Ci a ion: Feuch wange , J.;
E xeba ia, V.; Po illa, J.; Jugo, J.;
A edondo, I.; Badillo, I.; Asua, E.;
Vallis, N.; Elo za, M.; Albe di, B.; e al.
New Gene a ion Compac Linea
Accele a o o Low-Cu en ,
Low-Ene gy Mul iple Applica ions.
Appl. Sci. 2022,12, 4118. h ps://
doi.o g/10.3390/app12094118
Academic Edi o : Luigi Palumbo
Recei ed: 18 Ma ch 2022
Accep ed: 14 Ap il 2022
Published: 19 Ap il 2022
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2022 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
applied
sciences
A icle
New Gene a ion Compac Linea Accele a o o Low-Cu en ,
Low-Ene gy Mul iple Applica ions
Jo ge Feuch wange 1,2,* , Vic o E xeba ia 1, Joaquin Po illa 1, Josu Jugo 1, Iñigo A edondo 1, Ina i Badillo 1,
Es ibaliz Asua 1, Nicolas Vallis 1, Mikel Elo za 1, Beña Albe di 3, Ra ael Enpa an za 4, I a xe A iz 4, Iñigo Muñoz 4,
Unai E xebes e 5and Iñaki He nandez 5
1
IZPILab-Beam Labo a o y, Facul y o Science and Technology, Uni e si y o he Basque Coun y, UPV/EHU,
48940 Leioa, Spain; ic o [email p o ec ed] (V.E.); [email p o ec ed] (J.P.); [email p o ec ed] (J.J.);
[email p o ec ed] (I.A.); [email p o ec ed] (I.B.); [email p o ec ed] (E.A.);
[email p o ec ed] (N.V.); [email p o ec ed] (M.E.)
2Ike basque, Basque Founda ion o Science, 48009 Bilbao, Spain
3Helmhol z-Zen um Be lin (HZB), Albe -Eins ein-S asse 15, 14109 Be lin, Ge many;
[email p o ec ed]
4TEKNIKER, Basque Resea ch and Technology Alliance (BRTA), 20600 Eiba , Spain;
a ael.enpa an za@ eknike .es (R.E.); i a xe.a iz@ eknike .es (I.A.); inigo.munoz@ eknike .es (I.M.)
5Egile S.L., 20850 Menda o, Spain; [email p o ec ed] (U.E.); [email p o ec ed] (I.H.)
*Co espondence: jo [email p o ec ed]
Abs ac :
A new compac linea p o on accele a o p ojec (named LINAC 7) o mul iple low-cu en
applica ions, designed and buil in-house a he Beam Labo a o y o he Uni e si y o he Basque
Coun y (UPV/EHU) is desc ibed. The p ojec combines he Uni e si y, a esea ch echnology cen e
and a p i a e company wi h he aim o designing and building a compac , low-cu en p o on
accele a o capable o accele a ing pa icles up o 7 MeV. In his pape , we p esen an o e iew o
he accele a o design, summa ize he p og ess and es ing o he componen s ha ha e been buil ,
and desc ibe he componen s ha a e being designed ha will allow us o achie e he inal desi ed
ene gy o 7 MeV.
Keywo ds: pa icle accele a o s; ion sou ces; RF ca i ies; beam dynamics
1. In oduc ion
New compac pa icle accele a o s a e being de eloped a ound many kinds o s a e-
o - he-a echnologies and applica ions in such a way ha nea u u e indus ial elemen s
a e buil h ough a new gene a ion o ema kable impo an enhanced componen s cus om-
designed o hese newes accele a o s [
1
]. Ion linea accele a o s (LINACs) can be a alid
al e na i e o many impo an low-cu en , low-ene gy applica ions, including ma e ials
science analysis [
2
,
3
], doping semiconduc o s o polyme modi ica ion [
4
,
5
], as well as
in medical bioapplica ions [
6
,
7
], among o he ields. Ou LINAC 7 p ojec consis s o a
new compac linea p o on accele a o de eloped h ough he IZPILab-Beam Labo a o y a
he Uni e si y o he Basque Coun y (UPV/EHU), whose i s componen s a e al eady
ope a ional [
8
,
9
]. The inal 7 MeV ene gy was chosen because i can be achie ed wi h
no mally conduc ing elemen s and is high enough o ha e se e al p ac ical applica ions.
Fo example, i is high enough o p oduce neu ons i a li hium a ge is used. Mo eo e ,
LINAC 7 can also be used o p oduce sho -li ed adio iso opes o medical applica ions,
and, inally, i can be used as he injec o o o he s uc u es i highe ene gies a e equi ed.
