Neutron Sciences 2008 Annual Report - 17.79 MB - Spallation ...

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FACILITY DEVELOPMENT 2008 ANNUAL REPORT
Laser Removal of Electrons
When the ion beam in the SNS linear accelerator reaches
the proton accumulator ring, the negatively charged
ions undergo an identity change, becoming positively
charged protons. The postage-stamp-size diamond foil
that brings about this change has worked well and has
lasted longer than a traditional carbon foil likely would.
There are concerns with the diamond foil technology,
however. The design power of SNS is 1.4 megawatts; at
300 kilowatts the ion beam passing through the diamond
foil produced a red glow at an estimated temperature of
2000 degrees. One concern is that a few protons—say,
one out of every 10,000—will collide with carbon atoms
in the diamond foil, making the surrounding hardware
radioactive. Another concern is that the diamond foils
could lose integrity when power reaches between
1 and 2 megawatts. Both occurrences could dramatically
increase operating costs.
In a search for an alternative, Viatcheslav “Slava” Danilov
and his accelerator physics team devised a successful
laser stripping technology using an Nd:YAG (neodymium-doped
yttrium aluminum garnet) lasing crystal.
Danilov, who received an award from the European
Physical Society for this work, describes this approach
as a “paradigm shift.” In the initial experiment, a laser
beam with a pulse length of approximately 10 nanoseconds
was directed at a negative ion beam, successfully
removing electrons from the beam. The next step is to
increase the electron-removal efficiency.
A larger, more expensive laser system that can operate
more effectively for the full pulse length could be
needed when the beam power reaches 1.4 megawatts.
Nevertheless, laser-stripping technology could be one of
the keys to ensuring that SNS can reach its full power
potential.
Contact: John Galambos (galambosjd@ornl.gov)
ORNL NEUTRON SCIENCES neutrons.ornl.gov
HFIR’s proposed
second cold source.
Artist rendition of HFIR’s proposed
Neutron Science Center.