Cryogenic ion catchers using superfluid helium
and noble gases
Sivaji Purushothaman
KVI, University of Groningen
The Netherlands
Content
• Introduction
• Superfluid Helium
• Cryogenic gas catchers• Off-line • On-line
• Summary
• Future plans
(mg/cm3) (rel.)T (K)
1 bar He
gas
1 bar He gas
1 bar He gas
liquid He
superfluid He
et
Impurities get frozen out !!!
High density at low temperature
(mg/cm3) (rel.)T (K)
1-2 Kliquid
vapour
room Tvacuum
Cold RIBs from superfluid helium: concept
1. stop high-energy radioactive ions in superfluid helium
snowballs
2. transport to the surface by electric fields
3. extraction across the surface into the vapour regionel
ectr
odes
4. transport to a vacuum, room-temperature regiontri
vial
3. extraction across the surface into the vapour region
N. Takahashi e
t al.
-decay recoil ion source
ranges in LHe
recoil: 0.5 m: 500 m
ranges in LHe
recoil: 0.5 m: 500 m
223Ra source
-decaydetectio
n
€
rE He
gas
223Ra: source of 219Rn ions
1.8 ms
223Ra
219Rn
5-6 MeV
~ 100 keV
215Po
211Pb
211Bi
207Tl
207Pb
4.0 s
11.4 d
36 m
2.2 m
4.8 m
How to extract snowballs at low temperature ?
12
8
4
0
snowball efficiency (%)
2.01.61.2temperature (K)
25
20
15
10
5
0
extraction efficiency (%)
2.01.61.2temperature (K)
conflicting temperaturerequirements
conflicting temperaturerequirements
W.X. Huang et al., NIM B 204 (2003) 592N. Takahashi et al., Physica B 329 (2003) 1596
W.X. Huang et al., Europhys. Lett. 63 (2003) 687We
go for
low t
empera
ture
Electric-field assisted extraction
5 cm
43210
SourceBottom electrode
Guidingelectrodes
Focusing electrode
Collector foil
Detector holder LHe dewarLHe dewar
LN2 dewarLN2 dewar
1 K pot
SF Hecell
alphadetector
electrodes
foil
up to 1200 V/cm no enhanced extraction
up to 1200 V/cm no enhanced extraction
Evaporation by second sound
fixing holequartz
substrate
NiCr thin film(140 )
current pulse
heater designheater designSF helium cell configurationSF helium cell configuration
NiCrheater
alpha detector
Al foil-200 V
electrode520 V
223Ra540 V
Second sound - heat wave without a pressure wave
Release of ions by evaporation
219Rn trapped at the surface
square current pulse to the second sound heater
width: 50 speriod: 500 ms
0.20
0.15
0.10
0.05
0.00
219
Rn count rate (/s)
16012080400
peak pulse height (V)
1.05 K 219Rn released from the surfaceand transported to the foil
if thermal motion only: 0.04 %
7.2(6) % extractionefficiency
7.2(6) % extractionefficiency
few % overallefficiency
few % overallefficiency
1.05K
A cryogenic gas catcher
alpha detector
Al foil-200 V electrode
520 V223Ra540 V
1 bar at room temperature
heliumneonargon
transport of 219Rn
remove impurities
1) ultra-clean system• UHV compatible• bakeable• helium purification < ppb not trivial (esp. large cells)
2) freezing the impurities
impurities in noble gas ion catcherslimit the performance:
• neutralization of ions (near or at thermal velocities)
• formation of molecules/adducts
Efficiencies at low temperature
35 35
30 30
25 25
20 20
15 15
10 10
5 5
0 0
efficiency (%)
140 100 60 140 100 60180 140 100 60
temperature (K)
helium neon argon
28.7(1) %
22.1(2) %
17.0(2) %
P. Dendooven et al., NIM A 558 (2006) 580
Rutherford scattering beam monitor
Vac
