Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Study of ion backflow with 2GEMs + MICROMEGAS for the
Study of ion backflowwithupgrade
2GEMs + MICROMEGAS for the
ALICE-TPC
ALICE-TPC upgrade

Energy resolution (%)

K. Terasaki,∗1,∗2 H. Hamagaki,∗2 and T. Gunji∗2
K. Terasaki,∗1,∗2 H. Hamagaki,∗2 and T. Gunji∗2
ALICE is the dedicated experiment to study Quark
Gluon PlasmaALICE(QGP),
a hotand dense
Quantumis thededicatedexperiment
to study Quark
chromodynamics
heavyiondensecol- Quantum
Gluon(QCD)
Plasmamedium,(QGP), via
a hotandlisions at LHC.
The ALICE Time
Projection
Chamberchromodynamics(QCD)
medium,via heavy ion col1)(ALICE-TPC),
which
is thedevicein Projection
the cen- Chamberlisionsat LHC.
Themain
ALICETime1) particle identiﬁcation oftral barrel (ALICE-TPC),
for tracking andwhich is the main device in the cen3
charged particles,
consistsof a 90 mcylindertral barrel
for tracking
andparticle ﬁlled
identiﬁcation ofwith Ne/COcharged
particles, consists of a 90 m3 cylinder ﬁlled
2 /N2 (90/10/5).
SecondarywithionsNe/CO
generated
an electron-avalanche(90/10/5).
2 /N2 inprocess in the Secondary
TPC returnions
to thedrift space,
known
asgenerated
in anelectron-avalanche“Ion Backﬂow(IBF).”
BecauseIBF distorts
the elecprocess
in the
TPC returnto the drift
space, known as
Fig.
1. A schematic of measurement setup with 2GEMs +tric ﬁeld in “Ionthe drift
space,(IBF).”
its reduction
is essential
to theBackﬂow
BecauseIBF distorts
elecMICROMEGAS.
Fig. 1. A schematic of measurement setup with 2GEMs +achieve goodperformancethespace,
TPC.itsA reduction
gating grid
tric
ﬁeld in the ofdrift
is essential toMICROMEGAS.
system is widelyemployed
to reduce IBF;
however,
it gating gridachievegood performanceof theTPC. A
limits the dataacquisition
to thetoorderof IBF;kilo- however, it
systemis widely rate
employed
reducehertz. Thelimits
rate ofcollisionsrate
at tothethe
LHC
theheavy-ion
data acquisition
order of kilo- 20
will be 50 kHz
from2019.
ALICE-TPC
will beat the LHC
hertz.
The
rateTheof heavy-ion
collisions
2020
18
upgraded towillreadbeout
dataof Pb-Pb
collisions
con50thekHzfrom2019. The
ALICE-TPC
will be1818tinuously, which
requires
IBF out
andtheenergyupgraded
to readdataresolutionof Pb-Pb forcollisions con- 1655
1616
Fe to be lessthan 1.0%
12%, IBF
respectively,
at resolution
atinuously,
whichandrequiresand energy
for 142)55
gain of 2000 for
mixtures.
Fe Ne-based
to be lessgas
than1.0% and 12%, respectively, at a 121414
The performanceof quadruple
GEM
stacks as2)again of 2000
for Ne-basedgas mixtures.
1212
readout chamber
being investigatedfor thisup-stacks as a 10
The isperformanceof quadruple
GEM
1010grade. In addition,with 2GEMs+ MI-for this up- 8
readout investigations
chamber is being
investigated88
CROMEGAS
are Inbeing
carriedinvestigations
out. The MICROgrade.
addition,with 2GEMs + MI- 6
MEsh-GAeous
Structure are(MICROMEGAS)
has Thea MICRO- 0
CROMEGAS
being carried 3)
out.
0.5
1.5
2
2.5
366 1
IBF (%)
micromesh ∼100 µm aboveStructurea readout.(MICROMEGAS)
Electrons are 3) has aMEsh-GAeous
0.5
1.5
22.5
3300
0.5
111.522.5IBFIBF (%)(%)
multiplied throughapplicationa potential
diﬀermicromesh∼ 100 µmofabovea readout.
Electrons areFig.
2. Energy resolution as a function of IBF for Ne/CO2
ence between
the mesh throughand the readout(∆VMM
Secmultiplied
applicationof a). potential
diﬀer(black)and(red).
Fig.Ne/CO
2. Energy
as a function of IBF for Ne/CO2
2 /N2resolution
ondary ionsence
are absorbed
eﬃciently
on the meshwhenbetween themesh andreadout(∆VMM ). Sec(black)andNe/CO/N
22 (red).
the electric ﬁeldabove
is considerablyondary
ionsthearemeshabsorbed
eﬃcientlysmaller
on the mesh when(by a factortheof 100)
thanthat
below
mesh.
electric
ﬁeld
above
thethemesh
is considerably smaller
A schematicthe measurement
2GEMs(by ofa factorof 100) thansetup
thatwithbelow
the mesh. measurements are indicated by diﬀerent markers; forexample, theGEM1-MM arescanindicatedrepresents
pointsmarkers; formeasurements
by thediﬀerent+ MICROMEGAS
is shown
Fig. 1. Our
MI-with 2GEMs
A schematicof theinmeasurement
setup
correspondingtovariations
ofboth∆Vexample,theGEM1-MMscanrepresents
CROMEGAS
a 400 LPI (LinesPer Inch)mesh
GEM1 and the points+ has
MICROMEGAS
is shown
in Fig.
1. Our MI2∆Vtomaintain
thegainof2000.
Itshows
thatcorresponding
tovariationsofboth cer∆VGEM1 andlocated 128 CROMEGASµm above 120 has
readout
pads× 10 mm
MMa 400
LPI(8(LinesPer) Inch) mesh2
tain
pointsmeet
therequirementfor
Ne/CO(90/10)∆V
tomaintainthegainof2000.
Itshowsthat cer2
and the current
fromtheabove
readout
is summed
located128allµm120 pads
readout
pads (8 × 10 mm )MMandIBF
islessthan0.5%
atanenergy
resolution
oftainpointsmeet
therequirement
for
Ne/CO
up. Two 50
GEMs
above pads
MI- is summed
2 (90/10)
andµm-thickthe current
fromareallplaced
the readout
∼
12%
for
Ne/CO/N(90/10/5).
Additional
nitroandIBFis
lessthan0.5%
atanenergy
resolutionof
22
CROMEGAS.
is 50
deﬁnedas Ic /I
up. IBF
Twoµm-thick
GEMs
are Iplaced
a , where
c and above MIgen
leads
tobetterIBFbecausealargerpotential
dif∼
12%
for
Ne/CO/N(90/10/5).
Additional
nitroIa are the current
at the IBF
cathodeplane and22CROMEGAS.
is deﬁned
as Icthat/Ia , atwhere Ic andference
to achieve
thegainof 2000a andsubgen leads
to betterIBFbecauselargerpotential difthe anode pads,calculated
Ia are respectively.
the current atGain
the iscathodeplaneasand thatat is requiredsequently
theﬁeldratioofMICROMEGASdecreases.
ferenceisrequired
toachieve
thegainof2000
and subIa /(Nseed × theR × e),
whereNseed, R, and e areGain
the numanodepads,respectively.
is calculated as55Theevaluation
for
Ne/CO/N(90/10/5)
atabetter
sequently
theﬁeldratioofMICROMEGAS
decreases.
22ber of seed IelectronsforFe wherein Ne Ngas,
rate eofare the numR × e),
R, anda /(Nseed ×seed ,the55(and worseforIBF)
is in 2progress.
Even- at a better
The evaluation
Ne/CO/N2 (90/10/5)
X-ray from berFe,
chargeforof 55
anFeelectron,
re- the energyof andseed theelectrons
in Ne gas,
rate of resolution
55
tually,theperformanceofaMICROMEGAS
thathasenergyresolution(andworseIBF)
isinprogress.
Evenspectively. X-ray from Fe, and the charge of an electron, rea
780
LPI
micromesh
and
90µm
gap
will
beevaluated.
tually,theperformanceofaMICROMEGAS
thathasThe correlation
between energy resolution and IBF
spectively.
a780
LPI
micromesh
and
90µm
gap
will
beevaluated.
for Ne/CO2 (90/10)
and Ne/CO
with and IBF
The correlation
betweenenergy resolution
2 /N2 (90/10/5)
References
diﬀerent voltage
setups2 (90/10)
is shownand
in Fig.
2. 2Diﬀerent
for Ne/CO
Ne/CO/N2 (90/10/5)
with1)
CERN-LHCC-2000-001
References (2000).
diﬀerent voltage setups is shown in Fig. 2. Diﬀerent
GEM1-MM scan (VEnergy
Energy resolution
resolution (%)(%)

