Detailed knowledge of particle beam properties is of great importance to understand and push the performance of existing and next generation accelerators. This includes full knowledge of the particle distribution but also the characterization of femtocoulomb (fC) charge beams. We recently proposed a new phase space tomography method to reconstruct the full 5-dimensional (5D) phase space, i.e., the charge density distribution in all three spatial directions and the two transverse momenta. In this contribution, we first present the experimental demonstration of the method at the FLASHForward facility at DESY. This includes the reconstruction of the full 5D phase space distribution of an electron bunch, the use of this measured phase space to create a particle distribution for highly-realistic simulations, and the extraction of the 4D slice emittance. In a second part, we address the characterization of fC charge beams and present a diagnostic device based on silicon strip sensors that is able to measure the profile, time structure, and charge of beams with low charge density. The device demonstrates the applicability of silicon sensors as versatile beam instrumentation devices and can extend the capabilities of existing diagnostic devices to a new charge range.

Beam energy is a key parameter for free electron laser facilities (FELs). A commonly used nondestructive sys-tem uses a beam position monitor (BPM) to measure the bunch position in a magnetic bunch compressor. At the Shanghai Soft X-ray FEL facility (SXFEL), the chicane stripline beam position method is utilized for this pur-pose. However, this method relies on the initial bunch position before entering the chicane and has a limited linear region. A different non-destructive beam energy system, which measures the bunch flight time using two cavity-based bunch arrival time monitors, has been pro-posed and tested. This paper introduces the development of this system, including design details, build-up, and measurement results. Moreover, it also covers the compar-ison between the two different bunch energy measure-ment methods from several aspects: bunch position-based and bunch flight time-based.

At the Metrology Light Source in Berlin, the concept of Steady-state microbunching (SSMB) is evaluated in a proof-of-principle (PoP) experiment. SSMB has been proposed to deliver kilowatt level average power EUV radiation from an electron storage ring. In the PoP experiment, an energy modulation is impressed onto the electron beam using an infrared laser pulse co-propagating inside an undulator. We show that the beam energy can be measured absolutely by detuning the undulator gap from optimum resonance and observing the intensity of the resulting coherent synchrotron radiation.

The China Spallation Neutron Source Rapid Cycling Synchrotron (CSNS-RCS) is the first high-intensity pulsed proton accelerator in China and the fourth in the world. The space charge effect is a key factor limiting power enhancement. Measuring the frequency shift induced by the space charge effect is an important method for studying this phenomenon. In our experiments, we varied the beam current by adjusting the injection pulse length and chopping rate. Using a combination of narrow-band filtering and Fast Fourier Transform (FFT) techniques, we successfully observed a tune shift of approximately 0.02 induced by a beam power of 140 kW. These experimental results were compared with simulation outcomes, showing good agreement.

Accelerator technology development requires an increase in the precision of both the manufacturing of magnetic elements and their positioning during accelerator installation. In order to monitor the quality of the magnetic elements created, various methods are used. Most of the methods involve the use of precision stands, so magnetic elements are typically measured immediately after production and the data obtained is used for positioning. However, subsequent possible parameter changes are not taken into account. This work is dedicated to the study of an alternative optical magnetic measurement method*. The method is based on the magneto-optical phenomenon of light polarization plane rotation in optically active media, which allows visualizing the magnetic field projection in a given transverse direction. The use of a geodesic laser tracker as a light source could allow us to apply this method directly during accelerator component positioning, solving the aforementioned problem. Our main goal was to verify the feasibility of the method for determining magnetic axes in multipole magnets. A method for creating an optically active medium was developed, the sensitivity of the technique to magnetic fields was studied, and experiments to verify its accuracy on magnetic components produced for the SKIF photon source were conducted. The results of this study provide insight into the potential of this method and indicate directions for its future development.

All CERN circular accelerators are equipped with Base Band Tune (BBQ) measurement systems, based on the direct diode detection technique, allowing to measure the tunes of hadron beams by employing their residual betatron oscillations or very small external excitation. In the framework of the Future Circular Collider (FCC) project, a study was launched to optimise such a system for operation with short electron bunches. A prototype system has been recently installed in Solaris light source. The system has immediately allowed an unprecedented detection of residual betatron oscillations, whose amplitudes, estimated to be in the 100 nm range, are more than two orders of magnitude lower than the smallest beam oscillations used for tune measurements with the Beam Position Monitoring (BPM) system. The residual oscillations allowed reliable continuous tune measurements, which have also revealed spectral content never observed before. This paper provides an overview of the installed BBQ system and describes beam measurement results obtained so far. The aim of the paper is to disseminate new results in the light source community and provide information that may help in building and installing similar systems. It is hoped that wider usage of BBQ systems will help in better understanding the observed spectra of electron beam residual oscillations.

