Copper Cavity Research Articles

Deepest sensitivity to wavelike dark photon dark matter with superconducting radio frequency cavities

Wavelike, bosonic dark matter candidates like axions and dark photons can be detected using microwave cavities known as haloscopes. Traditionally, haloscopes consist of tunable copper cavities operating in the TM010 mode, but ohmic losses have limited their performance. In contrast, superconducting radio frequency (SRF) cavities can achieve quality factors of ∼1010, perhaps 5 orders of magnitude better than copper cavities, leading to more sensitive dark matter detectors. In this paper, we first derive that the scan rate of a haloscope experiment is proportional to the loaded quality factor QL, even if the cavity bandwidth is much narrower than the dark matter halo line shape. We then present a proof-of-concept search for dark photon dark matter using a nontunable ultrahigh-quality SRF cavity. We exclude dark photon dark matter with kinetic mixing strengths of χ>1.5×10−16 for a dark photon mass of mA′=5.35 μeV, achieving the deepest exclusion to wavelike dark photons by almost an order of magnitude. Published by the American Physical Society 2024

Extensive Search for Axion Dark Matter over 1 GHz with CAPP’S Main Axion Experiment

We report an extensive high-sensitivity search for axion dark matter above 1 GHz at the Center for Axion and Precision Physics Research (CAPP). The cavity resonant search, exploiting the coupling between axions and photons, explored the frequency (mass) range of 1.025 GHz (4.24 μeV) to 1.185 GHz (4.91 μeV). We have introduced a number of innovations in this field, demonstrating the practical approach of optimizing all the relevant parameters of axion haloscopes, extending presently available technology. The CAPP 12 T magnet with an aperture of 320 mm made of Nb3Sn and NbTi superconductors surrounding a 37 l ultralight-weight copper cavity is expected to convert Dine-Fischler-Srednicki-Zhitnitsky axions into approximately 102 microwave photons per second. A powerful dilution refrigerator, capable of keeping the core system below 40 mK, combined with quantum-noise-limited readout electronics, achieved a total system noise of about 200 mK or below, which corresponds to a background of roughly 4×103 photons per second within the axion bandwidth. The combination of all those improvements provides unprecedented search performance, imposing the most stringent exclusion limits on axion-photon coupling in this frequency range to date. These results also suggest an experimental capability suitable for highly sensitive searches for axion dark matter above 1 GHz. Published by the American Physical Society 2024

Near-quantum-limited haloscope search for dark-photon dark matter enhanced by a high- Q superconducting cavity

We report new experimental results on the search for dark photons based on a near-quantum-limited haloscope equipped with a superconducting cavity. The loaded quality factor of the superconducting cavity is 6×105, so that the expected signal from dark-photon dark matter can be enhanced by more than one order compared to a copper cavity. A Josephson parametric amplifier with a near-quantum-limited noise temperature has been utilized to minimize the noise during the search. Furthermore, a digital acquisition card based on field programmable gate arrays has been utilized to maximize data collection efficiency with a duty cycle being 100%. This work has established the most stringent constraints on dark photons at around 26.965 μeV. In the future, our apparatus can be extended to search for other dark matter candidates, such as axions and axionlike particles, and scrutinize new physics beyond the Standard Model. Published by the American Physical Society 2024

Calibration of the cryogenic measurement system of a resonant haloscope cavity* *Measurements were performed at Hunan Normal University in Changsha. This work was supported in part by the Scientific Instrument Developing Project of the Chinese Academy of Sciences (YJKYYQ20190049), the International Partnership Program of Chinese Academy of Sciences for Grand Challenges (112311KYSB20210012), the National Natural Science Foundation of China (12074117,

Possible light bosonic dark matter interactions with the Standard Model photon have been searched using microwave resonant cavities. In this paper, we describe the cryogenic readout system calibration of a 7.138 GHz copper cavity with a loaded quality factor whose operation at a temperature of 22 mK is based on a dilution refrigerator. Our readout system consists of High Electron Mobility Transistors working as cryogenic amplifiers at 4 K, plus room-temperature amplifiers and a spectrum analyzer for signal power detection. We tested the system with a superconducting two-level system based on a single-photon source in the microwave frequency regime. We obtained an overall 95.6 dB system gain and –71.4 dB attenuation in the cavity's input channel. The effective noise temperature of the measurement system is 7.5 K.

