The conditioning of room temperature cavities is a long process. Additionally, since the cavity or auxiliary equipment can be damaged, constant supervision or extensive safety precautions are required. To reduce the workload for everyone involved and to increase the efficiency of the conditioning process, it was decided to develop a machine learning algorithm with the goal of fully automated conditioning in mind. The initial model was trained on available data of the low energy-domain (up to 500 W). Since it was possible to expand the data to higher power levels during conditionings in 2024, the algorithm is now trained for power levels up to 30 kW. In this paper, the challenges of training with different power scales, as well as the first experimental results shall be discussed.

A 90-mA and 52.5-keV negative hydrogen ion (H⁻ ion) beam has been extracted from the J-PARC Radio Frequency (RF) H⁻ ion source. The 90-mA beam phase-space distribution at the entrance of the Radio Frequency Quadrupole (RFQ) cavity was measured at the test stand. Compared with the 60-mA beam condition for the present J-PARC user operation, reasonable increase in the operation parameters (the RF input power to the ion source, the electrostatic voltage for beam extraction, and the solenoid currents for Twiss matching with the RFQ) was observed. The normalized RMS emittance increased by a few 10 %, which is within the acceptable range of the RFQ. In addition, the dependence of the beam phase-space distribution was investigated with respect to the operation parameters. Numerical analyses show that the optimum solenoid current was determined to remove the beam halo component with the orifice in the beam transport section, which was originally installed for the differential vacuum pumping of the ion source and the RFQ. In the presentation, the effect between the beam current and the phase-space distribution are discussed in aspect of the H⁻ ion beam optics.

Accelerator-based boron neutron capture therapy (BNCT) has been studied worldwide for a novel cancer therapy using neutrons generated by an accelerator system. The iBNCT (Ibaraki BNCT) project began in collaboration with KEK, the University of Tsukuba, Ibaraki Prefecture, and private companies in Japan. The iBNCT project aims to realize linac-based BNCT with a compact and low-activation accelerator system based on the design and experiences of the J-PARC linac. It consists of an H+ ECR ion source, a 3-MeV RFQ, an 8-MeV Alvarez-DTL, and a beryllium neutron-generation target. Since a high neutron flux is required for the BNCT treatment, an average beam current of more than 1 mA is necessary with the combination of the 8-MeV proton and the beryllium target. By improving the vacuum, cooling water and low-level RF system, stable operation was achieved with an average beam current of 2 mA. After completion of the non-clinical studies in parallel with neutron beam characteristic measurements, the iBNCT project has started a clinical study in January 2024. In this contribution, the present status together with the conducted upgrade and prospects of the iBNCT accelerator will be presented.

CERN Linac4 was formally approved in 2007 in the framework of the LHC Injector Upgrade Project with the purpose of removing the first intensity bottleneck in the chain of CERN LHC injectors. Linac4 was inaugurated in 2017 and became the sole proton injector at CERN in 2020. The experience and know-how built over a decade through the Linac4 project has subsequently been applied to accelerators for societal applications via the Medical Application Office and the Knowledge Transfer Group at CERN. In this paper, we discuss the specific needs of accelerators for societal applications in terms of compactness, portability, and operability. We describe the specific beam dynamics that allow meeting those challenges and illustrate a few examples realized for medical applications and the analysis of fine art.

Astatine 211 is one of the most effective theragnostics isotopes for targeted alpha therapy of cancer. Connected to a carrier that links to cancer cells when injected in a patient, this powerful alpha emitter can selectively destroy cancerous cells. Accelerator production of 211At requires sending beams of fully stripped helium ions (alpha particles) on a bismuth target at the energy of 7.1 Me/u. To obtain sufficient doses for hospital production of 211At, currents higher than what provided by cyclotrons are required. For this type of particle and intensities, cyclotrons are limited by the large amount of beam loss and activation in the extraction region, while linacs are virtually loss-free and much better suited for At production. The design of an innovative linac for At production is presented, based on an alpha particle source of new design, a compact Radio Frequency Quadrupole, and a Quasi-Alvarez Drift Tube Linac (QA-DTL) going up to the final energy. Thanks to the QA-DTL low injection energy and compact design, the linac is only 10 meters in length. The overall design is presented, together with detailed RF and beam optics simulations.

