Simulation of Transient Effects in High-Temperature Superconducting Magnets

Particle colliders for high-energy physics are important tools for investigating the fundamental structure of matter. In circular accelerators, the collision energy of particles is proportional to the bending magnetic field and the radius of the machine. As a consequence, circular accelerators such as the Large Hadron Collider at CERN have traditionally relied on high-field magnets made of low-temperature superconductors, confining the particle beams within a complex of acceptable dimensions. This class of superconductors shows a practical limit in the achievable magnetic field in the magnet aperture of about 8 T for a Nb-Ti alloy, and 16 T for a Nb3Sn compound. Overcoming these limits requires the use of high-temperature superconductors (HTS) in accelerator magnets, in particular rare-earth barium copper oxide (ReBCO) tapes. With respect to the low-temperature counterpart, accelerator magnets based on ReBCO tapes are known to behave differently in terms of magnetic field quality and protection from quench events. The tapes are equivalent to wide and anisotropic mono-filaments, resulting in screening currents detrimentally affecting the magnetic field quality, in particular at low currents. At the same time, quenches are less likely to occur due to the enhanced thermal stability of the tapes, but are more difficult to detect and mitigate. Moreover, the dynamic behavior of accelerator magnets is also affected by the surrounding circuitry which must be taken into account, leading to multiphysics, multirate and multiscale problems. Numerical methods play a crucial role for overcoming the challenges related to magnetic field quality and quench protection. In this work, the magnetothermal dynamics in high-temperature superconducting magnets is modeled by means of an eddy-current problem in the time domain. A mixed field formulation is developed to cope with the nonlinear resistivity law of superconducting materials. The formulation is complemented with distribution functions for the coupling of external voltage and/or current source quantities. Further simplifications are discussed in case of tapes with high aspect ratio, and multifilamentary conductors. Moreover, a field-circuit coupling interface is derived as an optimized Schwarz transmission condition, such that the formulation can be used in field-circuit coupled problems by means of co-simulation methods. The implementation of the formulation in the finite element method is verified against analytical and reference solutions available in literature, and validated against measurements on the HTS-based dipole magnet Feather-M2. As a case-study, the formulation is applied to proof-of-concept ReBCO screens for the passive field-error cancellation in accelerator magnets. The proposed design is called HALO (harmonics-absorbing layered object) as it is made of stacks of tapes arranged in layers which are fully scalable and expandable. The screens are positioned such that their persistent magnetization shapes the magnetic field in the magnet aperture, canceling the undesired field imperfections. Experimental measurements at 77 K in liquid nitrogen show a significant reduction of the field error, up to a factor of four. Moreover, numerical extrapolation for accelerator-like conditions shows that a careful design of the superconducting screens allows matching the typical field quality requirements for accelerator magnets

Application of the Waveform Relaxation Technique to the Co-Simulation of Power Converter Controller and Electrical Circuit Models

In this paper we present the co-simulation of a PID class power converter controller and an electrical circuit by means of the waveform relaxation technique. The simulation of the controller model is characterized by a fixed-time stepping scheme reflecting its digital implementation, whereas a circuit simulation usually employs an adaptive time stepping scheme in order to account for a wide range of time constants within the circuit model. In order to maintain the characteristic of both models as well as to facilitate model replacement, we treat them separately by means of input/output relations and propose an application of a waveform relaxation algorithm. Furthermore, the maximum and minimum number of iterations of the proposed algorithm are mathematically analyzed. The concept of controller/circuit coupling is illustrated by an example of the co-simulation of a PI power converter controller and a model of the main dipole circuit of the Large Hadron Collider

Reflections on Covid19 nasopharingeal, faecal and peritoneal swabs in an infant with Wilms tumor: A case report

Proximal Sars-Cov-2 pandemic had radically changed the way surgeons work in many departments, forcing to reserve surgical treatment only for emergency and oncologic cases. We report a case of a ten months-old girl with right-sided Wilms tumor and a previous diagnosis of Sars-Cov-2 infection, who underwent open right nephrectomy. Surgery was planned after negativization of five nasopharyngeal tests, despite the simultaneous positivity of two rectal swabs. The procedure was performed safely with appropriate personal protective equipment (PPE). To better investigate viral excretion, the anesthetist repeated nasopharyngeal swab under general anesthesia, which resulted positive. At the same time, two peritoneal swabs were collected and showed the absence of the virus in the peritoneal fluid. This case highlights the importance of combining swabs from various sources to increase sensibility of the test. The value of nasopharyngeal swab under general anesthesia should be reinforced as it can result positive even after many negative tests. Very little is known abouttransmission of the virus through the peritoneum as both presence and absence of Sars-Cov-2 have been reported in the peritoneal fluid. Next literature will clarify which particular conditions determine viral penetration in this anatomical district

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

On the Stability of Mixed Finite-Element Formulations for High-Temperature Superconductors

In this work, we present and analyze the numerical stability of two coupled finite element formulations. The first one is the \haf and is well suited for modeling systems with superconductors and ferromagnetic materials. The second one, the so-called \taf with thin-shell approximation, applies for systems with thin superconducting domains. Both formulations involve two coupled unknown fields and are mixed on the coupling interfaces. Function spaces in mixed formulations must satisfy compatibility conditions to ensure stability of the problem and reliability of the numerical solution. We propose stable choices of function spaces using hierarchical basis functions and demonstrate the effectiveness of the approach on simple 2D examples

Mucosal Injury during Anti-Cancer Treatment: From Pathobiology to Bedside

Mucositis is one of the most common debilitating side effects related to chemotherapy (CT), radiation therapy (RT), targeted agents and immunotherapy. It is a complex process potentially involving any portion of the gastrointestinal tract and injuring the mucosa, leading to inflammatory or ulcerative lesions. Mechanisms and clinical presentation can differ according both to the anatomic site involved (oral or gastrointestinal) and the treatment received. Understanding the pathophysiology and management of mucosal injury as a secondary effect of anti-cancer treatment is an important area of clinical research. Prophylaxis, early diagnosis, and adequate management of complications are essential to increase therapeutic success and, thus, improve the survival outcomes of cancer patients. This review focuses on the pathobiology and management guidelines for mucositis, a secondary effect of old and new anti-cancer treatments, highlighting recent advances in prevention and discussing future research options

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

Monocyte-to-lymphocye ratio (MLR) and LDH level in metastatic colorectal cancer (mCRC) patients (pts)

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Optimization of demodulation rings in professional louspeakers

A new way to design demodulation rings in loudspeakers is explored, using the finite elements model.\nThe lossy inductance of the motor coil is characterized for small signals, then this process is extended to the large signals.\nThus a genetic algorithm, based on the differential evolution theory, is developed and coupled with the finite elements software Comsol:\nusing the Pareto optimality concept, the minimisation of impedance variation togheter with the amount of material used is found