Dielectric assist accelerating structures for compact linear accelerators of low energy particles in hadrontherapy treatments

Dielectric Assist Accelerating (DAA) structures based on ultralow-loss ceramic are being studied as an alternative to conventional disk-loaded copper cavities. This accelerating structure consists of dielectric disks with irises arranged periodically in metallic structures working under the TM02-π mode. In this paper, the numerical design of an S-band DAA structure for low beta particles, such as protons or carbon ions used for Hadrontherapy treatments, is shown. Four dielectric materials with different permittivity and loss tangent are studied as well as different particle velocities. Through optimization, a design that concentrates most of the RF power in the vacuum space near the beam axis is obtained, leading to a significant reduction of power loss on the metallic walls. This allows to fabricate cavities with an extremely high quality factor, over 100,000, and shunt impedance over 300 MΩ/m at room temperature. During the numerical study, the design optimization has been improved by adjusting some of the cell parameters in order to both increase the shunt impedance and reduce the peak electric field in certain locations of the cavity, which can lead to instabilities in its normal functioning.

Fuel ignition using remote generation of microwave plasma in air at atmospheric pressure

The high demand for a new ignition device for aeronautical engines has motivated the study on an innovative microwave approach, presented in this paper. A dedicated experimental set-up is presented in which we demonstrate the successful ignition of a kerosene spray by a remotely excited microwave plasma. This plasma is created in a Split Ring Resonator (SRR) gap, placed in a copper cavity, in air at atmospheric conditions at the frequency of f = 2.8467 GHz and a pulsed power injected into the cavity of Pcav ≈ 1500 W.

An experimental investigation on the nanofluids in a cavity under natural convection with and without the rotary magnetic field

This experimental study involves the use of two distinct categories of nanofluids, namely ferromagnetic and non-magnetic, within a square cavity that facilitates natural convection. There are five distinct concentrations associated with each nanofluid. Natural convection arises as a consequence of the thermal gradient between the opposing surfaces of the copper cavity, which has a thickness of 18 gauge. The purpose of utilizing the constructed electro-magnet assembly is to investigate the impact of the rotational magnetic field on the process of heat transfer. The manipulation of magnetic strength can be achieved by regulating the magnetic power and direct current (DC) power. The manipulation of the electromagnet’s spin can also be regulated. In the context of a rotational magnetic field, it is seen that the magnetic flux undergoes a transition from a positive value to an almost identical negative value throughout a full rotation. The optimal heat transfer performance is observed at a nanoparticle concentration of 0.1% by volume (φ) for both nanofluids. In the absence of a rotating magnetic field, the ferromagnetic nanofluid exhibited superior performance. When the Rayleigh number (Ra) is one order smaller than the critical Rayleigh number value, the heat transfer performance is often superior with nanofluid compared to demineralized water.

Temperature mapping on a niobium-coated copper superconducting radio-frequency cavity

Since the late ’80s, CERN has pioneered the development of niobium thin film radio-frequency (RF) cavities deposited on copper substrates for several particle accelerator applications. However, niobium thin film cavities historically feature a progressive performance degradation as the accelerating field increases. In this study, we describe a temperature mapping system based on contact thermometry, specially designed to obtain temperature maps of niobium-coated copper cavities and, consequently, study the mechanisms responsible for performance degradation. The first temperature maps on a niobium/copper 1.3 GHz cavity are reported along with its RF performance. In addition to some hotspots displayed in the temperature maps, we surprisingly observed a temperature decrease in a limited portion of the cavity cell as the accelerating field increased. This may shed new light on understanding the heat dissipation of niobium thin film cavities in liquid helium-I, which might be exploited to improve the RF cavity performance.

