Calabazas Creek Research, Inc. is developing a $2.865 \mathrm{GHz}, 200 \mathrm{~kW}$ CW multiple-beam klystron for accelerator applications. The design includes six beamlets with eight coaxial cavities. The calculated interaction efficiency is 80%. The design has been completed and is reported here.

Calabazas Creek Research, Inc. (CCR) is developing high-efficiency RF sources using advanced design techniques. The company is currently constructing a multiple beam klystron designed to operate at an efficiency approaching or exceeding 80% and producing 200 kW at 2.856 GHz. If successful, the klystron would be used to drive accelerators for sterilization, waste and water treatment, pest control, and other societal applications. These accelerators operate 24 hours a day, seven days a week, and efficiency is of primary importance.

As research accelerates to develop fusion power plants, the demand for gyrotrons for heating fusion plasmas is dramatically increasing. Publicly funded research facilities, including ITER, DTT, DEMO, STEP, and CFERT will need hundreds of gyrotrons by the early 2040s. Privately funded organizations are forecasting requirements for almost 200 gyrotrons by 2035. Given that the global production capacity is approximately ten gyrotrons per year, this presents a significant supply chain issue for fusion power development. Consequently, the Fusion Industry Association has indicated gyrotron availability is a major issue for the fusion industry [1].

Several accelerator projects are under construction or planned that require RF sources in the UHF frequency range. Unfortunately, there are few high-power RF sources available. Klystrons and solid-state sources are large, expensive, and inefficient in this frequency range. Gridded tubes are compact, low cost, and highly efficient; however, single beam devices are limited in output power. This presentation describes research in progress to develop multiple beam, gridded tubes providing higher power1.

Improved gyrotrons will be required for future fusion power plants. These gyrotrons must operate at efficiencies significantly higher than current gyrotrons, and the output must be in HE11 waveguide, rather than a Gaussian beam. This research is developing a gyrotron with an efficiency approaching or exceeding 70% with the output in corrugated waveguide. Machine Learning models are being developed to control the multiple power supplies for a plasma heating system.

A 200 kW CW, 2856 MHz multibeam klystron for accelerators is being developed based on CSM, an advanced method for achieving very high efficiencies. The design incorporates both second and third harmonic cavities while keeping the RF circuit length short.

Calabazas Creek Research, Inc. (CCR) and its collaborators are developing high efficiency RF sources operating from a few hundred MHz to C-Band and power levels from tens to hundreds of kilowatts with the goal of providing MW-relevant sources. The efficiencies approach or exceed 80% with projected costs as low as $0.50/ Watt. Sources under development include magnetrons with phase and amplitude control, single and multi-beam klystrons, multi-beam power grid tubes, and multiple beam IOTs. A magnetron system achieved more than 80% efficiency with fast amplitude control using modulation of the phase locking signal. This would be a low cost, high efficiency RF source for superconducting accelerators. An L-Band, single beam klystron was built with simulated efficiency of 80%. The klystron has yet to be tested to confirm the simulation results. CCR is currently developing a multi-beam klystron to produce more than 200 kW CW at 80% efficiency. Also in development is a multiple beam triode to produce 200 kW CW from 300 MHz to approximately 1 GHz. Not only does the simulated efficiency exceed 75%, but it would be the lowest cost RF source in this frequency range. Finally, CCR recently concluded research for a multiple beam IOT at 700 MHz using third harmonic drive to boost efficiency toward 85%. Successful development and transition to production of these sources will significantly alter the cost/performance landscape for RF power generation.

