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/cm 3 )  (rel.) T (K)   1 bar He gas   1 bar He gas  liquid He  superfluid He    e  t Impurities get frozen out !!! High density at low temperature  (mg/cm 3 )  (rel.) T (K)

1-2 K liquid vapour room T vacuum 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 region electrodes  4.transport to a vacuum, room- temperature region trivial 3.extraction across the surface into the vapour region N. Takahashi et al.

 -decay recoil ion source ranges in LHe recoil: 0.5  m   : 500  m ranges in LHe recoil: 0.5  m   : 500  m 223 Ra source  -decay detection He gas 223 Ra: source of 219 Rn ions 1.8 ms 223 Ra 219 Rn  5-6 MeV ~ 100 keV 215 Po 211 Pb 211 Bi 207 Tl 207 Pb      4.0 s 11.4 d 36 m 2.2 m 4.8 m

How to extract snowballs at low temperature ? conflicting temperature requirements conflicting temperature requirements W.X. Huang et al., NIM B 204 (2003) 592 N. Takahashi et al., Physica B 329 (2003) 1596 W.X. Huang et al., Europhys. Lett. 63 (2003) 687 We go for low temperature

Electric-field assisted extraction 5 cm Source Bottom electrode Guiding electrodes Focusing electrode Collector foil Detector holder LHe dewar LN2 dewar 1 K pot SF He cell alpha detector electrodes foil up to 1200 V/cm no enhanced extraction

Evaporation by second sound fixing hole quartz substrate NiCr thin film (140  ) current pulse heater design SF helium cell configuration NiCr heater alpha detector Al foil -200 V electrode 520 V 223 Ra 540 V Second sound - heat wave without a pressure wave

Release of ions by evaporation 219 Rn trapped at the surface square current pulse to the second sound heater width: 50  s period: 500 ms 219 Rn released from the surface and transported to the foil if thermal motion only: 0.04 % 7.2(6) % extraction efficiency 7.2(6) % extraction efficiency few % overall efficiency few % overall efficiency 1.05K

A cryogenic gas catcher alpha detector Al foil -200 V electrode 520 V 223 Ra 540 V 1 bar at room temperature helium neon argon transport of 219 Rn 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 catchers limit the performance: neutralization of ions (near or at thermal velocities) formation of molecules/adducts

Efficiencies at low temperature P. Dendooven et al., NIM A 558 (2006) 580

Rutherford scattering beam monitor Vacuum can 72 K shield 4 K shield Beam line Guiding electrodes cell Silicon detector Bottom electrode Al foil 1 K pot Ra source Plasma region 15 MeV Proton beam 223 Cryostat Rutherford Scattering beam monitor Online experimental setup (JYFL) Vacuum can 72 K shield Cryostat 4 K shield cell 1 K pot -240V -220V -350V -200V 250V Guiding electrodes Bottom electrode Silicon detector Al foil Ra source 223

On-line        Higher electric field is needed to get maximum efficiency at high beam intensities

On-line 10  35 

On-line 10  106 

@        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 10  35 106  35 

Summary of the data

Recombination loss - f Ramanan, G.; Freeman, Gordon R., Journal of Chemical Physics, 93, 1990, 3120 M.Huyse et al., NIMB, 187, 2002, Pages

Efficiency vs. Recombination loss

Off-line Measurements for different pressures and temperatures

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)