Development and commissioning of a hydrogen ion source for the CERN ALPHA experiment

This is a sel -a chi ed e sion o an o iginal a icle. This e sion may di e om he o iginal in pagina ion and ypog aphic de ails. Au ho (s): Ti le: Yea : Ve sion: Copy igh : Righ s: Righ s u l: Please ci e he o iginal e sion: CC BY 4.0 h ps://c ea i ecommons.o g/licenses/by/4.0/ De elopmen and commissioning o a hyd ogen ion sou ce o he CERN ALPHA expe imen © 2024 he Au ho s Published e sion Johnson, M.A.; Be sche, W.A.; Co áza , O.D; Fai clo h, D.; Kal as, T.; Law ie, S.; Megia Macías, A.M.; Ta ainen, O.; Ba ios Díaz, E. Johnson, M.A., Be sche, W.A., Co áza , O.D, Fai clo h, D., Kal as, T., Law ie, S., Megia Macías, A.M., Ta ainen, O., & Ba ios Díaz, E. (2024). De elopmen and commissioning o a hyd ogen ion sou ce o he CERN ALPHA expe imen . Jou nal o Ins umen a ion, 19(1), A icle C01021. h ps://doi.o g/10.1088/1748-0221/19/01/C01021 2024 Jou nal o Ins umen a ion PAPER • OPEN ACCESS De elopmen and commissioning o a hyd ogen ion sou ce o he CERN ALPHA expe imen To ci e his a icle: M.A. Johnson e al 2024 JINST 19 C01021 View he a icle online o upda es and enhancemen s. You may also like An ihyd ogen s udies in ALPHA N Madsen and o he ALPHA collabo a ion - Physics wi h an ihyd ogen W A Be sche, E Bu le , M Cha l on e al. - An ihyd ogen apping assis ed by sympa he ically cooled posi ons N Madsen, F Robicheaux and S Jonsell - This con en was downloaded om IP add ess 130.234.90.20 on 22/05/2024 a 10:57 2024 JINST 19 C01021 Published by IOP Publishing o Sissa Medialab Recei ed:Decembe 16, 2022 Accep ed:No embe 27, 2023 Published:Janua y 17, 2024 8 h In e na ional Symposium on Nega i e Ions, Beams and Sou ces O o Bo anico, Pado a, I aly 2–7 Oc obe 2022 De elopmen and commissioning o a hyd ogen ion sou ce o he CERN ALPHA expe imen M.A. Johnson, 𝑎,𝑏,𝑐,∗ W.A. Be sche, 𝑎,𝑐 O.D Co áza , 𝑑 D. Fai clo h, 𝑒 T. Kal as, 𝑓 S. Law ie, 𝑒 A.M. Megia Macías,𝑔,ℎ O. Ta ainen𝑒and E. Ba ios Díaz𝑑 𝑎School o Physics and As onomy, The Uni e si y o Manches e , Manches e M13 9PL, U.K. 𝑏ASTeC, STFC Da esbu y Labo a o y, Da esbu y, Wa ing on WA4 4AD, Cheshi e, U.K. 𝑐The Cockc o Ins i u e, Sci-Tech Da esbu y, Wa ing on, WA4 4AD, U.K. 𝑑Ins i u e o Ene gy Resea ch (INEI), Uni e si y o Cas illa-La Mancha, c/Moledo es s/n, 13071 Ciudad Real, Spain 𝑒STFC ISIS Pulsed Spalla ion Neu on and Muon Facili y, Ru he o d Apple on Labo a o y, Ha well OX11 0QX, U.K. 𝑓Uni e si y o Jy äskylä, Depa men o Physics, Su on ie 9D, 40500, Jy äskylä, Finland 𝑔Mechanical Enginee ing Depa men , ICAI, Comillas Pon i cal Uni e si y, Albe o Aguile a 25, 28015 Mad id, Spain ℎIns i u e o Resea ch in Technology, ICAI, Comillas Pon i ical Uni e si y, San a C uz de Ma cenado, 26, 28015 Mad id, Spain E-mail: [email p o ec ed] Abs ac : The CERN ALPHA expe imen makes p ecision measu emen s o an ihyd ogen a oms held in a supe conduc ing magne ic minimum ap. Recen s udies o he an ihyd ogen spec um ha e p o ided unique es s o undamen al physics, and o imp o e on hese s udies ALPHA is now p oposing upg ades o di ec ly compa e hyd ogen and an ihyd ogen wi hin hei exis ing a om ap. One ou e owa ds p oducing cold, neu al hyd ogen a oms is he in eg a ion o a hyd ogen ion sou ce in o he expe imen . Ideally, his should p o ide bo h posi i e (H + , H + 2 , H + 3 ) and nega i e (H − ) ions o acili a e di e en schemes o p oducing and apping hyd ogen a oms. Fo compa ibili y wi h ALPHA’s exis ing beamlines, he sou ce mus p oduce modes ( ∼10 μ A) beam cu en s a e y low inal ene gies ( <100 eV). PELLIS, p e iously de eloped a JYFL, is a ilamen -d i en ion sou ce ∗Co esponding au ho . c  2024 The Au ho (s). Published by IOP Publishing L d on behal o Sissa Medialab. O iginal con en om his wo k may be used unde he e ms o he C ea i e Commons A ibu ion 4.0 licence. Any u he dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s) and he i le o he wo k, jou nal ci a ion and DOI. h ps://doi.o g/10.1088/1748-0221/19/01/C01021 2024 JINST 19 C01021 ha gene a es 5–10 keV H − beams wi h small emi ances and ens o mic oamps o beam cu en . He e, we p esen a modi ied PELLIS design o p o ide bo h posi i e and nega i e hyd ogen ions o ALPHA. The use o an elec omagne il e ield in PELLIS allows o he op imisa ion o H − olume p oduc ion, and also uning o he posi i e ion species ac ion. We p esen simula ions o H − (and simila ly H + ) anspo h ough he ini ial ex ac ion op ics, which ha e been con igu ed o a lowe beam ene gy o 5 keV and designed o ma ch a p oposed beamline o in e ace wi h ALPHA. We p esen he esul s o de ailed acuum simula ions ha we e used o guide he op ics design, allowing he sou ce (a 10−2 mba ) o in e ace wi h a anspo beamline ∼0.5 m downs eam ha has s ic acuum equi emen s o <10−9 mba . We p esen expe imen al esul s om commissioning o he sou ce, and show ha i b oadly pe o ms as designed o bo h posi i e and nega i e hyd ogen ions. Keywo ds: Ion sou ces (posi i e ions, nega i e ions, elec on cyclo on esonance (ECR), elec on beam (EBIS)); Beam Op ics 2024 JINST 19 C01021 Con en s 1 In oduc ion 1 2 Ion sou ce design 2 2.1 Ex ac ion op ics 3 2.2 Di e en ial pumping 4 3 Commissioning esul s 5 4 Ou look and conclusions 7 1 In oduc ion The ALPHA expe imen , based a he CERN An ip o on Decele a o , makes p ecision measu emen s o an ihyd ogen ( H ) a oms con ined in a supe conduc ing magne ic minimum ap. Compa isons be ween he hyd ogen a om and i s an ima e coun e pa p o ide unique es s o undamen al symme ies and heo ies o new physics [ 1 ], and may help o explain why ou uni e se con ains so li le an ima e . In ecen yea s, ALPHA has made landma k s udies o he an ihyd ogen a om, ad ancing o a poin whe e many H can now be apped simul aneously [ 2 ], held o e long imescales, and subsequen ly p obed wi h lase s and mic owa es o de e mine hei p ope ies [ 3 , 4 ]. Recen de elopmen s, including he demons a ion o lase cooling in an ihyd ogen [ 5 ], may acili a e u u e measu emen s o he an ihyd ogen spec um a hyd ogen-like p ecision. In his egime, H spec oscopy measu emen s made a ALPHA a e likely o be domina ed by sys ema ic unce ain ies ha will complica e e o s o compa e hese measu emen s agains simila s udies o hyd ogen made elsewhe e. Consequen ly, he e a e signi ican mo i a ions o ALPHA o also pu sue hyd ogen spec oscopy, enabling di ec , model-independen compa isons be ween bo h species wi hin he exis ing ALPHA-2 a om ap. A ALPHA, an ihyd ogen is syn hesized by slowly me ging cold popula ions o posi ons (e + ) and an ip o ons ( ¯ p ) inside a cylind ical Penning ap. In a ypical expe imen al sequence, a ound 3×106 e + a e cooled o ∼20 K and mixed wi h app oxima ely 105¯ p , yielding a ound 20 apped H pe mixing a emp [ 2 ]. Ideally, hyd ogen spec oscopy a ALPHA should in ol e a oms p epa ed h ough a simila p ocess, ensu ing ha compa able popula ions o hyd ogen and an ihyd ogen a e used in expe imen s. One ou e owa ds p oducing neu al hyd ogen a oms in his manne is he in eg a ion o a low-ene gy sou ce o nega i e hyd ogen ions (H−) o p o ons in o he expe imen . Fo compa ibili y wi h ALPHA’s exis ing cha ged pa icle aps and beamlines [ 6 ], his ion sou ce should p oduce beams wi h simila p ope