The Proton Improvement Plan II (PIP-II) project is an essential upgrade to Fermilab's particle accelerator complex to enable the world's most intense neutrino beam for LBNF/DUNE and a broad particle physics program for many decades to come. PIP-II will deliver 1.2 MW of proton beam power from the Main Injector, upgradeable to multi-MW capability. The central element of PIP-II is an 800 MeV superconducting radio frequency (SRF) linac, which comprises a room temperature front end followed by an SRF section. The SRF section consists of five different flavors of cavities/cryomodules, including Half Wave Resonators (HWR), Single Spoke and elliptical resonators operating at, or above, state-of-the-art parameters. The first two PIP-II cryomodules, Half Wave Resonator (HWR) and Single Spoke Resonator 1 (SSR1) were installed in the PIP-II Injector Test facility (PIP2IT) and have accelerated beam to above 17 MeV. PIP-II is the first U.S. accelerator project that will be constructed with significant contributions from international partners, including India, Italy, France, United Kingdom and Poland. The project was baselined in April 2022, and the construction phase is underway.

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created. The first operation of the European X-ray free-electron laser facility accelerator based on superconducting technology is reported. The maximum electron energy is 17.5 GeV. A laser average power of 6 W is achieved at a photon energy of 9.3 keV.

A large, world-wide community of physicists is working to realise an exceptional physics program of energy-frontier, electron-positron collisions with the International Linear Collider (ILC). This program will begin with a central focus on high-precision and model-independent measurements of the Higgs boson couplings. This method of searching for new physics beyond the Standard Model is orthogonal to and complements the LHC physics program. The ILC at 250 GeV will also search for direct new physics in exotic Higgs decays and in pair-production of weakly interacting particles. Polarised electron and positron beams add unique opportunities to the physics reach. The ILC can be upgraded to higher energy, enabling precision studies of the top quark and measurement of the top Yukawa coupling and the Higgs self-coupling. The key accelerator technology, superconducting radio-frequency cavities, has matured. Optimised collider and detector designs, and associated physics analyses, were presented in the ILC Technical Design Report, signed by 2400 scientists. There is a strong interest in Japan to host this international effort. A detailed review of the many aspects of the project is nearing a conclusion in Japan. Now the Japanese government is preparing for a decision on the next phase of international negotiations, that could lead to a project start within a few years. The potential timeline of the ILC project includes an initial phase of about 4 years to obtain international agreements, complete engineering design and prepare construction, and form the requisite international collaboration, followed by a construction phase of 9 years.

The International Linear Collider (ILC) being proposed in Japan is an electron-positron linear collider with an initial energy of 250 GeV. The ILC accelerator is based on the technology of superconducting radio-frequency cavities. This technology has reached a mature stage in the European XFEL project and is now widely used. The ILC will start by measuring the Higgs properties, providing high-precision and model-independent determinations of its parameters. The ILC at 250 GeV will also search for direct new physics in exotic Higgs decays and in pair-production of weakly interacting particles. The use of polarised electron and positron beams opens new capabilities and scenarios that add to the physics reach. The ILC can be upgraded to higher energy, enabling precision studies of the top quark and measurement of the top Yukawa coupling and the Higgs self-coupling. The international -- including European -- interest for the project is very strong. Europe has participated in the ILC project since its early conception and plays a major role in its present development covering most of its scientific and technological aspects: physics studies, accelerator and detectors. The potential for a wide participation of European groups and laboratories is thus high, including important opportunities for European industry. Following decades of technical development, R&D, and design optimisation, the project is ready for construction and the European particle physics community, technological centers and industry are prepared to participate in this challenging endeavour.

