Cryogenic ion catchers using superfluid helium and noble gases Sivaji Purushothaman KVI, University...
-
Upload
easter-hood -
Category
Documents
-
view
217 -
download
0
Transcript of Cryogenic ion catchers using superfluid helium and noble gases Sivaji Purushothaman KVI, University...
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)