Cryogenic Losses Research Articles

Silicon Oxy-Nitride for the Low Refractive Index Layers in the Mirror Coatings of the Cryogenic Laser Interferometer Gravitational Waves Detector.

The low refractive index layers in the mirror coatings of the room-temperature laser interferometer gravitational waves detectors are silica deposited by the ion beam sputter method. However, the silica film suffers from the cryogenic mechanical loss peak, hindering its application for the next generation detector operated at cryogenics. New low refractive index materials need to be explored. We study amorphous silicon oxy-nitride (SiON) films deposited using the method of plasma-enhanced chemical vapor deposition. By changing the N_{2}O/SiH_{4} flow rate ratio, we can tune the refractive index of the SiON smoothly from nitridelike to silicalike of ∼1.48 at 1064nm, 1550nm, and 1950nm. Thermal anneal reduced the refractive index down to ∼1.46 and effectively reduced the absorption and cryogenic mechanical loss; the reductions correlated with the N─H bond concentration decrease. Extinction coefficients of the SiONs at the three wavelengths are reduced down to 5×10^{-6}∼3×10^{-7} by annealing. Cryogenic mechanical losses at 10K and 20K (for ET and KAGRA) of the annealed SiONs are significantly lower than the annealed ion beam sputter silica. They are comparable at 120K (for LIGO-Voyager). Absorption from the vibrational modes of the N─H terminal-hydride structures dominates over the absorption from other terminal hydrides, the Urbach tail, and the silicon dangling bond states in SiON at the three wavelengths.

High Temperature Superconducting Flux Pumps for Contactless Energization

The development of superconducting technology has seen continuously increasing interest, especially in the area of clean power systems and electrification of transport with low CO2 emission. Electric machines, as the major producer and consumer of the global electrical energy, have played a critical role in achieving zero carbon emission. The superior current carrying capacity of superconductors with zero DC loss opens the way to the next-generation electric machines characterized by much higher efficiency and power density compared to conventional machines. The persistent current mode is the optimal working condition for a superconducting magnet, and thus the energization of superconducting field windings has become a crucial challenge to be tackled, to which high temperature superconducting (HTS) flux pumps have been proposed as a promising solution. An HTS flux pump enables current injection into a closed superconducting coil wirelessly and provides continuous compensation to offset current decay, avoiding excessive cryogenic losses and sophisticated power electronics facilities. Despite many publications regarding the design and analyses of various types of HTS flux pumps, the practical application of HTS flux pumps in a high-performance superconducting machine has been rarely reported. Therefore, it is of significance to specify the main challenges for building and implementing a reliable HTS flux pump. In addition, the physical mechanisms of distinct HTS flux pumps have caused some confusion, which should be clarified. Above all, a systematic review of the recent development and progress of HTS flux pumps remains lacking. Given the above-mentioned issues, this paper summarized the most up-to-date advances of this emerging technology, clarified the working mechanisms and commonly adopted modeling approaches, presented objective analyses of the applicability of various HTS flux pumps, specified the primary challenges for implementing HTS flux pumps, and proposed useful suggestions to improve this wireless excitation technology. The overall aim of this work is to bring a deep insight into the understanding of HTS flux pumps and provide comprehensive guidance for their future research and applications.

Microwave calibration of qubit drive line components at millikelvin temperatures

Systematic errors in qubit state preparation arise due to non-idealities in qubit control lines such as impedance mismatch. Using a data-based methodology of short-open-load calibration at a temperature of 30 mK, we report calibrated 1-port scattering parameter data of individual qubit drive line components. At 5 GHz, cryogenic return losses of a 20-dB-attenuator, a 10-dB-attenuator, a 230-mm-long 0.86-mm silver-plated cupronickel coaxial cable, and a 230-mm-long 0.86-mm NbTi coaxial cable were found to be 35−2+3 dB, 33−2+3 dB, 34−2+3 dB, and 29−1+2 dB, respectively. For the same frequency, we also extract cryogenic insertion losses of 0.99−0.04+0.04 dB and 0.02−0.04+0.04 dB for the coaxial cables. We interpret the results using master equation simulation of all XY gates performed on a single qubit. For example, we simulate a sequence of two 5 ns gate pulses (X and Y) through a two-element Fabry–Pérot cavity with 276-mm path length directly preceding the qubit and establish that the return loss of its reflective elements must be >9.7 dB (>14.7 dB) to obtain 99.9% (99.99%) gate fidelity.

