In 1997, the authors initiated a development program in Los Alamos for high-current superconducting proton-linac technology to build prototypes components of this linac to demonstrate the feasibility. The authors are building 700-MHz niobium cavities with elliptical shapes, as well as power couplers to transfer high RF power to these cavities. The cavities and power couplers will be integrated in cryostats as linac cryomodules. In this paper, they describe the linac design and the status of the development program

K.C.D., Chan

UNT Digital Library

‘ .LA.UR-$)8-4~69Approved forpublic release;distribution is unlimited.Title: Application of RF Superconductivity To High-Current LinacAuthor(s): Kc. Dominic ChanLos AIamos National LaboratorySubmitted to: 1998 Applied Superconductivity ConferencePalm Desert, CASept. 13-18, 1998Los AlamosNATIONAL LABORATORYLos Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U.S.Department of Energy under contract W-7405 -ENG-36. By acceptance of this articla, the publisher recognizes that the U.S. Governmentretains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S.Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under theauspices of the U.S. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher’s right topublish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness.Form 836 (10/96)DISCLAIMERThis report was,.prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument..APPLICATION OF RF SUPERCONDUCTIVITYTO HIGH-CURRENT LINAC”K. C. Dominic ChanLos Alamos National Laboratory, Los Alamos, NM, USAFutureApplication 27. Beamstop~,1.5-kg Linac & Transport\Target/BlanketBeam Power 103.0 MW— R.54.4m RF Power 117.4 MW17.1m— No. of Klystrons 161 (1-MW)42.7m{AC for RF Power 237.0 MWPlant AC Power 311.8 MW54.4m29.3mR=27.2m — 1030.0 MeV 471.4 MeVZI 1.4 MelJ0.1 % BeamstopI I # {F85.4m~298.9m~ 185.4m ‘~ ~—- 235.1 m —~45.Om High-p SC Linac Section 2 Section 1NC LinacMedium-p SC LinacFig. 1 Design of APT JJnac .Abstract -- In 1997, we initiated a development programin Los Alamos for high-current superconducting proton-linac technology to build prototypes components of thislinac to demonstrate the feasibility. We are building 700-MHz niobium cavities with elliptical shapes, as well aspower couplers to transfer high RF power to thesecavities. The cavities and power couplers will beintegrated in cryostats as Iinac cryomodules. In thispaper, we will describe the linac design and the status ofthe development program.I INTRODUCTIONHigh-current proton linacs, using a spallation process,can produce neutrons for research and transmutationapplications. These Iinacs have multi-megawatts of beampower and are very power consuming.A RF superconducting (SC) linac has been proposed forthe Accelerator Production of Tritium (APT) Projectsponsored by The US Department of Energy [1] [2].Figure 1 shows the design of the ApT linac that has anominal production capacity of 1.5 kg of tritium per year.This design is upgradable to a capacity of 3.0 kg per yewby increasing the proton beam energy to 1700 MeV. TheIinac consists of a normal-conducting (NC) Linac and asupercondcuting (SC) Linac. The NC Linac uses theusual room-temperature copper technology. It is chosenbecause of its capability to produce a proton beam withhigh quality for further acceleration. The SC Linac usessuperconducting Nb technology. SC technology ischosen for the high-energy efficiency and low beam loss.The use of RF superconducting cavities in these linacshas enhanced energy efficiency because of the absence ofRF electrical resistance. The linac has reduced beam lossbecause of the large cavity apertures. The SC Linac has aMedium-p (~=0.64) SC Linac and a High-p (~=0.82) SCLinac. Each of them consists of identical cryomodules.To insure our capability of building such a Iinac, weimplemented an Engineering Development andDemonstration (ED&D) Program in Los Alamos [3].The scope of the program is to build and test SC cavitiesand power couplers for the proposed linac and integratethem in a prototype cryomodule. The goal is todemonstrate the required performances. Similardevelopment programs are now in place in Japan [4] andItaly [5]. Even though our program is designed for theAPT Project, the development is useful for theapplication of SC to high-current proton Iinacs.II CAVITIESFigure 2 shows the design of a ~=0.64 SC cavity. Thecavity has five cells made of niobium sheet metal. It issurrounded by inner and outer He vessels. The cylindricalinner vessel provides the needed mechanical strength andthe outer He vessel has a large volume to provide therequired He liquid even at fault conditions. These Hevessels are made of titanium to match the thermalexpansion of the niobium. The inner He vessel isconnected to the niobium cavity with titanium bellows.● Work supported by the US Department of EnergyEach cavity will be supplied with RF power using twopower couplers throughout the RF drive ports. Thediameter of the beam tube at the end with the RF driveport is larger to provide the required coupling between thecavity and power couplers. The tuner is mechanical innature and has all the drive gears at ambient temperatureto enhance reliability. It is a proven design usedsuccessfully at Cornell University.Each cell has an elliptical shape similar to that used forelectron accelerators with the exception that the length isshorter to maintain synchronism for the ~=0.64 beam.The slope of the sidewall is optimized to maintainmechanical stability under vacuum load without the use ofcostly stiffeners. It is required to operate at anaccelerating field of 4-6 MV/m with a QOof 5x109. Thisperformance requirement, peak surface field below 16MV/m, is conservative. It should be readily achievablewith readily available niobium with an RRR of 250 andstandard processing techniques, viz., e-beam welding,buffered chemical polish, and high-pressure rinsing. Wehave tested single-cell cavities with f3=0.48 and f3=0.64[6]. We achieved the required performance withoutobserving multipacting. Figure 3 shows the measuredperformance of a j3=0.48 single-cell cavity. The cavityattained our required field with a factor-of-two margin.. . . . . ...._ ~——. .