Superfluid Helium Temperature Research Articles

Signal amplification in multistage charge collection process in Si detectors in situ irradiated at superfluid helium temperature

The effect of charge multiplication in Si p+-n-n+ detectors observed in the unique conditions of the in situ irradiation with 23 GeV proton beam fragmented into 400 ms spills and the temperature of superfluid helium, 1.9 K, was analyzed. The current pulse responses of the detector irradiated to 5 × 1013 p/cm2 demonstrated a two-stage process of charge collection, in which, in the first stage, the current was induced by holes, and in the second, by electrons arising due to avalanche multiplication produced by holes. In the detector irradiated to 2.7 × 1014 p/cm2, the third stage of charge collection was observed that was related to avalanche multiplication produced by electrons reaching the n+ contact and sequential drift of generated holes back to the p+ contact. The developed procedure of data treatment allowed extracting the full set of carrier transport parameters and internal charge gain rising to 3.7 at the bias voltage of 400 V and the fluence of 5 × 1013 p/cm2. An evolution of charge multiplication at the p+ contact initiated by holes originated from a high rate of the hole trap introduction at 1.9 K described by a fivefold rise in the trapping probability at 1.9 K in comparison with its value at T = -10°C. This increases the electric field near the p+ contact and leads to the avalanche multiplication affecting the following stages of charge collection.

Design of cryogenic test platform for the seal structure in superfluid helium temperature

A cryogenic test platform was conceived and designed with a variable temperature from 1.8K to 300K to accomplish the research of cryogenic seal performance, and the main research object of this platform is to test the seal capacity of the flange structure in superfluid helium condition. This platform mainly includes a cryostat, a set of vacuum pumps, a sealed test chamber, a cryogenic physical property test chamber, a leak detection system, a superfluid helium acquisition system, and temperature control systems. The cold source is supplied by 1.5K superfluid helium, which will be obtained by combining throttling with decompression. Mechanical structure designs and detailed parameters of the entire platform will be presented in this paper.

Impact of external heat transfer on the performance of a cold compressor used in superfluid helium system

Cold compressors are the core components needed for the development of a facility for large-capacity refrigeration at superfluid helium temperature. The compressor impeller operates at extremely low temperature and low pressure which involves a performance penalty due to heat transfer from the warm side of the machine to the cold side and thus affects the recycle of the cold exergy downstream. To investigate the heat transfer effect on cold compressor performance, a conjugate heat transfer analysis is performed with commercial CFD solver and is then validated with the experimental data tested at different rotation speed. Then a series of configurations of different thermal boundaries are analyzed to investigate the influence of heat transfer on performance. The simulated results show that the external heat transfer has a negative impact on pressure distribution. The helium gas inside the impeller flow domain is more sensitive to external heat leakage comparing with that inside the diffuser flow. More than that, the mass flow leakage through blade tip clearance is highly affected by the external heat transfer, which counts for the performance degradation.

Investigating the Binding of Grains in Ultracold Dusty Plasmas

Steady-state interaction between stationary grains mediated by plasmas at ultracold superfluid helium temperatures is investigated using particle-in-cell (PIC) simulations with Monte-Carlo collisions. A wide-ranging parametric exploration of interdependence of the physical parameters and its consequence on overall grain–plasma dynamics for cryogenic dusty plasmas is presented. Charging of the grains and the density of trapped ions exhibit a remarkable dependence on the particle shape. Grain charging shares a direct relation with ion flow strength as well and manifests contrasting trends at flow strength $M_{\text {th}}\leq 5$ and $M_{\text {th}}\geq 5$ . A comparison of an isolated grain electric field and potential with the two-grain–plasma system asserts that the field due to an isolated grain is precisely of the same order as the two grain field at subsonic flows. Binding-energy range is estimated to be 0.16–22 eV at $M_{\text {th}}$ = 0–15 and supports the possibility of molecule-like dust structure formation at ultracold temperatures.

Plasma–grain interaction in ultracold complex plasmas

The present particle-in-cell simulation for grain–plasma interaction at cryogenic temperatures springs from recent experimental realization of ultracold dusty plasmas with atoms and ions at superfluid helium temperatures. In this work, we discuss the results of particle-in-cell simulations (taking into account ion-atom collisions) for dust particle charge, ion drag force, and interaction between grains in ultracold dusty plasmas. The single grain as well as two grain system is investigated, considering both streaming ions and equilibrium ions. The dependence of plasma mediated inter-grain interactions on the streaming velocity of ions and inter-particle separation is delineated in detail. Additionally, ion density distribution around grains is discussed. The interactions at cryogenic temperatures are distinct from those at room temperature by their differences in magnitude and interaction mechanism details. Most remarkable features are (i) the inter-grain attraction in equilibrium plasmas due to plasma absorption on the surface of grains, (ii) the ion drag force directed against ion streaming velocity in the case of a single dust particle, and (iii) non-linear response of the plasma polarization around grains with an increase in the streaming velocity of ions.