INDIRECT METHODS FOR DETERMINING THE MASS OF LIQUEFIED NATURAL GAS IN CRYOGENIC TRANSPORTATION TANKS

Objective . Flow metering and the evaluation of cryogenic product losses at production and consumption facilities involve determining the mass of the vapor-liquid medium in the tank equipment. Meth ods . The calculation of the mass of the cryogenic vapor-liquid medium is associated with the determination of the density of the vapor and liquid phases. The densities of media, in turn, depend on their component composition, pressure, and temperature, which, in general, cannot be determined reliably without direct measurements. However, for the estimation of mass in tanks, the state of the medium in which is accepted as equilibrium, the problem can be significantly simplified, and the missing information recovered based on indirect methods. This type of system includes cryogenic onboard fuel systems and, in particular, cryogenic fuel tanks, since the movement of the vehicle leads to mixing of the stored product, and an assumption can be made about the equilibrium of the vapor-liquid medium. Similarly, the methodology can be extended to transport tanks and multimodal reservoirs. Results. A review and comparison of the applied methods for calculating the density of the vapor-liquid medium and equilibrium compositions for hydrocarbon liquefied natural gas type mixtures in the cryogenic temperature range are presented. The existing methods for calculating the density and phase composition of cryogenic multicomponent media are complex in practical engineering and cannot be recommended for estimating the consumption of liquefied natural gas in the production tasks of fuel flow metering and quantity control. An easy-to-use simplified calculation device for determining the state of a vapor-liquid medium in cryogenic tanks based on approximation dependencies is proposed. Conclusion . The simplified method is approximate in nature but is based on strict physical dependencies, and therefore does not lead to a significant increase in the error when varying the initial conditions. The liquefied natural gas composition, which can be obtained from the product data sheet, and the pressure of the vapor-liquid medium are transmitted to the methodology as initial data.

Development of a low-loss magnetic-coupling pickup for 166.6-MHz quarter-wave beta $$=$$ 1 superconducting cavities

166.6-MHz quarter-wave $$\beta =1$$ superconducting cavities have been adopted for the High Energy Photon Source, a 6-GeV diffraction-limited synchrotron light source currently under construction. A large helium jacket was required to accommodate the enlarged cavity beam pipe for the heavy damping of higher-order modes; the original electric-probe pickup thus becomes inevitably long with unfavorable mechanical properties. Relocated to an existing high-pressure-rinsing port, a magnetic-loop pickup was designed, characterized by low radio-frequency and cryogenic losses and being multipacting-free and insensitive to manufacturing and assembly tolerances. The consequent removal of the original pickup port from the cavity largely simplified the helium jacket fabrication and may also reduce cavity contamination. This paper presents a comprehensive design of a low-loss magnetic-coupling pickup for quarter-wave $$\beta =1$$ superconducting cavities. The design can also be applied to other non-elliptical structures.

Rotating Permanent Magnets Based Flux Pump for HTS No-Insulation Coil

High-temperature superconducting (HTS) no-insulation (NI) coil is a promising design because of high current density, high thermal stability, and self-protection mechanism. Flux pumping is a contactless charging method for a superconducting magnet, which can reduce the cryogenic losses associated with current leads. In this study, we compared the charging performance of a rotating permanent magnets-based flux pump for two different types of HTS coils: an INS coil and an NI coil. Results showed that the rotating type flux pump works well with both coils. But the charging speed of NI coil is much slower, which results from the small parallel characteristic resistance of NI coil. Results also show that the output DC voltage and inherent dynamic resistance of the flux pump increase linearly with the increase of rotating speed.

Silicon nitride films fabricated by a plasma-enhanced chemical vapor deposition method for coatings of the laser interferometer gravitational wave detector

