de Prisco, Renato

Eshraqi, Mohammad

France, Alain

Miyamoto, Ryoichi

Piquet, Olivier

Ponton, Aurelian

Sargsyan, Edgar

English

Lund University Publications

LUND UNIVERSITYPO Box 117221 00 Lund+46 46-222 00 00ESS normal conducting linac status and plansPonton, Aurelian; de Prisco, Renato; Eshraqi, Mohammad; Miyamoto, Ryoichi; Sargsyan,Edgar; France, Alain; Piquet, Olivier2014Link to publicationCitation for published version (APA):Ponton, A., de Prisco, R., Eshraqi, M., Miyamoto, R., Sargsyan, E., France, A., & Piquet, O. (2014). ESS normalconducting linac status and plans. 948-950. Paper presented at LINAC2014.Total number of authors:7General rightsUnless other specific re-use rights are stated the following general rights apply:Copyright and moral rights for the publications made accessible in the public portal are retained by the authorsand/or other copyright owners and it is a condition of accessing publications that users recognise and abide by thelegal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private studyor research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portalRead more about Creative commons licenses: https://creativecommons.org/licenses/Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will removeaccess to the work immediately and investigate your claim.ESS NORMAL CONDUCTING LINAC STATUS AND PLANSA. Ponton ∗, B. Cheymol, M. Eshraqi, R. Miyamoto, R.de Prisco, E. Sargsyan, ESS AB, Lund, SwedenG. Bourdelle, M. Desmons, A. France, O. Piquet, B. Pottin, N. Sellami,CEA-Irfu, Gif-sur-Yvette, FranceI. Bustinduy, P. González, J. L. Muñoz, I. Rueda, F. Sordo, ESS-Bilbao, Bilbao, SpainL. Celona, S. Gammino, L. Neri, INFN/LNS, Catania, ItalyM. Comunian, F. Grespan, A. Pisent, , C. Roncolato, INFN/LNL, Legnaro, ItalyP. Mereu, INFN/Sezione di Torino, Torino, ItlayAbstractEfficient and low loss beam acceleration in the EuropeanSpallation Source (ESS) linear accelerator (linac) gives riseto specific technical challenges in the normal conducting(nc) section. The nc linac creates high current proton beams,produces the macro and micro structures (formation of thepulse and bunches respectively) of the beam and acceleratesthe latter up to 90MeV before injection in the supercon-ducting (sc) linac. Design and construction of the differentcomponents of the nc linac are part of a broad collaborationinvolving experts of various labs in Europe. Beam commis-sioning of the warm linac in the ESS tunnel is foreseen atthe beginning of 2019.INTRODUCTIONThe ESS aims at becoming the world’s most powerfulneutron source at the end of the decade. The spallationneutrons are produced by a 5MWproton beam hitting a solid,rotating tungsten target [1]. The acceleration of the protonbeam up to a final energy of 2GeV is ensured by a ∼ 400mRadio-Frequency linear accelerator (RF linac) whose maincharacteristics are 14Hz repetition rate, 62.5 mA peak beamcurrent and 2.86 ms beam pulse length. The layout of theESS linac can be seen in Fig. 1.The linac [2] is composed by a sequence of nc structuresfollowed by sc cavities hosted in cryomodules [3]. Thenc part of the linac, while giving only 5% of the power tothe beam, has to produce very high quality beams beforeinjecting into the sc linac. The layout of the nc linac andthe main technical challenges will be explained. The designand the construction of the warm linac as part of a broadEuropean collaboration is presented in the following. Statusand plans for construction and installation will finally begiven.Figure 1: Layout of the ESS linac.∗ aurelien.ponton@esss.seLAYOUT AND TECHNICALCHALLENGESGeneral LayoutThe proton beam is produced and accelerated to 75 keVin a Microwave Discharge Ion Source (MDIS) which is fol-lowed by a dual solenoid Low Energy Beam Transport line(LEBT) [4] transporting and matching the beam into theRadio-Frequency Quadrupole (RFQ). The latter acceleratesto 3.62MeV, focuses and transforms the beam pulse in a trainof bunches at 352.21MHz [5] to allow rf acceleration in thesubsequent structures. The beam is then transported throughthe Medium Energy Beam Transport line (MEBT) [6] andmatched into the Drift Tube Linac (DTL) [7]. The DTLfinally focuses and accelerates the beam up to 90MeV in 5tanks of 8m each.In order to allow efficient matching with acceptable andcontrollable beam loss during operation, the LEBT and theMEBT, even given the reduced space available, are equippedwith a set of diagnostics for current, energy and phase spacemeasurements [8].Technical ChallengesThe main goal of the warm linac is to inject high qualityproton beams with a given time