GEM1-MM scan (VGEM1-MM scan (V=210V) (Ne/CO )GEM22=230V) (Ne/CO )2=250V)GEM1-MM(Ne/CO ) scan (VGEM2
GEM2

GEM1 scan (Ne/CO /N2)2

Et1 scan (Ne/CO /N2)
22

GEM1-MM scan (V=210V) (Ne/CO(Ne/CO ))GEM222

GEM2
GEM222

GEM22=230V) (Ne/CO(Ne/CO ))GEM1-MM scanscan (V(VGEM2=250V)=250V) (Ne/CO(Ne/CO2))GEM1scan (Ne/COscan(Ne/CO /N/N ))GEM1-GEM2 scan (Ne/CO /NGEM1)
22 2222
Et1scan (Ne/CO(Ne/CO/Nscan/N22))
GEM2-MM scan (V=220V)Et1(Ne/CO/N )GEM1

GEM2-MM scan (VGEM2-MM scan (VGEM2-MM scan (V222222

GEM1-GEM2scan (Ne/CO(Ne/CO /N/N ))=230V)GEM1-GEM2(Ne/CO /N2) scan
22 222GEM2-MM(V=220V)
scan(V=220V) (Ne/CO(Ne/CO /N/N22))=240V)GEM2-MM(Ne/CO /Nscan)

GEM1
GEM1

GEM1
GEM122

GEM1
GEM122GEM12

GEM2-MM(Vscan(VGEM1=230V)=230V) (Ne/CO(Ne/CO2/N/N ))=250V)GEM2-MM(Ne/CO /Nscan)
GEM12 2222
GEM2-MM scan=240V)
GEM2-MMscan (V(V=240V) (Ne/CO(Ne/CO /N/N22))

GEM1

GEM2-MM scan
GEM2-MMscan (V(VGEM1=250V)=250V) (Ne/CO(Ne/CO2/N/N22))∗1∗22) CERN-LHCC-2013-020(2013).
1) CERN-LHCC-2000-001(2000).
RIKEN Nishina Center
3)
Y.
Giomatarisetal.:
Nucl.
Instr. and(2013).
Meth. A 376, 292)
CERN-LHCC-2013-020
Center for∗1NuclearStudy,Graduate
RIKEN
Nishina
CenterSchool of Science, Uni(1996).
versity of ∗2Tokyo3)
Y.
Giomatarisetal.:
Nucl.
Instr. and Meth. A 376, 29Center for Nuclear Study, Graduate School of Science, Uni(1996).

versity of Tokyo- 121 -

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