Silicon is a potential substrate material for the large-areal-size mirrors of the next-generation laser interferometer gravitational wave detector operated in cryogenics. Silicon nitride thin films uniformly deposited by a chemical vapor deposition method on large-size silicon wafers is a common practice in the silicon integrated circuit industry. We used plasma-enhanced chemical vapor deposition to deposit silicon nitride films on silicon and studied the physical properties of the films that are pertinent to application of mirror coatings for laser interferometer gravitational wave detectors. We measured and analyzed the structure, optical properties, stress, Young's modulus, and mechanical loss of the films, at both room and cryogenic temperatures. Optical extinction coefficients of the films were in the ${10}^{\ensuremath{-}5}$ range at 1550-nm wavelength. Room-temperature mechanical loss of the films varied in the range from low ${10}^{\ensuremath{-}4}$ to low ${10}^{\ensuremath{-}5}$ within the frequency range of interest. The existence of a cryogenic mechanical loss peak depended on the composition of the films. We measured the bond concentrations of $\mathrm{N}─\mathrm{H}$, $\mathrm{Si}─\mathrm{H}$, $\mathrm{Si}─\mathrm{N}$, and $\mathrm{Si}─\mathrm{Si}$ bonds in the films and analyzed the correlations between bond concentrations and cryogenic mechanical losses. We proposed three possible two-level systems associated with the $\mathrm{N}─\mathrm{H}$, $\mathrm{Si}─\mathrm{H}$, and $\mathrm{Si}─\mathrm{N}$ bonds in the film. We inferred that the dominant source of the cryogenic mechanical loss for the silicon nitride films is the two-level system of exchanging position between a ${\mathrm{H}}^{+}$ and electron lone pair associated with the $\mathrm{N}─\mathrm{H}$ bond. Under our deposition conditions, superior properties in terms of high refractive index with a large adjustable range, low optical absorption, and low mechanical loss were achieved for films with lower nitrogen content and lower $\mathrm{N}─\mathrm{H}$ bond concentration. Possible pairing of the silicon nitride films with other materials in the quarter-wave stack is discussed.

Design and Manufacturing of a Multistage Cooled Current Lead for Superconducting High Current DC Busbars in Industrial Applications

There is a high potential to use high-temperature superconductors instead of conventional busbars in high direct current industrial applications. Since current leads are typically the major source of losses in these applications, we investigate a multistage cooled current lead to operate at a current of 20 kA minimizing current lead losses. The design seeks to realize an efficient and at the same time economic current lead consisting of components which are market proven and reliable. The current lead operates from 300 to 77 K and is cooled with two intermediate cooling stages at 240 and 150 K. One key component is the joint between the resistive copper part and the YBCO high-temperature superconductor tapes, which is manufactured by a new soldering process. Moreover, electromagnetic finite element analyses of a high-temperature superconductor stack design have been done to optimize the current carrying capacity of the current lead. As a result, the multistage cooled current lead is designed to cryogenic losses of 22.4 W/kA at 77 K.

The optimised sc dipole of SIS100 for series production

At the international facility for antiproton and ion research (FAIR) in Darmstadt, Germany, an accelerator complex is developed for fundamental research in various fields of modern physics. In the SIS100 heavy-ion synchrotron, the main accelerator of FAIR, superconducting dipoles are used to bend the particle beam. The fast ramped dipoles are 3 m long super-ferric curved magnets operated at 4.5 K. The demands on field homogeneity required for sufficient beam stability are given by ΔB/B ≤ ±6 · 10−4. An intense measurement program of the First of Series (FoS) dipole showed excellent quench behavior and lower than expected AC losses yielding the main load on the SIS100 cryoplant. The FoS is capable to provide a field strength of 1.9 T. However, with sophisticated measurement systems slight distortions of the dipole field were detected. Those effects were tracked down to mechanical inaccuracies of the yoke proven by appropriate geometrical measurements and simulations. After a survey on alternative fabrication techniques a magnet with a new yoke was built with substantial changes to improve the mechanical accuracy. Its characteristics concerning cryogenic losses, cold geometry and the resulting magnetic-field quality are presented and an outlook on the series production of superconducting dipoles for SIS100 is given.

Impact of nitrogen doping of niobium superconducting cavities on the sensitivity of surface resistance to trapped magnetic flux

Future particle accelerators such as the SLAC “Linac Coherent Light Source-II” (LCLS-II) and the proposed Cornell Energy Recovery Linac require hundreds of superconducting radio-frequency (SRF) niobium cavities operating in continuous wave mode. In order to achieve economic feasibility of projects such as these, the cavities must achieve a very high intrinsic quality factor (Q0) to keep cryogenic losses within feasible limits. To reach these high Q0's in the case of LCLS-II, nitrogen-doping of niobium cavities has been selected as the cavity preparation technique. When dealing with Q0's greater than 1 × 1010, the effects of ambient magnetic field on Q0 become significant. Here, we show that the sensitivity to RF losses from trapped magnetic field in a cavity's walls is strongly dependent on the cavity preparation. Specifically, standard electropolished and 120 °C baked cavities show a sensitivity of residual resistance from trapped magnetic flux of ∼0.6 and ∼0.8 nΩ/mG trapped, respectively, while nitrogen-doped cavities show a higher sensitivity of residual resistance from trapped magnetic flux of ∼1 to 5 nΩ/mG trapped. We show that this difference in sensitivities is directly related to the mean free path of the RF surface layer of the niobium: shorter mean free paths lead to less sensitivity of residual resistance to trapped magnetic flux in the dirty limit (ℓ ≪ ξ0), while longer mean free paths lead to lower sensitivity of residual resistance to trapped magnetic flux in the clean limit (ℓ ≫ ξ0). These experimental results are also shown to have good agreement with recent theoretical predictions for pinned vortex lines oscillating in RF fields.

