A superconducting radio frequency (SRF) cryomodule (CM) for the International Linear Collider (ILC) Technology Network (ITN) is being developed at KEK. In the scope of this, a waveguide system is being designed. Its main features are a low center of gravity, a reduced number of corners and waveguide elements, and a compact bellow for connecting it to the input power coupler. Furthermore, the waveguide layout was designed to stay within the CM. This will avoid interference between components in the case of a multi-CM assembly. It is planned to adapt both the waveguide system and the installation process for the ITN. Analytical calculations and simulations have shown that most of the reflected power is dissipated in the load of the variable hybrid on removing the circulator. Thus, in the initial layout of the waveguide, the circulator is strategically installed to allow a future replacement with an H-corner integrated with a directional coupler, without disrupting the other waveguide components. Furthermore, a low-power test on a similar waveguide system showed that analytical calculations and simulation matched the measured values well.

The Advanced Photon Source at Argonne National Laboratory (ANL) is in the process of acquiring solid state amplifiers (SSA) from R&K Limited to replace four 1MW klystron rf systems that provide rf power to the storage ring cavities. This project is necessary primarily due to klystron obsolescence. Based on present needs for the APS Upgrade, twelve 160kW SS rf amplifier systems will be required to replace the legacy klystrons. Each of the 352-MHz SSA systems consist of a rack-mounted control unit, two 85kW amplifier cabinets, four 48-way coaxial combiners, and a single 4-way waveguide final combiner. The system is designed with particular attention to reliability and redundancy to help ensure high reliability metrics for the APS-U rf system.

The upcoming High-Luminosity Large Hadron Collider (HL-LHC) program requires a beam performance in the CERN Proton Synchrotron (PS) that is at the limits of the current RF systems. Following the discontinuation of the RF tube production of the driver amplifiers a new solid-state design has been developed using radiation-hard amplifier technology. In view that the current system architecture has reached its maximum achievable gain, the goal was to reduce the cavity impedance encountered by high-intensity circulating beams. This reduction is achieved by increasing the fast feedback gain around the 10 MHz cavities. A 400W modular driver amplifier based on GaN technology and its control system have been prototyped and are currently in the testing phase. The FETs have been qualified for radiation in J-PARC and they will undergo additional irradiation time in the PS tunnel at CERN to additionally qualify the amplifier in its entirety. The paper outlines the modeling phase, the challenges encountered during prototyping, and the achieved results.

Industrial accelerator applications require efficient, scalable, continuous wave (CW) microwave power systems. Magnetrons are inexpensive and efficient devices for converting electrical energy into microwave power; however, their power output is limited to approximately 100 kW. Cost effective power combining magnetron systems would serve the accelerator industry by providing practical and affordable RF power to accelerator applications. In a magic tee configuration, two oscillators can be power combined and locked to a common frequency. Researchers at General Atomics, in collaboration with Thomas Jefferson National Accelerator Facility, have constructed an experiment to demonstrate the power combining of magnetrons in a such a configuration. An analytic model is presented describing the power combining efficiency of a 4-port magic tee, accounting for two magnetron output signals, an injection signal, and a reactive load. The Adler-Chen model is solved numerically using robust computational geometry techniques*. These complete solutions provide insight to the phenomena of magnetron frequency locking and optimal combining efficiency, which are compared to experiment.

The Mainz Energy recovering Superconducting Accelerator MESA is a multi-turn energy recovery linac with beam energies in the 100 MeV regime currently under construction at Institut für Kernphysik (KPH) of Johannes Gutenberg-Universität Mainz. The main accelerator consists of two superconducting Rossendorf type modules, while the injector MAMBO (MilliAMpere BOoster) relies on normal conducting technology. The high power RF system is relying completely an solid state technology. After some in-depth testing of a 15 kW prototype amplifier in 2017-2019 a modified version of the amplifier modules was developed. In 2020 series production has begun at JEMA France and first amplifiers, a 74 kW, a 56 kW and two 15 kW have been delivered to KPH lately. In this paper we will present the results of the performance measurements of the amplifiers.

