THE ACTIVE TARGET
TIME PROJECTIONCHAMBERAT NSCL
D. Bazin!
National Superconducting Cyclotron Laboratory!
Michigan State University

Luminosity with slow radioactive beams‣ Solid targets provide poor luminosity‣

Inverse kinematics reactions in solid targets (probe)‣

Target-like particle has little energy to leave target material‣

Compromise between resolution and number of nuclei in target(resolution goes against luminosity)

D. Bazin, ARIS 2014, June 2, 2014

Luminosity with slow radioactive beams‣ Solid targets provide poor luminosity‣

Inverse kinematics reactions in solid targets (probe)‣

Target-like particle has little energy to leave target material‣

Compromise between resolution and number of nuclei in target(resolution goes against luminosity)‣ New approach: active target + time projection chamber‣

Target no longer inert material, but used also to detect particles‣

Gas target ideal for low energies‣

Time Projection Chamber tracks particles from the vertex of thereaction (no lost energy in inert target)
D. Bazin, ARIS 2014, June 2, 2014

Active Target Time Projection Chamber‣ A detector tailored to low energy reactions‣

Active gas target and full 4π angular coverage‣High luminosity without loss of resolution‣

Beam slowing in gas gives excitation function

D. Bazin, ARIS 2014, June 2, 2014

Active Target Time Projection Chamber‣ A detector tailored to low energy reactions‣

Active gas target and full 4π angular coverage‣High luminosity without loss of resolution‣

Beam slowing in gas gives excitation function‣ Requirements and restrictions‣

Target gas has to provide good electron amplification (mixtures)‣Trigger generation: slowing down beam particle ionize the gas‣

Time projection chamber is slow (rate limitation)

D. Bazin, ARIS 2014, June 2, 2014

Active Target Time Projection Chamber‣ A detector tailored to low energy reactions‣

Active gas target and full 4π angular coverage‣High luminosity without loss of resolution‣

Beam slowing in gas gives excitation function‣ Requirements and restrictions‣

Target gas has to provide good electron amplification (mixtures)‣

Trigger generation: slowing down beam particle ionize the gas‣

Time projection chamber is slow (rate limitation)‣ Very well adapted to rare isotope beams!
D. Bazin, ARIS 2014, June 2, 2014

Principle of operation
Insulator!gas!volume!(N2)

Field!shaping!rings

Cathode:!<!100!kVDC!(1kV/cm)
Pad!plane!and!
electron!
ampliﬁca$on!
device!
(Micromegas)

e'e' e' e

Beam' e' e'e'e'e'e'e' 'e 'eeldElectric!ﬁ

Ac$ve!gas!volume!
He,!H2,!D2!…
D. Bazin, ARIS 2014, June 2, 2014,'>,zem%,
1irD

Posi%on!
'>(x,,y)AT-TPC concept‣ Straight and tilted (7°)
configurationsYoke‣ Tilt relative to beamaxis to increaseaccuracy for smallangles

TPCBeam‣ Placed inside 2 Tesla

dionolesolenoid (increaserange and measureBrho)S‣ 250 liters (1 m by 55cm) active volume

D. Bazin, ARIS 2014, June 2, 2014

Detector details‣ Based on prototype design with few improvements

D. Bazin, ARIS 2014, June 2, 2014

Detector installation & servicing

D. Bazin, ARIS 2014, June 2, 2014

Electron amplifier: Micromegas
Ionizing charged particle
e-E = 1 kV/cme-e-e-e-e-e-

E = 100 kV/cm

micromegas mesh
Amplification gap (100 µm)
Pad plane (V=0)
Readout electronics‣‣‣

Negligible charge spread, sharp images
Very robust against sparking
Can operate in different conditions (gases, pressures)
D. Bazin, ARIS 2014, June 2, 2014

Close-up on Micromegas

D. Bazin, ARIS 2014, June 2, 2014

10,240 pad plane geometry‣ Optimized fordetector
inclinations from 0°
to 7° relative tobeam axis

‣ 4 small triangles in alarge one‣ Small triangle side= 4.67 mm‣ 55 cm diameter disk
D. Bazin, ARIS 2014, June 2, 2014

