Undulators are X-ray sources that are widely utilised in advanced synchrotron radiation sources and free-electron laser facilities. Due to sustainability and energy efficiency, the development focuses on small-scale, high-field, and especially compact undulators with short period lengths ($\leq$ 10 mm) and narrow magnetic gaps ($\leq$ 4 mm). Therefore, high-temperature superconducting (HTS) tapes, which can provide a high critical current density and high critical magnetic fields at higher temperatures, are extensively used and investigated at the Karlsruhe Institute of Technology. A new concept of superconducting undulators (SCUs) was introduced and further developed by laser-scribing a meander pattern into the superconducting layer to achieve a quasi-sinusoidal current path through the HTS tape. Here we present the complete and final design of such a compact SCU, in particular our latest results regarding the design of the liner with its tapering in the warm region, as well as the cryogenic cooling concept.

The damage mechanisms and limits of superconducting accelerator magnets due to the impact of high-intensity particle beams have been subject to extensive studies in the past years at CERN. Recently an experiment with dedicated sample coils made from Nb-Ti and Nb3Sn strands was performed at CERN's HiRadMat facility. This paper describes the design and construction of the sample coils as well as the results of their qualification before the beam impact. In addition, the experimental setup will be discussed. Finally, measurements during the beam experiment like the beam-based alignment, the observations during the impact of 440GeV protons on the sample coils and the achieved hot-spots and temperature gradients will be presented.

Laser-plasma accelerators, have extremely high accelerating gradients and can generate ultra-short electron bunches with micrometer bunch lengths which makes them a prominent candidate to drive the next-generation compact light sources and free-electron lasers (FELs). To fully exploit the advantages of this novel accelerating technology and to compensate for large chromatic effects in the beam transport line, novel compact beam optic elements based on high-temperature superconductor technology are studied. Moreover, the limited mechanical properties of the HTS ceramic-structured superconductors lead to many manufacturing issues during the coil winding process and to ease this difficulty, designing magnets with simple shape coils is of interest. In this paper, the magnet design as well as the fabrication and test of a demonstrator of a periodic iron-core miniature HTS quadrupole is discussed. This magnet features simple pancake coils that are capable of providing high field gradients and in the experiments were successfully powered in liquid nitrogen and liquid helium showing no degradation.

One of the key issues in the technology of superconductors is the protection against quenches. When designing a superconductor as a magnet, a coil or even current leads, the design should be made such that the superconductor withstands all operational conditions, especially those occurring rapidly, as fast discharges or pulsed loads. A model for a superconducting racetrack coil based on NbTi winding is investigated under pulsed transport current conditions (zero external field) utilizing finite element analysis within the Simulia Opera platform. A pulse duration of a few milliseconds and a peak current exceeding 1 kA is yielded by discharging a capacitor into an RLC circuit that includes the superconductor coil as an element. A quench multi-physics analysis has been performed comprising both thermal and electromagnetic solutions. The transition to normal state and quench occurrence has agreed with the expected critical curve together with the load-line estimated for the existing coil geometry.

Undulators are X-ray sources that are widely utilised in advanced synchrotron radiation sources and freeelectron laser facilities. Due to sustainability and energy efficiency, the development focuses on small-scale, high-field, and especially compact undulators with short period lengths (≤ 10 mm) and narrow magnetic gaps (≤ 4 mm). Therefore, hightemperature superconducting (HTS) tapes, which can provide a high critical current density and high critical magnetic fields at higher temperatures, are extensively used and investigated at the Karlsruhe Institute of Technology. A new concept of superconducting undulators (SCUs) was introduced and further developed by laser-scribing a meander pattern into the superconducting layer to achieve a quasi-sinusoidal current path through the HTS tape. Here we present the complete and final design of such a compact SCU, in particular our latest results regarding the design of the liner with its tapering in the warm region, as well as the cryogenic cooling concept.

Undulators are X-ray sources which are widely used in synchrotron storage rings and free-electron laser (FEL) facilities. As the development of future light sources envisages smaller and more compact undulators, it is necessary to construct small-scale high-field undulators with short period lengths $\lambda ~< $ 10 mm and narrow magnetic gaps $d_\text{mag} < $ 4 mm. Therefore, high-temperature superconducting (HTS) tapes are a promising candidate, since they offer both a high critical current density and a high critical magnetic field. Instead of the commonly used wounded coils of low-temperature superconducting (LTS) wires, such as NbTi, to generate the alternating magnetic dipole field, a meandering pattern is structured on the surface of the HTS tape with ps laser pulses to provide a sinusoidal current path through the tape. This technique leads to a precise structure and at the same time prevents damage to the superconducting layer due to overheating. A new concept has been developed and improved at KIT. The new concept involves two opposing stacks of 30 laser-structured HTS tapes. The ends of each tape are soldered and connected to the tape above, resulting in an accordion-like arrangement. This paper presents the general design and the preparation of the stacks of the compact SCU, followed by the results of a Biot-Savart magnetic field simulation. The magnetic field measurement setup and a first current carrying test of the two coils are included.