We discuss the design and whole-cavity simulation of a multibeam inductive output tube (MBIOT) that uses a third harmonic component to the drive voltage on the grid. High-efficiency IOTs are characterized by efficiencies of 70%–75%. However, efficiencies greater than 80% would substantially reduce the operating costs of next-generation accelerators. To achieve this, we consider the addition of a third harmonic component to the drive signal on the grid. We consider an eight-beam MBIOT with a 700 MHz resonant cavity using a voltage of 35 kV and an average current of 7.25 A yielding a perveance of about 1.1 $\mu $ P. We simulate this using the NEMESIS simulation code which has been extended using a 3-D Poisson solver based on the Petsc package from Argonne National Laboratory. The effect of the third harmonic is greatest when the third harmonic phase is shifted by $\pi $ radians with respect to the fundamental drive and with third harmonic powers greater than about 50% that of the fundamental. We show that efficiencies approaching 82% are possible. Designs for the MBIOT input coupler, grids, and output cavity have been developed based on these simulations and will be discussed.

Calabazas Creek Research, Inc. is developing a 5.8 GHz, 200 kW CW, multi-beam klystron (MBK) targeting an interaction efficiency of 80% or higher using recent klystron RF circuit design methods. While the “core oscillation method” (COM), the “bunch align collect”, and the “core stabilization methods” were investigated using the KlyC code, the COM design achieved the best performance. A hollow-beam approach resulted in an 84.1% simulated efficiency. When simulated in TESLA, the same RF design with adjusted external Q achieved 82.5% efficiency. For operation below 50 kV beam voltage and reasonable power density, a 6-beam MBK approach was chosen using coaxial cavities. Results from the RF cavity design (HFSS) and the beam optics design (BOA) will be presented.

Calabazas Creek Research, Inc. continues to maintain and upgrade our 3D, charged particle code, Beam Optics Analyzer. We will present several simulation results for actual devices, including heating of a target by backscattered electrons, long pulse particle transport in an electron gun, and a high efficiency multiple beam klystron,

A high efficiency, Multiple Beam Inductive Output Tube (MBIOT) with an efficiency greater than 80% would substantially reduce the operating costs of next-generation particle accelerators. We discuss the development of an MBIOT that employs a 3rd harmonic drive component on the grid to achieve efficiencies greater than 80%. We discuss a novel input coupler, grid design, and whole-cavity simulation of the output cavity using the NEMESIS code. This presents a path forward to the design and production of such high efficiency MBIOTs.

Improved gyrotrons will be required for future fusion power plants. These gyrotrons must operate at efficiencies significantly higher than current gyrotrons, and the output must be in HE 11 waveguide, rather than a Gaussian beam. This research is developing a gyrotron with an efficiency approaching or exceeding 70% with the output in corrugated waveguide.

Accelerators for High Energy Physics (HEP) are large users of energy, much of it in the form of radiofrequency (RF) power to accelerate particles to very high energies. Proposed HEP projects will require even larger amounts of RF energy. Increasing concerns of the cost and availability of energy will require the HEP community to use energy as efficeintly as possible. Successful transfer of HEP technology to the public and private sectors will be most effective if it is highly efficient.Historically, the HEP community has utilized available RF power sources, mainly in the form of vacuum tube technology, much of which was developed during the cold war or is otherwized used in the private sector. The private sector is moving to solid-state RF sources which do not exibit the electrical efficiency that is needed for future HEP projects.Here, we summarize the state of the development of a number of RF sources that promise efficeincies of 80% and above. We also outline future efforts that are needed to fully realize the potential of these sources.

Calabazas Creek Research, Inc. is developing several high efficiency RF sources ranging in frequency from 300 MHz to 2.45 GHz and higher at power levels ranging from a few kW to more than 200 kW CW. Applications range from driving high energy accelerators and colliders to high data rate communications. All devices are designed to provide efficiencies exceeding 80%. These devices include (1) a phase and amplitude controlled magnetron producing 100 kW at 1.3 GHz using phase modulation of a locking RF signal, (2) a multiple beam triode-based RF sources to produce 200 kW from 300-500 MHz, (3) a high efficiency klystron to produce 100 kW CW at 1.3 GHz, (4) a multiple beam inductive output tube to produce 200 kW at 700 MHz, and (5) a magnetron with frequency and phase control provided by varactor diodes to produce 5 kW CW at 2.45 GHz capable of 2Mb/second data transmission rate. The amplitude-controlled magnetron has been completed and tested, and the high efficiency klystron and triode-based source are being assembled with testing schedule for spring 2022. Drawings are in progress for the multiple beam IOT, and the design of the varactor-controlled magnetron is in progress. These devices will be described and available test results presented.