Ultracold ions wake in dusty plasmas

Motivated by the recent experimental realization of ultracold dusty plasma (2019 Sci. Rep. 9 3261), we present the results of particle-in-cell simulation with Monte-Carlo-collisions for wake behind a dust particle due to focusing of ions at superfluid helium temperature (∼2 K). Dynamical screening (wakefield) defines structural and dynamical properties of charged dust particles in plasmas such as phase transition, crystal formation, vibration modes (waves) etc. Here, we delineate in detail the dependence of wake strength on the streaming velocity of ions and on the ion-neutral charge exchange collision frequency (neutrals density) in the ultracold dusty plasma. Lowering the temperature to ultracold level leads to a wake pattern behind a dust particle that completely differs from the wake at normal conditions. For wide range of parameters, most remarkable features of the wakefield are (i) the formation of wake pattern with two maxima split in transverse to ion flow direction in the downstream area, (ii) pronounced inverse V shape of the wakefield closely resembling the wake in quark-gluon plasma and dense quantum plasma (warm dense matter), and (iii) the inter-dust attraction region in transverse direction. The latter shows that molecule-like interaction between dust particles is realized in ultracold dusty plasmas. These observations show a fundamental difference of ultracold dusty plasma physics from well studied complex plasmas at normal conditions.

Analysis of internal temperature distribution and its total parasitic heat leak for a cryogenic cold Compressor

Cold compressors are the core component needed for the development of a facility for large-capacity refrigeration at superfluid helium temperatures. The compressor impeller is operated at extremely low temperature and low pressure which involves technical issues including material properties at low temperature, heat transfer, failures of the actuating motor resulting from overheating and performance penalty due to heat transfer from the warm side of the machine to the cold side. To address these issues, it is important to understand the temperature distribution inside the housing of the machine. To analyze the temperature distribution, an integrated numerical model is created on the basis of the model of the cold compressor structure and then simulated through computational fluid dynamics. The actual temperature rise of the cold compressor is measured at two temperature measuring points and compared with the temperatures predicted by the simulation to validate the accuracy of the model. The results show that the internal flow field around the motor and bearings of the cold compressor is completely turbulent and the total parasitic heat transfer to the cold gas stream is closely related to the rotating speed of the high-speed motor.

Development of a Helium-3 Cryostat for a Ultra-Cold Neutron Source

Ultra-cold neutrons (UCNs) have a very small kinetic energy as a level of a few hundred neV and can be confined in a material bottle. The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration established for aiming to build a high-intensity UCN source on a dedicated proton beamline at TRIUMF. The source is composed of a combination of a spallation neutron target and a superfluid helium UCN converter. Estimated heat deposit from spallation reaction on the superfluid helium is approximately 10 W. In order to achieve the requirement of superfluid helium temperature, a high-power helium-3 cryostat has been developed. Heat transport property in superfluid helium at 1.0 K is also a key element of the UCN source cryogenics.

Performance of the Large Hadron Collider's Cryogenic Bypass Diodes Over the First Two Physics Runs, Future Projects, and Perspectives

Cryogenic bypass diodes have been installed in all superconducting dipole magnets (1232) and quadrupole magnets (392) of the Large Hadron Collider (LHC) at CERN, and operated during the physics runs since 2009. The bypass diodes are a fundamental ingredient of the quench protection system for those main dipoles and quadrupoles magnets. The diodes are located inside the magnet cryostats, operating in superfluid helium and exposed to ionizing radiation. The connection between the superconducting magnet and the bypass diode is made through a mechanical clamping system and copper bus bars. Since their first installation, all LHC diodes have undergone at least two full thermal cycles (from 1.9 K to room temperature and back to superfluid helium temperature). The evolution of electrical parameters as well as improvements and modifications made over a period of 10 years are reviewed in this paper. With CERN preparing for LHC's High Luminosity era, the long-term strategy for cold diodes is presented, based on the overall results and experience gathered so far, including the studies related to the tolerance with respect to the radiation doses and neutron fluences expected.

