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Latest News
January 13, 2011 - St. George has arrived at Notre Dame. ( Details )
September 22, 2010 - Conditioning of the Wien filter achieved to +/-110kV.
August 21,
2010 - Return from a 2 weeks visit at the Bruker facility in Karlsruhe.
Description
St. GEORGE (Strong Gradient
Electro-magnetic Online Recoil
separator for capture Gamma ray Experiments)
has been designed to study (a, g), and after
upgrade (p, g) reactions in inverse kinematics.
In inverse kinematics, the recoils are contained in a narrow forward
cone while the beam pass through the target without interacting. The
beam, which is up to 1015 more abundant than the recoils, has to be
deviated. St. George was designed to have a suppression factor better
than 1015 while transporting 100% of the most abundant charge state
of the reaction products within an acceptance of Θ ≤ 40 mrad
(2.29degree), δE ≤ +/-7.5%. The acceptance of St. GEORGE
is based on a set of nuclear reaction of astrophysical interest that
are planned to be studied. The system consists of a Wien filter (velocity
filter) and 6 dipole magnets with embedded higher order corrections,
eleven quadrupole magnets and a focal plane detection system with particle
identification using time of flight, and position sensitive silicon
detectors.
Technical design of St. George (Click on the image for larger one.)
After a bidding competition the design was
submitted to Bruker Biospin GmbH for construction of the complete system.
The complexity of the embedded higher order correction and loss in know-how
resulted in significant delays. The delivery is scheduled for the end
of 2010, nearly two years past the original deadline.
The target system for St. GEORGE is a 4He
jet which provides a point-like source. Helium at a pressure of several
bar enters the vacuum chamber through a convergent-divergent Laval nozzle,
thus forming a supersonic jet. The largest fraction of the gas is then
captured by a catcher and pumped by a combination of Roots Blowers and
Rotary Vane pumps. To reach the required high vacuum conditions in the
beamline, a total of 4 pumping stages, consisting of roots blowers and
turbomolecular pumps, reduces the pressure down to the 10-6
torr range. The central chamber of the gas target was designed to be
especially small allowing easy placement of g-ray
detectors covering large solid angles. Extensive tests of the jet characteristics
have been completed by mapping the jet extension and density (a few
1017 particles/cm-2) using elastic scattering
and radiative capture reactions.
St. George gas target coupled to the KN accelerator and design of the
central chamber
(Click on the image for larger one.)
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