The accele a o is composed o an elec on cyclo on esonance (ECR) ion sou ce, a low
ene gy beam anspo (LEBT), a adio equency quad upole (RFQ), a medium ene gy
beam anspo (MEBT), a d i ube linac (DTL), and, inally, a beam s op. In Figu e 1, a
simpli ied schema ic o he accele a o wi h he ene gies achie ed a e each elemen can
be seen. The boxes wi h solid bo de s indica e he componen s ha ha e been comple ed
Appl. Sci. 2022,12, 4118. h ps://doi.o g/10.3390/app12094118 h ps://www.mdpi.com/jou nal/applsci
Appl. Sci. 2022,12, 4118 2 o 11
and a e a di e en s ages o es ing. Do ed bo de s indica e componen s ha a e in he
design phase.
Figu e 1. Simpli ied schema ic o LINAC 7.
The di e en esea ch g oups ha a e aking pa in his p ojec came oge he be-
cause hey p o ide complemen a y expe iences ha , as a whole, a e needed o comple e
he p ojec . The Uni e si y o he Basque Coun y (UPV/EHU) p o ides he heo e ical
knowledge ha se es as he basis o he design, and is also esponsible o he ope a ion
and es ing o he componen s. TEKNIKER is a la ge esea ch ounda ion ha is e y
expe ienced in he design o ab ica ion o componen s and ha e been esponsible o
he deli e y o la ge componen s o Eu opean esea ch acili ies, such as RAL, STFC, and
ILL, among o he s. The las pa ne in his g oup is Egile, a company specializing in high
p ecision machining, and which has conside able expe ience in manu ac u ing pa s o
la ge accele a o acili ies, such as CERN.
2. LINAC 7 Accele a o Componen Desc ip ions
2.1. Ion Sou ce
The i s componen in he accele a o is an o - esonance elec on cyclo on esonance
(ECR) ion sou ce. I consis s o a plasma chambe made om a special leng h CF 63 acuum
pipe. One end o he ube is closed wi h a special cap ha includes a coaxial RF eed h ough
and a 3 mm ube o he gas eed. The o he end o he cylinde is pa ially closed o by
he plasma elec ode. The ECR magne ic ield is p o ided by a Hallbach- ype pe manen
magne a angemen o eigh ba s ha gene a es a ield coaxial wi h he chambe . Bo h
he magni ude o he magne ic ield, as well as he chambe dimensions, ha e been se o
co espond o a 3 GHz RF powe inpu . The RF powe is supplied o he chambe h ough
a DC b eak designed o allow RF o be ansmi ed, while isola ing he RF ampli ie om
he high ol age used o ex ac ion. The chambe is connec ed o he es o he sys em
h ough an alumina isola o . The se up can be seen in Figu e 2.
The ex ac ion op ics a e suppo ed by a special lange wi h a high ol age eed h ough
on he g ound side o he alumina isola o , and consis s o a se o h ee elec odes ha
ac as an Einzel lens. The wo elec odes on he ends a e connec ed o he g ound, while
he cen al elec ode is connec ed o a esis i e di ide ha always keeps i a hal o he
ex ac ion ol age, a oiding he need o an ex a high ol age supply. The p o on op ics
a e shown in Figu e 3. This was se up in his way o minimize he cos o he ion sou ce
by ha ing no ins umen s ha equi e powe o communica ions a high ol age. The ion
sou ce is designed o p oduce 30 keV p o ons.
Appl. Sci. 2022,12, 4118 3 o 11
Figu e 2. O - esonance ECR ion sou ce o LINAC 7.
Figu e 3.
Einzel lens o he ECR ion sou ce o LINAC 7 being measu ed a e inal assembly using a
Zeiss coo dina e measu ing machine a TEKNIKER.
2.2. Low Ene gy Beam T anspo
In o de o ma ch he beam ha he ion sou ce gene a es o he inpu equi emen s o
he adio equency quad upole (RFQ), a low ene gy beam anspo (LEBT) is used. Like
he ion sou ce, his elemen is buil and in use. I consis s o wo solenoids ha a e used o
ans o m he di e gen beam o m om he sou ce in o he con e gen one ha he RFQ
equi es. The acuum essel consis s o a cus om-made six-way c oss. Fou limbs ha a e
in he same plane ha e a nominal diame e o 100 mm, and ha e CF langes on he ends.
The o he wo limbs a e o a 40 mm nominal diame e and ha e quickCF langes on he
ends. The DN 40 limbs a e used as he beam pipe, and a solenoid i s o e each one o hem.
