In recent years, the magnet section at the Paul Scherrer Institute (PSI) has considerably strengthened its expertise in the design, fabrication, and qualification of advanced magnet technologies for particle accelerators. This progress, driven by flagship initiatives such as the Swiss Light Source upgrade (SLS 2.0) and the Swiss Accelerator Research and Technology (CHART) program, has led to the establishment of key competencies in magnet design, dedicated infrastructure, and high-precision magnetic qualification. A prominent example is the SLS 2.0 upgrade, which implements a unique combination of magnet technologies: NdFeB-based permanent magnets, compact combined-function copper electromagnets, and, in a later phase, NbTi superconducting dipoles with a longitudinal field gradient. All magnets are designed, assembled, and magnetically qualified in-house to meet the stringent field-quality and alignment requirements of the new storage ring. In parallel, low-temperature (Nb-Ti, Nb3-Sn) and high-temperature (REBCO) superconducting technologies are being developed and tested in prototype magnets, including those for the PSI Positron Production experiment and for future collider projects such as FCC-ee and FCC-hh, within the framework of CHART. This paper presents an overview of PSI's recent advancements in magnet technology and discusses prospects. These developments serve both PSI's internal research programs and collaborative projects with European and international partners, paving the way for a new generation of efficient and environmentally responsible accelerator magnets.

We present a systematic method to tune the turn-to turn contact resistance R-ct in high-temperature superconducting (HTS) solenoids by applying a polyvinyl butyral (PVB) thermoplastic coating filled with silver-coated copper flakes (SCCF). The filler type and its volume fraction determines the accessible resistance range in the final coil. R-ct strongly affects the charging dynamics and quench resilience of non-insulated (NI) HTS magnets, hence it is important to be able to control this parameter in a reliable and reproducible way. The coating is applied prior to winding in a continuous dip coating process and results in a dry polymeric film on the tape. After winding, the coating layers are fused above 60 degrees C and the final Rct is adjusted through the temperature and the duration of the heat-treatment. This method gives access to a wide range of R-ct. Values from about 50 to 10(6) & micro;Omega & centerdot; cm(2) can be obtained with the right choice of filler type, concentration and heat treatment conditions. An 80-turn demonstrator solenoid fabricated using this approach and tested at 77 K achieved the targeted R-ct of around 70 & micro;Omega & centerdot; cm(2). A finite-element model, calibrated with the measured field-decay time, was used to extract the average turn-to-turn resistance and validate the tuning method.

The decreasing cost and expanding production of REBCO tapes make them promising candidates for accelerator magnets operating at high current density and high magnetic field. Within the CHART program supporting accelerator-magnet development, we perform electromagnetic and thermal analyses of the first REBCO subscale (RS1) magnet developed in the MagDev Lab at PSI, designed to enable direct experimental comparison between HTS and LTS technologies. The RS1 magnet adopts the same configuration as a previously tested LTS SMCC common-coil magnet, in which the Nb3Sn cable is replaced by a straight, soldered REBCO tape-stack cable with comparable geometric parameters. The magnet comprises four racetrack winding layers, with two layers located on each side of the aperture.We present models of resistive and AC-loss induced heating in the REBCO stack under operating conditions relevant to superconducting magnets: liquid helium (4.5 K), gaseous helium (20 K), and liquid nitrogen (77 K). Magnetic-field harmonics and transient behavior in the REBCO cables are computed using an H–A formulation in FEM. The analysis further includes predictions for REBCO magnet protection using a dump resistor as well as alternative protection strategies. Numerical results are compared with experimental data from the two-layer configuration and the full magnet tested in liquid nitrogen, and predictions are provided for liquid- and gaseous-helium tests upcoming at CERN in 2026. These results support the development of accelerator magnets at higher magnetic fields where REBCO conductors offer significant potential.

This paper presents the design of a non-insulated (NI) high-temperature superconductor (HTS) 15 T solenoid with a 72 mm warm bore, intended for use in the PSI Positron Production (P^3) experiment. The P^3 experiment, scheduled to start in Q3 2026, aims to demonstrate a high-yield positron source that is relevant in the context of FCC-ee. The coils will be solder-impregnated using techniques developed with a small-bore HTS NI coil stack. This magnet produced a magnetic field of 18 T at 12 K and 2 kA, in a cryogen-free, conduction-cooled setup. Similarly, the P^3 magnet will be conduction-cooled by two cryocoolers. This larger-bore magnet is designed to operate at 15 K with a nominal operating current of 1.2 kA. To ensure the protection of the NI magnet, quench prevention is the preferred strategy. Several potential failure modes are analyzed, including thermal runaway in the event of failures in the current leads, power supply, or cryocoolers. By enhancing the cold mass' heat capacity through the addition of a large lead mass, the stored magnetic energy can be safely dissipated in the cold mass through the electrical path formed by the superconductor and the solder. Mechanical analysis indicates that the hoop, radial and axial stresses are kept below allowable limits.