Observation of internal multiplication of nonequilibrium charge in irradiated silicon detectors at a temperature of 1.9K

The development of modern high-energy physics is a powerful incentive for the progress of its experimental base. The use of semiconductor devices is standard for large accelerators and experimental setups at LHC, CERN, and perspective as sensors for monitoring beam loss and radiation fields in superconducting magnets and accelerating resonators operating at superfluid helium temperature (1.9 K). In these problems, the optimal type of radiation sensor is a compact silicon detector, the use of which in harsh radiation environment in combination with helium temperatures is a non-trivial task. The most important characteristics of such devices are the distribution of the electric field in the volume and the parameters of charge carrier transport, which determines the detector signal. The study considers specific kinetics of charge collection in silicon detectors at a temperature of 1.9 K in situ irradiated by relativistic hadrons.

Formation of solid helical filaments at temperatures of superfluid helium as self-organization phenomena in ultracold dusty plasma

A multimodal dusty plasma formed in a positive column of the direct current glow discharge at superfluid helium temperatures has been studied for the first time. Formation of a liquid-like dusty plasma structure occurred after injection of polydisperse cerium oxide particles in the glow discharge. The coupling parameter ~10 determined for the dusty plasma structure corresponds very well to its liquid-like type. The cloud of nanoparticles and non-linear waves within the cloud were observed at T < 2 K. Solid helical filaments with length up to 5 mm, diameter up to 22 μm, total charges ~106е, levitating in the gas discharge at the temperature ~2 K and pressure 4 Pa have been observed for the first time. Analysis of the experimental conditions and the filament composition allows us to conclude that the filaments and nanoclusters were formed due to ion sputtering of dielectric material during the experiments.

Development of a powerful UCN source at PNPI's WWR-M reactor

The WWR-M reactor at PNPI is planned to be equipped with a high-flux source for ultracold neutrons (UCNs). The method of UCN production is based on neutron conversion in superfluid helium, exploiting the particular qualities of that quantum liquid. As a result of optimizing the source parameters, we expect a temperature of superfluid helium of 1.2 K and a UCN density of 1.3 × 104 cm−3 in a neutron electric dipole moment (EDM) spectrometer. The expected flux densities of cold neutrons (with wavelengths in the range 2–20 Å) and very cold neutrons (50–100 Å) at the output of a neutron guide with a cross section of 30 × 200 mm2 are 9.7 × 107 cm−2s−1 and 8.3 × 105 cm−2s−1, respectively. The capability of maintaining a temperature of 1.37 K at a thermal load of 60 W was shown experimentally, while the theoretical load is expected to be 37 W. Calculations show that it is possible to decrease the helium temperature down to 1.2 K at similar heat load. The project includes the development of experimental stations at UCN beams, such as for a neutron EDM search, measurements of the neutron lifetime, and for a search for neutron-to-mirror-neutron transitions. In addition, three beams of cold and very cold neutrons are foreseen. At present, the vacuum container of the UCN source has been manufactured and the production of the low-temperature deuterium and helium parts of the source has been started.

Putting in operation a full-scale ultracold-neutron source model with superfluid helium

A project of the source of ultracold neutrons for the WWR-M reactor based on superfluid helium for ultracold-neutron production has been developed. The full-scale source model, including all required cryogenic and vacuum equipment, the cryostat, and the ultracold-neutron source model has been created. The superfluid helium temperature T = 1.08 K without a heat load and T = 1.371 K with a heat load on the simulator of P = 60 W has been achieved in experiments at a technological complex of the ultracold-neutron source. The result proves the feasibility of implementing the ultracold-neutron source at the WWR-M reactor and the possibility of applying superfluid helium in nuclear engineering.

Accelerated path integral methods for atomistic simulations at ultra-low temperatures.

Path integral methods provide a rigorous and systematically convergent framework to include the quantum mechanical nature of atomic nuclei in the evaluation of the equilibrium properties of molecules, liquids, or solids at finite temperature. Such nuclear quantum effects are often significant for light nuclei already at room temperature, but become crucial at cryogenic temperatures such as those provided by superfluid helium as a solvent. Unfortunately, the cost of converged path integral simulations increases significantly upon lowering the temperature so that the computational burden of simulating matter at the typical superfluid helium temperatures becomes prohibitive. Here we investigate how accelerated path integral techniques based on colored noise generalized Langevin equations, in particular the so-called path integral generalized Langevin equation thermostat (PIGLET) variant, perform in this extreme quantum regime using as an example the quasi-rigid methane molecule and its highly fluxional protonated cousin, CH5 (+). We show that the PIGLET technique gives a speedup of two orders of magnitude in the evaluation of structural observables and quantum kinetic energy at ultralow temperatures. Moreover, we computed the spatial spread of the quantum nuclei in CH4 to illustrate the limits of using such colored noise thermostats close to the many body quantum ground state.

