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High-power electron beams have a variety of applications in waste treatment, particularly in the processes that are required to break down municipal solid waste into reusable material. However, the required throughput to be practical at a municipal waste treatment plant can be 100 kW or more. To fulfill these requirements, a new electron source capable of extremely high current and efficiency needs to be developed. An ampere-class source would be capable of driving MW-power-level, compact, and efficient accelerators, such as those needed for waste treatment by electron beam irradiation. Energy of just over 1 MeV is required for throughput andmore » penetration. This kind of accelerator opens up a number of applications, including sterilization of wastewater sludge at throughputs not possible today. In Phase II, the electron source was been built and tested in several stages with both a single-phase and a three-phase transformer (the three-phase transformer is more efficient, with a higher duty cycle). The design is intended to eventually operate in a beam-driven mode to take full advantage of the transformer’s high efficiency. This system will be transformative for the treatment of municipal waste using electron beams.« less

One of the most exciting recent developments in superconducting RF technology has been the discovery of a nitrogen-doping process which can reliably increase the superconducting quality factor of niobium resonators well above 1010 at high frequency (>1 GHz). This process is now well demonstrated in particular for TESLA-style 9-cell cavities at 1.3 GHz, and is being used for cavities for LCLS-II, significantly increasing the cryogenic efficiency of the machine, and allowing significant capital cost reductions. This STTR project will expand the application of nitrogen doping to the low-frequency regime. Niowave is currently developing commercial superconducting electron linacs for a numbermore » of important applications including high-power free-electron lasers, the production of medical and industrial radioisotopes, materials processing, sterilization, and cargo scanning applications. These systems typically operate at 350 MHz, but at 4 Kelvin operating temperature, where reduction of BCS losses would be an important efficiency enhancement. Pushing commercial linacs into a regime where a small cryocooler could provide for the cryogenic load of the accelerating cavity would have a huge impact. Phase I of this STTR project has focused on the requirements to adapt Niowave’s commercial superconducting cavity designs to be compatible with the nitrogen-doping process developed at Fermilab. An existing niobium resonator was delivered to Fermilab for examination by the team currently performing nitrogen doping of 9-cell structures for LCLS-II. Commercial superconducting cavities use several types of materials that are not compatible with the Fermilab vacuum furnace. During Phase I, the vacuum flanges for a Niowave 350 MHz resonator were redesigned and a power coupler antenna and pickup antenna were designed that will allow the cavity to enter the vacuum furnace at Fermilab and also to be tested at cryogenic temperatures. In Phase II, Niowave and Fermilab will collaborate to bring high-quality-factor nitrogen-doped cavities to commercial systems. Two new resonators will be manufactured using the niobium-titanium flanges designed in Phase I and room-temperature RF measurements performed at Niowave. These cavities will then be delivered to Fermilab for nitrogen doping and cryogenic testing. Once high cavity quality factors have been demonstrated, one of the cavities will return to Niowave and be integrated into a high-power electron accelerator, while the other will remain at Fermilab for reprocessing and retesting.« less

This report summarizes the work completed in the development of higher order mode (HOM) couplers for the LHC superconducting crabbing cavities. Niowave worked with our partners at Old Dominion University (ODU) to take the RF dipole (RFD) copper prototype HOM coupler built in Phase I into a niobium design which was fabricated, including electron-beam welding. Niowave also designed and built a modified straight coupler for the Double Quarter Wave (DQW) cavity. Three copper prototype DQW couplers were built, and shared with Brookhaven National Laboratory and with Jefferson National Laboratory for testing. Brookhaven was able to do HOM damping measurements similarmore » to what has been done with RFD structures, and JLab has used the copper couplers to measure the induced frequency shift due to the coupler installation into the welded DQW cavities. In addition, we have developed, with the help of Old Dominion University, a cryogenic test structure for cooling the RFD couplers to liquid helium temperature and putting RF fields onto them. This cryogenic structure was built, and used to test the RFD HOM couplers with RF fields at 4 K with liquid helium. Also, an RF vacuum window was designed, built and tested, which is needed to handle the kW of power expected on the HOMs when in use at CERN. The following pages detail the parts that were fabricated and tested during this reporting period.« less

High-bunch-charge photoemission electron-sources operating in a continuous wave (CW) mode are required for many advanced applications of particle accelerators, such as electron coolers for hadron beams, electron-ion colliders, and free-electron lasers (FELs). Superconducting RF (SRF) has several advantages over other electron-gun technologies in CW mode as it offers higher acceleration rate and potentially can generate higher bunch charges and average beam currents. A 112 MHz SRF electron photoinjector (gun) was developed at Brookhaven National Laboratory (BNL) to produce high-brightness and high-bunch-charge bunches for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment. Lastly, the gun utilizes a quarter-wave resonator (QWR) geometrymore » for assuring beam dynamics, and uses high quantum efficiency (QE) multi-alkali photocathodes for generating electrons.« less

We present results from cryogenic tests of the multi-cell superconducting radio frequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving high average beam currents is particularly desirable for future light sources and particle colliders based on SRF energy-recovery-linacs (ERLs). Beam current in ERLs is limited by the beam break-up instability, caused by parasitic higher order modes (HOMs) interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The multi-cell cavity was designedmore » and fabricated of niobium. Two cryogenic (vertical) tests were conducted. The high unloaded Q-factor was demonstrated at a temperature of 4.2 K at accelerating gradients up to 3 MV/m. The measured value of the unloaded Q-factor was 1.55 × 10⁸, in agreement with prediction.« less