High order modes in Project-X linac

Project-X, a multi-MW proton source, is now under development at Fermilab. In this paper we present study of high order modes (HOM) excited in continues-wave (CW) superconducting linac of Project-X. We investigate effects of cryogenic losses caused by HOMs and influence of HOMs on beam dynamics. We find that these effects are small. We conclude that HOM couplers/dampers are not needed in the Project-X SC RF cavities.

Development of a Peltier Current Lead for the 200-m-Class Superconducting Direct Current Transmission and Distribution System

Reducing cryogenic heat leaks is critical for superconducting applications. Reduction of heat leak at the terminals is essential for uses with short-length applications, where cryogenic losses at the terminals dominate. We are developing a 200-m-class superconducting direct current (DC) transmission and distribution system (CASER-2), and have used a Peltier current lead (PCL) for heat insulation at the terminals. The PCL consists of thermoelectric elements and copper leads, which enhance the performance of superconducting systems. As DC flows through the current lead, thermoelectric elements on opposite terminations of a superconducting line can be used to decrease the heat ingress to the cryogenic environment (n-type on one end, p-type on the opposite end). During the current feeding and cooling test, a large temperature difference was observed across thermoelectric elements in the PCL. This demonstrates that we have successfully insulated the heat leak at the current lead. During the fourth cooling test, we established a new PCL design with p-type elements at terminal B, and then compared the performance of the terminals. Several improvements were implemented, including balancing the resistances of the PCL to enhance the stability of the superconducting systems.

Estimation of the recycled power associated with the cryogenic refrigeration power of a fusion reactor based on TORE SUPRA experiment and ITER design

The refrigeration power associated with the superconducting magnets and cryopumps of a steady-state fusion reactor is not negligible. The power has to be minimized because it plays a role in the power station global efficiency and in the required amplification factor Q. On the one hand, the long plasma discharges obtained in December 2003 on TORE SUPRA give an insight of the cryogenic losses that might be expected for a steady-state fusion reactor equipped with superconducting magnets. The superfluid bath of the windings in TORE SUPRA allows a simple calorimetric estimation of the cryogenic losses through the temperature evolution of the bath during the long discharge. The different kinds of losses in TORE SUPRA are estimated, discussed and explained. Not all of them will be present in a real reactor. On the other hand, in the framework of ITER preparation, the magnet system and the associated refrigerator have been dimensioned taking into account again all kinds of cold losses. This exercise is important because ITER, by its size, could be relevant to the steady-state reactor situation regarding refrigeration. Based on TORE SUPRA experiment and ITER design it is, therefore, possible to propose for the first time a preliminary figure for the cryoplant power of a steady-state reactor. The order of magnitude of the cryoplant power is ten times lower than that of the fusion reactor recycled power which can be considered acceptable.

New Directions in Superconducting Radio Frequency Cavities for Accelerators

Superconducting radio frequency (SRF) cavities used in present-day accelerators for the acceleration of charged particles near the speed of light are based on the axially symmetric TM010 mode of a pillbox cavity. Future accelerators such as the Linear Collider require high accelerating gradients to limit the length of the linac. Two techniques to improve the gradient are being explored: a cavity that is half reentrant to improve the electromagnetic characteristics, and improved heat transfer via cooling channels and surface modification at the helium interface. These changes could potentially increase the gradients and reduce the cryogenic losses. For other applications more important criteria are simplicity, acceleration of high beam current, or the ability to use advanced materials such as Nb/sub 3/Sn or high-T/sub c/ superconductors. A new type of cavity based on the TM01p pillbox mode with p>0 offers such improvements.

