DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Involved institutes:

* JYFL, Jyväskylä* GSI* KVI (not as contractor)

NUSTAR-5 Design and construction of a superfluid-helium stopping cell

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Objective

• Design of a cell, operated with superfluid helium, for the stopping of energetic radioactive ion beams. Tests and performance study with a prototype using radioactive beams available in Jyväskylä

5 cm

43210

SourceBottom electrode

Guidingelectrodes

Focusing electrode

Collector foil

Detector holder

alphadetector

electrodes

foil

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Present status (1)

219Rn trapped at the surface

0.20

0.15

0.10

0.05

0.00

21

9R

n c

ount

rate

(/s

)

16012080400

peak pulse height (V)

1.05 K

7.2(6) % extractionefficiency

7.2(6) % extractionefficiency

219Rn extracted fromthe surface

219Rn extracted fromthe surface

needs confirmation

NiCrheater

alpha detector

Al foil-200 V

electrode520 V

223Ra540 V

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Present status (2)

35 35

30 30

25 25

20 20

15 15

10 10

5 5

0 0

effi

ciency

(%

)

140 100 60 140 100 60180 140 100 60

temperature (K)

helium neon argon

28.7(1) %

22.1(2) %

17.0(2) %

- Proposed stopping cell dimensions may also be reached using a cryogenic gas catcher (T≤20 K) * 20 K technically less demanding than <2 K * ions do not need to cross the boundary between the liquid- and gas-phases

- 2×3 days of beam time used in 2005 * technical problems in the liquid helium cell tests * cryogenic helium gas catcher (77 K) tests gave promising results

freezing out of impurities workstechnically easier than ultra-pure at room temperature

fundamental upper limitthe measured efficiencies are determined by the cross sections

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Present status (3)

Recent measurements at JYFL overlayed on a compilation of other results

Extraction efficiency of helium gas ion catchers as a function of ionisation rate, as presented by D.J.Morrissey at the SMI-06 Workshop, Groningen, the Netherlands, March 27-28, 2006

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Deviation from original workplan

1) Delay:Tests done earlier this year at Jyvaskyla with the cryostat from KVI failed partly due to a technical problem (leak)

instead: measurements with the cryogenic gas catcher

2) New concept:Already stressed in January meeting, progress since then, tests in 2007,looks very promising

DIRAC Midterm Review, GSI, December 2006 NUSTAR-5, C. Scheidenberger

Outlook on completion

KVI: the study of the superfluid liquid-helium catcher will be pursued at KVI (off-line developments aiming at fast and efficient extraction via second sound waves), feasibility has to be demonstrated

JYFL:* study of cryogenic gas catcher will be pursued at JYFL, development of a system for on-line tests underway (drawings being prepared, construction starts early 2007)* confirm the off-line results and test the transport of ions from cryogenic cell to vacuum* proposal accepted, beam time in preparation

GSI:* beam time request under preparation

program will be finished within ~ 1 year