Numerical Analysis of the Screening Current-Induced Magnetic Field in the HTS Insert Dipole Magnet Feather-M2.1-2

Screening currents are field-induced dynamic phenomena which occur in superconducting materials, leading to persistent magnetization. Such currents are of importance in ReBCO tapes, where the large size of the superconducting filaments gives rise to strong magnetization phenomena. In consequence, superconducting accelerator magnets based on ReBCO tapes might experience a relevant degradation of the magnetic field quality in the magnet aperture, eventually leading to particle beam instabilities. Thus, persistent magnetization phenomena need to be accurately evaluated. In this paper, the 2D finite element model of the Feather-M2.1-2 magnet is presented. The model is used to analyze the influence of the screening current-induced magnetic field on the field quality in the magnet aperture. The model relies on a coupled field formulation for eddy current problems in time-domain. The formulation is introduced and verified against theoretical references. Then, the numerical model of the Feather-M2.1-2 magnet is detailed, highlighting the key assumptions and simplifications. The numerical results are discussed and validated with available magnetic measurements. A satisfactory agreement is found, showing the capability of the numerical tool in providing accurate analysis of the dynamic behavior of the Feather-M2.1-2 magnet.Comment: 14 pages, 18 figure

High-temperature superconducting screens for magnetic field-error cancellation in accelerator magnets

Accelerators magnets must have minimal magnetic field imperfections to reduce particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the magnetization due to persistent currents adds an undesired field contribution, potentially degrading the magnetic field quality. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field component, such that only the undesired field components are compensated. The screens are self-regulating, and do not require any externally applied source of energy. Measurements in liquid nitrogen at 77 K show for dipole-field configurations a significant reduction of the magnetic field error up to a factor of four. The residual error is explained via numerical simulations accounting for the geometric defects in the HTS screens, achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at 4.5 K, field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets

Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide

Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism-information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching

Towards a Muon Collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.Comment: 118 pages, 103 figure

Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

Erratum: Towards a muon collider

The original online version of this article was revised: The additional reference [139] has been added. Tao Han’s ORICD ID has been incorrectly assigned to Chengcheng Han and Chengcheng Han’s ORCID ID to Tao Han. Yang Ma’s ORCID ID has been incorrectly assigned to Lianliang Ma, and Lianliang Ma’s ORCID ID to Yang Ma. The original article has been corrected

Summary of the Workshop on Superconducting Detector Magnets

A ‘Superconducting Detector Magnets Workshop’ took place at CERN from September 12-14, 2022, bringing together the physics community, magnet designers and industry with the purpose to exchange about the future needs and efforts to be achieved in research and development in order to build the next magnet generations for Future Colliders and Beyond Collider Physics Experiments.The industrial capacities and their availabilities, with the foreseen prospects and plans, were addressed and representatives of industry working on all aspects of superconducting detector magnets were given. A topic of particular importance addressed was the availability of aluminium-stabilized Nb-Ti/Cu conductors.The workshop provided a forum for the exchange of ideas, concepts, and best practices, to advance on superconducting detector magnet technologies and to foster collaboration.In the seminar the key points coming out from the workshop will be summarised.</p

An experimental and computational study of strain sensitivity in superconducting Nb3Sn

The superconducting properties of Nb3Sn, a material that is commonly used in high-field magnet applications, are strongly reduced when the material is deformed. The sensitivity to strain is problematic in high-field magnet applications where thermal contraction differences between materials and Lorentz forces during operation may result in a significant reduction in the performance of the Nb3Sn conductor and thus of the application itself. In order to understand the strain sensitivity, an experimental and a computational investigation are combined into a comprehensive and validated model that explains the strain sensitivity of superconducting Nb3Sn.\ud Binary intermetallic A15 Nb-Sn thin films with various compositions were fabricated and characterized in terms of composition and morphology. The resistivity and critical current density of these thin films, as well as the resistivity of bulk samples, were measured as a function of temperature, magnetic field, longitudinal strain, and transverse strain. From the measurements, the strain dependence of the superconducting properties was parameterized.\ud The validity of the previously published MAG description of the temperature, magnetic field, and strain dependent critical current density Jc is demonstrated, which relates the strain sensitivity of the Jc of Nb3Sn to the strain dependent critical temperature Tc and upper critical magnetic field Hc2. Two other commonly used descriptions are found consistent with this description despite being presented in a different form. \ud A computational model is presented which combines ab-initio calculations with microscopic theory, and the results are shown to reproduce the experimentally observed, normal-state-resistivity-dependent martensitic transformation, critical temperature, and upper critical magnetic field. It is shown that the relatively large strain sensitivity of Tc and Hc2 is a result of a strain-induced distortion of the niobium chains, which is referred to as sublattice distortion. This calculation result is experimentally validated with measurements of the normal state resistivity, Tc, and Hc2 as a function of strain on Nb-Sn thin films, bulk samples, and high-Jc conductors. The lower strain sensitivity of Nb3Al and the much lower strain sensitivity of bcc Nb and Nb-Ti are explained in terms of a weaker and a non-existent sublattice distortion, respectively