Dale Schrage - Academia.edu (original) (raw)

Papers by Dale Schrage

Free Electron Lasers 2002, 2003

This project is a coordinated effort among NAVSEA, LANL and AES, to develop a key enabling techno... more This project is a coordinated effort among NAVSEA, LANL and AES, to develop a key enabling technology for high-power FEL called for by the High Energy Laser Joint Technology Office: a high current RF photoinjector capable of producing continuous average current greater than 100 mA. The specific aim is a π-mode, normal-conducting RF photoinjector, 5 nC of bunch charge, 100 mA of current (at 21.88 MHz bunch repetition rate) and emittance less than 10 mm-mrad. This level of performance will enable robust 100-kW-class FEL operation with electron beam energy <100 MeV, thereby reducing the size and cost of the FEL. This design is scalable to the MW power level by increasing the electron bunch repetition rate from 21.88 MHz (the 32nd sub-harmonic of 700 MHz) to a higher value. The major challenges are emittance control and high heat flux within the CW 700 MHz RF cavities. Preliminary results of RF cavity designs and cooling schemes are presented, including both high-velocity water and liquid-nitrogen cooling options. PACS codes: 41.60. Cr, 29.17+w, 29.27. Bd, 41.75. Fr

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

Approved forpublic rt,leaso; distribution is UnlhJitQd.

Proceedings of the 2005 Particle Accelerator Conference

An RF photoinjector capable of producing high average current with low emittance and energy sprea... more An RF photoinjector capable of producing high average current with low emittance and energy spread is a key enabling technology for high power CW FEL. The design of a 2.5-cell, π-mode, 700-MHz normal-conducting RF photoinjector cavity with magnetic emittance compensation is completed. With average gradients of 7, 7, and 5 MV/m in its three accelerating cells, the photoinjector will produce a 2.5-MeV electron beam with 3-nC charge per bunch and transverse rms emittance below 7 mm-mrad. Electromagnetic modeling has been used extensively to optimize ridge-loaded tapered waveguides and RF couplers, and led to a new, improved coupler iris design. The results, combined with a thermal and stress analysis, show that the challenging problem of cavity cooling can be successfully solved. Fabrication of a demo 100-mA (at 35 MHz bunch repetition rate) photoinjector is underway. The design is scalable to higher average currents by increasing the electron bunch repetition rate, and provides a path to a MW-class FEL. This paper presents the cavity design and details of RF coupler modeling.

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

We have manufactured a total of six β=0.64, 700-MHz 5-cell cavities. The APT (Accelerator Product... more We have manufactured a total of six β=0.64, 700-MHz 5-cell cavities. The APT (Accelerator Production of Tritium) specification requires Q 0 > 5 x 10 9 at an accelerating field of 5 MV/m. So far, the results of vertical tests have shown maximum accelerating fields of 12 MV/m (peak surface field of 41 MV/m) and maximum low-field Q 0 of 3.6 x 10 10 at 2 K. The present limitations are available input power, field emission and quench. This type of cavities will also be used for an ADTF (Accelerator-Driven Test Facility) for AAA (Advanced Accelerator Applications) project.

Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)

The design for the superconducting cavities of the highenergy accelerator for the Accelerator Pro... more The design for the superconducting cavities of the highenergy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.

The static and dynamic structural behavior of superconducting cavities for various projects was d... more The static and dynamic structural behavior of superconducting cavities for various projects was determined by finite element structural analysis. The {beta} = 0.61 cavity shape for the Neutron Science Project was studied in detail and found to meet all design requirements if fabricated from five millimeter thick material with a single annular stiffener. This 600 MHz cavity will have a Lorentz coefficient of {minus}1.8 Hz/(Mv/meter){sup 2} and a lowest structural resonance of more than 100 Hz. Cavities at {beta} = 0.48, 0.61, and 0.77 were analyzed for a Neutron Science Project concept which would incorporate 7-cell cavities. The medium and high beta cavities were found to meet all criteria but it was not possible to generate a {beta} = 0.48 cavity with a Lorentz coefficient of less than {minus}3 Hz/(Mv/meter){sup 2}.