Beam orbit stability is a crucial indicator that can be used to evaluate the performance of a synchrotron radiation source. It can be improved through precise orbit measurement with beam position monitors (BPMs) and appropriate orbit feedback. The move-ment of BPMs directly affects the measurement of the beam orbit and indirectly affects the beam orbit through orbit feedback (OFB) system. Two sets of BPM displacement measurement system were estab-lished at Hefei Light Source II (HLS II) storage ring and some machine learning work was carried out on the system.

VEPP-4M collider and KEDR detector are going to measure precisely $\Upsilon$(1S) mass and leptonic width. In this experiment the electron beam energy is precisely measured using resonant depolarisation tecnhique at "Laser Polarimeter" facility. The electron beam polarisation degree is measured using Compton backscattering with accuracy of 5\% in 100 seconds. The beam energy is measured during KEDR data acquisition runs every 30~minutes with accuracy of 20~keV. In this report the facility design and current status are discussed.

In the high current hadron machine, it is essential to reduce the beam loss along the machine for machine maintenance and safety reasons. The linac of Chinese Spallation Neutron Source (CSNS) delivery negative hydrogen bunches with power of 5kW to the RCS which increase the power to 100 kW. In the following several years, the power of the linac beam will be increased to from 5 kW to 100 kW, therefor it is important to deal the beam loss more carefully. In this paper, we present the reconstruction of the beam orbit along the linac using beam tracking software with the input data measured with BPMs. This kind of reconstruction is expected to provide suggestions for the future machine tuning. The requirements for the BPMs are also presented in this paper.

The fourth-generation synchrotron light source Siberian Ring Photon Source (SKIF), located in Novosibirsk, Russia, underwent the tuning of its linear accelerator segment successfully. By deploying a designed beam diagnostic system, crucial parameters of the beam including beam transverse and longitudinal dimensions, energy spread, emittance, and current, were accurately measured. To achieve these measurements, the system was equipped with several fluorescent screens, Cherenkov radiation detectors, a dipole energy spectrometer, and a Faraday cup. This paper elaborates on the design, mode of operation, and practical applications of these diagnostic devices during the accelerator's tuning process. Further, potential areas of optimization for these diagnostic methods are explored to provide feasible directions for enhancing the performance of the linear accelerator. These precise diagnostic tools have been pivotal in the successful tuning of the SKIF linear accelerator. The results thus gathered will form a significant reference point for the development and refinement of similar accelerators in the future.

DAFNE is an electron-positron collider in operation at INFN-LNF since 2001. Bunch-by-bunch feedback systems installed in each of the two rings allow to store high-intensity and stable beams, by counteracting coupled-bunch instabilities. The feedback systems can be also used as a diagnostic tool able to measure beam parameters which are significant for the evaluation of the instabilities. In this paper, we first describe the acquisition system used to collect the beam data provided by the feedback systems. Then we report recent transverse tune shift and grow-damp measurements with positron beams, performed using the feedback as a diagnostic tool. These measurements helped to characterize the electron-cloud beam instability, which is one of the main factors currently limiting the DAFNE performance. Finally, we describe the first measurements and feedback system setup designed to automatically record turn-by-turn bunch position displacements when a sudden loss in beam current occurs due to any faults in the collider. This tool can be very useful in identifying the causes of these events and performing beam dynamics studies and code validation.

The demonstration of a 100 mA, 4.6 MeV superconducting radio frequency linear electron accelerator, based on conduction cooling and developed by the Institute of Modern Physics (IMP), aims to validate the feasibility of stable beam commissioning in a liquid helium-free 5-cell-$\beta$opt=0.82 Nb3Sn elliptical cavity, and to offer guidance for subsequent industrial applications. The beam energy characteristics, considered one of the critical parameters, need to be precisely measured. Given the high beam energy and the need for a compact, straightforward accelerator layout, we achieved high-precision measurements using only a ordinary dipole, a slit, and a Faraday Cup (FC). This paper presents the online measurement results of beam energy at different cavity voltage and provides a thorough analysis and optimization of the various errors encountered during measurement.