Los Alamos Neutron Science Center (LANSCE) relies on 44 klystron modulator systems to feed the accelerating cavities and produce proton beam of 800 MeV. This paper focuses on the new VA-862A1 86kV 1.25 MW klystron units and aims to compare their performance with previously purchased units. Service hours for each klystron unit was used as the primary metric in the analysis and records from various sources cross-corroborated to confirm recorded information. Factors such as prior repair/rebuilds, factory acceptance tests and runtime notes were carefully inspected to provide a comprehensive view of the klystron performance during analysis. Klystron units currently being used in the LINAC were surveyed along with failed units and analysis performed to predict the next failure. The frequency and cause of failure was also compared with historical performance and failure data and results utilized for LANSCE SCCL performance optimization.

To meet phase stability requirements, a high peak power coaxial magnetron-based RF system with >70% efficiency would normally be injection locked to an RF source by using a circulator to send the locking signal into the magnetron through the antenna. This added requirement of a high-power circulator pushes the inherently low coaxial magnetron’s cost-per-watt to a high overall RF Power Source system cost-per- watt. For this project, the injected phase locking signal for the magnetron will use a novel input port that does not require a high- power circulator. The new input port uses the cathode stalk assembly to turn the filament-cathode into an antenna that couples to the resonant circuit of the magnetron. The coupling system between the cathode stalk, which runs at high voltage, and the RF input includes isolation for high voltage.

The National Synchrotron Radiation Research Center (NSRRC) has developed a 300 kW solid-state amplifier. This 300 kW solid-state amplifier RF transmitter has been operating continuously since August 2023, consistently delivering an output of 250 kW RF power during user beam time at 500 mA. This report describes the performance of the solid-state amplifier RF transmitter during this period, module failure rates, and specific instances of malfunction.

Efficient calculation of multi-dimensional derivatives of various performance metrics of RF sources with respect to different design parameters is a critical element of their optimization and sensitivity analysis. The direct approach is to change slightly the value of a design parameter of interest and compute the resulting change in the metric of interest; an example is a calculation of how a small change in klystron cavity spacing affect output power. The major problem with this approach is a number of required runs of a simulation code. For example, when there are many (N) design parameters of interest then (N+1) runs are required. N can be very large for detailed design of RF sources for accelerators [*, **]. By computing the solution of the adjoint of the perturbed equations for the beam-wave interaction, we have shown [***] that all N partial derivatives may be computed with only three runs of the simulation code, no matter how large (N) is. Once calculated, these partial derivatives may be used to specify manufacturing tolerances and/or used in a design optimization calculation. We will also present examples of applications of adjoint approach to klystron and TWT design.

Klystrons and Multiple-Beam Klystrons (MBKs) are widely used or proposed to be used in accelerators as high-power RF sources. Development and optimization of klystron and MBK’s designs is aided by the use of different simulation tools, including highly efficient large-signal codes. We present an overview of capabilities of the TESLA-family of 2.5D large-signal codes, which have been developed at the Naval Research Laboratory (NRL) and which are suitable for the accurate modeling of single-beam and multiple beam klystrons. TESLA algorithm does support proper treatment of ‘slow’ and ‘reflected’ particles, what enables accurate modeling of high-efficiency klystrons. Recently developed more general TESLA-Z algorithm is based on the impedance matrix approach and enabled accurate, geometry-driven large-signal modeling of devices with such challenging elements as multiple-gap cavities, filter-loading, couplers and windows. Finally, recent introduction of the reduced-order, 1.5D versions of the TESLA algorithms enabled much faster, but limited modeling options. Examples of applications of TESLA-family of codes to the modeling of advanced single-beam and MBKs will be presented.

We present new capabilities in the Neptune electromagnetic particle-in-cell (EM-PIC) simulation code and design environment created to support geometry-based design of high power RF sources. Neptune’s time-domain EM-PIC model to simulate high-voltage, high-current electron beam/RF interactions is a key component of the first-principles design codes created by NRL and Leidos, which provide a comprehensive, geometry-based approach to RF source design*. Neptune allows importing multi-part device geometry created by conventional CAD tools, which can simplify the design process for complex 3D devices. Imported CAD parts can be manipulated, modified and combined with other geometric elements as needed using a constructive solid geometry (CSG) model to create the device geometry to be used for simulation. New features of the EM-PIC model include an improved waveguide port model, with time-resolved waveguide mode diagnostics, and support for customized electron beam models. We will summarize the new capabilities and present examples of applications to high power RF sources.

Recent efforts at SLAC aim at developing high-power accelerators powered by compact, high-efficiency RF sources such as klystrons and Inductive output tubes (IOT). Stellant Systems (formerly L3Harris Electron Devices) has long pioneered the IOT design and recently leveraged its power toward various accelerator applications. In this talk, we show the progress of developing a 1.3 GHz HEIOT in terms of design, and manufacturing. We also show results of 3D space-charge beam dynamics simulation of an L-Band inductive output tube (IOT) RF electron gun using the accelerator code ACE3P as a transformative approach to HEIOT design. Based on the beam optics simulation we have designed an efficient output structure that results in >100 kW of average power with an upward of 80% power efficiency. We have designed the amplifier with special attention to cooling requirement at 100 kW including extensive thermal analysis of the anode, output structure and windows. We also commissioned a solid state driver for testing purposes. In this presentation we will discuss the progress of the amplifier build and the testing plans.

A superconducting radio frequency (SRF) cryomodule (CM) for the International Linear Collider (ILC) Technology Network (ITN) is being developed at KEK. In the scope of this, a waveguide system is being designed. Its main features are a low center of gravity, a reduced number of corners and waveguide elements, and a compact bellow for connecting it to the input power coupler. Furthermore, the waveguide layout was designed to stay within the CM. This will avoid interference between components in the case of a multi-CM assembly. It is planned to adapt both the waveguide system and the installation process for the ITN. Analytical calculations and simulations have shown that most of the reflected power is dissipated in the load of the variable hybrid on removing the circulator. Thus, in the initial layout of the waveguide, the circulator is strategically installed to allow a future replacement with an H-corner integrated with a directional coupler, without disrupting the other waveguide components. Furthermore, a low-power test on a similar waveguide system showed that analytical calculations and simulation matched the measured values well.

For achieving sufficient RF power from a solid state amplifier for accelerate particles applications usually many transistor stages need to be combined. Power levels of more than one kilowatt (kW) per transistor are state of the art for a variety of frequencies. Depending on the required total output power for multi ten kW systems a combining structure is needed. The approach of a sequential multi stage combining bears some advantages. As reflected power also plays a crucial role for the amplifies when used for particle acceleration in a cavity, we investigated the effect of a controlled short within a 6:1 smart combining structure and how it affects the reflected power into the loads in this design. The design we consider is a non-isolating combining with a circulator and load in each single transistor module so that no external customized circulators are needed for this system. Our findings illustrate that strong imbalances can occur, depending on the position of the different modules to each other. We will share experimental and simulation results on findings of a controlled short and the imbalances that can occur.

The magnetron as an efficient RF source for a compact industrial SRF accelerator has been proposed [1]. The performance of injection phase lock on two independent magnetron transmitters operated at 915 MHz, in CW mode with maximum power of 75 kW each has been demonstrated to satisfy for this application [2]. This industrial type magnetron has transformer and SCR rectifier on the DC anode power supply. Output power spectrum with phase locking can achieve noise reduction of -21 dBc at the 1st 60 Hz, -29 dBc at 1st 120 Hz with only -22.6 dBc injection power. Solenoid current increase of 16% can increase the magnetron relative natural frequency by 4e-4. Further solenoid current modulation with feedback control and the 2x75 kW power combining scheme with the WR975 magic-tee are to be further studied. We intend to use one 75 kW power station with InnoSys' switching DC power supplies to drive normal conducting and superconducting RF cavities for an industrial compact linac. We are also going to report on the 4x1.2 kW power combining experiment on the 2450 MHz magnetron system carried out at GA, including the control algorithm with modified magnetron heads with trim-coils and characterized at JLab.