High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The low fre... more High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The low frequency specifications required for heavy-ion acceleration typically result in large dimensions of the structure. By appropriate choice of the resonant structure for the Rare Isotope Accelerator (RIA) driver RFQ we have achieved moderate transverse dimensions of the cavity and high quality accelerating-focusing fields required for simultaneous acceleration of multiple-charge-state ion beams. In our application the RFQ must provide stable operation over a wide range of RF power levels to allow acceleration of masses from protons up to uranium. To demonstrate the technology and high-power operation we have built an engineering prototype of one-segment of the 57-MHz RFQ structure. The RFQ is designed as a 100% OFE copper structure and fabricated with a two-step furnace brazing process. The errors in the tip-to-tip distances of the vanes average less than 50 microns. The RF measurements show ...

The translation of the physics designs of linear accelerators into engineering and manufacturing ... more The translation of the physics designs of linear accelerators into engineering and manufacturing requirements is discussed. The stages of conceptual design, prototyping, final design, construction, and installation are described for both superconducting (LANL β = 0.175 Spoke Cavity) and normal-conducting (APT/LEDA 6.7 MeV RFQ) accelerators. An overview of codes that have linked accelerator cavity and thermal/structural analysis modules is provided.

Six 5-cell superconducting elliptical cavities have been fabricated at LANL and in industry and t... more Six 5-cell superconducting elliptical cavities have been fabricated at LANL and in industry and tested at LANL and TJNAF. The APT (Accelerator Production of Tritium) specification requires Qo > 5 x 109 at an accelerating field of 5 MV/m. So far, the results of vertical tests have shown maximum accelerating fields of 12 MV/m (peak surface field of 41 MV/m and 835 Oe ) and maximum Q0 of 3.6 x 1010 at 2 K (2.1 x 1010 at Eacc = 5 MV/m). The present limitations are available input power, field emission and quench. With a new 600 W amplifier and a mapping system for surface temperature and x-ray radiation, we are trying to identify and localize the emission/quench source(s) to further improve the cavity performance.

The use of hydrogen furnace brazing has been applied as a joining technology to the fabrication o... more The use of hydrogen furnace brazing has been applied as a joining technology to the fabrication of a Radio-Frequency-Quadrupole (RFQ) linac for the Los Alamos Accelerator Performance Demonstration Facility (APDF). The design concept provides a monolithic cavity with no longitudinal rf, vacuum, or mechanical joints. A 530 MHz, 0.46 meter long engineering model RFQ has been fabricated and tested at the Los Alamos National Laboratory as a technical demonstration of this concept. It is planned that two funneled RFQ`s for the APDF (7 MeV, 350 MHz, 100 mAmp CW, each eight meters in length) will be manufactured by this method.

Within the framework of the Advanced Accelerator Applications (AAA) project we are 'intereste... more Within the framework of the Advanced Accelerator Applications (AAA) project we are 'interested in building and testing IOW-@ spoke resonators (cavities). To familiarize us with the specifics of these structures Argonne National Laboratory (ANL) kindly loaned us one of their spoke cavities for evaluation. This is a p=0.291 2gap resonator at 340 MHz. We benchmarked our computer codes by comparing room temperature measurements of frequency, tuning sensitivity, tuning forces, etc. with our 3D simulation results. The cavity was tested at both 4 K and 2 K. The results showed maximum accelerating gradients of 12.5 MV/m (4 K) and 12.3 MV/m (2 K), which correspond to a peak electric field of 40 MV/m and a peak magnetic field of 1063 Oe. Q, values at 5 MV/m also exceeded by more than a factor 2 of present AAA specification. These results encouraged us toward development of spoke cavities for the low energy section (6.7 MeV to 109 MeV) of ADTF (Accelerator-Driven Test Facility) of AAA proj...