At the Japan Proton Accelerator Research Complex (J-PARC), low-emittance muon beams with a linear accelerator (linac) are proposed as a new approach to precisely measure the anomalous magnetic moment and electric dipole moment of the muon. Low-emittance muon beams can also be employed as new probes for non-destructive imaging techniques to see through structures. In the low-velocity section of the muon linac, a radio-frequency quadrupole linac (RFQ) and an interdigital H-mode drift tube linac (IH-DTL) are used to accelerate muons to β = v/c =0.08 and 0.28, respectively, at an operating frequency of 324 MHz. To reduce construction costs, the IH-DTL employs the alternating phase focusing (APF) method, which uses the transverse focusing force derived from the RF electric field. Because the APF method limits the transverse and longitudinal acceptances simultaneously, careful beam diagnostics and commissioning are essential to suppress the emittance growth derived from beam mismatches. In this paper, the results of the tracking simulation and the development status of the diagnostic and transport beamlines in the low-velocity section are described.

CEA is committed to delivering a study for a warm linac in the frame of the ICONE project. It aims at accelerating an 80-mA beam of protons up to 25 MeV, with a 6% duty cycle. The LINAC consists of: a proton source with low-energy beam transport line, an RFQ, a medium-energy beam transport line, and a warm DTL. All these components must be tuned at 352.2 MHz, to reach the required output energy. This document presents the RF studies made by CEA and INFN on the main RF components, including the RFQ, the rebunchers, IH- and Alvarez DTL cavities and the RF amplifiers.

The University of Sarajevo Physics Department, in collaboration with CERN’s Accelerator Beam Physics group, proposes a compact linear accelerator design for applied physics research spanning from beam dynamics studies to material surface analysis. The Sarajevo Ion Accelerator (SARAI) consists of an electron cyclotron resonance ion source, a low energy beam transport line (LEBT) and a radiofrequency quadrupole (RFQ). The ion source can produce an array of ions extracted with 30 kV. This study presents an iterative parameter optimization method that suggests two LEBT optics: one for beam diagnostics and another for compact beam matching to the RFQ acceptance. The RFQ discussed here is a 750 MHz, 2.5 MeV/u RFQ, used for medical applications. SARAI RFQ aims at 0.5 - 2 MeV/u. A novel RFQ technology allows a significant reduction in footprint. This paper further discusses plans for source commissioning and potential research applications.

The Frankfurt Neutron Source FRANZ will be a compact accelerator driven neutron source utilizing the 7Li(p,n)7Be reaction with a 2 MeV proton beam. The 700 keV RFQ has been sucessfully commissioned with a 10 mA proton beam. Conditioning of the subsequent IH-type cavity has been performed up to 10 kW. We also report on RFQ emittance measurements performed with a slit grid emittance device. In addition, a fast faraday cup (FFC) was used for bunch shape measurements behind the RFQ.

The radio frequency quadrupole (RFQ) is known for bunching, focusing and acceleration of ion beam and more importantly, it does not require transverse focusing element like quadrupole magnets between accelerating cells compared to drift tube linacs. By pushing the limits of handling surface electric field between RFQ vanes, it is possible to make a standalone 352 MHz RFQ reaching 1.8 MeV/u energy gain for swift heavy ions upto mass to charge ratio (A/q) ≤ 4. Special RFQ vane material of cryo Cu* is considered by which surface electric fields can be pushed around 50 MV/m** and the whole RFQ is designed within a length of 5m which is substantially less than any RFQ + DTL combination of equivalent energy gain accelerator for heavy ions. Such systems are highly promising for compact medical LINACS and as well as standalone facilities for nuclear physics experiments. The adiabatic bunching and focusing inherently stabilize the beam dynamics at proper RFQ power and cavity tuning. We present the beam optics design using PARMTEQ code and RFQ cavity design along with thermal analysis using CST MWS. The error analysis is provided to support the design in terms of practical feasibility.

Currently, in the J-PARC linac, beam commissioning between the ion source and RFQ mainly involves adjusting the extraction voltage of the ion source and the two solenoid magnets in the Low Energy Beam Transport line (LEBT) installed between the ion source and the RFQ. These parameters are determined to maximize the measured beam current at the current monitor (SCT) downstream of the RFQ. Previously, the SCT used as a reference had measured the beam current by cutting out a part of the macro bunch. However, to further improve the beam quality, we adjusted LEBT parameters using the newly measured method, which is an integrated whole macro bunch signal. The optimum value obtained by the new method differed from the previous. Therefore, to investigate the cause, we saved all the beam current waveforms of the SCT for reference and compared the ion sources and LEBT parameters of each. As a result, the current of the beam that passed through the RFQ changed over time within the macro bunch for certain ion source and LEBT parameter settings. In this presentation, we will introduce the above study results and discuss the cause of the temporal changes in beam current.

