Solenoid Magnet Research Articles

Beam characterization measurement of a duoplasmatron ion source for the Nanjing Proton Source

The beam characterization studies in terms of beam current, beam profile and RMS normalized emittance have been carried out in a duoplasmatron ion source developed for the Nanjing Proton Source (NPS). A test chamber installed a Faraday cup, a beam profile monitor and an Allision type scanner have been developed to perform the beam current, beam profile and beam emittance measurement, respectively. To solve the sparking problem of the ion source, we have used physical vapor deposition (PVD) to coat a zirconia film with a thickness of 3μm on the full surface of the extraction electrodes. The beam parameters have been measured at two locations (1) after beam extraction at the ion source end, (2) after focusing the beam using two solenoid magnets of low energy beam transport (LEBT). The relationship between arc current and gas pressure has been studied and the optimal operating point of gas pressure is found to be 1.0 × 10−3 Pa with corresponding hydrogen flow rate is 0.5 SCCM. At the ion source end, the results show that the measured beam current is 40.3 mA, the beam diameter is less than 5 cm and the RMS normalized emittance is less than 0.2 π mm-mrad. In addition, The variation of beam current has been studied as a function of the extraction voltage, gas pressure, and arc current. The variation of RMS normalized emittance of the proton beam has been studied as a function of extraction voltage and arc current. In addition, the results show that the measured beam current is 28.5 mA, the beam diameter is around 0.7 cm and the RMS normalized emittance is 0.31π mm-mrad after focusing at the LEBT end.

DYNAMICS OF AN ELECTRON BEAM FORMED BY MAGNETRON GUN WITH THE SECONDARY EMISSION CATHODE IN THE DECLINING MAGNETIC FIELD OF SOLENOID: EXPERIMENT AND SIMULATION

The article presents the results of research and calculations on the formation of a radial electron beam by a magnetron gun with a secondary emission cathode in the electron energy range 35...65 keV and measuring its parameters during transportation in the total decreasing magnetic field of thesolenoid and the stray field of permanent magnets. The beam was transported in a system consisting of copper rings with an inner diameter of 66 mm,located at a distance of 85 mm from the exit of the magnetron gun. The dependence of the beam current on the amplitude and gradient of the fielddecay has been studied. The studies carried out have shown the possibility of stable formation of a radial electron beam with an energy of tens of keVin the decreasing magnetic field of the solenoid. By optimizing the distribution of the magnetic field (created by the solenoid and ring magnets) and itsdecay gradient, it is possible to achieve an increase in the incident of electrons on one ring (up to ~72% of the beam current). On the basis of themathematical model of the movement of the electron flow, a software tool has been synthesized that makes it possible to obtain and interpret thecharacteristics of the resulting flows. The obtained numerical dependences are in satisfactory agreement with the experimental results for a magneticfield with a large decay gradient. Various configurations of the magnetic field are considered. Solutions to the direct problem of modeling electrontrajectories for given initial conditions and parameters are obtained. Various configurations of the magnetic field are considered. It is shown that forthe selected initial conditions for the electron beam and the distributions of the longitudinal magnetic field along the axis of the gun and the transportchannel, the electron flux falls on a vertical section, the length of which is on the order of a millimeter. Thus, by changing the amplitude anddistribution of the magnetic field, it is possible to control the current in the radial direction along the length of the pipe, and, therefore, the place of theelectron irradiation.

Design of New Resonant Haloscopes in the Search for the Dark Matter Axion: A Review of the First Steps in the RADES Collaboration

With the increasing interest in dark matter axion detection through haloscopes, in which different international groups are currently involved, the RADES group was established in 2016 with the goal of developing very sensitive detection systems to be operated in dipole magnets. This review deals with the work developed by this collaboration during its first five years: from the first designs—based on the multi-cavity concept, aiming to increase the haloscope volume, and thereby improve sensitivity—to their evolution, data acquisition design, and finally, the first experimental run. Moreover, the envisaged work within RADES for both dipole and solenoid magnets in the short and medium term is also presented.

Strap-On Magnets: A Framework for Rapid Prototyping of Magnets and Beam Lines

We describe a framework to assemble permanent-magnet cubes in 3D-printed frames to construct dipole, quadrupole, and solenoid magnets, whose field, in the absence of iron, can be calculated analytically in three spatial dimensions. Rotating closely spaced dipoles and quadrupoles in opposite directions allows us to adjust the integrated strength of a multipole. The contributions of unwanted harmonics were calculated and found to be moderate. We then combined multiple magnets to construct beam-line modules: a chicane, a triplet cell, and a solenoid focusing system.

Numerical study and improvement of the dynamic performance of dilation x-ray imager.

We present in this Note a numerical study on the dynamic performance of a Dilation X-ray Imager (DIXI). The DIXI including a photoelectron tube (PT) and a magnetic solenoid is modeled in 3D space. The initial parameters of the photoelectrons are sampled with a Monte Carlo code. The trajectories of the photoelectrons are calculated by using the particle-in-cell method, and the transit time spread (TTS) and temporal magnification are analyzed in detail. We have designed a PT with a double-microstrip structure and compared the performance of the double-microstrip PT with the traditional single-microstrip PT. The results show that the sensitivity of the TTS and the temporal magnification to the emission time of the photoelectrons can be significantly reduced by using the double-microstrip PT, resulting in an improvement of the time window. Therefore, the dynamic performance of the DIXI is improved.

Development of 4kA Current Leads Using Stacked REBCO Tapes for BESIII Detector Magnet

For the Beijing Spectrometer III (BESIII) superconducting solenoid magnet (SSM) backup valve box upgrade project, a pair of 4kA HTS current leads was designed, manufactured and tested. The baseline design of the current leads adopted a stacked REBCO (Rare-Earth Barium-Copper-Oxide) conductor solution to achieve a lower thermal load at 4 K, improve the stability of the magnet, and meet the requirements in the upgrade project such as leaving the existing cryogenic system and the internal space of the valve box unchanged. Owing to the adoption of REBCO conductor, the heat leakage was effectively controlled.Construction of offline test platform and a preliminary test result are discussed, verified the current capacity of the current lead prototype. The development of a novel soldered stacked REBCO conductor is also described.

Continuum sensitivity and design optimization of superconducting systems under critical current densities with magnetic field dependence

This paper presents an approach for deriving the continuum sensitivity of superconducting systems operating at critical current densities and an optimization method based on the continuum sensitivity. In the sensitivity problem, the superconducting systems is represented by a variational state equation, wherein the magnetic permeability depends on the magnetic field, which is transformed from a state equation with a field-dependent source. The design sensitivity is derived using the material derivative concept of continuum mechanics and the adjoint variable method. The adjoint system has a material property represented as a symmetric tensor that contains the sensitivity of the current density with respect to the magnetic field. The design sensitivity is represented in the analytical form of a surface integral on the interface between the superconducting material and its surroundings, which depends on the sensitivity of the current density. The optimization scheme is constructed based on the continuum design sensitivity. In the design optimization, the level set method is used to express the shape variation of the superconducting materials. The numerical example of infinite solenoids demonstrates that the design sensitivity provides an accurate design solution considering the critical current condition. In addition, the design example of a magnetic resonance imaging solenoid shows that the derived design sensitivity has the inherent ability for attaining the compact design by treating the input current of a superconducting system as a critical condition.

Mechanism analysis of magnetohydrodynamic shock control in hypersonic flow

The effects of external magnetic fields on the shock-wave configuration at hypersonic plasma flow field are investigated in this paper. A series of numerical simulations over various geometry configurations, namely, a blunt body and a fixed-geometry inlet forebody, have been conducted by varying the applied magnetic field under different freestream conditions. Results show that magnetohydrodynamic shock control capabilities under three types of magnetic field are ranked from weak to strong as dipole magnet, solenoid magnet, and uniform magnet field. Under the same applied magnetic field, it is easier to deflect the shock at a relatively high altitude condition, compared with the low altitude case. The bow shock standoff distance is dependent on the distribution of counter-flow Lorentz force right after shock in the stagnation region. For the oblique shock control, the function of two components of Lorentz force is different that the counter-flow one decelerates the flow and increases the shock-wave angle, while the normal one squeezes the oblique shock and deflects the streamlines.

ITER plasma control system final design and preparation for first plasma

The ITER plasma control system (PCS) has successfully completed its final design for the first plasma (FP) and engineering operations (EOs) phase and plant system commissioning has begun as ITER prepares for this first operation phase. Commissioning of the essential plant systems will continue as each plant system is completed and made ready for operation. Tokamak assembly has begun with the base and lower cylinder of the cryostat and the lower most poloidal field (PF) coil installed in the tokamak pit. The first vacuum vessel (VV) sector and accompanying two toroidal field (TF) coils are being prepared for transfer to the pit. Once the tokamak is assembled, the cryostat top lid is closed and pump down begins, this will start approximately one year of integrated commissioning (IC) to prepare all of the relevant plant systems for FP operation. After a scheduled one month of plasma operation with the goal of achieving a plasma current > 100 kA for at least 100 ms, there will be about six months of EO to complete commissioning of the superconducting central solenoid, PF, and TF magnet systems to full current, without plasma, to complete this initial ITER operation phase. The PCS final design for FP will be described as well as the IC sequence of the main plant systems required for this operations phase. The plans for the FP operation campaign will be described, including specific challenges present on ITER due to large VV eddy currents, issues associated with electron cyclotron heating (ECH) assist, neutral pressure and impurities. This will be followed by the EO phase to commission full current operation of the superconducting magnets, possibly including plasma operation at full TF of 5.3 T to have improved conditions both for Ohmic plasma initiation and ECH absorption.

Metamodeling and On-Line Clustering for Loss-of-Flow Accident Precursors Identification in a Superconducting Magnet Cryogenic Cooling Circuit

In the International Thermonuclear Experimental Reactor, plasma is magnetically confined with Superconductive Magnets (SMs) that must be maintained at the cryogenic temperature of 4.5 K by one or more Superconducting Magnet Cryogenic Cooling Circuits (SMCCC). To guarantee cooling, Loss-of-Flow Accidents (LOFAs) in the SMCCC are to be avoided. In this work, we develop a three-step methodology for the prompt detection of LOFA precursors (i.e., those combinations of component failures causing a LOFA). First, we randomly generate accident scenarios by Monte Carlo sampling of the failures of typical SMCCC components and simulate the corresponding transient system response by a deterministic thermal-hydraulic code. In this phase, we also employ quick-running Proper Orthogonal Decomposition (POD)-based Kriging metamodels, adaptively trained to reproduce the output of the long-running code, to decrease the computational time. Second, we group the generated scenarios by a Spectral Clustering (SC) employing the Fuzzy C-Means (FCM), in order to identify the main patterns of system evolution towards abnormal states (e.g., a LOFA). Third, we develop an On-line Supervised Spectral Clustering (OSSC) technique to associate time-varying parameters measured during plant functioning to one of the prototypical groups obtained, which may highlight the related LOFA precursors (in terms of SMCCC components failures). We apply the proposed technique to the simplified model of a cryogenic cooling circuit of a single module of the ITER Central Solenoid Magnet (CSM). The framework developed promptly detects 95% of LOFA events and around 80% of the related precursors.

CAPP-8TB: Axion dark matter search experiment around 6.7 [formula omitted]ev

CAPP-8TB is an axion dark matter search experiment dedicated to an axion mass search near 6.7μeV. The experiment uses a microwave resonant cavity under a strong magnetic field of 8T produced by a superconducting solenoid magnet in a dilution refrigerator. We describe the experimental configuration used to search for a mass range of 6.62 to 6.82μeV in the first phase of the experiment. We also discuss the next phase of the experiment and its prospects.

Improved pulsed field magnetisation in MgB2 trapped-field magnets

Bulk superconductors can act as trapped-field magnets with the potential to be used for many applications such as portable medical magnet systems and rotating machines. Maximising the trapped field, particularly for practical magnetisation techniques such as pulsed field magnetisation (PFM), still remains a challenge. PFM is a dynamic process in which the magnetic field is driven into a superconducting bulk over milliseconds. This flux motion causes heating and a complex interplay between the magnetic and thermal properties. In this work, the local flux density during PFM in a MgB2 bulk superconductor has been studied. We find that improving the cooling architecture increases the flux trapping capabilities and alters the flux motion during PFM. These improvements lead to the largest trapped field (0.95 T) for a single MgB2 bulk sample magnetised by a solenoidal pulsed field magnet. The findings illustrate the fundamental role bulk cooling plays during PFM.