In this paper, we present the electromagnetic and structural design of a low-b superconducling sp... more In this paper, we present the electromagnetic and structural design of a low-b superconducling spoke resonator for a beam-test in the Low Energy Demonstration Accelerator (LEDA). This test is part of the Advanced Accelerator Applications (AAA) project. Recently, the sole use of superconducting resonators from 6.7 MeV on has been approved for this project. The beam test will use the lowest- resonator from this accelerator design. The choices of the cavity dimensions are driven by its use imrnediately after the LEDA Radio-Frequency Quadrupole (RFQ). The frequency is 350 MHz, the lengt corresponds to a geometric p (Ps) of 0.175. Our design approach has been to carry out an integrated RF and mechanical design from the start. The final cavity is well understood in terms of IW: and mechanical properties. The RF properties, like Q, WQ, peak surface fields and acceleration efficiency are very reasonable for such a low- structure. 'The design also includes power coupler, vacuum and pick-...

arXiv: Accelerator Physics, 2004

A high-current emittance-compensated RF photoinjector is a key enabling technology for a high-pow... more A high-current emittance-compensated RF photoinjector is a key enabling technology for a high-power CW FEL. A preliminary design of a normal-conducting, 2.5-cell pi-mode, 700-MHz CW RF photoinjector that will be built for demonstration purposes, is completed. This photoinjector will be capable of accelerating a 100-mA electron beam (3 nC per bunch at 35 MHz bunch repetition rate) to 2.7 MeV while providing an emittance below 7 mm-mrad at the wiggler. More than 1 MW of RF power will be fed into the photoinjector cavity through two ridge-loaded tapered waveguides. The waveguides are coupled to the cavity by "dog-bone" irises cut in a thick wall. Due to CW operation of the photoinjector, the cooling of the coupler irises is a rather challenging thermal management project. This paper presents results of a detailed electromagnetic modeling of the coupler-cavity system, which has been performed to select the coupler design that minimizes the iris heating due to RF power loss in ...

To date, all high-energy proton linear accelerators have been room temperature (or higher) machin... more To date, all high-energy proton linear accelerators have been room temperature (or higher) machines. To produce a high-energy beam over a reasonable accelerator length (high accelerating gradient), these machines require large amounts of radio-frequency (rf) power to maintain accelerating fields. A substantial amount of this power, up to 50% in some cases, is dissipated as heat in the cavity walls. Using a superconducting accelerator minimizes this wasted power. In addition to the power savings, a superconducting cavity has a large velocity acceptance. This velocity acceptance minimizes the number of cavity designs necessary for a given accelerator. Also, superconducting cavities permit a large bore diameter, which reduces the interaction with the beam halo. These types of cavities have been successfully applied in electron accelerators. At the Los Alamos National Laboratory, a prototype design of proton superconducting cavities has been developed for the Accelerator Production of T...

The upgrade for the ATLAS facility is designed to increase the efficiency and intensity of beams ... more The upgrade for the ATLAS facility is designed to increase the efficiency and intensity of beams for the user facility(1,2). This will be accomplished with a new CW normal conducting RFQ, which will increase both transverse and longitudinal acceptance of the LINAC. This RFQ must operate over a wide range of power levels to accelerate ion species from protons to uranium. The RFQ design is a split coaxial structure and is made of OFE copper. The geometry of the design must be stable during operation. Engineering studies of the design at different RF power levels were conducted to ensure that the geometry requirements were met. Frequency shift analysis was also completed to determine the effects of high power levels. Thermal stress analysis was completed to show that the structure frequency is repeatable.

A key technology issue on the path to high-power FEL operation is the demonstration of reliable, ... more A key technology issue on the path to high-power FEL operation is the demonstration of reliable, high-brightness, high-power injector operation. We describe two ongoing programs to produce 100 mA injectors as drivers for 100 kW free-electron lasers. In one approach, in collaboration with the Thomas Jefferson National Accelerator Facility, we are fabricating a 750 MHz superconducting RF cryomodule that will be integrated with a room-temperature DC photocathode gun and tested at the Laboratory. In the other approach, in collaboration with Los Alamos National Laboratory, a high-current 700 MHz, normal-conducting, RF photoinjector is being designed and will undergo thermal management testing at the Laboratory. We describe the design, the projected performance and the status of both injectors.