To improve the performance of the Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI), an upgrade is ongoing (referred to as SLS 2.0), 2021-2025, that includes the complete renewal of the storage ring, providing about 40 times lower emittance in user operation mode and therefore an enhanced brightness. SLS 2.0 imposes very strict requirements in terms of field quality and magnetic alignment on more than 1000 magnets, which are being produced and magnetically qualified. For the first time a light source will operate with a combination of three types of magnets: i) NdFeB based permanent magnets; ii) Electro-magnets; iii) 5-T Nb-Ti superconducting longitudinal gradient dipoles (installed in the second phase of the machine upgrade). This article provides an overview of the project's progress with respect to the design and production aspects of the magnets, the assembly and measurement strategy, and the challenges associated with series magnetic tests requiring 10 -3 relative accuracy level.

We worked out an approach for obtaining “clean” magnets by introducing oxygen during the reaction heat treatment (RHT) of a single glass fiber insulated Nb 3 Sn Rutherford cable in a channel. A reduction of the RRR by 16% was measured while the glass fiber insulation and support structure was visually clean after the RHT. We developed a filled wax system, consisting of fully refined paraffin wax, carnauba wax and alumina particles, which is compatible with the common glass fiber insulation on Rutherford cables. The filled wax showed a flexural modulus of 19 GPa at −100 °C and a thermal shrinkage of −1.2% from RT to 77 K. We used a commercial glass ceramic coating on stainless steel as primary insulation in single cable in a channel applications or as secondary electrical insulation from the former. The coating survives the RHT and operation temperatures and keeps its electrical insulation properties.

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.

At the Paul Scherrer Institute (PSI), we are setting up an experiment to search for the electric dipole moment (EDM) of the muon using the frozen-spin technique. The discovery of a muon EDM would indicate violation of charge conjugation parity symmetry (CP-violation) and lepton flavor universality, beyond the Standard Model. The experiment aims to achieve a sensitivity of σ ( d μ ) ≤ 6 × 10 -23 e · cm. This study is taking place during the first phase of the experiment and it focuses on the off-axis injection of muons into a 3 T storage solenoid. Muons need to be transported from the exit of the PSI beamline, a low magnetic-field region, into the strong magnetic-field of the solenoid. For this purpose, two magnetically shielded channels are being developed. In the direct vicinity of the injection helix inside the solenoid bore, we will use superconducting (SC) shielding to avoid any hysteresis effect, while farther away in the fringe field we will use iron tubes. Three prototypes of SC injection tubes will be produced: the first will use a commercial high temperature superconducting (HTS) tape wrapped around a hollow copper tube, the second will utilize several Nb-Ti/Nb/Cu sheets obtained from CERN, wrapped and mechanically clamped around another hollow copper tube, while the third will consist of a commercial cast Bi-2223 superconducting tube coiled with HTS tape. To evaluate the effectiveness of the different SC-shields, we will measure their shielding factors and determine the muon injection efficiency from the beamline into the solenoid.

The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV with a beam currents of up to 1.4 A per beam. The high beam current of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully reconsidered and revisited, including the injection time structure. The entire beam dynamics studies for the full linac, damping ring and transfer lines are major activities of the injector complex design. A key point is that any increase of positron production and capture efficiency reduces the cost and complexity of the driver linac,

For the High Luminosity Upgrade project (HL-LHC) of the CERN Large Hadron Collider (LHC), lower β* quadrupole magnets based on advanced Nb 3 Sn conductors will be installed on each side of the ATLAS and CMS interaction points. To quantify the endurance and technological limits of these magnets, beyond their maximum operational conditions, two short length model magnets have been extensively tested at the CERN SM18 test facility. Both magnets were subjected to eight thermal cycles. One of them was trained beyond its ultimate current (17.89 kA, corresponding to 143 T/m field gradient and 12.2 T peak field), reaching a maximum of 19.57 kA at 1.9 K (corresponding to 155 T/m, 13.4 T peak field and 95.4% of the short sample limit) in a 150 mm diameter bore. This magnet currently has the record highest field gradient of this quadrupole magnet class. The second short model had zero re-training quenches up to nominal (16.47 kA) and ultimate current at 1.9 K during the thermal cycles; more than 1000 current cycles to nominal current; and provoked quenches to simulate the most severe failure scenarios of the protection system. After all these tests, both magnets continue to perform beyond requirements for operating current and temperature. In this paper, the tests performed on the two magnets are discussed.