In general, it is not easy to measure the drifting RF properties of a device during its operation. If the scatter matrix changes depending on the temperature, the vector network analyzer provides only a static or a starting point of the thermal development. In particular, it is impossible to fully characterize the component that has more than two ports only by the online measurement. So, in the model proposed, assuming that the heat source defined as the average dissipation is given by stored power in the device and the duty cycle, preliminary measurements for several average dissipations are performed. Analytical solutions are derived by using the preliminary and online measurement for the same average dissipation based on the input-output power pickups. As study case, the method is applied to the circulators and the RFQ of the Linear IFMIF Prototype Accelerator, for the three-port and eight-port device case respectively. The model, the results of experiments, and discussions will be summarized in this report.

The radio-frequency quadrupole test stand (RFQ-TS) was prepared for conditioning the spare RFQ in the J-PARC Linac. Additionally, the RFQ-TS is used for the development of accelerator components and the acquisition of beam parameters. The digital feedback system of the Low-Level RF (LLRF) in the RFQ-TS was previously using the discontinued cPCI system, which had been in use for 20 years since its development. In order to continue improvements of the RFQ-TS and to allow for future development, the system has been upgraded to use $\mu$TCA.4-based system, which can be developed further. In this presentation, we will report the details of the upgrade, as well as the feedback and feedforward adjustments.

The Linear IFMIF Prototype Accelerator (LIPAc) in Rokkasho, Japan, designed to accelerate p+ to 4.5 MeV and D+ to 9 MeV at 62.5 mA and 125 mA in Continuous Wave (CW) mode, respectively, is under commissioning and about to enter into its final stages. A high-power test bench was developed for the testing and conditioning of the Radio-Frequency (RF) couplers of the RF Quadrupole (RFQ) cavity. The processing, requiring thermomechanical validation up to 200 kW and CW, is currently ongoing. Several tests were done, during which multipacting and thermal outgassing was observed in numerous power bands, particularly at 70 - 90 kW for the couplers, which is crucial for RFQ conditioning at nominal voltage. Subsequent tests showed that the cavity and couplers performed as expected at forward power levels close to beam operation (~ 160 kW).

Radio frequency quadrupole (RFQ) is one of the first cavities in a protons or ions accelerator. It aims to focus, bunch, and accelerate the beam, using a high-intensity electric field concentrated between rods or vanes. At CEA, similarly to other labs, a method to evaluate the inter-vane voltage and to tune the cavity (usually with 4 vanes) has been developed, based on the bead pull measurement. It consists of inserting a small bead in the back of each of the 4 quadrants. The induced magnetic field perturbation aims to evaluate the electric field close to the beam axis. This method requires the insertion of a bead along the cavity, whose length can be about several meters. In this paper, we propose to study the possibility of measuring and tuning the cavity using the insertion of slug tuners which would demonstrate the feasibility of obtaining this diagnostic, without opening the cavity.

This paper presents studies on advanced accelerator technologies conducted under the I.FAST (Innovation Fostering in Accelerator Science and Technology) EU project, focusing on additive manufacturing (AM) advancements. AM, particularly powder bed fusion, is giving unique production capabilities for accelerator components. As a proof-of-principle, a full-size pure copper Radio Frequency Quadrupole (RFQ) was successfully manufactured earlier. Low-power RF tests and bead-pull measurements performed on this prototype confirmed the precise electromagnetic field distribution, validating design accuracy and repeatability. Furthermore, high-field gradient tests conducted in the CERN's DC pulsed measurement system showed that AM copper electrodes spaced of 94 µm can achieve gradients up to 42 MV/m. These promising results highlight the transformative potential of additive manufacturing in producing high-frequency accelerator components, advancing both precision and reliability.

