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For PIP-II project Fermilab is developing 650 MHz couplers to deliver up to 50 kW CW RF power to the superconducting low-beta (LB650) and high-beta (HB650) cavities. To meet project requirements two different designs of the couplers were proposed, one is conventional design with copper plated stainless steel walls. In second design (EM-shielded) a copper screen is used to shield stainless steel wall from electromagnetic field. For prototyping we built two couplers of each type and tested them at 50kW with full reflection at different reflection phases. In each test the assembly of two couplers were processed with DC bias up to +5 kV, starting with short pulses and ramping power up to 100 kW. Final run for 2 hours in CW mode at 50 kW to reach equilibrium temperature regime and qualify couplers. One pair of couplers was also processed without DC bias. Finally, all four couplers demonstrated full requirements and were qualified. Based on test results the conventional coupler with some modification was chosen as a baseline design. Modified version of coupler is now ordered for prototype of HB650 cryomodule. In paper we will discuss details of coupler processing and results, Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Design of the high beta 650 MHz prototype cryomodule for PIP-II is currently undergoing at Fermilab. The cryomodule includes six 5-cell elliptical SRF cavities with accelerating voltage up to 20 MV and low heat dissipation (Q₀ > 3.3 · 10^{z}EhNZeHn). Characterization of performance of fully integrated jacketed cavities with high power coupler and tuner is crucial for the project. Such a characterization of jacketed cavity requires a horizontal test cryostat. The Fermilab Spoke Test Cryostat (STC) has been upgraded to accommodate testing of 650 MHz cavities. Commissioning of upgraded STC has been reported at SRF’19 conference. In this paper we present results of testing of the prototype HB650 cavity in upgraded STC facility. We characterize cavity performance and qualify it for the prototype HB650 cryomodule assembly., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The Proton Improvement Plan - II (PIP-II) project is underway at Fermilab with an international collaboration involving CEA in the development and testing of 650 MHz cryomodules. One of the first main contributions of the CEA was the participation in the design efforts for the current 50 KW CW 650 MHz power couplers. This paper reports some of the results of thermal and paramet-ric studies carried out by the CEA on these power couplers, Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The design of a thermionic electron source connected directly to a superconducting cavity, the key part of an SRF gun, is described. The results of beam dynamics optimization are presented which allow lack of beam current intercepting in the superconducting cavity. The electron source concept is presented including the cathode-grid assembly, thermal insulation of the cathode from the cavity, and the gun resonator design. The cavity thermal load caused by the gun is analyzed including the static heat load, black body radiation, backward electron heating, etc., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

High-current low-emittance CW electron beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and gamma-rays (in Compton sources). Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality. We report on the upgrade of the unique and fully functional CW SRF 1.25 MeV SRF gun, built as part of the Coherent electron Cooling (CeC) project, which has demonstrated sustained CW operation with CsK2Sb photocathodes generating electron bunches with record-low transverse emittances and record-high bunch charge exceeding 10 nC. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step with the goal to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum (UHV) environment of the SRF gun, which has never been successfully demonstrated in RF accelerators., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Low-beta and high-beta sections of PIP-II linac will use nine low-beta cryomodules with four cavities each and four high-beta cryomodules with six cavities each. These cavities will be produced and qualified in collaboration between Fermilab and the international partner labs. Prior to their installation into prototype cryomodules, several dressed cavities, which include jacketed cavities, high power couplers, and tuners, will be qualified in STC horizontal test bed at Fermilab. After qualification of bare β = 0.9 cavities at Fermilab, several pre-production β = 0.92 and β = 0.61 cavities have been and are being fabricated and qualified. Procurements have also been started for high power couplers and tuners. In this contribution we present the current status of prototype dressed cavity qualification for PIP-II., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A prototype cryomodule containing eight Single Spoke Resonators type-1 (SSR1) operating at 325 MHz and four superconducting focusing lenses has been successfully assembled and cold tested in the framework of PIP-II project at Fermilab. The performance of cavities and focusing lenses along with test results of other cryomodule’s key parameters are presented in this contribution., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A prototype FerroElectric Fast Reactive Tuner (FE-FRT) for superconducting cavities has been developed, which allows the frequency to be controlled by application of a potential difference across a ferroelectric residing within the tuner. This technique has now become practically feasible due to the recent development of a new extremely low loss ferroelectric material. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated. This is a significant first step in the development of an entirely new class of tuner. These will allow electronic control of cavity frequencies, by a device operating at room temperature, within timescales that will allow active compensation of microphonics. For many applications this could eliminate the need to use over-coupled fundamental power couplers, thus significantly reducing RF amplifier power., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Proton Improvement Plan – II (PIP-II) project is under go in Fermi National Laboratory. Main part of the project is 800 MeV proton superconducting accelerator which includes 116 superconducting cavities of 5 different types and three 162.5, 325 and 650 MHz frequencies. Key elements of accelerator which determine a reliable operation are main couplers for superconducting cavities. This paper describes the latest progress in design and testing of main couplers for PIP-II projects., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Two couplers for RFQ of PXEI facility were designed and manufactured. Each coupler designed to deliver 50 KW, CW to RFQ at 162.5 MHz. Results of couplers operation are reported., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