ies o hose o ou exis ing an ip o on sou ce. P io o an ihyd ogen syn hesis, he ¯ p and e + a e ini ially p epa ed in sepa a e Penning aps app oxima ely 12 m apa . A ound 107¯ p a e ecei ed om he CERN ELENA decele a o e e y 100 s a ene gy 100 keV , and di ec ed h ough a deg ade oil so ha 5% o each bunch can be cap u ed in a –1– 2024 JINST 19 C01021 high- ol age ( 5 kV ) Penning ap wi h a magne ic ield o 3 T . The esul ing an ip o on cloud is cooled and comp essed o a adius o ∼0.4 mm , be o e being ex ac ed o anspo in o one o ALPHA’s wo H syn hesis aps. Cha ged pa icles a e ans e ed be ween ALPHA’s Penning aps as low-ene gy ( ≲100 eV ) bunches, o med by quickly ( 1μs ) manipula ing he elec ic po en ial along he ap axis so ha pa icles a e ejec ed in one di ec ion. PELLIS, p e iously de eloped a The Uni e si y o Jy äskylä (JYFL) [ 7 ], is a 10 keV H − ion sou ce ha gene a es beams wi h low emi ances and cu en s o up o 50 μA . Due o i s modes beam cu en , low ex ac ion ene gy and high b igh ness, PELLIS is well-sui ed o ALPHA’s equi emen s o a nega i e hyd ogen ion sou ce. In p inciple, posi i e ions ( H+ , H+ 2 and H+ 3 ) can also be ex ac ed om a PELLIS- ype sou ce by simply in e ing he applied ol ages, acili a ing a ange o schemes o neu al hyd ogen p oduc ion a ALPHA. P e ious wo k [ 8 ] has explo ed he p oposed in eg a ion o such an ion sou ce in o he ALPHA expe imen ia a low-ene gy elec os a ic beamline, showing ha such a beamline could deli e bunches o up o 3×108H−a ene gies below 100 eV. He e, we desc ibe a modi ied PELLIS sou ce ha has been de eloped o p o ide bo h H − ions and p o ons o ALPHA. In sec ion 2 , we p esen simula ions o he sou ce ex ac ion op ics, which ha e been op imised o a educed ( 5 keV ) ex ac ion ene gy and igh ly in eg a ed in o a di e en ial pumping sys em. In sec ion 3 , we p esen an analysis o expe imen al da a collec ed du ing commissioning o he sou ce a STFC ISIS, and show ha i al eady exceeds ALPHA’s equi emen s in e ms o ex ac ed beam cu en o bo h H−and posi i e ions. 2 Ion sou ce design A de ailed desc ip ion and cha ac e isa ion o he o iginal JYFL PELLIS sou ce is p esen ed in e . [7] . This sec ion will desc ibe modi ica ions o he o iginal PELLIS design ha we e implemen ed o compa ibili y wi h he p oposed anspo beamline o ALPHA [ 8 ]. A b ie e iew o he ion sou ce design and ele an beam pa ame e s is gi en below. Figu e 1shows a c oss-sec ion o he ALPHA PELLIS sou ce. PELLIS is a ilamen -d i en mul icusp ion sou ce, o iginally designed o he olume p oduc ion o H − beams wi h e y small emi ances. Typically, he ilamen chambe ( o he le in igu e 1 ) is illed wi h H 2 gas a 5×10−3mba , such ha a ilamen (a c) cu en o 5.6 A can gene a e 50 μA o H − beam cu en a 10 keV . Based on s udies o he o iginal JYFL PELLIS sou ce [ 7 ], H − beams a e ex ac ed om he 2 mm plasma elec ode ape u e wi h a 95% no malised emi ance o 0.015 mm m ad. The PELLIS il e ield is c ea ed by a pai o elec omagne s buil in o he on pla e o he sou ce, which can be uned o op imise he olume p oduc ion o H − wi hin he ex ac ion egion. Toge he , hese magne s p oduce peak ields anging om 0–30 mT pe pendicula o he beam axis when ene gised wi h cu en s up o 5 A . In p inciple, he il e magne s can also be used o une he species ac ion o he beam when he sou ce is con igu ed o p oduce posi i e ions. P e ious wo ks ha e shown ha s ong il e ields can supp ess he ex ac ion o molecula hyd ogen ions in small mul icusp ion sou ces such as PELLIS [ 9 ], wi h some au ho s achie ing p o on a ios as high as 90% [ 10 ]. He e, we de ine he p o on a io as he ac ion