structure and sufficient en-ergy in the sc linac.The required peak beam current on target is 62.5mA. Asa result, proton transport through the warm linac is verychallenging due to high space charge forces acting on thebeam. In particular, performing the injection of the matchedbeam into the RFQ requires to understand theoretically andexperimentally how much the ionization of the residual gasby the proton beam reduces the space charge of the beam it-self: the so-called space charge compensation (scc) process.In addition, reducing the development of halo is mandatoryto avoid hazardous losses, which must remain below 1W/mat high energy, therefore requiring good beam matchingbetween sections since mistmatch is known to be one ofthe main mechanisms of halo production. The RFQ is alsoforeseen to perform efficient bunch capture with negligibleproduction of longitudinal tail that potentially transfers intotransverse halo and losses. In the MEBT collimator strategyis being studied to intercept part of the transverse halo [9].Challenges in terms of beam performances are summarizedin Tab. 1 (see [10] for a deeper analysis).THPP044 Proceedings of LINAC2014, Geneva, SwitzerlandISBN 978-3-95450-142-7948Copyright©2014CC-BY-3.0andbytherespectiveauthors02 Proton and Ion Accelerators and Applications2A Proton Linac ProjectsTable 1: Nominal Beam Performances Requirements (99% means that values are foreseen for 99% of the nominal current).Emittances are Normalized.Sections Nominal performancesOutput Extracted Proton 99% ellipse area 99% divergenceenergy current fraction Trans. Trans.[MeV] [mA] % [π·mm·mrad] [mrad]IS 0.075 ± 0.00001 74 > 80 < 1.8 < 80Output Input design Beam 99% Ellipse area Transverseenergy current transmission Trans. Twiss parameters[MeV] [mA] [%] [π·mm·mrad] α β [mm/mrad]LEBT 0.075 ± 0.00001 74 > 95 < 2.5 1.02 ± 20% 0.11 ± 10%Output Input design Beam 99% ellipse area Transverse Longitudinalenergy current transmission Trans. Long. Twiss parameters Twiss parameters[MeV] [mA] [%] [π·mm·mrad] [π·deg·MeV] α β [mm/mrad] α β [deg/MeV]RFQ 3.62 ± 0.01 70 > 90 < 2.43 < 1.60 −0.05 ± 10% (H) −0.21 ± 10% (H) 0.48 ± 10% 613 ± 10%−0.31 ± 10% (V) 0.37 ± 10% (V)MEBT 3.62 ± 0.01 63 > 99.3 < 3.00 < 1.66 1.34 ± 8% (H) 0.21 ± 7% (H) −0.12 ± 50% 274 ± 7%−4.19 ± 8% (V) 0.77 ± 7% (V)DTL > 89 62.5 ∼ 100 < 3.20 < 1.79 −2.34 ± 10% (H) 5.20 ± 8% (H) −0.17 ± 110% 32 ± 13%2.33 ± 10% (V) 4.74 ± 8% (V)The required pulse length is 2.86 ± 0.001ms due to Ma-chine Protection System (MPS) [11] purposes. In order toreach this precision, the beam pulse is cleaned to removethe transient coming from the rise time of the IS with a two-step-chopping scheme: a slow and a fast chopper with avoltage rise time of 100 ns and 10 ns in the LEBT and theMEBT respectively. Even though the rise time of the LEBTchopper seems short, the scc, and thus the matched beamparameters into the RFQ, are expected to be recovered, afterthe chopper is turned off, within a tens of microseconds [12].Likewise, 10 ns in the MEBT might appear fast given therequired pulse length precision. However, a very fast risetime is mandatory in order to reduce the risk of losses due topartially kicked bunches during the transient of the MEBTchopper voltage which might be transported after the MEBTchopper-dump [13].Table 2 gives a summary of the pulse length requirementsfrom the ion source to the MEBT indicating the maximalpulse length and the minimal pulse flat top length. The flattop is reached when the following stable conditions are met:the nominal current is produced with fluctuations of lessthan 3.5% within the pulse after the IS and the matchedbeam parameters given in Tab. 1 are produced.Table 2: Nominal Beam Pulse Requirements.Section Total pulse Flat topoutput length [ms] length [ms]IS < 6 > 3LEBT < 2.88 > 2.86MEBT 2.86 ± 0.001 2.86 ± 0.001Another technical challenge is the ability to produce differ-ent levels of currents [14] to allow a wide range of neutronproduction modes. A collimator will be installed in betweenthe solenoids of the LEBT. With 6 independent blades, thecollimator system shall be adjustable in order to produceon target at least 10 steps of currents ranging from 6.5 to62.5mA with a maximal step size of 6.3mA and a precisionof 1mA.COLLABORATIONThe ESS warm linac design activities have been con-ducted with the expertise of a broad European collaboration(see Fig. 2): INFN/LNS for the IS-LEBT, CEA-Irfu for theRFQ, ESS-Bilbao for the MEBT and finally INFN/LNL andINFN/Sezione di Torino for the DTL.Negotiations are currently being held between ESS and therelevant member states to define the level of their in-kindcontribution to the different nc linac sections during theconstruction phase.Figure 2: The NC linac collaboration.STATUS AND PLANSStatus• The preparation of the test stand area for the IS hasbeen achieved in the INFN/LNS premises. The highvoltage platform is being equipped in order to install theProceedings of LINAC2014, Geneva, Switzerland THPP04402 Proton and Ion Accelerators and Applications2A Proton Linac ProjectsISBN 978-3-95450-142-7949 Copyright©2014CC-BY-3.0andbytherespectiveauthorsion source body whose executive drawings are beingcompleted.