Cryogenic Loss Research Articles

Towards the solution of coating loss measurements using thermoelastic-dominated substrates

Abstract The characterization of thin film parameters derives from the measurement difference between the coated and bare substrate. This method of comparison is based on the stationarity of the substrate: the characteristics of the substrate do not depend on the presence of the film. However, the thermoelastic loss of a coated substrate depends on the thermo-mechanical parameters of the film as well, which are generally unknown. When thermoelastic loss is dominant, the coating loss measurements are completely altered. In this paper, we propose a model that helps to understand the role of each material property in the thermoelasticity of layered plates, and with this we identified three possible cases in which any coating-substrate combination could be classified. In particular, we analyzed the IBS silica film deposited on silicon. Using the model, we were able to explain the experimental results and also selected a thinner substrate for future coating loss measurements. With this choice, cryogenic loss measurements on bare substrate confirm that thermoelastic loss becomes irrelevant for temperatures below 130 K-180 K, depending on the mode.

Study on the interstitial oxygen diffusion to understand the reduction of cryogenic RF loss for the superconducting radio-frequency niobium cavities

Abstract Medium-temperature baking (Mid-T baking) is an innovative method employed to enhance the unloaded quality factor Q0 of superconducting radio-frequency (SRF) niobium (Nb) cavities at cryogenic temperatures. This study presents an interstitial oxygen diffusion model based on the decomposition of the natural oxide to clarify the improved performance of the Nb cavities after undergoing Mid-T baking. Additionally, the correlation between the interstitial oxygen within the RF penetration depth and the surface resistance of the Nb cavities has been explored. The parameter for the oxide decomposition was determined using in-situ X-ray photoelectron spectroscopy (XPS), where the thickness of the oxide/carbide layer was calculated from the peak fitting of Nb 3d spectra and the attenuation law of the photoelectron beam. The interstitial oxygen diffusion model, validated by the semi-quantitative distribution along the depth determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), quantifies the oxygen atomic concentration within the RF penetration depth in Mid-T baked Nb material. In the baking temperature range of 300~400 ℃, the calculated oxygen concentration from the interstitial oxygen diffusion model demonstrates a more pronounced dependence on the baking temperature than the baking time. This suggests that more precise control of the interstitial oxygen concentration can be achieved by adjusting the baking temperature. Furthermore, it has been observed that maintaining a uniform and moderate oxygen concentration throughout the depth is essential for optimal BCS resistance. This study paves the way for more efficient processing optimization and enhancing understanding of the mechanism behind RF loss in Nb cavities.

Probing Enzyme@Metal-Organic Framework Interactions for Enhanced Stability and Catalytic Efficiency Using Cryogenic Electron Energy Loss Spectroscopy (CryoEELS) and Energy-Filtered TEM (EF-TEM)

Probing Enzyme@Metal-Organic Framework Interactions for Enhanced Stability and Catalytic Efficiency Using Cryogenic Electron Energy Loss Spectroscopy (CryoEELS) and Energy-Filtered TEM (EF-TEM)

Cryogenic mechanical loss of amorphous germania and titania-doped germania thin films

The mechanical loss of amorphous thin films of germania (GeO2) and titania-doped germania (Ti:GeO2) deposited by ion-beam sputtering onto silicon double-paddle oscillators was studied from 10 K to 290 K. Undoped germania was found to show a wide cryogenic mechanical loss peak centered at K with , which decreases to as Ti-concentration increases to 44%. In addition to decreasing the height of this low-temperature peak, Ti-doping increases its width, and shifts its position toward lower temperatures. Annealing reduces the room temperature mechanical loss of Ti:GeO2 and increases its cryogenic mechanical loss, which is consistent with trends observed in most amorphous oxides.

Understanding Ion-Beam Damage to Air-Sensitive Lithium Metal With Cryogenic Electron and Ion Microscopy.

It is essential to understand the nanoscale structure and chemistry of energy storage materials due to their profound impact on battery performance. However, it is often challenging to characterize them at high resolution, as they are often fundamentally altered by sample preparation methods. Here, we use the cryogenic lift-out technique in a plasma-focused ion beam (PFIB)/scanning electron microscope (SEM) to prepare air-sensitive lithium metal to understand ion-beam damage during sample preparation. Through the use of cryogenic transmission electron microscopy, we find that lithium was not damaged by ion-beam milling although lithium oxide shells form in the PFIB/SEM chamber, as evidenced by diffraction information from cryogenic lift-out lithium lamellae prepared at two different thicknesses (130 and 225 nm). Cryogenic energy loss spectroscopy further confirms that lithium was oxidized during the process of sample preparation. The Ellingham diagram suggests that lithium can react with trace oxygen gas in the FIB/SEM chamber at cryogenic temperatures, and we show that liquid oxygen does not contribute to the oxidation of lithium process. Our results suggest the importance of understanding how cryogenic lift-out sample preparation has an impact on the high-resolution characterization of reactive battery materials.

