found for the termolecular and four-body conversion reactions, respectively. In addition, rate coefficients for the following ${\mathrm{Ne}}^{+}$ conversion reactions were measured: ${\mathrm{Ne}}^{+}+\mathrm{He}+\mathrm{He}\ensuremath{\rightarrow}{(\mathrm{HeNe})}^{+}+\mathrm{He}$, (2.3 \ifmmode\pm\else\textpm\fi{} 0.1) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$; ${\mathrm{Ne}}^{+}+\mathrm{He}+\mathrm{Ne}\ensuremath{\rightarrow}{(\mathrm{HeNe})}^{+}+\mathrm{Ne}$ or $\mathrm{Ne}_{2}^{}{}_{}{}^{+}$ + He, (8.0 \ifmmode\pm\else\textpm\fi{} 0.8) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$; and ${\mathrm{Ne}}^{+}+\mathrm{Ne}+\mathrm{Ne}\ensuremath{\rightarrow}\mathrm{Ne}_{2}^{}{}_{}{}^{+}+\mathrm{Ne}$, (5.1 \ifmmode\pm\else\textpm\fi{} 0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. All rate coefficients are at a gas temperature of 295 K.

Experimental study of thermal conductivity of neon-helium mixtures at high temperatures

Experimental data on the thermal conductivity of neon-helium mixtures in the temperature range 350–15QO°K are presented. Above 800°K these are the first such experimentally obtained data.

Spark channel formation in helium-neon mixtures

Spark channel formation in helium-neon mixtures

Spark channel formation in helium-neon mixtures

An image convertor is used to study the development of breakdown in a uniform field produced between two 5 cm plane electrodes. The discharge is simultaneously photographed with streak and still cameras. The formation and propagation of the ionization fronts are seen to move towards the cathode and the anode. Special attention is paid to the secondary avalanches that originate from the cathode and move towards the cathode ionizing wave. The densitometry of recordings gives rise to the characterization of the isodensity lines through which the authors obtain a detailed analysis of the spatio-temporal growth of light emission from the discharge.

Differential and cumulative integral cross sections of electron-field pair production: Experimental study at 2.614 MeV using a streamer chamber

The cross sections for electron-field pair production by photons (triplets) are studied in helium and in two helium-neon mixtures with a streamer chamber at an incident photon energy of 2.614 MeV. The streamer chamber is triggered by the coincidence between the electron and the positron detectors. The chamber is located between two Helmholtz coils giving a magnetic field of 300 G. A detailed analysis of the false triplet events is performed by using new kinematical criteria. The results are the following: (1) Experimental differential energetic distributions for the two electrons and the positron are consistent with those recently calculated by Mork and Haug. (2) These cross sections are very different for pair and triplet production. (3) Differential angular cross sections agree with the distribution predicted by Mork and Haug. (4) The measured cumulative integral cross sections in helium and in the helium-neon mixtures, compared with Mork and Jarp's theoretical predictions and within experimental uncertainties, are consistent with the total cross section of 12.8 \ensuremath{\mu}b/electron predicted by Mork and Haug. (5) An upper limit for the total multiplet cross section in Ne was determined to be ${10}^{\ensuremath{-}8}$ b/electron.

The development of breakdown in a homogeneous field at high overvoltages in helium-neon mixtures and nitrogen

The development of breakdown in a homogeneous field at high overvoltages in helium-neon mixtures and nitrogen

The development of breakdown in a homogeneous field at high overvoltages in helium-neon mixtures and nitrogen

The development of predisruptive processes up to breakdown can be visually displayed using high-speed cinematographic techniques. This study was carried out in helium-neon mixtures and in pure nitrogen. The primary electrons are released from the cathode by a powerful UV flash, and under those conditions the anode streamer is set off near the cathode. The propagation of the anode-directed streamer is observed in a homogeneous applied field for very high overvoltages (200-300%) and for E/p values of up to 55 V cm-1 Torr-1 for the helium-neon mixtures, and up to 190 V cm-1 Torr-1 for nitrogen. The velocities of the streamer's various stages are measured. The recordings show that, in its propagation from cathode to anode, the streamer proceeds into two distinct phases separated by a transition zone.

Time dependence of the vacuum-uv emissions from neon, and energy transfers to the resonance statesNe(P11)andNe(P13)in helium-neon mixtures

Time dependence of the vacuum-uv emissions from neon, and energy transfers to the resonance states<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Ne</mml:mi><mml:mo>(</mml:mo><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow /><mml:mrow /><mml:mrow /><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow><mml:mo>)</mml:mo></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Ne</mml:mi><mml:mo>(</mml:mo><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow /><mml:mrow /><mml:mrow /><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow><mml:mo>)</mml:mo></mml:math>in helium-neon mixtures

1366. Mobilities of electrons in helium and helium-neon mixtures: E E Mainwaring and J D Swift, Proc of 11th Inter Conf on Phenon in Ioniz Gases, Prague 1973, 1

1366. Mobilities of electrons in helium and helium-neon mixtures: E E Mainwaring and J D Swift, Proc of 11th Inter Conf on Phenon in Ioniz Gases, Prague 1973, 1