o he o al beam cu en ca ied by p o ons a he han molecula hyd ogen ions. The ex ac ion op ics ( sec ion 2.1 ), consis ing o wo Einzel lenses, a se o pa allel pla es and a collima o , we e con igu ed o a lowe ini ial beam ene gy ( 5 keV ) and o ma ching in o he –2– 2024 JINST 19 C01021 Figu e 1. Schema ic showing a c oss sec ion o he ALPHA PELLIS sou ce, including he di e en ial pumping chambe and ex ac ion op ics. The ed ou line indica es he egion shown in igu e 2. p oposed anspo beamline [ 8 ]. As shown in igu e 1 , he ex ac ion op ics a e igh ly in eg a ed in o a di e en ial pumping sys em ( sec ion 2.2 ), which p o ec s he ul a-high acuum (UHV) en i onmen o he ALPHA expe imen (< 10−9mba ) om he H2gas load inside he ion sou ce. 2.1 Ex ac ion op ics The e ised ex ac ion op ics we e de eloped and op imised based on ex ensi e IBSimu [ 11 ] simula ions. Fo cla i y, his sec ion will only desc ibe simula ions o H − beams ex ac ed om he ion sou ce; howe e , e y simila dynamics we e ound in calcula ions whe e posi i e ions ( H+ 𝑛 ) we e anspo ed h ough he ex ac ion op ics. Figu e 2 shows he simula ed ajec o ies o 5 keV H − ions om he plasma elec ode up o he midplane o he di e en ial pumping chambe , o an ini ial beam cu en o 50 μA. As in he o iginal PELLIS sou ce, elec ons ha a e co-ex ac ed wi h he H − beam a e de lec ed in o an elec on dump by a se o pe manen magne s, which a e in eg a ed in o he pulle elec ode in a dipole-an idipole con igu a ion. The ion beam is la gely una ec ed by hese magne s, bu none heless eme ges a a small ( 5 m ad ) angle o he nominal beam axis. In ou sou ce, he esidual de lec ion is co ec ed using a se o pa allel pla es 128.5 mm om he plasma elec ode. By quickly swi ching he ol age on hese pla es, he H − beam can be chopped in o 1μs pulses, so ha ions a e only deli e ed o ALPHA when equi ed (see igu e 2b) . Assuming an ini ial beam cu en o 50 μA , he bunch cha ge is 50 pC ( 3×108 ions), a in excess o ALPHA’s likely equi emen s o neu al hyd ogen p oduc ion. A 20 mm long, 5 mm ape u e a he cen e o he di e en ial pumping chambe (see igu e 1) ac s as bo h a collima o o he H − beam and a pumping es ic ion be ween he ion sou ce and anspo beamline. The ape u e dimensions we e chosen wi h inpu om acuum calcula ions –3– 2024 JINST 19 C01021 Figu e 2.IBSimu simula ion showing he ajec o ies o 5 keV H − ions h ough he e ised ex ac ion op ics, wi hin he highligh ed egion o igu e 1 . Simula ions a e shown wi h he pa allel pla es se o a) align he beam h ough he collima o , o b) de lec he beam in o a Fa aday cup moun ed a ound he ape u e. (see sec ion 2.2 ) o maximise he p essu e d op ac oss he di e en ial pumping chambe while minimising beam losses. As shown in igu e 2 , he ups eam Einzel lens ol age ( −3.1kV ) was op imised o ocus ions h ough he collima o . The downs eam Einzel lens (shown o he igh in igu e 1 ) will be used o ma ch he H − beam in o he p oposed anspo beamline. IBSimu was used o ack H − beams om he collima o o he exi o he di e en ial pumping chambe o a ange o Einzel lens ol ages. The esul ing pa icle dis ibu ions we e used o ini ialise sepa a e simula ions o he anspo beamline, which ha e been desc ibed elsewhe e [ 8 ]. Figu e 3 shows he ans e se phase spaces o a simula ed H − beam obse ed 134 mm a e he downs eam Einzel lens, o he op imal lens ol age o 9 kV . The beam has a no malised emi ance o 0.021 mm m ad in bo h planes, only sligh ly la ge han he emi ance epo ed o he o iginal JYFL PELLIS sou ce ope a ing a 10 keV. 2.2 Di e en ial pumping To maximise he li e imes o apped an ipa icles, ALPHA is subjec o s ic