Proton Improvement Plan-II at Fermilab is an 800 MeV superconducting pulsed linac which is also capable of running in CW mode. The high energy section operates from 185 MeV to 800 MeV instigated using 650 MHz elliptical cavities. The low-beta (LB) βG =0.61 portion will accelerate protons from 185 MeV-500 MeV, while the high-beta (HB) βG = 0.92 portion of the linac will acceler-ate from 500 to 800 MeV. The development of both LB and HB cavities is taking place under the umbrella of the Indian Institutions Fermilab Collaboration (IIFC). This paper presents the design methodology adopted for both low-beta and high-beta cavities starting from the RF design yielding mechanical dimensions of the cavity cells and, then moving to the workable dressed cavity design. Designs of end groups (main coupler side and field probe side), helium vessel, coupler, and tuner are the same for both cavities everywhere where it is possible. The design, analysis and integration of dressed cavity are presented in detail., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

The PIP-II 800 MeV linac employs 650 MHz elliptical 5-cell CW-capable cavities to accelerate up to 2 mA peak beam current of H⁻ in the energy range 185 - 800 MeV. The low beta (LB) βG = 0.61 portion should accelerate from 185 MeV-500 MeV using 33 LB dressed cavities in 11 cryomodules. The high beta (HB) βG = 0.92 portion of the linac should accelerate from 500 to 800 MeV using 24 HB dressed cavities in 4 cryomodules. The development of both LB and HB cavities is going on under IIFC collaboration. The development of LB cavity initiated at VECC Kolkatta and HB cavity is going at RRCAT, Indore. This paper present design methodology adopted starting from RF design to get mechanical dimensions of the RF cells and then explains dressing of the cavity for both low beta and high beta cavities. Further the tuner design and its integration to the dressed cavity is discussed. Paper also explains the salient design features of these dressed cavities., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

LCLS-II linac is based on SRF technology developed for the XFEL project. The XFEL 3rd harmonic system built by INFN is based on the original designs of cavity and power coupler developed and built by Fermilab for the FLASH facility at DESY. For LCLS-II application both designs of the 3.9 GHz cavity and the power coupler have been modified for an operation in the continuous wave regime up to 2 kW average RF power. In this paper we discuss coupler modifications and the result multiphysics analysis for various operating regimes. For the initial test of a proposed design, we decided to modify two spare warm sections of power couplers, built for the FLASH facility, by shortening both of two inner bellows and making a thicker copper plating. Modification of the existing coupler test stand and the test program are briefly discussed in this paper., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The Project X Injector Experiment (PXIE) at Fermilab will include one cryomodule with eight 325 MHz single spoke superconductive cavities (SSR1). Each cavity requires approximately 2 kW CW RF power for 1 mA beam current operation. A future upgrade will require up to 8 kW RF power per cavity. Fermilab has designed and procured ten production couplers for the SSR1 type cavities. Status of the 325 MHz main coupler development for PXIE SSR1 cryomodule is reported., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The LCLS-II superconducting accelerator supposedly will use 3.9 GHz (3-d harmonic) superconductive cavities. A new possible configuration of 3.9 GHz main coupler is presented in the papar. This configuration contains two coaxial ceramic windows, a cold and a warm one. Inner conductors of windows are connected through the capacitive gap and have no mechanical no thermal contacts. It allows to avoid using bellows and thus avoid the problem of heating and cooling. The windows have shields protecting shields against the electron, and this prevents the window ceramics from charging. Results of computer simulation of the new coupler are posted., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Accelerators developed for Science now are used broadly for industrial, medical, and security applications. Over 30,000 accelerators touch over $500B/yr in products producing a major impact on our economy, health, and well being. Industrial accelerators must be cost effective, simple, versatile, efficient, and robust. Many industrial applications require high average beam power. Exploiting recent advances in Superconducting Radio Frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, a collaboration of Fermilab-CSU-NIU has developed a design for a compact SRF high-average power electron linac. Capable of 5-50 kW average power and continuous wave operation this accelerator will produce electron beam energies up to 10 MeV and small and light enough to mount on mobile platforms, such accelerators will enable new in-situ environmental remediation methods and new applications involving in-situ crosslinking of materials. More importantly, we believe this accelerator will be the first of a new class of simple, turn-key SRF accelerators that will find broad application in industry, medicine, security, and science., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The linear accelerator for the PIP-II program utilizes two types of 325 MHz Single Spoke resonator cavities: SSR-I and SSR-II. Operating power of SSR-II is about 17 kW and requires input couplers which can reliably work at power levels > 20 kW with full reflection at any reflected phase. Currently only one 10 kW RF amp is available for coupler testing. To increase testing power, a special resonance configuration were used. This configuration allows us to raise RF power approximately 3 times. The testing scheme and results are discussed in the paper., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