O he DN 100 b anches, wo a e used o beam diagnos ics, one o he u bomolecula
pump ha gene a es he acuum o he ion sou ce and he LEBT, and he las o a acuum
gauge and a acuum swi ch. The en i e se up can be seen in Figu e 4; he le side shows
Appl. Sci. 2022,12, 4118 4 o 11
a pho og aph o he sys em and he igh side a c oss-sec ion o he CAD model wi h he
elemen s labeled.
Figu e 4.
On he (
le
), a pho og aph o he LEBT as buil . On he (
igh
), a c oss-sec ion o he 3D
CAD model, 1 is he ion sou ce, 2 is he solenoids, 3 is he peppe po and 4 is he Fa aday cup.
A Fa aday cup and a peppe po a e used as beam diagnos ics in he LEBT—bo h
we e cus om designed and buil o his LEBT. Thei size is such ha hey can cap u e he
en i e beam when deployed and i en i ely inside hei espec i e DN 100 b anches when
e ac ed so ha hey do no in e e e wi h he beam du ing no mal ope a ion. S anda d
mo o ized acuum posi ione s a e used o posi ion he diagnos ics.
2.3. Radio F equency Quad upole (RFQ)
The pa icle beam gene a ed in he sou ce will be accele a ed using a adio equency
quad upole. This elemen is s ill in he design phase. In o de o educe he size o he
RFQ i s ope a ing equency was chosen o be 750 MHz. To u he educe he leng h,
he choice was made o dispense wi h he gen le bunche sec ion o he RFQ. This comes
a he cos o a lowe pa icle ansmission, bu his is no an issue since he goal is a low
cu en accele a o . The pa icles will be los a he en ance o he RFQ, meaning hey
will no ha e enough ene gy o gene a e any ac i a ion o he coppe . The inal RFQ is
expec ed o achie e an ou pu ene gy o 4 MeV a he end o 1.5 m, and cap u e be ween
15% and 30% o he pa icles a he en ance. The inpu pa ame e s o he RFQ we e se by
he measu ed alues o he beam in he LEBT. The design o he ca i y has been comple ed
and a cold model was manu ac u ed by Egile ou o ETP coppe (elec oly ic ough pi ch
coppe , UNS C11000) o alida e he design p ocess, as well as he abili y o machine he
RFQ wi h he equi ed p ecision, ha is, ole ances lowe han 0.1 mm. Figu e 5shows he
RFQ cold model unde measu emen . ETP coppe was used because he cold model is no
in ended o a acuum, bu i s ill p o ides in o ma ion abou he achie able ole ances and
su ace inishes du ing machining, and has oughly he same conduc i i y as oxygen- ee
high-conduc i i y coppe o he elec omagne ic es ing.
A key pa o he machining p ocess o he RFQ is he modula ion. Fo his eason he
cold model includes a dummy modula ion ha is ep esen a i e o wha can be expec ed
in he inal RFQ. Figu e 6shows one o he mino segmen s o he RFQ cold model whe e
he dummy modula ion is clea ly isible.
Geome ic ole ances we e e i ied using a Zeiss CMM (coo dina e measu ing ma-
chine, Ca l Zeiss Ibe ia, S.L.—Di ision Me ologia Indus ial, T es Can os, España) a
TEKNIKER. All gene al dimensions we e ound o be wi hin less han 0.1 mm o he design
alues and below 0.05 mm in he modula ion. Design o he inal modula ion is in p ocess;
he main goal is o achie e he highes accele a ion in he sho es dis ance a he expense
o pa icle ansmission.
Appl. Sci. 2022,12, 4118 5 o 11
Figu e 5.
RFQ cold model being ins alled o RF cha ac e iza ion uning and elec omagne ic
ield measu emen .
Figu e 6. Mino ane inside he RFQ cold model clea ly showing he dummy modula ion.
2.4. Medium Ene gy Beam T anspo (MEBT)
Once he design o he RFQ is inalized he ou pu pa ame e s will be analyzed, and,
based on hem, a decision will be made on whe he an MEBT is needed o no , be o e
passing he beam on o he nex accele a ing s uc u e. I an MEBT is needed, he opology
will be e y con en ional—i will consis o pill-box ype bunching ca i ies, magne ic
quad uples and will include bu on- ype beam posi ion moni o s o check he posi ion o
he beam in he pipe and o measu e he cu en .
Appl. Sci. 2022,12, 4118 6 o 11
2.5. D i Tube Linac (DTL)
The inal ene gy desi ed o he accele a o is 7 MeV as his is su icien o p oduce
adio chemicals o medical diagnos ics, and, i impac ed agains a li hium a ge , i can be
used o p oduce a low low o neu ons. This is impo an o he design p ocess o he DTL
because hese applica ions only equi e he igh ene gy and no as high a quali y beam
as one ha is o be u he accele a ed. The design o he DTL will be concu en wi h he
decision on he need o he MEBT, wi h he goal o inding he lowes cos solu ion ha
minimizes pa icle loss because, unlike a he beginning o he accele a o , he e pa icle
loss will esul in unwan ed adia ion p oduc ion. The DTL is a s anding wa e s uc u e
de o ed o accele a e pa icles based on he Al a ez d i ube. The idea was p oposed
a long ime ago bu emains in use in mos p o on and o he ion linacs. The esul ing
s anding wa e is employed o accele a e he pa icles. D i ubes a e suspended by s ems
and he beam passes h ough hem a he loca ions a which he oscilla ing s anding wa e
would p oduce beam decele a ion. D i ubes include ocusing magne s which help o
a oid beam spa ial dispe sion. In o de o educe he numbe o powe supplies needed,
he p oposed DTL will use pe manen magne quad uples in he d i ubes.
2.6. Beam S op
A beam s op is a c ucial elemen o he commissioning and es ing o he accele a o .
Fo his eason, i was decided o mo e he design and ab ica ion o he beam s op o he
beginning o he p ojec . Ra he han choosing a simple beam dump, i was decided o
design a Fa aday cup capable o con inuously wi hs anding he inal beam cu en and
ene gy o be used as he beam dump. This elemen will be used a e e y s age o he p ojec
and will be mo ed o he back o e e y new elemen ha is ins alled a he end o he
beam line.
Figu e 7shows a pho og aph o he comple ed beam s op du ing acuum es ing
ins alled a he end o he LEBT. G aphi e was chosen o he ac ual beam s ike su ace
o se e al easons. I is a conduc i e ma e ial wi h a e y high mel ing poin , bu , mos
impo an ly, as is epo ed in he li e a u e, no neu ons a e p oduced when a 7 MeV
p o on beam impac s agains i . To minimize he ene gy lux on he su ace, he beam is
impac ed a a shallow angle agains he g aphi e. The ene gy deposi ion on he g aphi e
was simula ed using GEANT4 [
10
], and he esul ing powe deposi ion map was used o
simula e he hea gene a ion in Ansys [
11
]. I was ound ha he beam s op can unc ion
wi hou wa e cooling when placed a e he ion sou ce, bu has o be wa e -cooled when
used o he ull 7 MeV beam. Howe e , as a sa e y measu e, he beam s op was designed
so ha i could ope a e o up o 5 min wi hou he ex e nal su ace o he acuum enclosu e
exceeding 300 deg ees Celsius. Two he mocouple wells we e d illed in o he coppe piece
ha suppo s he g aphi e, and he empe a u e measu emen s will be used as inpu s o he
sa e y sys em. Should he e be an in e up ion in he cooling wa e supply he empe a u e
ise will igge a shu down. The o e design o he beam s op p o ides enough ime o
his o be comple ed sa ely be o e he empe a u e inc ease could cause any damage.
Appl. Sci. 2022,12, 4118 7 o 11
Figu e 7.
LINAC 7 beam s op (Fa aday cup). Ins alled beam s op a he end o he LEBT o ini ial
es ing unde low ene gy. Top igh shows a c oss-sec ion o he cad model; he slan ed impac ace is
isible he e.
2.7. Con ol Sys ems
Each o he elemen s o he accele a o equi es a se o speci ic auxilia y sys ems o
unc ion, o example, as acuum, e ige a ion, high ol age powe supply, magne powe
supply, o RF powe . In o de o main ain he modula i y o he accele a o , each accele a o
elemen has i s own con ol cabine s ha house he con olle s o he auxilia y sys ems.
All hese cabine s a e connec ed o a gene al con ol sys em.
