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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
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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–