Since the last workshop we have tested six b=0.64, 700 MHz, 5-cell elliptical superconducting cav... more Since the last workshop we have tested six b=0.64, 700 MHz, 5-cell elliptical superconducting cavities in collaboration with JLAB in vertical cryostats. All the cavities exceeded the requirements for Accelerator Production of Tritium (APT) (Q0 = 5 x 109 at Eacc = 5 MV/m) with ample margin. The low-field Q0 at 2 K was 2-3 x 1010 and the maximum accelerating field reached 12 MV/m, which corresponds to peak electric and magnetic fields of 41 MV/m and 835 Oe, respectively. Power couplers have also been tested in a test bench up to over 1 MW. Since the APT project has transitioned to Advanced Accelerator Applications (AAA) project, a new type of superconducting accelerating structure called spoke cavity emerged as an excellent candidate for the low energy sections between the RFQ and the elliptical cavities. We tested a b=0.29, 340 MHz, 2-gap spoke cavity on loan from Argonne National Laboratory. The results showed Q0 = 2 x 109 at low fields and a maximum accelerating field Eacc = 12.5 M...

Two 350-MHz β = 0.175 two-gap superconducting (SC) spoke resonator cavities have been fabricated ... more Two 350-MHz β = 0.175 two-gap superconducting (SC) spoke resonator cavities have been fabricated in industry under an R&D project for the Advanced Accelerator Applications (AAA) program at LANL. This paper describes the structure, presents the test results of mechanical properties, tuning sensitivity at room temperature, and Q – E curves at 4 K. A maximum accelerating field of 11.6 MV/m has been obtained, which exceeds our present goal of 7.5 MV/m with ample margin.

Free Electron Lasers 2002, 2003

This project is a coordinated effort among NAVSEA, LANL and AES, to develop a key enabling techno... more This project is a coordinated effort among NAVSEA, LANL and AES, to develop a key enabling technology for high-power FEL called for by the High Energy Laser Joint Technology Office: a high current RF photoinjector capable of producing continuous average current greater than 100 mA. The specific aim is a π-mode, normal-conducting RF photoinjector, 5 nC of bunch charge, 100 mA of current (at 21.88 MHz bunch repetition rate) and emittance less than 10 mm-mrad. This level of performance will enable robust 100-kW-class FEL operation with electron beam energy <100 MeV, thereby reducing the size and cost of the FEL. This design is scalable to the MW power level by increasing the electron bunch repetition rate from 21.88 MHz (the 32nd sub-harmonic of 700 MHz) to a higher value. The major challenges are emittance control and high heat flux within the CW 700 MHz RF cavities. Preliminary results of RF cavity designs and cooling schemes are presented, including both high-velocity water and liquid-nitrogen cooling options. PACS codes: 41.60. Cr, 29.17+w, 29.27. Bd, 41.75. Fr

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

Approved forpublic rt,leaso; distribution is UnlhJitQd.

Proceedings of the 2005 Particle Accelerator Conference

An RF photoinjector capable of producing high average current with low emittance and energy sprea... more An RF photoinjector capable of producing high average current with low emittance and energy spread is a key enabling technology for high power CW FEL. The design of a 2.5-cell, π-mode, 700-MHz normal-conducting RF photoinjector cavity with magnetic emittance compensation is completed. With average gradients of 7, 7, and 5 MV/m in its three accelerating cells, the photoinjector will produce a 2.5-MeV electron beam with 3-nC charge per bunch and transverse rms emittance below 7 mm-mrad. Electromagnetic modeling has been used extensively to optimize ridge-loaded tapered waveguides and RF couplers, and led to a new, improved coupler iris design. The results, combined with a thermal and stress analysis, show that the challenging problem of cavity cooling can be successfully solved. Fabrication of a demo 100-mA (at 35 MHz bunch repetition rate) photoinjector is underway. The design is scalable to higher average currents by increasing the electron bunch repetition rate, and provides a path to a MW-class FEL. This paper presents the cavity design and details of RF coupler modeling.

