Compensation of the impact of low-cost manufacturing techniques in the design of E-plane multiport waveguide junctions

In this work, a full-wave tool for the accurate analysis and design of compensated E-plane multiport junctions is proposed. The implemented tool is capable of evaluating the undesired effects related to the use of low-cost manufacturing techniques, which are mostly due to the introduction of rounded corners in the cross section of the rectangular waveguides of the device. The obtained results show that, although stringent mechanical effects are imposed, it is possible to compensate for the impact of the cited low-cost manufacturing techniques by redesigning the matching elements considered in the original device. Several new designs concerning a great variety of E-plane components (such as right-angled bends, T-junctions and magic-Ts) are presented, and useful design guidelines are provided. The implemented tool, which is mainly based on the boundary integral-resonant mode expansion technique, has been successfully validated by comparing the obtained results to simulated data provided by a commercial software based on the finite element method.All the data necessary to understand, evaluate, replicate, and generate the figures and results presented in this paper have been included in the present manuscript. A full-wave custom code and the commercial software Ansys HFSS have been used to generate the simulated results provided by the authors. This work was supported by the Ministerio de Economia y Competitividad, Spanish Government, under the Research Projects TEC2013-47037-C5-1-R and TEC2013-47037-C5-4-R.San Blas Oltra, ÁA.; Roca, JM.; Cogollos Borras, S.; Morro, JV.; Boria Esbert, VE.; Gimeno Martinez, B. (2016). Compensation of the impact of low-cost manufacturing techniques in the design of E-plane multiport waveguide junctions. Radio Science. 51(6):619-628. https://doi.org/10.1002/2016RS006027S61962851

Search of dark-matter axions in the microwave frequency range with full-wave modal techniques

Axions, originally proposed to solve the strong Charge-Parity problem of Quantum Chromo-Dynamics theory, emerge now as leading candidates of dark matter. In fact, the search of dark-matter axions in the microwave frequency range has been developed by different research groups during the last twenty years. In this demanding scenario, several microwave passive components (haloscopes) have been designed and fabricated for such axions detection based on the use of cavities and multi-cavities. From an electromagnetic point of view, comercial software (ANSFT HFSS, CST MICROWAVE STUDIO, etc ) has been employed for the design of different kind of haloscopes. In this work we propose to use the BI-RME 3D method (Boundary Integral – Resonant Mode Expansion) as an alternative to analyze the axion-photon coupling existing within an haloscope. This full-wave modal technique has provided interesting wide-band results for the design of new haloscopes

Wide-band full-wave electromagnetic modal analysis of the coupling between dark-matter axions and photons in microwave resonators

The electromagnetic coupling axion-photon in a microwave cavity is revisited with the Boundary Integral - Resonant Mode Expansion (BI-RME) 3D technique. Such full-wave modal technique has been applied for the rigorous analysis of the excitation of a microwave cavity with an axion field. In this scenario, the electromagnetic field generated by the axion-photon coupling can be assumed to be driven by equivalent electrical charge and current densities. These densities have been inserted in the general BI-RME 3D equations, which express the RF electromagnetic field existing within a cavity as an integral involving the Dyadic Green functions of the cavity (under Coulomb gauge) as well as such densities. This method is able to take into account any arbitrary spatial and temporal variation of both magnitude and phase of the axion field. Next, we have obtained a simple network driven by the axion current source, which represents the coupling between the axion field and the resonant modes of the cavity. With this approach, it is possible to calculate the extracted and dissipated RF power as a function of frequency along a broad band and without Cauchy-Lorentz approximations, obtaining the spectrum of the electromagnetic field generated in the cavity, and dealing with modes relatively close to the axion resonant mode. Moreover, with this technique we have a complete knowledge of the signal extracted from the cavity, not only in magnitude but also in phase. This can be an interesting issue for future analysis where the axion phase is an important parameter.Comment: 37 pages, 14 figures, 40 reference

RADES axion search results with a High-Temperature Superconducting cavity in an 11.7 T magnet

We describe the results of a haloscope axion search performed with an 11.7 T dipole magnet at CERN. The search used a custom-made radio-frequency cavity coated with high-temperature superconducting tape. A set of 27 h of data at a resonant frequency of around 8.84 GHz was analysed. In the range of axion mass 36.5676 $\mu$eV to 36.5699 $\mu$eV, corresponding to a width of 554 kHz, no signal excess hinting at an axion-like particle was found. Correspondingly, in this mass range, a limit on the axion to photon coupling-strength was set in the range between g$_{a\gamma}\gtrsim$ 6.2e-13 GeV$^{-1}$ and g$_{a\gamma}\gtrsim$ 1.54e-13 GeV$^{-1}$ with a 95% confidence level.Comment: 19 pages, 8 figure

Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions

A technique for the accurate computation of the time domain electromagnetic fields radiated by a charged distribution traveling along an arbitrarily shaped waveguide region is presented. Based on the transformation (by means of the standard Fourier analysis) of the time-varying current density of the analyzed problem to the frequency domain, the resulting equivalent current is further convolved with the dyadic electric and magnetic Green's functions. Moreover, we show that only the evaluation of the transverse magnetic modes of the structure is required for the calculation of fields radiated by particles traveling in the axial direction. Finally, frequency domain electric and magnetic fields are transformed back to the time domain, just obtaining the total fields radiated by the charged distribution. Furthermore, we present a method for the computation of the wakefields of arbitrary cross-section uniform waveguides from the resulting field expressions. Several examples of charged particles moving in the axial direction of such waveguides are included.The authors would like to thank ESA/ESTEC for having cofunded this research activity through the Network Partnering Initiative program and through the project "Multipactor Analysis in Planar Transmission Lines" (contract 20841/08/NL/GLC). We also are grateful to the Spanish government and the local Council of Murcia for their support through the projects CICYT Ref. TEC2010-21520-C04-04 and SENECA Ref. 08833/PI/08, respectively.Jimenez Nogales, M.; Marini, S.; Gimeno Martinez, B.; Alvarez Melcon, A.; Quesada Pereira, FD.; Boria Esbert, VE.; Soto Pacheco, P.... (2012). Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions. Radio Science. 47(5):1-14. https://doi.org/10.1029/2012RS005008S114475Alvarez-Melcon, A., & Mosig, J. R. (2000). 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Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method. IEEE Transactions on Microwave Theory and Techniques, 51(12), 2378-2390. doi:10.1109/tmtt.2003.819776Conciauro, G., Bressan, M., & Zuffada, C. (1984). Waveguide Modes Via an Integral Equation Leading to a Linear Matrix Eigenvalue Problem. IEEE Transactions on Microwave Theory and Techniques, 32(11), 1495-1504. doi:10.1109/tmtt.1984.1132880Deshpande , M. D. 1997 Analysis of discontinuities in a rectangular waveguide using dyadic Green's function approach in conjuntion with Method of Moments Langley Res. Cent., NASA Hampton, Va.Felsen, L. B., & Marcuvitz, N. (1994). Radiation and Scattering of Waves. doi:10.1109/9780470546307Figueroa, H., Gai, W., Konecny, R., Norem, J., Ruggiero, A., Schoessow, P., & Simpson, J. (1988). Direct Measurement of Beam-Induced Fields in Accelerating Structures. 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Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440). doi:10.1109/pac.2003.1289954Jing, C., Liu, W., Xiao, L., Gai, W., Schoessow, P., & Wong, T. (2003). Dipole-mode wakefields in dielectric-loaded rectangular waveguide accelerating structures. Physical Review E, 68(1). doi:10.1103/physreve.68.016502Kim, S. H., Chen, K. W., & Yang, J. S. (1990). Modal analysis of wake fields and its application to elliptical pill‐box cavity with finite aperture. Journal of Applied Physics, 68(10), 4942-4951. doi:10.1063/1.347079Lutman, A., Vescovo, R., & Craievich, P. (2008). Electromagnetic field and short-range wake function in a beam pipe of elliptical cross section. Physical Review Special Topics - Accelerators and Beams, 11(7). doi:10.1103/physrevstab.11.074401Ng, K.-Y. (1990). Wake fields in a dielectric-lined waveguide. Physical Review D, 42(5), 1819-1828. doi:10.1103/physrevd.42.1819Palumbo, L., Vaccaro, V. G., & Wustefeld, G. (1984). 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First results of the CAST-RADES haloscope search for axions at 34.67 µeV

We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 µeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of ga¿ ¿ 4 × 10-13 GeV-1 over a mass range of 34.6738 µeV < ma< 34.6771 µeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 µeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities. © 2021, The Author(s)

Physics potential of the International Axion Observatory (IAXO)

We review the physics potential of a next generation search for solar axions:the International Axion Observatory (IAXO). Endowed with a sensitivity todiscover axion-like particles (ALPs) with a coupling to photons as small as$g_{a\gamma}\sim 10^{-12}$ GeV$^{-1}$, or to electrons $g_{ae}\sim$10$^{-13}$,IAXO has the potential to find the QCD axion in the 1 meV$\sim$1 eV mass rangewhere it solves the strong CP problem, can account for the cold dark matter ofthe Universe and be responsible for the anomalous cooling observed in a numberof stellar systems. At the same time, IAXO will have enough sensitivity todetect lower mass axions invoked to explain: 1) the origin of the anomalous"transparency" of the Universe to gamma-rays, 2) the observed soft X-ray excessfrom galaxy clusters or 3) some inflationary models. In addition, we reviewstring theory axions with parameters accessible by IAXO and discuss theirpotential role in cosmology as Dark Matter and Dark Radiation as well as theirconnections to the above mentioned conundrums

Thin Film (High Temperature) Superconducting Radiofrequency Cavities for the Search of Axion Dark Matter

5 pages, 6 figures. v2: minor updates after referee comments, matches published version in IEEEThe axion is a hypothetical particle which is a candidate for cold dark matter. Haloscope experiments directly search for these particles in strong magnetic fields with RF cavities as detectors. The Relic Axion Detector Exploratory Setup (RADES) at CERN in particular is searching for axion dark matter in a mass range above 30 $\mu$eV. The figure of merit of our detector depends linearly on the quality factor of the cavity and therefore we are researching the possibility of coating our cavities with different superconducting materials to increase the quality factor. Since the experiment operates in strong magnetic fields of 11 T and more, superconductors with high critical magnetic fields are necessary. Suitable materials for this application are for example REBa$_2$Cu$_3$O$_{7-x}$, Nb$_3$Sn or NbN. We designed a microwave cavity which resonates at around 9~GHz, with a geometry optimized to facilitate superconducting coating and designed to fit in the bore of available high-field accelerator magnets at CERN. Several prototypes of this cavity were coated with different superconducting materials, employing different coating techniques. These prototypes were characterized in strong magnetic fields at 4.2 K.This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871 (ARIES-TNA). BD and JG acknowledge funding through the European Research Council under grant ERC-2018-StG-802836 (AxScale). We also acknowledge funding via the Spanish Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project PID2019- 108122GB-C33, and the grant FPI BES-2017-079787 (under project FPA2016-76978-C3-2-P). Furthermore we acknowledge support from SuMaTe RTI2018-095853-B-C21 from MICINN co-financed by the European Regional Development Fund, Center of Excellence award Severo Ochoa CEX2019- 000917-S and CERN under Grant FCCGOV-CC-0208 (KE4947/ATS).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe