The P3^3 Experiment: A Positron Source Demonstrator for Future Lepton Colliders

The PSI Positron Production (P$^3$ or P-cubed) experiment is a demonstrator for a e+ source and capture system with potential to improve the state-of-the-art e+ yield by an order of magnitude. The experiment is driven by the FCC-ee injector study and will be hosted in the SwissFEL facility at the Paul Scherrer Institute in Switzerland. This paper is an overview of the P$^3$ design at an advanced stage, with a particular emphasis on a novel e+ capture system and its associated beam dynamics. Additionally, a concept for the experiment diagnostics is presented, as well as the key points of the ongoing installation works

Superconducting magnets for magnetic density separation: A NbTi based demonstrator

The presented work concerns the design of a superconducting magnet for use in Magnetic Density Separation (MDS). This magnet is being constructed at the University of Twente and will serve in a demonstrator set-up for the separation of shredded electronic materials. MDS is a novel separation technology, that can be used in for example the recycling industry. The technique is based on the combination of a fluid that is strongly attracted by magnetic fields (a ferrofluid) and a magnetic field with a strong gradient in a single direction. When shredded non-magnetic particles are inserted in the fluid bed, they will move towards different stable depths in the fluid that corresponds to their mass density. This means the MDS process can separate multiple densities in one single step, for example different plastics or electronics. State-of-the-art MDS systems use permanent magnets. Compared to these magnets, superconductors can generate a stronger magnetic field, increasing the upwards force. This allows the separation of dense particles. Another advantage that comes with the stronger magnetic field is that a lower concentration of magnetic nanoparticles in the fluid can be used while maintaining a strong upwards force. This reduces operation expenditure, because the ferrofluid is expensive and must be regularly replenished due to post-processing losses. A second advantage in using superconducting magnets for MDS results from the fact that the separation resolution scales linearly with the pole size of the magnet. Electromagnets can use a wider pole size than permanent magnets and thus an enhanced separation resolution is possible. The work involves the design and construction of the first superconducting magnet for use in magnetic density separation. The magnet consists of a conduction-cooled set of three NbTi-based racetracks, providing a gradient of 20 T/m at the bottom of the fluid bed. Electromagnetic-, mechanical- and thermal design aspects are covered. The main MDS specific design challenge was to minimize the distance between the coils and the fluid. The thesis also estimates the potential performance of future high-field MDS magnets

Radiation Load Studies for the FCC-ee Positron Source with a Superconducting Matching Device

International audienceFor an electron-positron collider like FCC-ee, the production of positrons plays a crucial role. One of the design options considered for the FCC-ee positron source employs a superconducting solenoid made of HTS coils as an adiabatic matching device. The solenoid, which is placed around the production target, is needed to capture positrons before they can be accelerated in a linear accelerator. A superconducting solenoid yields a higher peak field than a conventional-normal conducting magnetic flux concentrator, therefore increasing the achievable positron yield. In order to achieve an acceptable positron production, the considered target is made of tungsten-rhenium, which gives also a significant flux of un-wanted secondary particles, that in turn could generate a too large radiation load on the superconducting coils. In this study, we assess the feasibility of such a positron source by studying the heat load and long-term radiation damage in the superconducting matching device and surrounding structures. Results are presented for different geometric configurations of the superconducting matching device

Comparison of Different Matching Device Field Profiles for the FCC-ee Positron Source

International audienceIn this report, we compared different matching device field profiles for the FCC-ee positron source. The matching device is used to capture positrons with magnetic field. A flux concentrator was designed with a conical inner chamber. A smaller aperture and a larger aperture were studied. An analytic field profile was also studied using an adiabatic formula. The peak field of the analytic profile as well as beam and target parameters was optimised to achieve a maximum positron yield. A safe energy deposition in the target was guaranteed by requiring a constraint on the deposited power and peak energy deposition density