-1—. ----- . ..Fig.2 J5=().64 5-ceH cavity~~lo, ! ! ,q—-+------+ 1—-. .— ———---h–--j-f–---–f’---= ‘/ I ~APT Specifi@ion———i—. .—— —. _-T=2Kt B~k~ 103.4 mT~~9r+ t--- —._-— ___ _-_ —. —_-—- —.- —----+.-...___+_...._+——_’_ !I Ii_ IC&ity 0.48-1138]pm Polish108 1 .,,1.,,,0 10 20 30 40 50E,k (MV/m)Figure 3: Typical test results of a ~=0.48 cavityWe completed the design of the ~=64 5-cell cavities.Four cavities have been ordered from industry. Wecompleted the fabrication of one “prototype cavity” at LosAlamos (Figure 4), i.e., a niobium cavity without Hevessels. This cavity is undergoing testing.We completed a cost analysis, including both capitaland operating costs. The cost analysis shows that theoptimum temperature is at 2.4 K and the optimum isbroad. The cost changes only by 10% with changes intemperature of +0.2 K. In addition, we would prefer tooperate in the superfuild regime of to take advantage ofthe high thermal conductivity of superfluid He. Thereforewe want to operate the cavity at the highest temperature,but with a controllable margin below the criticaltemperature so that the critical temperature will not beexceeded. Presently, we have nominally fixed the cavityoperating temperature at 2.15 K.Fig. 4 Prototype ~=0.64 5-cell Nb cavityIII POWER COUPLERWe need to develop a power coupler that can transmit210 kW of CW power. The highest rated couplerpresently is 188 kW to the beam. Figure 5 illustrates thedesign of the APT coupler. It has three sections: coaxialcoupler, transition, and RF-window assembly. We havechosen the coaxial design because it has a better-understood geometry and was the highest rated design atthe time our design was conceived. The RF window isusually the point of failure for couplers. We choose touse double warm windows for increased reliability. Thewindow assembly is being fabricated by the klystronindustry as one complete unit. We have done extensivemodeling using 3-D electromagnetic codes to design thetransition section. Using the tuning sleeve, we haveminimized reflection and interactions betweencomponents.The design was reviewed in May 1998. The reviewcommittee underscored the importance of thermal designand testing of the coupler. Because of the high powertransmitted, the RF loss in each coupler is as high as 200W. It is important to prevent this energy from reachingthe LHe for good cryogenic efficiency. Presently, we areconsidering options of cooling the coupler outerconductors [7]. The options include the use of a double-.temperature thermal intercept and an heat exchanger. Theselection will be made in consideration with thecryomodule and cryoplant designs. We are nowfabricating the power coupler components. We haveplanned a detailed test program to test thecoupler for itspower-carry ingcapability andmuhipacting characteristics.We will also test the bellows and copper plating usedinthe present design.#-cTuning Sleeve RF windowFig, 5 Illustration of power couplerIV CRYOMODULEWe held a review of the Conceptual Design inSeptember 1997 and have since been developing thisdesign. A final design review is planned for November1998. Figure 6 shows the cryomodule design for ~=0.64[8]. The cryostat will contain two 5-cell cavities and fourpower couplers. The cryostat has a center section and twoend domes. It has removable panels for the center sectionfor easy access. This design is based on the LEP-11cryomodule design. The thermal shield consists of twoaluminum halves and is pipe cooled. The magnetic shieldwill reduce the magnetic fields at cavities to 10 mGaussto enhance cavity performance. The vacuum pumping isprovided by oil-free turbopumps. The pumps are arrangedto have redundancy to increase availability.We have also developed the assembly process of thecryomodule, Because we are not using cold windows, theinstallation of the cavities and couplers is required to bedone in a cleanroom. The assembly after the cleanroomwill be rotated 90 degrees to facilitate the installation ofmagnetic and thermal shields.e He inlet‘ndsec’ion=Centersection[1][2][3][4][5][6]V SUMMARYThe Engineering Development and DemonstrationProgram for the APT superconducting linac is progressingwell. We are finishing our design phase and are enteringthe fabrication phase.[7][8]Cavity T A..Fig. 6 Illustration of cryomoduleREFERENCESG. P. Lawrence, High-Power Proton Linac for APT;Status of Design and Development, presented in theIntentional Conference LINAC ’98, Chicago, IL,August 23-28, 1998.K. C. Dominic Chan et al., Development of RFLinac for High-Cument Applications, Proceedings ofthe Fifth European Conference on Accelerators inApplied Research and Technology (ECAART-5),Eindhoven, The Netherlands, 26-30 August 1997, pp394-400.K. C. D. Chan et al., Progress of APTSuperconducting Linac Engineering Development,presented in the Intentional Conference LINAC ‘98,Chicago, IL, August 23-28, 1998.M. Mizumoto, A High Intensity Proton LinacDevelopment for the JAERI Neutron Science Project,ibid.C. Pagani, Superconducting Accelerators for NuclearWaste Transmutation, presented in this conference.W. B. Hayes et al., Medium-Beta Superconductingcavity Tests at Los Alamos National Lab for High-Current Proton Linac, presented at the S’hWorkshopon RF Superconductivity, Oct. 6-11, 1997, Padova,Italy.J. A. Waynert et al., Thermal Analysis of the APTRF Power Coupler and Similarities toSuperconducting Magnet Current Leads, presented inthis conference.B. M. Campbell et al., Engineering Design of theAPT Cryomodule, presented in the IntentionalConference LINAC ’98, Chicago, IL, August 23-28,1998.

Application of RF Superconductivity to High Current Linac

https://digital.library.unt.edu/ark:/67531/metadc709796/m2/1/high_res_d/759686.pdf

Application of RF Superconductivity to High Current Linac

Abstract

Similar works

Full text

Available Versions

UNT Digital Library