A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase coupling between cells, thus high group velocity, while still maintaining a high shunt impedance. This is crucial for achieving high efficiency high gradient acceleration in the short rf pulse acceleration regime. Research of these structures has produced traveling wave structures that are powered by very short (~9 ns), very high power (400 MW) RF pulses using two beam acceleration to produce these pulses. In testing, these structures have withstood more than 320 MW of power and produced accelerating gradients of over 100 MV/m. The next step of testing these structures will use a more conventional, klystron power source. A new standing wave DDA structure is being fabricated for testing on the Nextef2 test stand at KEK. Simulation results of this structure show that at 50 MW of input power, the DDA produces a 457 MV/m gradient. It also has a large shunt impedance of 160 MΩ/m and an r/Q of 21.6 kΩ/m. Cold testing of this structure will be conducted July 2024 with high power testing to be done in August.

The ALBA injector consists of a 110 MeV Linac, a Linac-to-Booster Transfer Line and a full energy Booster that further accelerates the electrons up to 3 GeV. The Linac consists of two pre-bunchers, a buncher and two accelerating structures and it is powered by two pulsed 37 MW klystrons at 3 GHz. To overcome an eventual klystron failure the injector has been adapted to keep operative at lower Linac beam energy. In 2014 the injection into the Booster was optimized for a Linac beam of 67 MeV, the energy achieved using only one klystron. However, the procedure of switching the injector from a Linac beam of 110 MeV to a 67 MeV one is not straightforward and it requires to be periodically updated. After a recent waveguide modification the RF power sent to the first accelerating structure is equally distributed between both accelerating structures. As a result, a Linac beam of 80 MeV is achieved using only one klystron. At this energy the injection into the the Booster is more efficient. Then, setting the nominal Linac beam energy at 80 MeV the injector operation is ensured by the hot-spare klystron in case of klystron failure.

The Linac for Diamond Light Source has been running with two 3 GHz klystrons, powering two 5.2m-long accelerating structures to deliver 100 MeV electron beam since the start of operation. By introducing a SLED pulse compressor system to generate a pulse capable to power both structures from one klystron, redundancy and reliability will be improved. With a 5 µs total pulse, it is possible to charge the SLED cavities for 4 µs and generate a high peak pulse for the last 1 µs able to power both structures. An arbitrary waveform generator function was implemented in digital low-level RF to generate a flat top pulse, which can be utilized for both single bunch and multi bunch operation. Details of the waveguide network, low-level RF design and high-power operation will be described. Results from full energy operation will also be shown.

This work describes a C-band RF system for the SAPS (Southern Advanced Photon Source of China) test bench linear accelerator.SAPS' RF testing system comprises of a photocathode electron gun and a 2-metre-long equal gradient acceleration device.The klystron power source delivers energy to the photocathode electron gun and the travelling wave acceleration structure,respectively.Test the photocathode electron gun first,followed by the travelling wave acceleration structure.We investigated a short-pulse C-band spherical pulse compressor.The photocathode electron gun's preliminary high-power testing is now complete.

Los Alamos Neutron Science Center uses a coupled-cavity linac (CCL) to accelerate H- beam from 100 to 800 MeV. This was the first CCL put into operation (1972) and is powered by forty-four 1.25 MW 805 MHz klystrons developed in the same era. A new initiative is underway to develop a replacement RF amplifier that fits in place of one klystron with HV modulator tank, and is functionally equivalent or better in RF performance. Conventional LDMOS transistors based on silicon have reduced power above 500 MHz, and are also limited in peak power by the maximum drain voltage (50-65 volts). Changing wireless infrastructure is causing leading manufacturers to introduce and discontinue products within a decade. Long term operation of LANSCE requires continuity of product availability. We have chosen leading-edge high voltage Gallium Nitride (GaN) on Silicon Carbide transistors to be able to reduce the number of active devices and the complexity of power combing. GaN has inherent higher temperature and voltage capability. We are testing devices for 3.6 kW of saturated power at 100 volts, and improvements are underway. Combining technology is also under study as part of the overall system.

The Los Alamos Neutron Science Center (LANSCE) accelerator is MW-class H-/H+ 800 MeV linear accelerator that serves five distinct user facilities that support Los Alamos National Laboratory (LANL) national security missions, commercial applications, and the Department of Energy’s Office of Science medical isotope production program. Now into it’s sixth decade of continuous operation, major accelerator systems are showing their age with decreased reliability and diminished vendor support due to equipment obsolescence. With plans to continue LANSCE operations for several more decades, LANL is exploring different avenues to modernize large portions of the accelerator. We will present the current status of those plans and an overview of supporting R&D.

Transverse Deflecting Structures (TDS) are commonly used in Free Electron Laser (FEL) facilities for the measurement of longitudinal information of electron beam, including bunch length, temporal distribution, slice emittance, etc. Shenzhen Superconducting Soft-X-ray Free Electron Laser (S3FEL) is a high-repetition-rate FEL recently proposed for scientific research and applications. In S3FEL, TDSs that work at S-band (2997.222 MHz) and X-band (11988.889 MHz) will be utilized for the diagnosis and analysis of longitudinal phase space of electron bunches along the beamline. In this manuscript, we present the preliminary design of both S-band and X-band TDS systems of S3FEL, including system layout, deflecting structures, pulse compressors, RF distribution networks, etc. Additionally, we introduce a new parallel-coupled TDS cavity with variable polarization for multi-dimensional phase space diagnostics.

Several measures were developed and deployed at the pulsed linacs FLASH and European XFEL operated at DESY in order to reduce the energy consumption of the RF systems. A staged implementation of several techniques allowed energy savings up to 25% for both facilities, at the cost of reducing the RF overhead and increasing the complexity of the low-level radio frequency (LLRF) system. However, through tool development and automation, the energy saving linac configuration could be implemented without compromising the RF stability, maximum beam energy, accelerator availability and with minimal impact on the setup time.

A new storage ring based on a multi-bend achromat (MBA) lattice has been built at the Advanced Photon Source. Currently, the commissioning process is underway to bring beamlines back into operation. The APS linac consists of two S-band thermoionic cathode guns at the front end and thirteen S-band traveling-wave RF structures, all powered by five klystrons. A major upgrade is in progress to enhance the RF system in the APS linac. Specifically, the high power undulators and klystrons will be replaced with a newly designed solid-state switching modulator systems. Additionally, the RF control and diagnostic systems are being replaced by brand-new digital LLRF systems. As of now, one RF station has been successfully upgraded, commissioned, and it has been operating for half a year. Notably, the RF stability at this station shows significant improvement compared to other stations.

The delivery of high RF power---from hundreds of kW to MW---by klystrons, is linked with a high overall energy consumption. A research programme led by CERN in collaboration with the industry is being conducted to understand what limits klystron efficiency and how to develop high-efficiency klystrons. As a result of this program, two first prototypes of X-band (11.994 GHz) high-efficiency klystrons have been successfully designed and manufactured in collaboration with Canon Electron Tubes and Devices. The first results look promising, revealing a remarkable ~60% efficiency, and validating the proposed HE klystron technology. A comprehensive characterisation campaign has been conducted at CERN to verify and demonstrate these results. The methodology for the HEK tubes characterisation is based in two independent measurements: a RF power measurement, and a calorimetric methodology ---less subject to calibration inaccuracies. We describe the setups, principle of the calorimetry methodology, and we discuss the feasibility and precision of the results.

The CSNS-II superconducting Linac accelerator includes 20 sets of 324 MHz superconducting spoke cavities and 24 sets of 648 MHz superconducting Ellipsoidal cavities. The beam energy at the end of the superconducting Linac accelerator reaches 300 MeV. The 324 MHz solid-state power source supplies RF power to superconducting Spoke cavity, while the 648 MHz klystron power source supplies RF power to superconducting Ellipsoid cavity. The RF pulse width of the 648 MHz klystron is 1.2 ms, the repetitive frequency is 50 Hz, and the peak power is 800 kW. The 1.5 ms long pulse solid-state modulator provides high voltage pulse for the klystron, and each modulator is equipped with four klystrons.

We designed, built and commissioned a beam diagnostic system based on a short S-band defector and a commercial klystron transmitter. A two feet long transverse-horizontally deflecting S-band rf structure (STCAV2) is installed the LCLS-II post-laser-heater diagnostic beamline at 100 MeV electron beam energy to measure the absolute electron bunch length and to allow time-resolved beam quality measurements such as vertical slide emittance and slice energy spread. The deflector is designed to produce 0.48 MeV peak kick at 300 kW of input power. The klystron transmitter, which uses a commercial solid-state modulator, is installed in the klystron gallery at the grade level. The low-level RF system is based on ATCA and developed in-house. We will report on the overall performance of the project, which was successfully completed, on May 31, 2024.