Calabazas Creek Research, Inc. (CCR) is collaborating with a number of institutions to develop new RF sources for accelerators and colliders. An overriding focus is on reducing acquisition cost as well as the continuing cost by increasing efficiency. Consequently, the goal of these programs is efficiencies exceeding 80% at power levels above 100 kW CW. Two research efforts involve modifying or controlling magnetrons to allow fast control of the frequency, amplitude and phase for beam loading compensation. Two techniques are described. Research is also investigating two multiple beam sources that achieve high efficiency through Class C operation. A 350 MHz RF source, nearing completion, uses power grid tubes, and a 700 GHz source will use an inductive output tube. An L-Band klystron is also nearing completion and is designed to produce 100 kW at 80% efficiency. These programs will be briefly described.

Calabazas Creek Research, Inc., in collaboration with the SLAC National Accelerator Laboratory, is developing a high efficiency, 1.3 GHz, 100 kW klystron for driving accelerators. The goal for the efficiency is at least 85%. Designs for the RF circuit, electron gun and collector are presented.

The need for enhanced performance of high-power RF vacuum electron devices has led to the investigation of multiple-beam, sheet beam, and annular beam configurations. A key issue with such devices is the magnetic field shaping required producing high-power, laminar beams. Field shaping is difficult when Pierce-type gun geometries are employed. The development of high current density cathodes makes the necessary beam power achievable without compression. Such cathodes can operate within a uniform magnetic field yielding advantages for both single and distributed-beam RF devices. However, the quality of the resulting beams presents problems. A project to optimize beam quality in zero-convergence electron guns was undertaken by Calabazas Creek Research, Inc. (CCR) and North Carolina State University (NCSU). The surprising result was that high-quality electron beams can be generated in uniform magnetic fields using convex (dome)-shaped cathodes. The underlying physics involves perturbation of the beam cyclotron motion by a nonadiabatic radial electric field impulse. This article examines this physical mechanism and extends the initial result to additional diode and beam geometries.

Calabazas Creek Research, Inc., Fermilab, and Communications & Power Industries, LLC, developed a 100 kW peak, 10 kW average, 1.3 GHz, magnetron-based, RF system for driving accelerators. Efficiency varied between 81% and 87%. Phase locking uses a novel approach that provides fast amplitude and phase control when coupled into a superconducting accelerator cavity [1]. The system was successfully tested at Fermilab and produced 100 kW in 1.5 ms pulses at a repetition rate of 2 pps. A locking bandwidth of 0.9 MHz was achieved with a drive signal of 269 W injected through a 4 port circulator. The phase locking signal was 25 dB below the magnetron output power. The spectrum of the phase locked magnetron was suitable for driving accelerator cavities. Phase modulation was demonstrated to 50 kHz (the limit of the available driver source). The average power was limited by available conditioning time. Scaling indicates 42 kW of average power should be achievable. Estimated cost is less than $1/Watt of delivered RF power, exclusive of power supplies or modulators. System design and performance measurements will be presented.

Calabazas Creek Research, in collaboration with Communications & Power Industries and JP Accelerator Works, is developing low cost, high efficiency RF sources using multiple beam triodes. Triodes are very low cost and operate at efficiencies approaching 90%. Single beam triodes generate beam power to approximately 40 kW, which is insufficient for many accelerator and industrial applications. This program is incorporating eight triode grid-cathode assemblies into a single package to provide up to 250 kW of beam power.