Digital Readout Electronics‣ Accommodateelectronics for the10,240 pads without
cable connections‣ 40 front-end cards fit inpentagonal pattern‣ Shielding covers

electronics cards bypairs‣ Only 7,000 channels

instrumented (3 receivercards on loan in France)
D. Bazin, ARIS 2014, June 2, 2014

GET (General Electronics for TPCs)‣ Trigger needs to filter out unreacted beam events‣

GET electronics provides
discriminators on each pad‣

Running multiplicities of each
AsAd routed to MuTanT
through CoBos‣

Trigger configuration can beprogrammed‣ AGET front-end chips provide

various gains and shaping times‣ GET: CEA-Saclay, CENBG-Bordeaux, GANIL-Caen, NSCL
D. Bazin, ARIS 2014, June 2, 2014

Example of reconstructed event‣ Track from alphasource placed inside
the active volume

D. Bazin, ARIS 2014, June 2, 2014

Example of reconstructed event‣ Track from alphasource placed inside
the active volume‣ 3D plot clearly show
time correlation

D. Bazin, ARIS 2014, June 2, 2014

Example of reconstructed event‣ Track from alphasource placed inside
the active volume‣ 3D plot clearly show
time correlation‣ Individual tracesshow difference inamplitude between
small and large pads

D. Bazin, ARIS 2014, June 2, 2014

Trigger generation‣ Define pad regions•with different trigger •attributes

Trigger enabled
Reading if hit••

Trigger disabled
Reading always

200‣ Example shows

configuration forelastic scattering

1000‣ More complex pattern

triggering
configuration can beprogrammed • Pad not connected
-100

-200

-200

D. Bazin, ARIS 2014, June 2, 2014••-1000100
Triggerdisabled
Reading if hit

200Commissioning on ReA3 linac
4He
Beam
provided:‣@ 6 MeVAT-TPC‣ Gas target: He (90%)
CO2 (10%) 100 Torr

‣ No magnetic field‣ Measure excitation

function of (4He,4He)
elastic scattering

ReA3

D. Bazin, ARIS 2014, June 2, 2014

Online event display‣ Atypical eventshows twoscattering eventsin one shot

‣ Maximum drift
time of 40 µs‣ instantaneous

beam rate of ~3kHz (600 Hz @20% duty cycle)
D. Bazin, ARIS 2014, June 2, 2014

Experimental program with PAT-TPC‣ Alpha cluster structure of neutron-rich nuclei‣

Resonant scattering: 6He+4He, 10Be+4He, 8He+4He (not yet): TWINSOL @U. of Notre-Dame, ISAC @ TRIUMF (not yet)

‣ Fusion cross section studies‣

6He+40Ar sub-barrier fusion cross sections: TWINSOL @ U. of Notre-Dame‣ Isobaric analog proton scattering‣

Test on 124Sn+p, experiment on 132Sn+p (not yet): ATLAS @ Argonne
National Laboratory12‣ 3α decay mode of Hoyle state in C‣

β-decay of 12B implanted in PAT-TPC: TWINSOL @ U. of Notre-Dame
D. Suzuki et al., Nuclear Instruments and Methods in Physics Research A 691 (2012) 39–54
D. Bazin, ARIS 2014, June 2, 2014

64 D. SUZUKI et al.

He+ He scattering

reconstruction‣ Ex from TKE, scattering
4angle of He and energy
6of He(a)Counts /0.1 MeV‣ Missing mass×103+2scatter in Exθ from‣
6He(4He,2n)8Be channel

32+1210‣ Energy of He before(b)E θx [MeV]θ from angles onlyE‣ xHex3

6reaction known fromvertex determination

60gs

4θcm>90°

20-2-202

4E x [MeV]
D. Suzuki et al., Phys. Rev. C 87, 054301 (2013)

FIG. 5. (Color online) (a) Excitation-energy spectrum of 6 He
(unshaded histogram). The best-fit result (thin red line) is shown
D. Bazin, ARIS 2014, June 2, 2014
together with the contribution of the background from the 6 HeThe backg
line accou
In themass met
curve whregion andprecise po
might resspectrum fhistogramstructure,matics. To
energies a
obtained f
between thquire the kcan correc
as long as
emission a
The scattegate was
90 degrees
α nuclei.
0 MeV indstate haveof eventsof the pea
systematicstate wide
angles of sExcitation functions & Angular distributions
D. SUZUKI et al.

‣ Elastic and inelastic scattering
measured between 2 and 6MeV60

θ c.m. = 65 - 135°(a)

θ c.m. = 65 - 75°

(b)

× 1.5
× 1.54020‣ Angular distributions measured60

θ c.m. = 75 - 85°(c)θ c.m. = 85 - 95°

(d)

× 1.5

between 40° and 130°

× 1.5

to 9.98(15) MeV resonance in10Be, identified as 4+‣ Deduced partial width Γα/Γ of0.49(5) indicate highly
developed α structured σ/d Ω [mb/sr]

40‣ Peak at 2.56 MeV corresponds

PHYSICA

2060

θ c.m. = 95 - 105°(e)θ c.m. = 105 - 115°(f)× 1.5× 1.5

40

FIG. 7
tions of 6
integratedand (b)–(hThe data f
the filledscattering
open circle
scaled bydotted line
respective2060

θ c.m. = 115 - 125° (h)(g)θ c.m. = 125 - 135°

× 1.5

× 1.5

40
20

D. Suzuki et al., Phys. Rev. C 87, 054301 (2013)

234562345

6

E c.m. [MeV]

be measured in the present study due to the lack of acceptanceat this energy. While there are no resonances as strong as theobserved
D. Bazin, ARIS 2014,oneJune
2, 2014 in the elastic channel, a small peak is visible at
4.4 MeV in the inelastic channel consistently over the angular

until the cross sections are en
In the inset of Fig. 8(h), the2.7 MeV (filled circles) are cdata at Ec.m. = 3.3 MeV (opeExcitation functions & Angular distributions
RESONANT α SCATTERING OF 6 He: LIMITS . . .

‣ Elastic and inelastic scattering
measured between 2 and 6MeV10101‣ Deduced partial width Γα/Γ of0.49(5) indicate highly
developed α structure(b) E c.m. = 5.4 MeV(c) E c.m. = 5.1 MeV(d) E c.m. = 4.7 MeV

10d σ/d Ω [mb/sr]

between 40° and 130°

to 9.98(15) MeV resonance in
10
Be, identified as 4+(a) E c.m. = 5.8 MeV102‣ Angular distributions measured‣ Peak at 2.56 MeV corresponds

CRC
CRC (+ ~0.5 MeV)

21102
101(e) E c.m. = 4.2 MeV(f) E c.m. = 3.8 MeV

102
101D. Suzuki et al., Phys. Rev. C 87, 054301 (2013)

measurestimat
range θdepend%α /% i%α /% rToreaction
the codof Kho
were mbasic mdoublepotenti

500(g) E c.m. = 3.3 MeV
406080100120 1404060 80 100120

60

θ c.m. [degrees]

80

whereRC = 1
real pois theRW =The paobtain
The do(h) E c.m. = 2.7 MeV

DFPOT

100

nuclearFermi dprotonthat ρnthe FC6
1.8-Me120

140

FIG. 8. (Color online) Angular distributions of elastic 6 He + αscattering. The results of CRC calculations (solid lines) are compared
D. Bazin, ARIS 2014, June 2, 2014
to the data. The CRC results at the higher energy bins are also shownOriginal AT-TPC scientific program‣ National Science Foundation funding of $688k‣ Exciting physics program planned and to develop!

D. Bazin, ARIS 2014, June 2, 2014

AT-TPC team and collaboration‣ NSCL team of 10 people‣

Faculty: D. Bazin, W. Mittig, B. Lynch‣

Engineers: N. Usher, F. Abu-Nimeh‣

Post-docs: D. Suzuki (until 2012), T. Ahn, S. Beceiro-Novo‣

Ph.D. students: A. Fritsch, J. Bradt‣ Outside collaborators‣

J. Kolata, U. Garg (U. of Notre-Dame)‣F. Bechetti (U. of Michigan)‣R. Kanungo (Saint Mary’s U.)‣M. Heffner (LLNL)‣

I-Yang Lee, L. Phair (LBL)
D. Bazin, ARIS 2014, June 2, 2014