Calibration of a superconducting transformer by measuring critical current of a NbTi Rutherford cable

Large high field superconducting magnets often require high current superconducting cables. To develop these cables, a facility capable of providing a high magnetic field with large sampling area as well as electrical current of tens of kA is essential. A superconducting transformer (SCT) is an energy-efficient and low-cost way to provide large current to superconducting cables. Previously, we co-developed an SCT and successfully tested it to a maximum output current of 45 kA in zero magnetic field. In this work, this SCT is installed to the 12 T split solenoid magnet at the National High Magnetic Field Laboratory (NHMFL). We calibrated it by using this facility to measure the critical current of an NbTi Rutherford cable as a function of magnetic field up to 10 T, and compared the results with those available in the literature. In addition, a strand extracted from the NbTi cable was tested for critical current. The critical current of the extracted strand is scaled and compared with the critical current of the cable. The accuracy of the critical current measurement using this SCT is discussed in detail. This work concludes the commissioning of this SCT, which combined with the 12 T split magnet will provide a unique cable testing capability for future cable development for the NHMFL and its users.

Research on Solenoidal Permanent Magnet for Guiding and Focusing Annular Electron Beams

The vacuum oscillators generally utilize high current annular relativistic electron beams to generate high-power microwaves. The annular electron beams are usually guided and focused by strong axial magnetic fields. A permanent magnet is developed for the application of annular electron beams. The configuration of the permanent magnet is based on the Halbach structure. A new method is proposed to design this solenoidal permanent magnet. The permanent magnet flux source can generate a 0.88 T axial magnetic field at the interaction region and a peak field of 0.94 T. The diameter of its clear bore is 50 mm. The total weight of the permanent magnet is 320 kg. The design, fabrication, and test results are presented in this article.

Experimental study on critical current of bent ReBCO tapes in CORC type cable

Cabling the ReBCO conductor on a round core (CORC) has potential of application for future fusion magnets to carry high current and generate high magnetic field. However, the tape needs to experience the combined tension, compression, bending and torsion stresses during magnet manufacturing. In order to understand the stress effect on the critical current of ReBCO tape with a substrate thickness of 0.05 mm and width of 3 mm, one and multi- layers of CORC specimens have been prepared and bent with a diameter ranging from 300 mm to 60 mm. Critical current measurements were carried out on the tapes located on the outermost layer at 77 K and self-field. The aim is to check the response of the tape's critical current with respect to the cable bending diameter. Simultaneously, a small 2-turn solenoid was constructed and measured at 77 K and self-field to check whether it affect by the cable length or not. These CORC cables are flexible and most of the wound tapes on cable retain around 90% of their initial critical current after bending to a diameter of 100 mm. It will provide parameter support for design of insert solenoid magnets in the future.

Compatible braidings with Hopf links, multiloop, and Borromean rings in (3+1) -dimensional spacetime

Braiding phases among topological excitations are key data for physically characterizing topological orders. In this paper, we provide a field-theoretical approach towards a complete list of mutually compatible braiding phases of topological orders in (3+1)D spacetime. More concretely, considering a discrete gauge group as input data, topological excitations in this paper are bosonic \particles carrying gauge charges and loops carrying gauge fluxes. Among these excitations, there are three classes of root braiding processes: particle-loop braidings (i.e., the familiar Aharonov-Bohm phase of winding an electric charge around a thin magnetic solenoid), multi-loop braidings [Phys. Rev. Lett. 113, 080403 (2014)], and particle-loop-loop braidings [i.e., Borromean Rings braiding in Phys. Rev. Lett. 121, 061601 (2018)]. A naive way to exhaust all topological orders is to arbitrarily combine these root braiding processes. Surprisingly, we find that there exist illegitimate combinations in which certain braiding phases cannot coexist, i.e., are mutually incompatible. Thus, the resulting topological orders are illegitimate and must be excluded. It is not obvious to identify these illegitimate combinations. But with the help of the powerful (3+1)D topological quantum field theories (TQFTs), we find that illegitimate combinations violate gauge invariance. In this way, we are able to obtain all sets of mutually compatible braiding phases and all legitimate topological orders. To illustrate, we work out all details when gauge groups are $\mathbb{Z}_{N_1},\mathbb{Z}_{N_1}\times\mathbb{Z}_{N_2},\mathbb{Z}_{N_1}\times\mathbb{Z}_{N_2}\times\mathbb{Z}_{N_3}$, and $\mathbb{Z}_{N_1}\times\mathbb{Z}_{N_2}\times\mathbb{Z}_{N_3}\times\mathbb{Z}_{N_4}$. Finally, we concisely discuss compatible braidings and TQFTs in (4+1)D spacetime.