Optimization of a superferric nuclotron type dipole for the GSI fast pulsed synchrotron

GSI plans to upgrade its accelerator facilities. A fast-pulsed synchrotron (rigidity 100 Tm, dipole field/ramp rate 2T/4T/s) is one of the main parts of the GSI future project. Superconducting magnets of the Nuclotron type are foreseen for this synchrotron. R&D work has been done in order to improve the DC field quality and to reduce the cryogenic AC losses. Linear 2-D calculations were used to optimize the pole shape of the dipole magnet. Consequently, a negative shimming was introduced. Subsequent nonlinear extension led to the introduction of air slits in the iron yoke which improved the field quality at higher levels. Nonlinear 3-D simulations were then used to optimize the homogeneity of the integral field, by varying the ratio between the yoke and coil length. We built a model magnet with this optimized iron lamination cross section. In order to reduce the AC losses, we used stainless steel end plates, low coercitivity iron, better insulated iron lamination sheets and reduced the superconductor filament size to 6 /spl mu/m. Various contributions to the losses of the magnet were analyzed. Numerical calculations of the eddy current effects due to field components perpendicular to the iron laminations at the end of the magnet showed that this part must not be neglected. The magnet test results are presented and compared with the expected field quality and losses.

High-Tc superconducting materials for electric power applications

Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable. This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K. Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form. So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices. The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven. Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds.

2 MJ SMES for an uninterruptible power supply

A low temperature 2 MJ SMES is being built for an uninterruptible power supply. The superconducting magnet is designed for a carry over time of 8 s at a mean power of 200 kW. The maximum power of the SMES is 800 kW at an operating current of 1 kA. The magnet is being built as a liquid helium bath cooled solenoid. The cryogenic system is designed for no boil-off operation and cryocoolers are used for recondensation of the evaporated helium. Low cryogenic losses are achieved by the use of HTS-current leads, AC losses of the magnet are reduced by using a mixed matrix Cu/CuNi/NbTi superconductor. The SMES is connected to the power electronic of the UPS by a chopper circuit and a DC link capacitor. This paper describes the system design and focuses on the superconducting magnet.

Experimental results on an hybrid superconducting current limiter

The superconducting current limiter, a device without classical equivalent, appears to be one of the most promising and innovative applied superconducting devices for electric power systems. Its operation is based on the ultra-fast and natural transition of a superconducting coil when the current oversteps a predetermined threshold value. The authors propose a hybrid device consisting of a resistive series transformer and superconducting coils. The superconducting coils trigger the limitation. The latter is ensured by the primary self inductance of the transformer. This design allows the reduction of the current through the superconducting cable, the volume of superconductor and the cryogenic losses under normal operation. These advantages are brought about by a transformer whose magnetic coupling between the windings changes accordingly to the mode of operation. To study this device experimentally, a 150 V-50 A model has been developed. This model has been exposed to a number of tests under normal and fault operations. The results have demonstrated the satisfactory performance of this hybrid device, at least at a reduced scale. With a view to an industrial device, a 63 kV-1250 A system has been theoretically designed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hybrid superconducting a.c. current limiter extrapolation 63 kV-1 250 A

Following the developement of a.c. superconducting wires a.c. current superconducting limiters have emerged. These limiters limit the fault currents nearly instantaneously, without detection nor order giver and may be suitable for high voltages. They are based on the natural transition from the superconducting state to the normal resistive state by overstepping the critical current of a superconducting coil which limits or triggers the limitation. Our limiter device consists essentially of two copper windings coupled through a saturable magnetic circuit and of a non inductively wound superconducting coil with a reduced current compared to the line current. This design allows a simple superconducting cable and reduced cryogenic losses but the dielectric stresses are high during faults. A small model (150 V/50 A) has experimentally validated our design. An industrial scale current limiter is designed and the comparisons between this design and other superconducting current limiters are given.

Hybrid AC superconducting current limiter: small-scale experimental model

The recently developed ultralow AC loss superconducting wires have made possible the design of AC current limiters based on the transition from the superconducting state to the normal state by overstepping the critical current. The original superconducting limiter described is formed by two magnetically coupled copper windings connected in parallel through a superconducting noninductive coil which triggers the inductive limitation. A different number of turns for the two normal windings reduces the current through the superconductor and the cryogenic losses, and simplifies the superconducting cable. A magnetic circuit with variable coupling coefficient makes it possible to limit the thermal stresses on the superconducting coil during limitation. The design, optimisation and tests of a single-phase 150 V/50 A model are presented. It has successfully proved its operation.