The Large Hadron Collider luminosity upgrade requires the replacement of standard 8.3 T Nb-Ti main dipole magnets with pairs of shorter 11 T Nb 3 Sn dipole magnets. After the manufacturing and testing of several 2 m-long 11 T models, the full-length 11 T magnet series production is now ongoing. As a result of a degraded quench performance in several short models, attributed to excessive stress in the coils' midplanes, an upper hard limit for the coils' pre-stress was set to avoid any conductor degradation. With the aim of further investigating the influence of a lower pre-stress, an additional double-aperture short model was manufactured. The first aperture was assembled with the standard pre-stress target, in line with the series production. The second aperture was assembled with half of the standard pre-stress. Both apertures were then assembled into a 2-in-1 structure, but connected individually in order to power them independently to allow for comparison studies. Contrary to previously built 11 T magnets, the conductor type is also different as Powder-in-tube (PIT) cable was used, instead of standard Restacked-Rod-Process (RRP) cable. Additionally, the quench heaters for magnet protection were not impregnated as previously done, but placed on the outer radial surface of the coils, in agreement with the final decision for the 11 T series production. This paper describes the manufacturing and testing campaign results of this last 11 T short model.

Achieving the targets of the High Luminosity LHC project requires the installation of new inner triplet magnet circuits for the final focusing of the particle beams on each side of the two main interaction points. Each of the four circuits will include six 150 mm aperture, 132.2 T/m gradient, Nb3Sn quadrupole magnets to be installed in the LHC tunnel. The recently updated circuit topology is such that the protection of each magnet can be studied from a single magnet point-of-view. To limit the hot-spot temperature and the peak voltage-to-ground, a protection system was designed that quickly and reliably transfers voluminous parts of the coil to the normal-conducting state, hence distributing more homogeneously the magnets stored energy in the windings. This system is based on two elements: quench heaters attached to the outer layers of the magnet coils and CLIQ (Coupling-Loss Induced Quench). The performance of the protection system is investigated by simulating the electro-magnetic and thermal transients occurring after a quench with the program STEAM-LEDET, and by conducting dedicated experiments at the CERN and FNAL magnet test facilities. The effectiveness of the quench protection system is assessed at all representative operating current levels. Furthermore, the coils hot-spot temperature and peak voltage to ground are analyzed for various failure cases, conductor parameters, and parameter distribution among the four coils. It is concluded that the proposed design assures an effective, reliable, and fully redundant quench protection system.

In the context of CERN's high-luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC), a new double aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These 2.2 m long NbTi dipoles are built with the canted cosine theta (CCT) technique. The two independently powered apertures are oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A full-length double aperture prototype was built and tested at CERN in the SM18 test facility. Here we present the results of powering tests at 1.9 and 4.5 K: training of each aperture, magnetic field quality and cross-talk effects, quench detection system effectiveness, quench protection performance and quench-back with several energy extraction systems.

This paper discusses the simulated and experimentally observed quench behavior of the first HL-LHC Twin Aperture Orbit Corrector Prototype, also known as the MCBRDp1 magnet. This superconducting magnet features two independently powered apertures. Each aperture comprises two concentric canted-cosine-theta-type Nb-Ti/Cu coils that together generate a dipolar magnetic field over the bore. These coils are held in place by conductive aluminum-alloy formers. The circuit is protected by a combination of energy extraction and quench-back in the coils. When the coils are discharged over an energy extractor, eddy currents are generated in the formers, and the resulting heat quickly and efficiently brings the Nb-Ti/Cu strands above their current sharing temperature, provided that the resistive voltage over the energy extractor is sufficiently large. This paper compares simulations and experimental observations. It is shown that with the BBQ tool, the initial voltage development after a training quench is correctly reproduced. The ProteCCT simulation tool is shown to be consistent with experimentally observed discharges of the MCBRDp1 prototype for different bath temperatures, energy extractor types, and initial operating currents. The baseline energy extractor resistor value of 1.5 Ω and the non-linear varistor option both give worst-case hotspot temperatures below the 200 K hotspot temperature limit. At ultimate current, the resulting hotspot temperatures are 143 and 167 K, and the peak voltages-to-ground are 590 and 440 V, respectively.