uum
can
72 K
shi
eld
4 K
shi
eld
Beam line
Guiding electrodes
cell
Silicon detector
Bottom electrode
Al foil
1 K pot
Rasource
Plasma region15 MeV Proton beam
223
Cry
osta
t
Rutherford Scattering
beam monitor
Online experimental setup (JYFL)
Vac
uum
can
72 K
shi
eld
Cry
osta
t
4 K
shi
eld
cell
1 K pot
-240V
-220V
-350V
-200V
250V
250V
Guiding electrodes
Bottom electrode
Silicon detector
Al foil
Rasource
223
On-line measurements
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Effeciency(%)
1.7 pA
5 pA
40 pA
14 pA
0.5 pA
50 pA
@
Higher electric field is needed to get
maximum efficiency
at high beam intensities
On-line measurements
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Effeciency(%)
120 pA
185 pA
45 pA
1.5 pA
12 pA
210 pA
410 pA
615 pA
@ 1035
On-line measurements@ 10106
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Efficiency (%)
660 pA
310 pA
10pA
1pA
30pA
100 pA
@
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Effeciency(%)
120 pA
185 pA
45 pA
1.5 pA
12 pA
210 pA
410 pA
615 pA
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Efficiency (%)
660 pA
310 pA
10pA
1pA
30pA
100 pA
0.01
0.10
1.00
10.00
100.00
1 10 100 1000
Electric field (V/cm)
Effeciency(%)
1.7 pA
5 pA
40 pA
14 pA
0.5 pA
50 pA
Different behavior of efficiency curve
may be due to the
high mobility of electrons and
low mobility of positive ions
at low temperature
&
Re-ionization by beam
@ 1035 @ 10635
Summary of the data
blue to red = low to high E/n
(log scale, 0.1-6 x 10-18
V cm2)
77 K, 280 mbar10 K, 35 mbar
10 K, 106 mbar
Recombination loss - f
Ramanan, G.; Freeman, Gordon R., Journal of Chemical Physics, 93, 1990, 3120
f∝ Q P
ET − T,n
M.Huyse et al., NIMB, 187, 2002, Pages 535-547
v = E
+ =oT
P−=− T,n
−Mobility cm V s−
E −Electricfield V cm−
T −TemperatureK
P−Pressure
n−Densitycm−
f =Q α d
2
6 v− v+
Q − ionizing rate cm− 3s− 1
α − recombination coefficient cm3s− 1
v − Drift velocity cm s− 1
Efficiency vs. Recombination loss
4
6
0.1
2
4
6
1
2
4
6
10
2
Efficiency (%)
104
105
106
107
108
Recombination loss (arbitrary unit)
10 K, 35 mbar
10 K, 106 mbar
77 K, 280 mbar
Off-line Measurements for different pressures and
temperatures
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
0 50 100 150 200 250
Electric field (V/cm)
Efficiency (%)
30 K - 626 mbar
20 K - 420 mbar
10 K - 204 mbar
5 K - 104 mbar
5 K - 54 mbar
10 K - 104.5
20 K - 219 mbar
30 K - 325 mbar
30 K - 103 mbar
20 K - 69 mbar
10 K - 33 mbar
5 K - 17 mbar
Summary
• Evidence for 2nd sound assisted extraction from superfluid helium
• Cryogenic gas catchers work
• High beam intensities require high electric fields
Near future plans
• Off-line test of second sound assisted extraction from superfluid helium
• On-line test of cryogenic gas catcher using radioactive ion beams
• Transport of ions to high vacuum, room temperature region
Collaborators
• Juha Äysto (JYFL, Jyväskylä)• Peter Dendooven (KVI, Groningen)• Kurt Gloos (University of Turku)• Takahashi Noriaki (Osaka Gakuin University) • Heikki Penttilä (JYFL, Jyväskylä)• Kari Peräjävi (JYFL, Jyväskylä) • Sami Rinta-Antila (JYFL, Jyväskylä) • Perttu Ronkanen(JYFL, Jyväskylä) • Antti Saastamoinen (JYFL, Jyväskylä)• Tetsu Sonoda (JYFL, Jyväskylä)