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

We have manufactured a total of six β=0.64, 700-MHz 5-cell cavities. The APT (Accelerator Product... more We have manufactured a total of six β=0.64, 700-MHz 5-cell cavities. The APT (Accelerator Production of Tritium) specification requires Q 0 > 5 x 10 9 at an accelerating field of 5 MV/m. So far, the results of vertical tests have shown maximum accelerating fields of 12 MV/m (peak surface field of 41 MV/m) and maximum low-field Q 0 of 3.6 x 10 10 at 2 K. The present limitations are available input power, field emission and quench. This type of cavities will also be used for an ADTF (Accelerator-Driven Test Facility) for AAA (Advanced Accelerator Applications) project.

Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)

The design for the superconducting cavities of the highenergy accelerator for the Accelerator Pro... more The design for the superconducting cavities of the highenergy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.

The static and dynamic structural behavior of superconducting cavities for various projects was d... more The static and dynamic structural behavior of superconducting cavities for various projects was determined by finite element structural analysis. The {beta} = 0.61 cavity shape for the Neutron Science Project was studied in detail and found to meet all design requirements if fabricated from five millimeter thick material with a single annular stiffener. This 600 MHz cavity will have a Lorentz coefficient of {minus}1.8 Hz/(Mv/meter){sup 2} and a lowest structural resonance of more than 100 Hz. Cavities at {beta} = 0.48, 0.61, and 0.77 were analyzed for a Neutron Science Project concept which would incorporate 7-cell cavities. The medium and high beta cavities were found to meet all criteria but it was not possible to generate a {beta} = 0.48 cavity with a Lorentz coefficient of less than {minus}3 Hz/(Mv/meter){sup 2}.

High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The low fre... more High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The low frequency specifications required for heavy-ion acceleration typically result in large dimensions of the structure. By appropriate choice of the resonant structure for the Rare Isotope Accelerator (RIA) driver RFQ we have achieved moderate transverse dimensions of the cavity and high quality accelerating-focusing fields required for simultaneous acceleration of multiple-charge-state ion beams. In our application the RFQ must provide stable operation over a wide range of RF power levels to allow acceleration of masses from protons up to uranium. To demonstrate the technology and high-power operation we have built an engineering prototype of one-segment of the 57-MHz RFQ structure. The RFQ is designed as a 100% OFE copper structure and fabricated with a two-step furnace brazing process. The errors in the tip-to-tip distances of the vanes average less than 50 microns. The RF measurements show ...

The translation of the physics designs of linear accelerators into engineering and manufacturing ... more The translation of the physics designs of linear accelerators into engineering and manufacturing requirements is discussed. The stages of conceptual design, prototyping, final design, construction, and installation are described for both superconducting (LANL β = 0.175 Spoke Cavity) and normal-conducting (APT/LEDA 6.7 MeV RFQ) accelerators. An overview of codes that have linked accelerator cavity and thermal/structural analysis modules is provided.

Six 5-cell superconducting elliptical cavities have been fabricated at LANL and in industry and t... more Six 5-cell superconducting elliptical cavities have been fabricated at LANL and in industry and tested at LANL and TJNAF. The APT (Accelerator Production of Tritium) specification requires Qo > 5 x 109 at an accelerating field of 5 MV/m. So far, the results of vertical tests have shown maximum accelerating fields of 12 MV/m (peak surface field of 41 MV/m and 835 Oe ) and maximum Q0 of 3.6 x 1010 at 2 K (2.1 x 1010 at Eacc = 5 MV/m). The present limitations are available input power, field emission and quench. With a new 600 W amplifier and a mapping system for surface temperature and x-ray radiation, we are trying to identify and localize the emission/quench source(s) to further improve the cavity performance.