The a chi ec u e o he con ol sys em is designed ollowing a modula scheme. Each
main elemen in he linac has a dedica ed con olle implemen ed in PXI o Compac RIO
ha dwa e and hese con olle s a e connec ed o each o he o e a TCP/IP ne wo k. The aux-
ilia y sys ems and diagnos ics connec o hei assigned con olle di ec ly o e a TCP/IP
connec ion. The PXIs o cRIOs ha e local con olle s unning in eal- ime LabVIEW and ac-
cep commands om he supe ision and moni o ing sys em. The local con olle s acqui e
he ele an da a om he machine and manage he local auxilia y elemen s and diagnos-
ics, allowing, o example, o he inse ion o e ac ion o he Fa aday cup o peppe po
in he LEBT. The high powe RF o he ca i ies, such as he RFQ,will be con olled by a
low-le el RF con ol sys em, which will use a di ec digi al a chi ec u e ollowing he wo k
p esen ed in [
12
]. The con ol cabine s also include he in e locks and sa e y con ol sys em,
which is implemen ed using PILZ sa e y PLC ha dwa e. The con olle s o each elemen
connec o he Pilz ha dwa e ha insu es he sa e y o he ins alla ion, especially he pa s
ha could pose a dange o people, o example, unla ching he high- ol age enclosu e
o he ion sou ce. All da a is au oma ically sen o a moni o ing sys em and selec ed
pa ame e s and measu emen s a e sa ed in an InFluxDB da abase. Because his con ol
a chi ec u e is modula , he scalabili y o he sys em is assu ed, allowing he in eg a ion o
o he echnologies ollowing a s uc u e simila o an EPICS ne wo k ha , in he u u e,
could be in eg a ed in o an ac ual EPICS ne wo k.
3. Expe imen and Simula ions
3.1. Ion Sou ce
The desc ibed ECR ion sou ce is wo king as equi ed o LINAC 7. As an illus a ion
o he ex ac ed p o on beam, Figu e 8shows an image measu ed o a simple 6 keV beam
spo on a P43 phospho escen sc een when ocused o he smalles size achie able.
Appl. Sci. 2022,12, 4118 8 o 11
Figu e 8.
Image in ensi y p o ile measu ed om he image gene a ed on he P43 sc een o e y low
ene gy p o on beam, and he Gaussian ha i s i .
The ion sou ce has been shown o be capable o gene a ing beam cu en s o up o
10 uA
wi h emi ances
e
x = 0.0099543 mm m ad and
e
y = 0.0122865 mm m ad, measu ed
wi h a peppe po [13]. These measu emen s a e shown in Figu e 9.
Figu e 9.
Beam emi ance as measu ed wi h he peppe po loca ed in he cen al sec ion o he LEBT.
3.2. Low-Ene gy Beam T anspo
The LEBT is wo king as designed in conjunc ion wi h he ion sou ce, h ough he
double p o on op ics combina ion comp ising he Einzel elec ic ield lens and he solenoids
magne ic ield lens, shown in Figu e 10, o anspo he p o on beam om he ion sou ce
o he RFQ.
Appl. Sci. 2022,12, 4118 9 o 11
Figu e 10.
On he le , simula ion o he beam (in blue) i s ocused a he ex ac ion om he ion
sou ce, and hen a he wo solenoids in he LEBT. On he igh , he pa icle dis ibu ion in he X-Y
plane o a 3000 pa icle simula ion.
3.3. Radio F equency Quad upole
A high- ol age has o be p oduced be ween he RFQ anes by exci ing a quad upola
mode in such a way ha an ex emely e ec i e elec os a ic lens e ec is p oduced o e he
pa icle beam a elling along he axis o he RFQ. The modula ion o he ane elec odes
shapes along he s uc u e enables pa icle accele a ion oge he wi h he ocusing and
bunching e ec by means o a single RF quad upola ield a he esonan equency.
A con inuous, al e na ing quad upole channel is o med along he RFQ axis wi h pe iodic
leng h. The uni a y leng h depends on he wa eleng h and he inc easing ene gy o he
pa icles along he RFQ. The RFQ ope a es unde acuum condi ions o a oid collisions
be ween ai molecules and he pa icle beam. The goals o he EM design a e o p o ide
he desi ed RF ield s uc u e a he wo king equency, which consis s o a TE210 mode
wi h minimal losses, by keeping away in equency o he undesi ed modes ha can appea
close o he desi ed mode due o he complex geome y o he RFQ. The EM design also
has o conside he signal injec ion, uning elemen s, and he e ec o o he elemen s, such
as acuum po s, signal pick-ups, e c. Typical Q ac o s achie ed a e o he o de o se e al
housand, bu he ope a ion o an RFQ needs a high amoun o RF powe , so he mal
issues ha e o be managed in o de o a oid undesi ed e ec s. The mal simula ions a e
needed o op imize he RFQ, bo h om he EM and he mechanical poin s o iew. Wa e
channels a e commonly implemen ed h ough he anes along he s uc u e o dissipa e
he mal powe in he ane ips, whose shape is c i ical o he RFQ ope a ion. In Figu e 11,
he p oposed ans e sal sec ion and he quad upola elec ical ields can be obse ed. The
co esponding magne ic ields a e shown in Figu e 12.
Figu e 11. Quad upola elec ic ields in a ans e sal cu o he RFQ s uc u e.