Some vacuum chambers in particle accelerators perform a waveguide- or resonator-like behavior due to their unique geometries. Electron multipacting caused by such a structural property might be able to overwhelm the classical beam-induced multipacting. This article shows that the wakefields of particle beams could stimulate the resonant modes of a vacuum chamber with a near-rectangular waveguide shape and accordingly induce much stronger electron avalanche in the chamber. Especially, it has been believed that the multipacting is responsible for pressure rise in a vacuum chamber, where energetic secondary electrons with growing numbers collide with gas particles at the chamber wall. Based on numerical simulations, the electron multipacting mechanism with the mode resonance is proposed, which can explain the significant pressure variation measured in our cryogenic vacuum chamber.

Synchrotron radiation (SR) originated at superconducting bending magnets is known to be at the origin of several beam detrimental effects related to vacuum instabilities. One of the major challenges in the design of the vacuum beam pipes of high-energy hadron colliders is the SR coping strategy. In the case of the future circular hadron collider (FCC-hh), a Cu-coated beam screen (BS) operating in the range of 40-60 K has been designed with the aim of protecting the superconducting magnet cold bores from direct synchrotron irradiation. In order to experimentally study the FCC-hh BS vacuum and cryogenic performance, two sample prototypes were manufactured and installed in the beam screen test-bench experiment (BESTEX) at the Karlsruhe Research Accelerator (KARA) at the Karlsruhe Institute of Technology (KIT). The emitted SR has a critical energy of 6.2 keV, very similar to the 4.6 keV of FCC-hh. Irradiation at both room (RT) and cryogenic (77 K) temperatures showed a significant reduction of the molecular photostimulated desorption yields (eta) of the FCC-hh beam screen compared to those of Cu samples. A first approximation of eta and its evolution with the photon dose accumulated on the FCC-hh BS prototype at 77 K allows to estimate that a machine conditioning period of similar to 1.2 months would be needed to reduce the photostimulated molecular density at the necessary levels to ensure a 100 h beam lifetime at nominal FCC-hh operation.

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

The Karlsruhe Institute of Technology and Bilfmger Noell jointly develop superconducting undulators for light sources. After the R&D phase the collaboration has completed the first worldwide superconducting undulator product. The full scale superconducting undulator with 20 mm period length (SCU20) was installed in the storage ring KARA in December 2017. Since January 2018 SCU20 is in operation serving as radiation source for the NANO beamline We present here the commissioning of SCU20 with electron beam, as well as the first results of the spectral characterization.

The Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT), and the Babcock Noell GmbH are collaborating to develop superconducting undulators for ANKA and low-emittance light sources. The collaboration is now focusing on a superconducting undulator with a period length of 20 mm (SCU20) planned to be the source of the NANO beamline at ANKA. The local magnetic field and the field integrals of the SCU20 1.5-m-long-coils have been characterized in a conduction-cooled horizontal test facility developed at KIT IBPT. Here we complement the main results reported in a previous work with a more detailed analysis, including the measurements of the geometrical deviations from the ideal case of the undulator coils at room temperature used to simulate the magnetic field profile with the program Radia and a quantitative explanation of the magnetic field measurements in cold conditions. A comparison of the photon spectrum calculated from the measured field with the one from the field simulated with Radia considering the geometry measured at room temperature is also presented.

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years.

Superconducting undulators (SCUs) can produce higher photon flux and can cover a wider photon energy range compared to permanent magnet undulators (PMUs) with the same vacuum gap and period length....

We present an estimate of survival probability from an eikonal mini- jet model implemented with a proposal for soft gluon resummation to all orders. We compare it with experimental data for diffractive di-jet production from LHC experiments, CMS and ATLAS, both at LO and NLO order.

The available variety of commercial high temperature superconducting (HTS) coated conductors resulted in the development of many different HTS based applications. One promising application to realize superconducting undulators for table top free electron lasers considers meander-structured stacked HTS tapes to provide the desired sinusoidal magnetic field pattern. One of the biggest challenges of this layout is to keep the resistance of the joints between the stacked tapes small. This paper presents a novel concept of a jointless undulator wound from a single HTS tape scribed with picoseconds laser pulses, preventing damage to the superconducting layer from overheating.

The performance of superconducting insertion devices (IDs) in an electron storage ring strongly depends on their magnetic field quality. Therefore, it is essential to characterize the local field distribution and field integrals of the superconducting coils before installation in the final ID cryostat. The synchrotron radiation facility ANKA of the Karlsruhe Institute of Technology and Babcock Noell GmbH are collaborating on an R&D program on superconducting undulators (SCUs), which foresees the design, manufacturing, and characterization of an SCU with a 20-mm-period length (SCU20). Following this program, a magnetic measurement setup for conduction-cooled superconducting coils up to 2-m length (CASPER II) was built and commissioned. The system allows for performing training to maximum coil currents, measurements of the local field quality, and the first and second field integrals as well. In this contribution, we describe the measurement setup and, shortly, the magnet design and focus on the tests and measurement results of a 30-cm-long SCU20 coil package to highlight the potentiality of the test facility.