The use of hydrogen furnace brazing has been applied as a joining technology to the fabrication o... more The use of hydrogen furnace brazing has been applied as a joining technology to the fabrication of a Radio-Frequency-Quadrupole (RFQ) linac for the Los Alamos Accelerator Performance Demonstration Facility (APDF). The design concept provides a monolithic cavity with no longitudinal rf, vacuum, or mechanical joints. A 530 MHz, 0.46 meter long engineering model RFQ has been fabricated and tested at the Los Alamos National Laboratory as a technical demonstration of this concept. It is planned that two funneled RFQ`s for the APDF (7 MeV, 350 MHz, 100 mAmp CW, each eight meters in length) will be manufactured by this method.

Within the framework of the Advanced Accelerator Applications (AAA) project we are 'intereste... more Within the framework of the Advanced Accelerator Applications (AAA) project we are 'interested in building and testing IOW-@ spoke resonators (cavities). To familiarize us with the specifics of these structures Argonne National Laboratory (ANL) kindly loaned us one of their spoke cavities for evaluation. This is a p=0.291 2gap resonator at 340 MHz. We benchmarked our computer codes by comparing room temperature measurements of frequency, tuning sensitivity, tuning forces, etc. with our 3D simulation results. The cavity was tested at both 4 K and 2 K. The results showed maximum accelerating gradients of 12.5 MV/m (4 K) and 12.3 MV/m (2 K), which correspond to a peak electric field of 40 MV/m and a peak magnetic field of 1063 Oe. Q, values at 5 MV/m also exceeded by more than a factor 2 of present AAA specification. These results encouraged us toward development of spoke cavities for the low energy section (6.7 MeV to 109 MeV) of ADTF (Accelerator-Driven Test Facility) of AAA proj...

In this paper, we present the electromagnetic and structural design of a low-b superconducling sp... more In this paper, we present the electromagnetic and structural design of a low-b superconducling spoke resonator for a beam-test in the Low Energy Demonstration Accelerator (LEDA). This test is part of the Advanced Accelerator Applications (AAA) project. Recently, the sole use of superconducting resonators from 6.7 MeV on has been approved for this project. The beam test will use the lowest- resonator from this accelerator design. The choices of the cavity dimensions are driven by its use imrnediately after the LEDA Radio-Frequency Quadrupole (RFQ). The frequency is 350 MHz, the lengt corresponds to a geometric p (Ps) of 0.175. Our design approach has been to carry out an integrated RF and mechanical design from the start. The final cavity is well understood in terms of IW: and mechanical properties. The RF properties, like Q, WQ, peak surface fields and acceleration efficiency are very reasonable for such a low- structure. 'The design also includes power coupler, vacuum and pick-...

arXiv: Accelerator Physics, 2004

A high-current emittance-compensated RF photoinjector is a key enabling technology for a high-pow... more A high-current emittance-compensated RF photoinjector is a key enabling technology for a high-power CW FEL. A preliminary design of a normal-conducting, 2.5-cell pi-mode, 700-MHz CW RF photoinjector that will be built for demonstration purposes, is completed. This photoinjector will be capable of accelerating a 100-mA electron beam (3 nC per bunch at 35 MHz bunch repetition rate) to 2.7 MeV while providing an emittance below 7 mm-mrad at the wiggler. More than 1 MW of RF power will be fed into the photoinjector cavity through two ridge-loaded tapered waveguides. The waveguides are coupled to the cavity by "dog-bone" irises cut in a thick wall. Due to CW operation of the photoinjector, the cooling of the coupler irises is a rather challenging thermal management project. This paper presents results of a detailed electromagnetic modeling of the coupler-cavity system, which has been performed to select the coupler design that minimizes the iris heating due to RF power loss in ...