The ANTHEM (Advanced Technologies for Human-centered Medicine) research project will establish a Research and Clinical Center in Caserta, Italy, for the study and application of Boron Neutron Capture Therapy (BNCT). The INFN (LNL, Pavia, Napoli, Torino) has in charge the design and construction of the epithermal neutron source, that will assure a flux of $10^9\ n/(s\ cm^2)$ with characteristics suited for deep tumors treatment. The Radio-Frequency Quadrupole (RFQ), designed by INFN, produces $30\ mA$ of protons at $5\ MeV$ and is composed of 3 super modules, each of which at $600\ kg$ in weight and $2.5\ m$ in length. The supports perform the iso-statical alignment during the modules assembly, coupling and alignment, and are also used to align the RFQ respect to the Nominal Beam Line, using a Laser Tracker to monitor the position with a tolerance of $0.1\ mm$. This paper details the chosen kinematic configuration, the supports design, the calculation and simulations for design validation, the procedures for regulation and alignment and the achieved results.

The Japan Proton Accelerator Complex (J-PARC) linac is operated with a peak current of 50 mA to deliver the 1-MW beam to the neutron target through the rapid cycling synchrotron (RCS). One of the source of the beam loss to limit the beam power is a leakage beam from an radio-frequency (RF) beam chopper at the frontend of the linac. Since the leakage beam is presented in the unintended RF bucket, it becomes the beam loss the during the acceleration in the RCS. Recently, the bunch-shape monitor (BSM) dedicated for the low-energy beam has been developed to measure longitudinal profiles after an radio-frequency quadrupole linac (RFQ)*. It is useful to investigate the leakage beam because the BSM is located at just after the chopper. Asymmetric longitudinal profiles were observed with the BSM, but the sensitivity should be improved to observe the leakage beam. Measuring the induced current from the target probe by using the BSM in the same way as the wire-scanner monitor, the leakage beam was observed in the horizontal profile measurement. Latest results are presented with discussing the classification of the leakage beam with respect to its time scale and source.

Since 2020 LINAC4 provides the protons for the entire CERN accelerator complex. It accelerates H- ions to a kinetic energy of 160 MeV and injects them into the Proton Synchrotron (PS) Booster using a charge exchange injection mechanism. The performance requirements have been successfully met since 2021. This paper presents the operational experience gained, together with availability and reliability statistics for LINAC4, during its first four years of operation, and details the key performance indicators for beam quality and stability. It also discusses the main issues encountered and the implemented solutions that have allowed further improvements to be made. Recent developments on the H- ion source have led to an increase of the beam current from the original 35 mA to 50 mA, opening the possibility to increase the intensity delivered to the PS Booster for the benefit of CERN's experimental programmes. Beam energy modulation in LINAC4 has also been developed to increase the PS Booster bunch intensity for which the results of beam tests are presented.

The application of Raspberry Pi cameras as cost-effective, versatile beam diagnostic tools is currently being explored at the Frankfurt Neutron Source (FRANZ). These compact imaging systems have been deployed to investigate proton beams at energies of 60 keV and 700 keV, including configurations where cameras are installed both externally and directly inside the accelerator’s RF resonator. Such setups provide opportunities to visualize beam profiles and related phenomena, potentially offering new insights into beam dynamics and cavity conditioning. This contribution will present the latest developments in camera integration, image acquisition, and preliminary image analysis techniques. By showcasing ongoing work and recent findings, we aim to highlight the potential of this approach for enhancing beam diagnostics in future accelerator environments.

The FRANZ linac, consisting of a coupled RFQ-IH cavity and a subsequent CH rebuncher, requires an LLRF system with moderate performance demands. These include amplitude control to maintain a constant field in the cavity, constant phase synchronization between the accelerator and rebuncher, and plunger control to stabilize the cavities frequency at 175 MHz. Given the dead time from LLRF RF output to probe input is approximately 150 ns and the system operates in cw or 1 ms pulsed mode, a decision was made to design a system with a reaction time of 1 µs. To ensure flexibility, the system was designed with digital control. Consequently, an analog-digital hybrid system was implemented. The RF signal processing is performed using classical analog components, while the control and readout of the analog signals are managed by a ZYNQ SoC, which combines FPGA and ARM processors. The first proof-of-concept prototype for amplitude control, including reflection and vacuum monitoring, has been successfully operational with the RFQ since late 2023. Development of the next version, which will include phase and plunger control, is underway and is expected to undergo beam testing in 2025.