A Numerical Adiabatic Model for the Quench Behavior Analysis of the Ag-Matrix Bi-2212 Round Wire

To study the quench behavior of the Bi-2212 round wire as a promising superconductor for future fusion reactor coils and high-field magnets, a numerical adiabatic model has been developed at the Institute of Plasma Physics, Chinese Academy of Sciences. The model is in 1-D and the partial differential equation is solved with the implicit method. Quench energy is simulated by introducing heat in a section of the wire, and the temperature and voltage are calculated as the function of time and space. The minimum quench energy and normal zone propagation velocity were calculated at different conditions. The results from the model were compared with analytical solution and experiment data. The analysis and discussion are presented in this paper

Optimisation of the FCC-ee Positron Source Using a HTS Solenoid Matching Device

International audienceIn this paper, we present the simulation and optimisation of the FCC-ee positron source, where a high-temperature superconducting (HTS) solenoid is used as the matching device to collect positrons from the target. The "conventional" target scheme is used which simply consists of amorphous tungsten. The target is placed inside the bore of the HTS solenoid to improve the accepted positron yield at the entrance of the damping ring and the location of the target is optimised. The latest recommended baseline beam parameters are used and presented. An optimisation of the ideal positron yield using the analytic SC solenoid on-axis field is also performed and shows that the design of the HTS solenoid is optimal as far as the accepted positron yield is concerned

Experiments and FE modeling of stress-strain state in ReBCO tape under tensile, torsional and transverse load

For high current superconductors in high magnet fields with currents in the order of 50 kA, single ReBCO coated conductors must be assembled in a cable. The geometry of such a cable is mostly such that combined torsion, axial and transverse loading states are anticipated in the tapes and tape joints. The resulting strain distribution, caused by different thermal contraction and electromagnetic forces, will affect the critical current of the tapes. Tape performance when subjected to torsion, tensile and transverse loading is the key to understanding limitations for the composite cable performance. The individual tape material components can be deformed, not only elastically but also plastically under these loads. A set of experimental setups, as well as a convenient and accurate method of stress–strain state modeling based on the finite element method have been developed. Systematic measurements on single ReBCO tapes are carried out combining axial tension and torsion as well as transverse loading. Then the behavior of a single tape subjected to the various applied loads is simulated in the model. This paper presents the results of experimental tests and detailed FE modeling of the 3D stress–strain state in a single ReBCO tape under different loads, taking into account the temperature dependence and the elastic-plastic properties of the tape materials, starting from the initial tape processing conditions during its manufacture up to magnet operating conditions. Furthermore a comparison of the simulations with experiments is presented with special attention for the critical force, the threshold where the tape performance becomes irreversibly degraded. We verified the influence of tape surface profile non-uniformity and copper stabilizer thickness on the critical force. The FE models appear to describe the tape experiments adequately and can thus be used as a solid basis for optimization of various cabling concepts

Update on the FCC-ee positron source design studies

International audienceThe studies and R&D on the high-intensity positron source for the FCC-ee have been initiated for a while. The positrons are produced by a 6 GeV electron drive-beam incident on a target-converter at 200 Hz. The drive beam comes in 2 bunches spaced by 25 ns with a maximum charge of ~5 nC per bunch. Two scenarios using conventional and hybrid targets are being studied for positron production. According to the FCC CDR, the Flux Concentrator is used as the matching device for the capture system, followed by several accelerating structures embedded in the solenoidal field. Then, the positrons are further accelerated to be injected into the damping ring. Recently, the feasibility study on using a SC solenoid for the positron capture has been started, and the design based on the HTS technology is under investigation. In addition, the large aperture 2 GHz RF structures, which have been specially designed for the FCC-ee positron capture system, are used with the goal of demonstrating accepted positron yield values well beyond the values obtained with state-of-the-art positron sources. The purpose of this paper is to review the current status of the FCC-ee positron source design, highlighting the recent research into the positron production, capture system, primary acceleration, and injection into the damping ring