Dipole magnet vacuum chambers are among the critical and costly components of rapid-cycling accelerator facilities. Alternative approaches to traditional ceramic chambers have been explored for the implementation of fast-ramping dipole-magnet vacuum chambers, including thin-wall metallic beam pipe chambers strengthened with transverse ribs. Here, we report a novel 3D-printed titanium alloy cage inside the thin-wall vacuum chamber, which is designed for HIAF project to reduce manufacturing difficulty and cost, shorten the production cycle, and improve the quality. Because the beam impedance aspects are highly important for beam stability, comprehensive studies were undertaken to characterize the impedance of the 3D-printed titanium alloy cage inside thin-wall vacuum chamber. The beam-coupling impedance of the new thin-wall vacuum chamber were studied numerically. Strategies for further reducing the beam-coupling impedance were explored. In addition, impedance bench measurements using the “half wavelength” resonant method were conducted to identify the longitudinal and transverse impedance of this thin-wall vacuum chamber prototype experimentally. The simulated and measured results for the impedance were consistent. Furthermore, a campaign for resonance-check measurements on this thin-wall vacuum chamber prototype was launched. This novel thin-wall vacuum chamber structure has been ready for installation in the Booster Ring (BRing).

The Energy Recovery Linac (ERL) serves as a primary means to simultaneously achieve high energy utilization efficiency, high average beam current, and high-brightness electron beams. The Chinese Academy of Engineering Physics’ Infrared Terahertz Free-Electron Laser (CAEP IR-THz FEL) aims to produce FEL light within the 0.1-125 THz spectrum with updated beam energy and undulators. Another goal of the project is to build Chinese first ERL experimental research platform. The original CAEP THz FEL accelerator will be the injector of the ERL. This paper focuses on the generation and measurement of high repetition rate, low emittance electron beams of the injector, combining numerical simulation optimization with experimental measurements. The beam dynamics of the injector is optimized with ASTRA. The fully beam parameters, including beam transverse emittance, bunch charge, beam energy and energy spread and bunch length are measured and analyzed in detail, which will be used for further ERL beam dynamics design.

H- ion source produces mixed beam of H- and electrons. Usually, a bending magnet is needed to measure the contents of mixed beam. However, bending magnet is generally lacked in H- machine, because bending magnet increases the transport line length, leading to more serve decline of H-. How to measure the H- content in mixed beam without the help of bending magnet is worthy to be studied. In this paper we describe a method to measure the H- content utilizing common devices in low energy beam transport line. This method is mainly based on a solenoid. the H- and electron contents can be obtained by analyzing the change of the beam transmission when sweeping the solenoid current. The experiments were performed.

The final-focus solenoids of the round-beam e+e- collider VEPP-2000 can cause stopbands in the betatron tune plane. This specific stopband domain limits the available tune space in the most important region above the integer tunes. We present a study of the combined effect of coupling resonances caused by the decompensated solenoids and the integer-tune parametric resonances. The results are compared with numerical investigations of this combined effect. Presented experimental data includes scanning of the available betatron tune plane domain and evaluation of coupling RDTs using beam oscillation histories from BPMs.

BEPCⅡ is a double ring e+ e- collider running in the tau-charm energy region. We proposal reusing the beamline of a dismantled wiggler magnet to implement a Compton polarimeter detecting scattered γ photons, to measure the self-polarization of the electron beam at BEPCⅡ. As a testbed for future colliders like the CEPC, this would enable resonant depolarization，and thus provide precision beam energy calibration for BEPCⅡ. In this paper, the preliminary design of this Compton polarimeter is presented, as well as the tentative plan for implementation and commissioning in the coming years are shown.

The method of varying the strength of the corrector magnet installed upstream and minimising the position variation in diagnostics located downstream is widely used for identifying the centre of the magnetic field produced by a quadrupole magnet. However, in the case of a solenoid magnet, unlike a quadrupole magnet, it is not suitable to apply the variable separation method in the x-y direction since both field components are correlated, and the focusing of the magnetic field occurs in the azimuthal direction. In this presentation, we propose an analytical method for finding the centre of a solenoid magnet and present results validated by simulations.

Beam based alignment is a well-known technique for obtaining a small emittance beam which is critical in an injector of an accelerator or a matching section between two accelerators. The simplest beam based alignment can be performed with a corrector, a quadrupole, and a beam position monitor. This work presents a beam based alignment technique with double correctors located before the quadrupole magnet. The merit function was used to find the corrector settings of each beam based alignment. The measurement results showed that minimum corrector strengths could be achieved to have the ideal beam based alignment by using the fitting results of the merit function.