Low Temperature Test of HWR Cryomodule

Low temperature test for half-wave resonator (HWR) cryomodule is performed at the superfluid helium temperature of 2 K. The effective temperature is defined for non-uniform temperature distribution. Helium leak detection techniques are introduced for cryogenic system. Experimental set up is shown to make the low temperature test for the HWR cryomodule. The cooldown procedure of the HWR cryomodule is shown from room temperature to 2 K. The cryomodules is precooled with liquid nitrogen and then liquid helium is supplied to the helium reservoirs and cavities. The pressure of cavity and chamber are monitored as a function of time. The vacuum pressure of the cryomodule is not increased at 2 K, which shows leak-tight in the superfluid helium environment. Static heat load is also measured for the cryomodule at 2.5 K.

Superfluid Helium Cryostat for Sensitive Elements Cooling

The objective of the research is super fluid helium cryostat development for navigational sensitive elements (SE) cooling at the temperature of 2K. The peculiarities of the given cryostat are the long-term independent operating mode, the high stability of the SE unit and the high accuracy and stability of super fluid helium temperature maintenance. The SE unit high stability is achieved by the construction. The long-term independent operating mode is carried out by means of helium vapors liquefier-recondensers. High accuracy and stability of superfluid helium temperature maintenance is realized with the help of the modern and advanced thermometry and proportional-integral-differential control.

CERN-RD39 collaboration activities aimed at cryogenic silicon detector application in high-luminosity Large Hadron Collider

Beam Loss Monitors (BLM) made of silicon are new devices for monitoring of radiation environment in the vicinity of superconductive magnets of the Large Hadron Collider. The challenge of BLMs is extreme radiation hardness, up to 1016 protons/cm2 while placed in superfluid helium (temperature of 1.9K). CERN BE-BI-BL group, together with CERN-RD39 collaboration, has developed prototypes of BLMs and investigated their device physics. An overview of this development—results of the in situ radiation tests of planar silicon detectors at 1.9K, performed in 2012 and 2014—is presented. Our main finding is that silicon detectors survive under irradiation to 1×1016p/cm2 at 1.9K. In order to improve charge collection, current injection into the detector sensitive region (Current Injection Detector (CID)) was tested. The results indicate that the detector signal increases while operated in CID mode.

Achievement of 1020 MHz NMR

We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the world’s highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the 2H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a 1H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as 17O; a 17O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.

Charge collection in Si detectors irradiated in situ at superfluid helium temperature

Silicon and diamond detectors operated in a superfluid helium bath are currently being considered for the upgrade of the LHC beam loss monitoring system. The detectors would be installed in immediate proximity of the superconducting coils of the triplet magnets. We present here the results of the in situ irradiation test for silicon detectors using 23GeV protons while keeping the detectors at a temperature of 1.9K. Red laser (630nm) Transient Current Technique and DC current measurements were used to study the pulse response and collected charge for silicon detectors irradiated to a maximum radiation fluence of 1×1016p/cm2. The dependence between collected charge and irradiation fluence was parameterized using the Hecht equation and assumption of a uniform electric field distribution. The collected charge was found to degrade with particle fluence for both bias polarities. We observed that the main factor responsible for this degradation was related to trapping of holes on the donor-type radiation-induced defects. In contrast to expectations, along with formation of donors, acceptor-type defects (electron traps) are introduced into the silicon bulk. This suggests that the current models describing charge collection in irradiated silicon detectors require an extension for taking into account trapping at low temperatures with a contribution of shallow levels. New in situ irradiation tests are needed and planned now to extend statistics of the results and gain a deeper insight into the physics of low temperature detector operation in harsh radiation environment.

Interaction-induced localisation of protons in hydrogen bonds at superfluid helium temperatures

It is common wisdom to expect that protons are more delocalised than much heavier nuclei due to quantum effects, for instance, in hydrogen bonds D−H⋆ ⋅ ⋅ ⋅ A, where the shared proton H⋆ is suspended in between the donor and acceptor heavy sites. Here, we demonstrate that this simple quasi-classical perspective fails at sufficiently low temperatures as a result of intramolecular covalent bonding accompanied by the non-covalent intermolecular interactions which induce strong localisation in the deep quantum regime. Using the water dimer as well as H2O ⋅ ⋅ ⋅ HCl as generic models, path integral simulations at temperatures characteristic to superfluid helium conditions (about 1 K) reveal that the shared proton in such hydrogen bonds gets extremely confined to a spatial region that is comparable to – or even smaller than – that of the heavy atoms. This counter-intuitive so-called interaction-induced localisation phenomenon is also effective for the heavier nuclei, although to a much lesser extent. It is the elevated temperature (about 100 K) that restores the familiar quasi-classical picture, in which atomic spread follows the usual mass dependence of de Broglie wavelength.