PXIE is a prototype front end system for the proposed PIP-II accelerator upgrade at Fermilab. An integral component of the front end is a 162.5 MHz, normal conducting, continuous wave (CW), radiofrequency quadrupole (RFQ) cavity. Two identical couplers will deliver approximately 100 kW total CW RF power to the RFQ. Fermilab has designed and procured main couplers for the CW RFQ accelerating cavity. The mechanical design of the coupler, along with production status, is presented below., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

At Fermilab there is a plan for improvements to the Fermilab accelerator complex aimed at providing a beam power capability of at least 1 MW on target. The essential element of the plan (the Proton Improvement Plan II – PIP-II) is a new 800 MeV superconducting linac. The PIP-II linac includes a room temperature front-end and high energy part based on five types of superconducting cavities used to cover the entire velocity range required for beam acceleration. The room temperature front end is composed of an ion source, low energy beam transport line (LEBT), radio frequency quadrupole (RFQ), and a medium energy beam transport line (MEBT). The paper reports RF design of the re-buncher for MEBT along with thermal analysis of the cavity., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A waveguide vacuum valve for WR90 waveguide was designed, fabricated and tested. The valve consists of a modified commercial gate valve sandwitched with smooth tapers. The TE10 traveling wave in WR90 waveguide is "transmoded" into TE¹¹⁺TM11 mode in the taper, going through the gate valve and is tapered back to the normal mode in WR90. The test has been successfully done. The valve stably trasmitted 40MW peak power with 500ns pulse width and this is limited by available RF power source., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The concept design of the 2.5 GeV superconducting CW linac of the Project X is discussed. The linac structure and break points for different cavity families are described. The results of the RF system optimization are presented as well as the lattice design and beam dynamics analysis., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The BST based ferroelectric-oxide compounds have been found as suitable materials for a fast electrically-controlled RF switches and phase shifters that are under development for accelerator applications in X, Ka and L - frequency bands. The BST(M) material (BST ferroelectric with Mg-based additives) allows fast switching and tuning in vacuum and in air both; switching time of material samples 10 ns has been demonstrated*. One of the problems related to accelerator application of BST ferroelectric is its high dielectric constant. Decreasing the permittivity however is usually strongly correlated with a decrease in the tunability (k(E)=ε(0)/ε(E)) of ferroelectrics. The use of linear dielectric inclusions in BST ceramics could result in significant suppression of the mentioned k(E) dependence, with the best case being that the tunability vs. ε decrease could be unchanged. On the basis of our measurements we report here two unusual phenomena observed**: (i) the increase both the dc and the dynamic tunability with a decrease of the dielectric constant; (ii) the dynamic tunability was observed to exceed the static tunability at specific magnitudes of the applied field., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Six 650 MHz high-power couplers will be integrated into the prototype High Beta 650 MHz (HB650) cryomodule for the PIP-II project at Fermilab. The design of the coupler is described, including design optimizations from the previous generation. This paper then describes the coupler life-cycle, including manufacturing, assembly, testing, conditioning and the lessons learned at each stage., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

A new test stand dedicated to Superconducting Radiofrequency (SRF) cryomodule testing, CMTS1, has been commissioned and is now in operation at Fermilab. The first device to be cooled down and powered in this facility is the prototype 1.3 GHz cryomodule assembled at Fermilab for LCLS-II. We describe the demonstrated capabilities of CMTS1, report on steps taken during commissioning, provide an overview of first test results, and survey future plans., Comment: 4 pp. Proceedings of LINAC2016, East Lansing, MI, USA