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.

An Ultra-wide Bandwidth Low-frequency Radio Astronomical Cryogenic Receiver for FAST Telescope

This paper presents an ultra-wide bandwidth (UWB) low-frequency radio astronomical cryogenic receiver for the Five-hundred-meter Aperture Spherical radio Telescope (FAST). It covers 6.6:1 bandwidth from 0.5 to 3.3 GHz. The receiver consists of a Quad-Ridged Flared Horn (QRFH), a cryogenic microwave unit, an optical transceiver and a warm microwave and frequency mixing unit. A QRFH with a concentric-loaded dielectric spear is developed: the average return losses are larger than 20 dB; the average ports polarization isolation is 43.87 dB; the average dish efficiency is higher than 65%. Many UWB cryogenic low loss components are developed for the fabrication of a cryogenic microwave unit. The average noise temperature lower than 14.2 K and 22.5 K are achieved as referred to the input ports of cryogenic Dewar and the output of horn, respectively. Compared to other similar advanced UWB receivers, such as Parkes 0.7–4.2 GHz (6:1 bandwidth) receiver and FAST 0.27–1.62 GHz (6:1 bandwidth) receiver, wider relative bandwidth of the proposed receiver is achieved and it is a new attempt to expand the bandwidth of UWB low-frequency receiver.

Quasi-monocrystalline silicon for low-noise end mirrors in cryogenic gravitational-wave detectors

Mirrors made of silicon have been proposed for use in future cryogenic gravitational-wave detectors, which will be significantly more sensitive than current room-temperature detectors. These mirrors are planned to have diameters of $\ensuremath{\approx}50$ cm and a mass of $\ensuremath{\approx}200$ kg. While single-crystalline float-zone silicon meets the requirements of low optical absorption and low mechanical loss, the production of this type of material is restricted to sizes much smaller than required. Here we present studies of silicon produced by directional solidification. This material can be grown as quasi-monocrystalline ingots in sizes larger than currently required. We present measurements of a low room-temperature and cryogenic mechanical loss comparable with float-zone silicon. While the optical absorption of our test sample is significantly higher than required, the low mechanical loss motivates research into further absorption reduction in the future. While it is unclear if material pure enough for the transmissive detector input mirrors can be achieved, an absorption level suitable for the highly reflective coated end mirrors seems realistic. Together with the potential to produce samples much larger than $\ensuremath{\approx}50$ cm, this material may be of great benefit for realizing silicon-based gravitational-wave detectors.

Amorphous silicon nitride deposited by an NH3-free plasma enhanced chemical vapor deposition method for the coatings of the next generation laser interferometer gravitational waves detector

Cryogenic mechanical loss of the mirror coatings will result in thermal noise and limit the sensitivity of the next generation laser interferometer gravitational wave detectors operated at cryogenics. Amorphous silicon nitride (aSiN) films deposited by NH3 plasma enhanced chemical vapor deposition (NH3-PECVD), a coating method with potential in large area uniform coatings for the next generation detectors, were found previously to have a low cryogenic mechanical loss and without loss peaks that are common in current coatings for room temperature detectors. A positive correlation between N–H bond density and cryogenic mechanical loss in the aSiN films has been observed previously, and the existence of an N–H bond-related asymmetrical two-level system was postulated to account for the cryogenic mechanical loss. In this report, we studied an NH3-free PECVD process to reduce the N–H bond concentration and hence reducing the cryogenic mechanical loss. The N–H bond density of all films deposited by the NH3-free PECVD method was reduced to below the detection limit (<1020 cm−3). The composition of the optimized film is SiN0.33H0.58 which shows the lowest extinction coefficient (1.21 × 10−5 @ 1550 nm), a high refractive index (2.68 @ 1550 nm), and excessively low stress (20.8 MPa), respectively. From 10 K to 120 K, cryogenic mechanical loss of the as-deposited SiN0.33H0.58 varies from 5 × 10−5 to 8 × 10−5 which is two to three times lower than that of the best NH3-PECVD silicon nitride previously obtained. No distinctive cryogenic loss peak was found as well.

Measuring Cryogenic Waveguide Loss in the Terahertz Regime

Waveguide attenuation due to conductor loss increases significantly in the terahertz regime. There are a variety of models to estimate this loss but the accuracy is unverified at cryogenic temperatures above 100 GHz. In this article, we present a new technique for measuring the conductor loss of these waveguides. The technique is based on measurements of a waveguide cavity resonator and uses a frequency- to distance-domain transform to isolate the different orders of transmission through the cavity. By calculating the relative loss between successive orders, we can estimate the loss of the resonator and calculate the waveguide attenuation constant. This technique is less susceptible to calibration errors and standing waves in the measurement system, making it suitable for cryogenic high-frequency measurements. For the purposes of this study, we measured the attenuation constant of several WR-2.8 and WR-3.0 waveguides made from aluminum, gold-plated aluminum, and tellurium copper. At room temperature, the measured attenuation constants were between 0.25 and 0.40 dB/cm in the 260- to 350-GHz frequency range. At cryogenic temperatures (4 K), the attenuation range reduced to between 0.18 and 0.26 dB/cm.