Graphene passivation effect on copper cavity resonator preserves Q-factor

Proposed resonator design and measurement technique is a promising solution to estimate the value of materials surface conductivity. In the developed device, there are no mechanical connections, that interrupt the flowing microwave currents, which eliminates losses due to poor metal contact and related measurement errors. The main losses (60%) in the resonator are concentrated in a small sample under study - resonance element sample, which ensures high sensitivity to changes in surface conductivity. The influence of annealing the copper cavity resonator surface conducting microwave currents, as well as the effect of graphene coating on its intrinsic quality factor and frequency, was experimentally studied. Technological procedures for modifying a copper surface such as annealing in an H2/Ar atmosphere at a temperature of 1070 °C and subsequent coating with graphene by chemical vapor deposition method are studied. The modification of copper resonator surface texture during heat treatment in hydrogen and argon atmospheres has been studied. It is shown that during annealing, the resonator quality factor increases. The increase of the quality factor was associated with a decrease of resistance of copper, with the growth of crystalline grains, this effect disappears when the resonator is exposed to an air atmosphere. It was found that the graphene coating does not make a significant contribution to the change in the quality factor, but prevents the active growth of the oxide layer and prevents impurities deposition on the copper surface from the atmosphere. Thus, after annealing in hydrogen atmosphere and subsequent coating with graphene, the increased quality factor is retained. The considered procedures can be used to increase and stabilize the resonators quality factor, to eliminate oxidation and contamination of their surface. The results of this work can be used in the designing of microwave devices to study the thin films surface impedance.

Multi-mode analysis of surface losses in a superconducting microwave resonator in high magnetic fields.

This paper reports on a surface impedance measurement of a bulk metal niobium-titanium superconducting radio frequency (SRF) cavity in a magnetic field (up to 10T). A novel method is employed to decompose the surface resistance contributions of the cylindrical cavity end caps and walls using measurements from multiple TM cavity modes. The results confirm that quality factor degradation of a NbTi SRF cavity in a high magnetic field is primarily from surfaces perpendicular to the field (the cavity end caps), while parallel surface resistances (the walls) remain relatively constant. This result is encouraging for applications needing high Q cavities in strong magnetic fields, such as the Axion Dark Matter eXperiment because it opens the possibility of hybrid SRF cavity construction to replace conventional copper cavities.

Energy, Exergy and Economic (3E) analysis of evacuated tube heat pipe solar collector to promote storage energy under North African climate

Evacuated tube solar collectors are solar water heating devices known to be technically viable and economically attractive. In contrast, these systems encounter several problems owing to the unavoidable heat and water losses along the manifold, essentially conduction and convection losses. In warm weather, heat pipes become partially filled with water and boil, increasing the need for a pressure vessel. One of the popular strategies used to tackle this technical trouble is integrating Phase Change Materials (PCMs) into the evacuated tube solar collectors. In this paper, this problem was approached with a broader perspective by assembling three collectors technically modified, thermally optimized, and economically profitable. The first configuration presents a normal industrial solar collector (1). While in the second and third configurations, the solar system was improved through several modifications. In the second system, the manifold was re-insulated all around (2). In the third, the manifold was surrounded by PCM filled into a copper cavity (3). To well highlight the performed amendments, a comparative approach between the three vacuum tube heat pipe solar collectors is presented. The established methodology is based on energy and exergy analysis and is supplemented by an economic evaluation. It was found that the energy and exergy efficiencies for the conventional collector were 41 % and 15 % respectively. While the thermal energy performance recorded for the second collector was ranged between 60 % and 80 %. Concerning the third collector with insulation and thermal storage unit, the total solar energy absorbed during a typical day was 39.68 MJ, the total useful energy recuperated during a day was 4.11 MJ and the daily thermal efficiency was 13 %. The efficiency of the improved collector (3) was further improved until 28 MJ of energy storage was recorded of which 4.3 MJ were delivered to the water overnight. Moreover, an economic feasibility study was carried out, in which the economic feasibility for the last new system.showed an amortization period of five years.

Reverse coating technique for the production of Nb thin films on copper for superconducting radio-frequency applications

In the framework of the Future Circular Collider Study, the development of thin-film coated superconducting radio-frequency copper cavities capable of providing higher accelerating fields (10–20 MV m−1 against 5 MV m−1 for the Large Hadron Collider) represents a major challenge. The method investigated here for the production of seamless niobium-coated copper cavities is based on the electroforming of the copper structure around a sacrificial aluminium mandrel that is pre-coated with a niobium thin film. The first feasibility study, applied to a flat aluminium disk mandrel, is presented. Protective precautions are taken towards the functional niobium film during the production process and it is shown that this technique can deliver well performing niobium films on a seamless copper substrate. This way, the non-trivial chemical treatments foreseen by the standard procedures (e.g. SUBU, EP) for the preparation of the copper surface to achieve the proper adhesion of the niobium layer are also avoided. The only major chemical treatment involved in the reverse-coating method is represented by the chemical dissolution of the aluminium mandrel, which has the advantage of not affecting the copper substrate and therefore the copper-niobium interface.