To date, all high-energy proton linear accelerators have been room temperature (or higher) machin... more To date, all high-energy proton linear accelerators have been room temperature (or higher) machines. To produce a high-energy beam over a reasonable accelerator length (high accelerating gradient), these machines require large amounts of radio-frequency (rf) power to maintain accelerating fields. A substantial amount of this power, up to 50% in some cases, is dissipated as heat in the cavity walls. Using a superconducting accelerator minimizes this wasted power. In addition to the power savings, a superconducting cavity has a large velocity acceptance. This velocity acceptance minimizes the number of cavity designs necessary for a given accelerator. Also, superconducting cavities permit a large bore diameter, which reduces the interaction with the beam halo. These types of cavities have been successfully applied in electron accelerators. At the Los Alamos National Laboratory, a prototype design of proton superconducting cavities has been developed for the Accelerator Production of T...

The upgrade for the ATLAS facility is designed to increase the efficiency and intensity of beams ... more The upgrade for the ATLAS facility is designed to increase the efficiency and intensity of beams for the user facility(1,2). This will be accomplished with a new CW normal conducting RFQ, which will increase both transverse and longitudinal acceptance of the LINAC. This RFQ must operate over a wide range of power levels to accelerate ion species from protons to uranium. The RFQ design is a split coaxial structure and is made of OFE copper. The geometry of the design must be stable during operation. Engineering studies of the design at different RF power levels were conducted to ensure that the geometry requirements were met. Frequency shift analysis was also completed to determine the effects of high power levels. Thermal stress analysis was completed to show that the structure frequency is repeatable.

A key technology issue on the path to high-power FEL operation is the demonstration of reliable, ... more A key technology issue on the path to high-power FEL operation is the demonstration of reliable, high-brightness, high-power injector operation. We describe two ongoing programs to produce 100 mA injectors as drivers for 100 kW free-electron lasers. In one approach, in collaboration with the Thomas Jefferson National Accelerator Facility, we are fabricating a 750 MHz superconducting RF cryomodule that will be integrated with a room-temperature DC photocathode gun and tested at the Laboratory. In the other approach, in collaboration with Los Alamos National Laboratory, a high-current 700 MHz, normal-conducting, RF photoinjector is being designed and will undergo thermal management testing at the Laboratory. We describe the design, the projected performance and the status of both injectors.

Since the last workshop we have tested six b=0.64, 700 MHz, 5-cell elliptical superconducting cav... more Since the last workshop we have tested six b=0.64, 700 MHz, 5-cell elliptical superconducting cavities in collaboration with JLAB in vertical cryostats. All the cavities exceeded the requirements for Accelerator Production of Tritium (APT) (Q0 = 5 x 109 at Eacc = 5 MV/m) with ample margin. The low-field Q0 at 2 K was 2-3 x 1010 and the maximum accelerating field reached 12 MV/m, which corresponds to peak electric and magnetic fields of 41 MV/m and 835 Oe, respectively. Power couplers have also been tested in a test bench up to over 1 MW. Since the APT project has transitioned to Advanced Accelerator Applications (AAA) project, a new type of superconducting accelerating structure called spoke cavity emerged as an excellent candidate for the low energy sections between the RFQ and the elliptical cavities. We tested a b=0.29, 340 MHz, 2-gap spoke cavity on loan from Argonne National Laboratory. The results showed Q0 = 2 x 109 at low fields and a maximum accelerating field Eacc = 12.5 M...

Two 350-MHz β = 0.175 two-gap superconducting (SC) spoke resonator cavities have been fabricated ... more Two 350-MHz β = 0.175 two-gap superconducting (SC) spoke resonator cavities have been fabricated in industry under an R&D project for the Advanced Accelerator Applications (AAA) program at LANL. This paper describes the structure, presents the test results of mechanical properties, tuning sensitivity at room temperature, and Q – E curves at 4 K. A maximum accelerating field of 11.6 MV/m has been obtained, which exceeds our present goal of 7.5 MV/m with ample margin.