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)