Optimal design and HOM damping of a 500 MHz 5-cell copper cavity for SAPS

In order to meet the requirements of the Southern Advanced Photon Source (SAPS), a slot-coupled π-mode 5-cell copper cavity with higher order mode (HOM) damping was proposed and developed. In this study, we present the optimal design of a 5-cell copper cavity and an investigation of HOM impedances. A prototype of 5-cell copper cavity based on this design was manufactured. The RF characteristics of 5-cell copper cavity have been tested. The results show that a flat accelerating electric field is obtained, with a coupling coefficient of 1.7% and a shunt impedance more than 19.5 MΩ/m. To damp these HOMs with high impedance, two inductive HOM couplers and two capacitive HOM couplers were designed. Finally, the impedances of all the HOMs are below the threshold of coupled-bunch instabilities (CBI) for SAPS.

High- Q Microwave Dielectric Resonator for Axion Dark-Matter Haloscopes

The frequency band 1--15 GHz provides exciting prospects for resonant axion haloscopes as indicated by cosmological and astrophysical arguments. Among the challenges currently addressed to reach the required sensitivity, the development of high-quality factor cavities that tolerate multitesla fields plays a central role. We report a three-dimensional resonator based on a right-circular copper cavity with hollow cylinders that confine higher-order modes around the cylinder axis. Its effective volume at 10.3 GHz is $3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ l, and under an 8-T field we measure an internal quality factor of more than nine million. A fine-tuning system limited to approximately $1$-MHz range is tested, useful for understanding the conditions required to run a haloscope with a cavity exceeding the axion quality factor.The cavity parameters we report demonstrate the potential of this unique resonator to probe galactic dark-matter axion at scan rates exceeding 2 MHz/day when the cavity is readout by a quantum-limited receiver.

A preliminary study of 4He convective heat switches

Heat switches are key components in sub-kelvin refrigeration. It is widely used in cryogenic systems, such as controlling thermodynamic cycle, coupling/decoupling redundant cryocoolers, accelerating the cooling of cryogenic components and so on. Convective heat switch features simple structure, no moving parts and great thermal conductance, which is mainly used to precool cryogenic components. In order to accelerate the pre-cooling of a test platform to 4K, the passive convective heat switch is investigated in this paper, which consists of a circuit comprising two identical stainless steel tubes and two copper cavities respectively connected to the cold and warm stages. The ON/OFF state of the switch is realized by the presence/absence of a gravity-driven convective helium-4 gas loop. Several convective heat switches with different cavity structures and charge pressures are designed and assembled. The preliminary experimental results on thermal conductance are presented. With a typical dimension of a cylindrical cavity with a diameter of 28mm and a height of 16.8mm, a stainless steel tube with a diameter of 9.6mm and a length of 72mm, thermal conductance of 40-50mW/K in ON state has been obtained.

Magnetic Field Resilience of Three-Dimensional Transmons with Thin-Film Al/AlOx/Al Josephson Junctions Approaching 1 T

Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and ${T}_{1}$ remains above $1\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\text{s}$ over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.

Development of a novel approach for construction of high gradient braze-free S-band cavities

Vacuum breakdown is one of the main limitations to the operating accelerating gradient in radio frequency linear accelerators. Recent studies of copper cavities have been shown that harder copper conditions more quickly and can reach higher accelerating gradients than soft copper cavities. Exploiting this advantage requires the development of assembly methods that do not involve the copper-softening high-temperature heating cycles that are used in for example bonding and brazing. A shrink-fit method, which was already implemented successfully in the operation the IPM linac, is proposed for the construction high-gradient test S-band standing wave structure operating at 2998.5 MHz. The three cells cavity is designed to have a maximum gradient in the middle cell that is twice that of the adjacent cells. Mechanical considerations relating to the shrink-fit construction method have been performed using Ansys. To validate the simulations and ensure the feasibility of construction by shrink-fit method, a sample cavity was constructed and cold tests was performed.