• The LEBT lattice is in a very advanced stage with focuson the mechanical integration of the vacuum systemsand the beam diagnostics. Emphasis is put on the def-inition of the interface region between the LEBT andthe RFQ where sit among other systems a beam currenttransformer, a vacuum gate valve, a repeller electrode,the dump for the chopped beam and its cooling systemand a potential vacuum pump port to limit the gas loadinto the RFQ.• The beam dynamics and RF designs of the RFQ havebeen completed. Thermomechanical analysis is on-going to define the cavity water cooling scheme and thecorresponding cooling skid. In addition, prototypes ofa RF power coupler loop, a vacuum grid and a movabletuner are under study. They will be tested under highRF power to validate the RFQ design choices.• TheMEBT lattice is in a very advanced stage with focuson the mechanical integration of the vacuum systemsand the beam diagnostics. Moreover, tests are beingperformed on the buncher cavity prototype (see Fig. 3)including copper plating and RF characterization. De-tailed engineering design for the magnets has started.Different technologies for the chopper system are alsobeing investigated and thermomechanical calculationson the chopper dump and the halo collimators are beingperformed.• The beam dynamics, RF and mechanical design ofthe DTL are being finalized. In parallel to design ac-tivities, 3 DT prototypes, equipped with a PermanentQuadrupole Magnet (PMQ) that can be seen in Fig. 4,a magnetic steerer and a beam position monitor respec-tively, are under construction. Machining is achieved inthe mechanical workshop of INFN/Sezione di Torinoand assembly and brazing are handled in INFN/LNL.Figure 3: Picture of thebuncher prototype after ma-chining.Figure 4: Picture of theDTL PMQ prototype.PlansMain milestones of the nc linac are reported in Fig. 5April 2015 April 2016 July 2017 April 2018 March 2019 September 2019 Figure 5: Warm linac main milestones.REFERENCES[1] S. Peggs editor, "The ESS technical design report" (2013)[2] M. Eshraqi et al., "The ESS Linac", In proceedings ofIPAC’14, Dresden, Gerany, THPME043 (2014)[3] C. Darve et al., "Requirements for ESS Superconducting Ra-dio Frequency Linac", In proceedings of IPAC’14, Dresden,Germany, THPME039 (2014)[4] L. Neri et al., "The proton injector for the European SpallationSource" In this conference, LINAC14, PP085 (2014)[5] A. Ponton, "Note on the ESS RFQ design update", ESS tech-nical note, (2013)[6] I. Bustinduy et al., "Progress on ESS medium Energy BeamTransport", In this conference, LINAC'14, TUPP025 (2014)[7] F. Grespan et al., "ESS DTL design and drift tube prototyp-ing", In this conference, PP087 (2014)[8] B. Cheymol et al. "Overview of the European SpallationSource warm linac beam instrumentation" In proceedings ofIBIC’13, Oxford, UK, TUPC01 (2013)[9] R. Myamoto et al., "A Study of ESS Linac Collimation", Tobe published in proceedings of HB’2014[10] R. de Prisco, "Effect of multipoles and errors on the ESSnormal conducting LINAC", In this conferenceTHPP042 (2014)[11] A. Nordt et al., "Overview of the design of the Machine Pro-tection System for ESS", In proceedings of IPAC’14, Dresden,Germany, MOPME045 (2014)[12] L. Neri et al., "Improved design of proton source and lowenergy beam transport line for European Spallation Source",Rev. Sc. Inst. 85, 02A723 (2014)[13] R. Myamoto et al., "Dynamics of Bunches Partially Choppedwith theMEBTChopper in the ESS Linac", In this conference,MOPP039 (2014)[14] E. Sargsyan and R. Miyamoto, “ESS Linac Beam Modes”,In this conference, THPP045 (2014) THLINAC'14, TH, LINAC'14,THPP044 Proceedings of LINAC2014, Geneva, SwitzerlandISBN 978-3-95450-142-7950Copyright©2014CC-BY-3.0andbytherespectiveauthors02 Proton and Ion Accelerators and Applications2A Proton Linac Projects

ESS normal conducting linac status and plans

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ESS normal conducting linac status and plans

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