21 research outputs found
Suppression of electrical breakdown phenomena in liquid TriMethyl Bismuth based ionization detectors
Organometallic liquids provide good properties for ionization detectors.
TriMethyl Bismuth (TMBi) has been proposed as a detector medium with charge and
Cherenkov photon readout for Positron Emission Tomography. In this work, we
present studies for the handling of TMBi at different electric fields and under
different environmental conditions to find applicable configurations for the
suppression of electrical breakdowns in TMBi at room temperature. A simple
glass cell with two electrodes filled with TMBi was constructed and tested
under different operation conditions. Working at the vapour pressure of TMBi at
room temperature of about 40 mbar and electric fields of up to 20 kV/cm in
presence of a small oxygen contamination we found the formation of a discharge
channel in the liquid and a steady increase in the current. Further reduction
of pressure by pumping caused the TMBi to boil and a spontaneous combustion.
Eliminating the oxygen contamination led the TMBi under the same condition to
only decompose. When operating the setup under an argon atmosphere of 1 bar we
did not observe breakdowns of the electrical potential up to field strengths of
20 kV/cm. Still, in presence of a small oxygen contamination fluctuating
currents in the nA range were observed, but no decomposition or combustion. We
conclude from our experiments that TMBi at room temperature in a pure argon
atmosphere of 1 bar remains stable against electrical breakdown at least up to
electric field strengths of 20 kV/cm, presumably because the formation of
gaseous TMBi was prevented.Comment: 14 page, 8 figure
Observation of the hyperfine transition in lithium-like Bismuth : Towards a test of QED in strong magnetic fields
We performed a laser spectroscopic determination of the hyperfine
splitting (HFS) of Li-like and repeated the measurement
of the HFS of H-like . Both ion species were
subsequently stored in the Experimental Storage Ring at the GSI
Helmholtzzentrum f\"ur Schwerionenforschung Darmstadt and cooled with an
electron cooler at a velocity of . Pulsed laser excitation of
the hyperfine-transition was performed in anticollinear and collinear
geometry for and , respectively, and
observed by fluorescence detection. We obtain for , different from the literature
value, and for .
These values provide experimental evidence that a specific difference between
the two splitting energies can be used to test QED calculations in the
strongest static magnetic fields available in the laboratory independent of
nuclear structure effects. The experimental result is in excellent agreement
with the theoretical prediction and confirms the sum of the Dirac term and the
relativistic interelectronic-interaction correction at a level of 0.5%
confirming the importance of accounting for the Breit interaction.Comment: 5 pages, 2 figure
XUV Fluorescence Detection of Laser-Cooled Stored Relativistic Ions
An improved moveable in vacuo XUV fluorescence detection system was employed for the laser cooling of bunched relativistic ( β = 0.47) carbon ions at the Experimental Storage Ring (ESR) of GSI Helmholtzzentrum Darmstadt, Germany. Strongly Doppler boosted XUV fluorescence (∼90 nm) was emitted from the ions in a forward light cone after laser excitation of the 2s–2p transition (∼155 nm) by a new tunable pulsed UV laser system (257 nm). It was shown that the detected fluorescence strongly depends on the position of the detector around the bunched ion beam and on the delay (∼ns) between the ion bunches and the laser pulses. In addition, the fluorescence information could be directly combined with the revolution frequencies of the ions (and their longitudinal momentum spread), which were recorded using the Schottky resonator at the ESR. These fluorescence detection features are required for future laser cooling experiments at highly relativistic energies (up to γ ∼ 13) and high intensities (up to 10 11 particles) of ion beams in the new heavy ion synchrotron SIS100 at FAIR
Laser cooling taken to the extreme: cold relativistic intense beams of highly-charged heavy ions
Recent storage ring experiments have demonstrated the power and the potential of laser cooling of bunched relativistic ion beams. Encouraged by this, the heavy-ion synchrotron SIS100 at FAIR (Darmstadt, Germany) will be equipped with a truly unique laser cooling facility. A sophisticated combination of 3 newly developed UV (257 nm) laser systems and modest rf-bunching will allow for fast cooling of injected intense heavy-ion beams. There will be two powerful pulsed laser systems with MHz repetition rates and variable pulse duration (1-50 ps and 50-740 ps) and one powerful tunable cw laser system. The picosecond laser pulses are broad in frequency and will enable fast cooling of injected ion beams with a large initial longitudinal momentum spread. The cw laser can be rapidly tuned over a large frequency range and has high spectral power density, forcing the ion beams to remain cold during storage. This combination of 3 UV laser beams should be up to the challenge of suppressing intra-beam scattering and space charge effects. We will present new experimental results from the ESR storage ring and the status of the SIS100 laser cooling facility