Phase-Modulated Cavity Magnon Polaritons as a Precise Magnetic Field Probe

We describe and operate a spin-magnetometer based on the phase modulation of cavity magnon polaritons. In this scheme a rf magnetic field is detected through the sidebands it induces on a pump, and the experimental configuration allows for a negligible pump noise and a high-frequency readout. The demonstrator setup, based on a copper cavity coupled to an yttrium iron garnet sphere hybrid system, reached a sensitivity of $2.0\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 220 MHz, evading the pump noise and matching the theoretical predictions. An optimized setup can attain a rf magnetic field sensitivity of about $8\phantom{\rule{0.2em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at room temperature. An orders of magnitude improvement is expected at lower temperatures, making this instrument one of the few magnetometers accessing the subfemtotesla limit.

Selective Binding and Redox-Activity on Parallel G-Quadruplexes by Pegylated Naphthalene Diimide-Copper Complexes.

G-quadruplexes (G4s) are higher-order supramolecular structures, biologically important in the regulation of many key processes. Among all, the recent discoveries relating to RNA-G4s, including their potential involvement as antiviral targets against COVID-19, have triggered the ever-increasing need to develop selective molecules able to interact with parallel G4s. Naphthalene diimides (NDIs) are widely exploited as G4 ligands, being able to induce and strongly stabilize these structures. Sometimes, a reversible NDI-G4 interaction is also associated with an irreversible one, due to the cleavage and/or modification of G4s by functional-NDIs. This is the case of NDI-Cu-DETA, a copper(II) complex able to cleave G4s in the closest proximity to the target binding site. Herein, we present two original Cu(II)-NDI complexes, inspired by NDI-Cu-DETA, differently functionalized with 2-(2-aminoethoxy)ethanol side-chains, to selectively drive redox-catalyzed activity towards parallel G4s. The selective interaction toward parallel G4 topology, controlled by the presence of 2-(2-aminoethoxy)ethanol side chains, was already firmly demonstrated by us using core-extended NDIs. In the present study, the presence of protonable moieties and the copper(II) cavity, increases the binding affinity and specificity of these two NDIs for a telomeric RNA-G4. Once defined the copper coordination relationship and binding constants by competition titrations, ability in G4 stabilization, and ROS-induced cleavage were analyzed. The propensity in the stabilization of parallel topology was highlighted for both of the new compounds HP2Cu and PE2Cu. The results obtained are particularly promising, paving the way for the development of new selective functional ligands for binding and destructuring parallel G4s.

High-gradient rf tests of welded X -band accelerating cavities

Linacs for high-energy physics, as well as for industry and medicine, require accelerating structures which are compact, robust, and cost-effective. Small foot-print linacs require high-accelerating gradients. Currently, stable-operating gradients, exceeding $100\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, have been demonstrated at SLAC National Accelerator Laboratory, CERN, and KEK at X-band frequencies. Recent experiments show that accelerating cavities made out of hard copper alloys achieve better high-gradient performance as compared with soft copper cavities. In the scope of a decade-long collaboration between SLAC, INFN-Frascati, and KEK on the development of innovative high-gradient structures, this particular study focuses on the technological developments directed to show the viability of novel welding techniques. Two novel X-band accelerating structures, made out of hard copper, were fabricated at INFN-Frascati by means of clamping and welding. One cavity was welded with the electron beam and the other one with the tungsten inert gas welding process. In the technological development of the construction methods of high-gradient accelerating structures, high-power testing is a critical step for the verification of their viability. Here, we present the outcome of this step---the results of the high-power rf tests of these two structures. These tests include the measurements of the breakdown rate probability used to characterize the behavior of vacuum rf breakdowns, one of the major factors limiting the operating accelerating gradients. The electron beam welded structure demonstrated accelerating gradients of $90\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ at a breakdown rate of ${10}^{\ensuremath{-}3}/(\mathrm{pulse}\text{ }\mathrm{meter})$ using a shaped pulse with a 150 ns flat part. Nevertheless, it did not achieve its ultimate performance because of arcing in the mode launcher power coupler. On the other hand, the tungsten inert gas welded structure reached its ultimate performance and operated at about a $150\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ gradient at a breakdown rate of ${10}^{\ensuremath{-}3}/(\mathrm{pulse}\text{ }\mathrm{meter})$ using a shaped pulse with a 150 ns flat part. The results of both experiments show that welding, a robust, and low-cost alternative to brazing or diffusion bonding, is viable for high-gradient operation. This approach enables the construction of multicell standing and traveling-wave accelerating structures.