acuum equi emen s, wi h a maximum p essu e o 10−9mba in oom empe a u e pa s o he expe imen ’s beamlines. The in eg a ion o PELLIS- ype sou ce, wi h a p essu e o 10−2mba in he ilamen chambe , he e o e equi es a di e en ial pumping sys em o educe he esidual H 2 p essu e by six o de s o magni ude wi hin se e al me es. Ape u es buil in o he plasma elec ode and ex ac ion op ics a e used as he i s pumping es ic ions in his sys em, as shown in igu e 1. The H 2 p essu e wi hin he ion sou ce and anspo beamline was calcula ed using Mol low+ [ 12 ]. Figu e 4 shows he esidual p essu e as a unc ion o longi udinal dis ance om he ion sou ce backpla e, wi h he ilamen chambe held a 5×10−3mba . In each simula ion, H 2 gas is e acua ed om he di e en ial pumping chambe using a pai o acuum pumps a anged on ei he side o he pumping es ic ion. Fo ou chosen pumping a e o 500 L/s (p o ided by wo P ei e HiPace 400 u bomolecula pumps, ins alled on ei he side o he chambe ), we expec o achie e p essu es o 3×10−5mba wi hin he ups eam sec ion o he chambe , and ∼10−7mba a e he pumping es ic ion. As e idenced by he calcula ion, he p essu e in he anspo beamline is ul ima ely ∼10−9mba , meaning ha negligible gas load is in oduced o ALPHA om he ion sou ce. –4– 2024 JINST 19 C01021 Figu e 3. Simula ed ans e se phase spaces o a 50 μA H − beam measu ed 134 mm om he second Einzel lens. The solid (dashed) whi e line shows he one ( wo) sigma RMS phase space ellipse o he Twiss pa ame e s anno a ed abo e each phase space. 3 Commissioning esul s The ALPHA PELLIS sou ce was commissioned on he VESPA es s and [ 13 ] a STFC ISIS in Ap il and May 2022. P io o beam commissioning, H 2 gas was in oduced o he ilamen chambe o alida e he design o he di e en ial pumping sys em. Fo consis ency wi h he Mol low+ modelling in igu e 4 , an addi ional 10 mm squa e ape u e was ins alled be ween he ion sou ce and VESPA (app oxima ely 0.53 m om he sou ce plasma elec ode), ep esen ing he in e ace o he p oposed anspo beamline. Wi h he ilamen chambe a i s nominal p essu e, he ups eam (downs eam) po ion o he di e en ial pumping chambe ul ima ely eached a p essu e o 2×10−5mba (3×10−7mba ), consis en wi h he modelled pe o mance o he sys em. Fo beam commissioning, he sou ce was ini ially con igu ed o ex ac H − ions, and la e econ igu ed o posi i e ion p oduc ion. Beam cu en measu emen s we e p ima ily made using VESPA’s la ge-bo e Fa aday Cup (FC), loca ed app oxima ely 0.94 m om he PELLIS plasma elec ode. The il e magne s, pa allel pla es and ups eam Einzel lens we e coa sely op imised o maximise he beam cu en anspo ed o he FC a 5 keV . The il e magne s we e se o 1.9 A ( 12 mT ) o ex ac H − ions, and ini ially u ned o du ing posi i e ion p oduc ion. The op imal Einzel lens ol age was a ound −3.2kV, consis en wi h he IBSimu simula ions de ailed in sec ion 2.1. Figu e 5 shows he ex ac ed beam cu en measu ed as a unc ion o a c cu en , o bo h posi i e and nega i e hyd ogen ions. The ALPHA PELLIS sou ce achie ed a maximum beam cu en o 32 μA o H − ions, and 22 μA o posi i e hyd ogen ions. As shown in igu e 5 , hese alues a e somewha lowe han he 50 μA o H − cu en achie ed by he o iginal JYFL PELLIS sou ce, which is ope a ed a 10 keV . We expec ha he educed beam cu en is p ima ily due o he lowe ex ac ion ene gy; howe e , he coa se op imisa ion o o he pa ame e s and inc eased dis ance o he FC h ough wo limi ing ape u es may also esul in some pa icle losses. None heless, he achie ed beam cu en s exceed ALPHA’s likely equi emen s o neu al hyd ogen p oduc ion using ei he H−o p o ons (a leas 106ions pe 1 μs bunch). –5–