The Nb3Sn block coil dipole magnet FRESCA2 was developed within the framework of a collaboration between CEA Saclay and CERN, in the continuity of the European project EuCARD and EuCARD2. With an aperture of 100 mm and a target bore field of 13 T at 10.6 kA, the magnet is required for a new FRESCA2 cable test facility at CERN. In 2017, the magnet was pre-loaded to retain the forces while the magnet was powered to achieve 13.3 T in the magnet bore. Results of these tests were published. In 2018, the loading of the magnet has been increased for powering to higher current. In this paper, the updated results of the cold powering tests are discussed in terms of training, memory, and stable operation. The loading of the magnet and the mechanical measurements during cooldown are shown and compared to the earlier loading steps. The protection of the magnet is further reviewed and measured results are compared to the model simulations.

In the frame of the compact linear collider project, a high-field short-period superconducting damping wigglers will be required to reduce the emittance of the electron and positron beams. The use of Nb3Sn as superconducting material is being investigated, as a valid option for its smaller size and increased working margin. At CERN, Geneva, Switzerland, a second Nb3Sn damping wiggler short model has been developed, assembled, and tested. In this paper, the cold power test of that magnet is discussed in terms of training, quench detection, protection, endurance, and other tests.

For the high luminosity upgrade of the CERN large hadron collider, lower $\beta$* quadrupole magnets based on advanced Nb$_\text{3}$Sn conductors will be installed on each side of the ATLAS and compact muon solenoid (CMS) experiment insertion zones. As part of the technological developments needed to achieve the required field gradient of 132.6 T/m within a 150-mm aperture, short length model magnets, named MQXFS, are tested both at the CERN SM18 and Fermilab test facilities. The model magnets rely on two types of Nb$_\text{3}$Sn conductors (restack rod process (RRP) and powder-in-tube (PIT)) and on an innovative bladders and keys design to provide mechanical support against the Lorentz forces. In 2016 and 2017, the powering tests of the first two models MQXFS3 (RRP) and MQXFS5 (PIT) proved that nominal performance (16.5 kA) could be reached with excellent memory of the quench current after thermal cycle. However both magnets showed a slow training behavior with clear observations of voltage disturbances before the quench. Besides, only MQXFS5 could reach ultimate current (17.9 kA) whereas erratic behavior was observed on MQXFS3 due to conductor local degradation at the head of one of the coils. In 2018, this limiting coil was changed and the applied azimuthal prestress increased. While ultimate current could then be reached, no stable current could be maintained due to identified defect on the outer layer of the new coil. Finally the outcome of the test of the new model MQXFS4, featuring the final RRP conductors that will be used for the series production and variation on the inner layer quench heater designs are here reported in details.

In the frame of the high-luminosity upgrade project for the large hadron collider, new twin aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long canted cosine theta NbTi dipoles, with two independently powered apertures oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A 0.5 m model magnet in single and double aperture configuration and a full-length double aperture prototype were built and tested at CERN. In this paper, the performance of these magnets at 1.9 K in terms of training behavior, quench detection and protection, and other tests is discussed. In addition, the thermal response of the magnet to a hypothetical beam discharge is simulated and analyzed.

A study was performed to understand the quench behavior and ensure adequate quench protection of the canted cosine theta (CCT) twin aperture orbit corrector magnet, a superconducting magnet under development as part of the high-luminosity upgrade of the Large HadronCollider (HL-LHC). The cosine theta geometry features canted superconducting coils, which together produce a magnetic dipole field. The NbTi/Cu strands are placed in slots inside formers that maintain the shape of the coils. The presence of these formers affects the quench behavior of the magnet by preventing direct thermal contact between adjacent groups of strands. At the same time, a discharge of the stored energy over an external resistor results in significant eddy current heating inside the formers, which quickly brings the entire superconducting magnet to a normal state. A calculation model was developed that describes the electrical and thermal behavior of this type of magnet, and the results of this model are compared to experimental observations on a 0.5 m CCT model coil. It is found that the calculation results and experimental observations are generally consistent, although the simplified manner in which the eddy current heating is described in the model leads to a modest overestimation of the hotspot temperature. The calculation results indicate that a proposed quench protection configuration, featuring a discharge over a 0.7 Omega energy extractor and a 0.05 Omega crowbar, is sufficient to protect both the 0.5 m CCT model magnet and the 2.2 m CCT prototype magnet, resulting in hotspot temperatures of 63 and 193 K, and peak voltages to ground of 300 and 310 V, respectively.