We report the direct observations of the correlation of higher order modes (HOMs) generated by off-axis electron beam steering in TESLA-type SCRF cavities and submacropulse beam centroid shifts (with the potential concomitant effect on averaged beam size and emittance). The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a PC rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. The ~100-kHz oscillations with up to 300μm amplitudes at downstream locations were observed in a 3-MHz micropulse repetition rate beam with charges of 100, 300, 500, and 1000 pC/b, although the effects were much reduced at 100 pC/b. INTRODUCTION The interest in beam quality preservation through accelerator structures [1] continues as the community constructs larger facilities and pushes toward brighter beams. Several major facilities depend on the superconducting RF TESLA-type L-band accelerator modules [2,3] including the FLASH free-electron laser (FEL) [4], the European XFEL [5], the under-construction LCLS-II XFEL [6], the proposed MaRIE XFEL at Los Alamos [7], and the International Linear Collider (ILC) under consideration in Japan [8]. A recent study at FLASH using one specific TE111 HOM showed that the root mean squared (rms) relative alignments were about 342 μm for the 40 cavities in the 5 cryomodules with some close to 600 μm off axis [9]. The assessment of the effects on beam quality of such implementations warrants further study as higher brightness electron beams are sought and achieved. We have explored the effects of beam-induced higher order modes on the pulse train at the Fermilab Accelerator Science and Technology (FAST) facility which is based on TESLA-type cavities [10]. Direct measurement of the transverse magnetic dipole modes’ power in the first two passbands as outcoupled were tracked and correlated with the beam motion as a complement of studies on cavity misalignments [9,11-15]. Initial calculations reproduced a key feature of the phenomena. In principle, these results may be scaled to cryomodule configurations of major accelerator facilities. EXPERIMENTAL SETUP/TECHNIQUES The FAST linac [15] is based on an L-band rf photocathode (PC) gun which generates and accelerates an electron beam with a 3-MHz micropulse (or bunch (b)) repetition rate up to 5 MeV. The gun’s Cs2Te photocathode is irradiated by the UV component of the drive laser system [16]. The two HOM-instrumented SCRF capture cavities denoted CC1 and CC2 follow [15]. These accelerate the electron beam up to 50 MeV for transport through the remaining low energy beamline as shown in Fig. 1. Under nominal low-energy operation conditions, the magnet at beamline location 122 bends the beam downward into the low energy absorber to provide a final beam energy measurement. This and other nominal beam parameters for these studies are summarized in Table 1. Table 1: Beam Parameters at the FAST Linac For the purposes of these studies, the final beam energy was kept constant at 33 MeV with a range of micropulse charges utilized as indicated. The basic diagnostics for the HOM studies include the rf BPMs (denoted as B1xx) located before, between, and after the two cavities as shown in Fig. 1 as well as ten BPMs before the low energy spectrometer dipole. These are supplemented by the imaging screens inserted into beam line vacuum crosses (Xyyy) denoted at X107, X111, X121, and X124. The HOM couplers Beam Parameter Units Value Micropulse Charge pC 100-1000 Micropulse Rep. rate MHz 1,3 Beam sizes (sigma) μm 100-1200 Emittance Norm. Bunch length Total Energy mm mrad

LCLS-II 4 GeV linac consist of 35 (+5 spares) of 1.3 GHz cryomodules (CM) and three of 3.9 GHz CM’s including one spare. Fermilab responsible for the CM design and share responsibility with JLAB for module assembly and testing. CM production is almost on the middle of production stage. Paper will overview the performance of the CM’s tested at Fermilab, lessons learned and modifications in design to improve performance.

We report the direct observations of sub-macropulse beam centroid oscillations correlated with higher order modes (HOMs) which were generated by off-axis electron beam steering in TESLA-type superconducting RF cavities. The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a photocathode rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. Oscillations of ~100 kHz in the vertical plane and ~380 kHz in the horizontal plane with up to 600-{\mu}m amplitudes were observed in a 3-MHz micropulse repetition rate beam with charges of 100, 300, 500, and 1000 pC/b. However, the effects were much reduced at 100 pC/b. The measurements were based on HOM detector circuitry targeting the first and second dipole passbands, rf BPM bunch-by-bunch array data, imaging cameras, and a framing camera. Calculations reproduced the oscillation frequencies of the phenomena in the vertical case. In principle, these fundamental results may be scaled to cryomodule configurations of major accelerator facilities.

Repair actions of different extent have been performed at 61 modules of the 100 accelerating series modules for the European XFEL to qualify them for the tunnel installation. Four modules could not be repaired in time. CEA Saclay managed to perform three major repairs in parallel to the series module integration, the residual repair actions took place at DESY Hamburg. In this paper we will give an overview on the various technical problems which required being fixed before the tunnel installation and on the repair actions performed.

As In-Kind contributor to the E-XFEL project, CEA is committed to the procurement of around one third (31) cold beam position monitors (BPM) of the re-entrant RF cavities type and to the assembly on the Saclay site of the 101 cryomodules of the superconducting linac. Each cryomodule is equipped with a beam position monitor connected to a quadrupole at the high-energy end of the cavity string. The industrial process of those BPMs, used in an ultra-clean environment at cryogenic temperature, includes several steps and involves a quality control in collaboration with industrial partners. This paper describes the different steps of the re-entrant cavity BPM fabrication process: machining, copper coating, thermal treatment, EB welding, cleaning and mounting in clean room on the quadrupole. Problems encountered and the lessons learnt will be also reported.

The 101 cryomodules of the XFEL cold linac will be integrated at Saclay under the CEA responsability by the industrial operator ALSYOM, at the production rate of cryomodule per week. Each cryomodule includes a string of 8 Niobium superconducting cavities and a BPM-quadripole unit (downstream end). To avoid particle contamination of the RF cavities, the strings are assembled in an ISO4 cleanroom by following strict cleaning and high-vacuum procedures. The major technical challenge of the string integration thus lies in the capacity to realize 25 connections in two weeks while protecting the cavity and coupler RF surfaces and to check their leak-tightness up to 10-10 hPA.l/s. The partial demonstration was made by the CEA team with the first pre-series module XM-3 which achieves a total accelerating voltage of 232 MV preserving the individual performances of cavities. In this paper the status and challenges of the production line is presented, including the quality management, equipment and operator training aspects. The optimisation process toward a faster assembly while preserving or actually decreasing the cavity exposure to contamination sources is also described.