Cryogenic microwave loss in epitaxial Al/GaAs/Al trilayers for superconducting circuits

Epitaxially grown superconductor/dielectric/superconductor trilayers have the potential to form high-performance superconducting quantum devices and may even allow scalable superconducting quantum computing with low-surface-area qubits such as the merged-element transmon. In this work, we measure the power-independent loss and two-level-state (TLS) loss of epitaxial, wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped element superconducting microwave resonators at millikelvin temperatures and down to single-photon powers. The power-independent loss of the device is (4.8±0.1)×10−5, and the resonator-induced intrinsic TLS loss is (6.4±0.2)×10−5. Dielectric loss extraction is used to determine a lower bound of the intrinsic TLS loss of the trilayer of 7.2×10−5. The unusually high power-independent loss is attributed to GaAs’s intrinsic piezoelectricity.

Resolving Heterogeneity in Battery Interphases By Cryogenic Electron Microscopy

The stability of lithium batteries is tied to the physicochemical properties of the solid-electrolyte interphase (SEI), a surface passivation layer on the battery anode. However, owing to the difficulty in characterizing this sensitive interphase with nanoscale resolution, the distribution of SEI components at the nanoscale is poorly understood. Here, we use cryogenic scanning transmission electron microscopy (cryo-STEM) and electron energy loss spectroscopy (EELS) to map the spatial distribution of sensitive SEI components across the metallic Li anode. We reveal that LiF, an inorganic SEI component widely believed to play an important role in battery passivation, is absent within the compact SEI film (~15 nm) in direct contact with the active material. Instead, LiF particles (100-400 nm) are found to precipitate across the electrode surface independently from compact SEI formation. Based on these observations, we conclude that LiF cannot be a dominant contribution to anode passivation nor does it influence Li+ transport across the compact SEI film. Using cryo-STEM and EELS, we refine the traditional view of the SEI structure derived from ensemble-averaged characterizations and nuance the role of SEI components on battery performance.

Higher order mode coupler for the circular electron positron collider

A conceptual design report (CDR) for the Circular Electron Positron Collider (CEPC) was published in September 2018. CEPC will use a 650 MHz radiofrequency (RF) system with 240 two-cell cavities. The collider will be a double ring with shared cavities for Higgs operation and separate cavities for W and Z operations. The higher order modes (HOMs) excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. This study examined the impedance budget and HOM damping requirements for the CEPC ring to keep the beam stable, and a coaxial HOM coupler was considered for extracting the beam-induced HOM power. A double-notch coupler was chosen because of its wide bandwidth for the fundamental mode. Each cavity has two detachable coaxial HOM couplers mounted on the cavity beam pipe with a HOM power handling capacity of 1 kW. This paper presents the design process of the HOM coupler: the RF design, thermal analysis, and mechanical aspects. To validate the design, a prototype of the HOM coupler and a coaxial line test bench were fabricated and tested, and the test results agreed well with the simulation results. The HOM damping results for a real 650 MHz two-cell cavity were also measured and compared with the damping requirements.

HOM damping requirements and measurements for CEPC 650-MHz 2-cell cavity

The circular electron–positron collider (CEPC) will use a 650-MHz RF system with 240 two-cell cavities for the collider. The collider is a double ring with shared cavities for Higgs operation and separate cavities for W and Z operations. The higher-order modes (HOM) excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. To get the real damping results, two prototypes of HOM coupler have been fabricated and installed on the 650-MHz two-cell cavity. The HOMs have been verified by bead pulling method. A test bench with two 2-cell cavities is used to measure the real damping results and study HOM propagating properties for a cavity string. In this paper, the impedance budget, HOM damping and HOM power requirements for the CEPC collider ring are given. The damping results measured for the fundamental mode and HOMs seem good compared with the simulated results. The absorbing efficiency of the absorber and the extraction power efficiency of HOM couplers were also achieved.

Low cryogenic mechanical loss composite silica thin film for low thermal noise dielectric mirror coatings.