A High-Current-Density Electron Beam for Millimeter-Wave Amplifiers

We present experimental characterization of a 20-kV, 130-mA thermionic electron gun, which is a component of a ${W}$ -band traveling-wave tube (TWT) power amplifier. The electron beam is strongly focused by a 6.6-kG permanent magnet solenoid, producing a peak current density up to 800 A/cm2. The cathode temperature, focus electrode voltage, and modulating anode voltage are varied to characterize the emitted cathode current and beam transport through the beam tunnel of the TWT RF circuit. We observe the variation of the cathode current from 107 to 155 mA and peak beam transmission of 95% measured at the collector. Experimental results are compared to 2-D simulations with the electron gun and collector design code MICHELLE.

Modular Design of 3 MJ/2 MW Toroidal Magnet and Analysis of Dynamic Temperature Rise

The power industry is changing rapidly. One approach to accommodate a part of the change is the use of energy storage, in particular superconducting magnetic storage systems (SMES). Both solenoidal and toroidal magnets storing a few megajoules have been designed and valuated for this application. Solenoidal magnets have extensive stray fields, which are one of the serious limitations. Toroidal magnets require more conductor and are more complicated in terms of construction and insulation. The existing power systems require 100 s of megawatts of power from energy storage systems, whereas the power capacity of a single SMES installation will be quite limited. Modular SMES may provide a solution to this limitation. This article describes a 3 MJ/2 MW modular toroidal SMES using YBCO tape. The design approach is aimed at the reduction of the insulation requirement; and a slit structure of the cooling plate is designed to reduce the eddy current loss. The cooling process and losses of the magnet are analyzed.

Conceptual Design of High Field Central Solenoid for Fusion Nuclear Science Facility

Fusion Nuclear Science Facility (FNSF) is a critical fusion nuclear step in the US beyond ITER before proceeding to a larger and electricity producing fusion power plant. Although FNSF is a steady state machine to be operated at high duty cycle, a high field and high current density central solenoid magnet is needed for plasma startups. Due to space constraints in the FNSF in-board radial build, the magnetic field and coil current density required exceed conventional low temperature superconductor (LTS) performance limits and the design can only be achieved by high temperature superconductors (HTS). The design for the central solenoid, also called the ohmic heating (OH) magnet for FNSF shall meet the 100 Weber double flux swing requirement for plasma startups. The stresses at such a high field and high current density coil may require a bucked and wedged TF-OH design to accommodate space for coil winding support structures in in-board system radial build for high field FNSF operations.

Design and Test of an 8T Focusing Superconducting Solenoid of FRIB Driver Linac

The Facility for Rare Isotope Beams (FRIB) was funded by the U.S. Department of Energy, which is the world’s most powerful isotope beam device. We have developed an 8T superconducting solenoid magnet which is used to focus and steer the heavy ion beams for FRIB Driver Linac. The solenoid consists of a main focusing coil, two shielding coils and two pairs of corrector dipoles, fabricated by NbTi wire only. A helium vessel was designed and fabricated to accommodate the coils with an entire length of 652 mm with end flange. The magnet in an operating current of 89.6 A achieved the maximum magnetic field of 8T in 40-mm cold bore without quench. In this paper, the overall design of the whole magnet was introduced, including the magnetic design, mechanical design, quench simulation and the protection circuit. Moreover, the winding process and the test results were showed.