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The main fabrication stages of niobium and copper prototypes of coaxial half-wave resonators (HWR) operating at frequency 325 MHz for the Nuclotron-based Ion Collider fAcility (NICA) injector are presented and discussed. Results of intermediate measurements and electromagnetic properties control for niobium and copper cavities of equivalent geometrical characteristics are compared and analyzed. The comparison of electromagnetic properties of Cu- and Nb-prototypes allows estimating specific features and differences of intermediate "warm" measurements of niobium and copper cavities. The presented results will be used for further development and production of superconductive niobium cavities with a similar design for the NICA-project., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

We propose an original technique for the fabrication of terahertz (THz) metasurfaces comprising a 3D printed regular array of polymer hemispheres covered with a thin conductive layer. We demonstrate that the deposition of a thin metal layer onto polymer hemispheres suppresses the THz reflectivity to almost zero, while the frequency range of such a suppression can be considerably broadened by enhancing the structure with graphene. Scaling up of the proposed technique makes it possible to tailor the electromagnetic responses of metasurfaces and allows for the fabrication of various components of THz photonics.

The practical realization of a prototype of the frequency tuning system (FTS) for coaxial half-wave cavities (HWR) for the Nuclotron-based Ion Collider fAcility (NICA) injector is presented. The impact of FTS on electromagnetic parameters of copper HWR prototype is experimentally studied and discussed. The most important parameters like tuning range, tuning sensitivity, the dependence of the resonant frequency on the position of the plungers are estimated. The effective operation algorithms of the proposed FTS are discussed and analyzed. The dynamic characteristics of FTS are investigated and showed the ability to adjust the frequency with an accuracy of about 70 Hz., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Since 2015 the superconducting (SC) linac-injector development for Nuclotron NICA (JINR, Dubna, Russia) is carried out by the collaboration of JINR, NRNU MEPhI, INP BSU, PTI NASB. This new SC linac is to accelerate protons up to 20 MeV and light ions to 7.5 MeV/u with possible energy upgrade up to 50 MeV for proton beam. This paper reports the current status of the development and manufacturing of superconducting accelerating cavities for a new linear accelerator of the injection complex of the Nuclotron-NICA project., Proceedings of the 27th Russian Particle Accelerator Conference, RuPAC2021, Alushta, Russia

Design of the prototype cryomodule for testing low-beta 325 MHz half-wave cavities is currently undergoing at INP BSU. The cryomodule allows performing intermediate vacuum-, temperature-, and rf-tests during the fabrication of half-wave resonators. The first experimental results of cryomodule cooling down to liquid nitrogen temperatures are presented and discussed. The pressure and temperature control allow us to estimate the main cooling/heating characteristics of the cryostat at different operation stages. The presented test cryomodule will be used for further development and production of superconductive niobium cavities for the Nuclotron-based Ion Collider fAcility (NICA) injector., Proceedings of the 27th Russian Particle Accelerator Conference, RuPAC2021, Alushta, Russia

The design of a prototype of the frequency tuning system (FTS) for superconductive coaxial half wave cavities (HWR) [1] developed for the Nuclotron-based Ion Collider fAcility (NICA) injector is presented. The proposed system is based on mobile plungers placed in the technological holes in the end caps of the resonator. The FTS allows controlling the penetration depth of plungers, which is monotonically related to the resonant frequency shift of the cavity. The developed FTS includes slow/fast tuner parts and is more compact and simple in comparison to traditional mechanical systems, which deform reversibly the HWR by applying an effort on the beam ports [2]. The similar plunger-based tuner design was considered for QWR cavities in [3]. The results of numerical simulations of the resonant frequency for a wide range of plunger parameters are presented and discussed. The most important parameters for effective frequency shift are estimated., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The microwave conductivity and permittivity of both single-walled and multi-walled carbon nanotube (SWCNT and MWCNT) sponges were measured while compressing the samples. Compression leads to a huge variation of the absorptance, reflectance, and transmittance of the samples. The dependence of the microwave conductivity on the sponge density follows a power-law relation with exponents 1.7±0.1 and 2.0±0.2 for MWCNT and SWCNT sponges, respectively. These exponents can be decreased slightly by the addition of a non-conducting component which partly electrically separates adjacent tubes within the samples. The conductivity of MWCNT sponge was measured in the terahertz range while heating in air from 300 to 513 K and it increased due to an increase of a number of conducting channels in MWCNTs.

The progress in R&D of QWR and HWR superconducting cavities will be discussed. These cavities are designed for the new injection linac constructed for Nuclotron-NICA complex at JINR. The goal of new linac is to accelerate protons up to 25 MeV (and up to 50 MeV at the second stage) and light ions to ~7.5 MeV/u for Nuclotron-NICA injection. Current results of beam dynamics simulations, SC cavities design and SRF technology development will be presented in this report., Proceedings of the 61\textsuperscript{st} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2018, Daejeon, Korea

We present the electromagnetic scattering theory for a finite-length nanowire with an embedded mesoscopic object. The theory is based on a synthesis of the integral equation technique of classical electrodynamics and the quantum transport formalism. We formulate Hallén-type integral equations, where the canonical integral operators from wire antenna theory are combined with special terms responsible for the mesoscopic structure. The theory is applied to calculate the polarizability of a finite-length single-walled carbon nanotube (CNT) with a short low-conductive section (LCS) in the microwave and subterahertz ranges. The LCS is modeled as a multichannel two-electrode mesoscopic system. The effective resistive sheet impedance boundary conditions for the scattered field are applied on the CNT surface. It is shown that the imaginary part of the polarizability spectrum has three peaks. Two of them are in the terahertz range, while the third is in the gigahertz range. The polarizability spectrum of the CNT with many LCSs has only one gigahertz peak, which shifts to low frequencies as the number of LCSs increases. The physical nature of these peaks is explained, and potential applications of nanoantennas are proposed.

Propagation of an electron beam over a graphene/dielectricsandwich structure is considered assuming the distance between layers tobe large enough to prevent interlayer tunnelling. A dispersionequation for the surface electromagnetic modes propagating along graphene sheets is derived and \v{C}erenkov synchronism betweensurface wave and non-relativistic electron beam is predicted at achievable parameters of the system.The generationfrequency tuning is proposed by varying the graphene doping, thenumber of graphene sheets, the distance between sheets, etc.

The new collaboration of JINR, NRNU MEPhI, INP BSU, PTI NASB, BSUIR and SPMRC NASB starts in 2015 the project of linac-injector design in 2015. The goal of new linac is to accelerate protons up to 25 MeV (and up to 50 MeV at the second stage) and light ions to ~7.5 MeV/u for Nuclotron-NICA injection. Current results of the linac general design and development, beam dynamics simulations, SC cavities design and SRF technology development are presented in this report., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The joint collaboration of JINR, NRNU MEPhI, INP BSU, PTI NASB, BSUIR and SPMRC NASB started in 2015 a new project on the development of superconducting cavities production and test technologies and new linac-injector design. This linac intend for the protons acceleration up to25 MeV (up to 50 MeV after upgrade) and light ions acceleration up to ~7.5 MeV/u for Nuclotron-NICA injection. Current status of linac general design and results of the beam dynamics simulation and SRF technology development are presented in this report., Proceedings of the 25th Russian Particle Accelerator Conf., RuPAC2016, St. Petersburg, Russia