exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

X direction (mm)
Y direction (mm)
Figure 2 : Vertical section of the 130 kV Pegase
platform with the main elements
umn including the ion source, the lens, the Wien
filter, and which duplicates the Orion facility working
at the Tandem terminal since 1993 at around
10 MeV. The focusing of the new equipment will
be, however, much improved in order to reach the
micron objective. This set up is then connected to
a diagnostic chamber containing deflection plates,
a collimator holder with different size collimators
and a Faraday cup. The collimator position is precisely
adjustable and the Faraday cup measures
the intensity of the beam selected by the Wien filter
and passing through the collimator chosen by the
user at the platform level. All the power supplies
and the electronics are set on this platform, driven
and controlled via about thirty optical fibers. The
acceleration occurs after the diagnostic chamber
through an accelerator gap made of 2 tubes one of
which is a “trumpet” calculated by J. Arianer (fig 2)
In the first experiments, we use the focusing properties
of this gap.
The future focusing beam line incorporates a
“Russian” quadruplet with weak aberrations [7]
which permits to obtain one µm beam spot (fig 3).
This PEGASE project submitted in July 2007 by
E.A. Schweikert to the NSF was accepted in February
2008. The realization started at the end of
June 2008 and was finished at the end of November
2009 when the platform was transferred to the
Texas A&M University, after it was delivered and
tested at the IPN in October.
The IPN tests went up to 100 kV and gave a total
beam intensity of 300 nA. The transmission is better
than 80 %. A selected Au 400 4+ beam was accelerated
at 480 keV with a 1 nA intensity. The first
gold nanodroplets beam at 35 km/s was obtained
on October the 22 nd .
The first experiments started in February 2010, at
Texas A&M University, the Pegase platform being
connected to a Time-of-Flight mass spectrometer.
The first secondary ions spectra have been obtained
from a silicon wafer and a CsI target. These
first experiments permitted to test the transmission
of the cluster beams and simultaneously the ToF
mass spectrometer and the first stage of the electron
emission microscope.
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5
0
5
10
0 500 1000 1500 2000
Beam line distance from the source (mm)
Figure 3: An example of simulation of the Pegase
Beam line from the LMISource to the
Russian quadrupoles with the full cluster
beam. There are clearly two focussing
points one behind the 130 kV acceleration
lens (Pegase first step) and the other behind
the Russian quadrupoles
After these tests the experiments in progress concern
the measurement of the massive cluster energy
losses. At Orsay with 200 keV/atom massive
cluster ions we showed that there was no pronounced
coherent effect after the passage through
25 nm of matter, the zone close to the surface
where the coherent effect is strongest is thus negligible
with respect to the total range [8].
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