Thermal noise in dielectric mirror-coatings is the limiting factor for ultra-high-precision metrologies employing optical cavities and being operated at cryogenic temperatures. Silica film is an indispensable low-refractive-index material for mirror coatings but suffers from high cryogenic mechanical loss and hence contributes to high thermal noise. We partitioned a thick silica film into thin layers by introducing blocking layers of titania. The cryogenic mechanical loss of silica was significantly suppressed; the effect was more profound for thinner partitions. Elimination of the transitions of the long-range two-level systems with scales that exceed the thickness of the silica partition is hypothesized. Dielectric mirror coatings with blocking layers are proposed to reduce the cryogenic thermal noise of the coatings. The calculated reflectance spectrum is consistent with that of the conventional quarter-wave (QW) stack around 1550nm, and the calculated absorptance increases 2.2 times over that of a conventional titania/silica QW stack where the titania is absorptive.

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.

Jointless Pancake Coil Winding for Minimizing Electrical Loss in HTS SMES for Wind Power

Many different applications of superconducting devices have been designed using a modular pancake arrangement. It has been reported that this modular pancake structure provides excellent mechanical holding, effective cooling, and high magnetic flux density for stability of the superconducting coil. However, soldering for interconnecting each double pancake causes current decay, cryogenic coolant loss, and thermal stress. Thus, this paper investigates an improved double pancake winding, named the “jointless double pancake coil winding” and demonstrates the efficacy for minimizing the electrical loss of the high-temperature superconducting (HTS) coil, assembled in the modular double pancake types. It presents a winding method that avoids soldering between the pancake connections and thus removes the primary cause of the electrical loss generated in the existing design. This proposed winding method can effectively achieve zero electrical loss. This paper particularly presents the application of the proposed winding for the HTS-SMES and demonstrates the feasibility and improved functional benefits with reference to the conventional coil. This paper should maximize the operational benefits of using the SMES coil employing the proposed winding method in charge and discharge operations and should increase the effectiveness and efficiency in cryogenic systems.

Thermal noise reduction and absorption optimization via multimaterial coatings

Future gravitational wave detectors (GWDs) such as Advanced LIGO upgrades and the Einstein Telescope are planned to operate at cryogenic temperatures using crystalline silicon (cSi) test-mass mirrors at an operation wavelength of 1550 nm. The reduction in temperature in principle provides a direct reduction in coating thermal noise, but the presently used coating stacks which are composed of silica (${\mathrm{SiO}}_{2}$) and tantala (${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$) show cryogenic loss peaks which results in less thermal noise improvement than might be expected. Due to low mechanical loss at low temperature amorphous silicon (aSi) is a very promising candidate material for dielectric mirror coatings and could replace ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$. Unfortunately, such an $\mathrm{aSi}/{\mathrm{SiO}}_{2}$ coating is not suitable for use in GWDs due to high optical absorption in aSi coatings. We explore the use of a three material based coating stack. In this multimaterial design the low absorbing ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ in the outermost coating layers significantly reduces the incident light power, while aSi is used only in the lower bilayers to maintain low optical absorption. Such a coating design would enable a reduction of Brownian thermal noise by 25%. We show experimentally that an optical absorption of only $(5.3\ifmmode\pm\else\textpm\fi{}0.4)\text{ }\text{ }\mathrm{ppm}$ at 1550 nm should be achievable.

Effects of longitudinal parasitic modes on the beam dynamics for the ADS driving linac in China

For the accelerator driven subcritical system (ADS) main linac in China, two families of superconducting elliptical radio frequency (RF) cavities will be used to accelerate the proton beam from 180 MeV to 1.5 GeV. When the proton beam traverses in the RF cavity, the excited parasitic modes, like high order modes (HOMs) and same order modes (SOMs), may drive the beam to become unstable and increase the cryogenic load, thus putting a limitation on the normal operation of the accelerator. In this paper, by using a numerical code SMD based on the ROOT environment, the effects of longitudinal parasitic modes on the beam dynamics for the ADS driving linac in China have been investigated systematically, while parasitic modes which increase cryogenic loss have not been included in this paper. Some conclusions concerning the beam energy ranging from 180 MeV to 1.5 GeV have been obtained.

Cryogenic Loss Monitors with FPGA TDC Signal Processing

Radiation hard helium gas ionization chambers capable of operating in vacuum at temperatures ranging from 5K to 350K have been designed, fabricated and tested and will be used inside the cryostats at Fermilab's Superconducting Radiofrequency beam test facility. The chamber vessels are made of stainless steel and all materials used including seals are known to be radiation hard and suitable for operation at 5K. The chambers are designed to measure radiation up to 30 kRad/hr with sensitivity of approximately 1.9 pA/(Rad/hr). The signal current is measured with a recycling integrator current-to-frequency converter to achieve a required measurement capability for low current and a wide dynamic range. A novel scheme of using an FPGA-based time-to-digital converter (TDC) to measure time intervals between pulses output from the recycling integrator is employed to ensure a fast beam loss response along with a current measurement resolution better than 10-bit. This paper will describe the results obtained and highlight the processing techniques used.