Environmental
CYCLOTRONS & BEAMS
The Berkeley Accelerator Space Effects facility operates in conjunction with the
88-Inch Cyclotron at the Lawrence Berkeley National Laboratory in California to
provide beams of heavy ions, protons, and neutrons for radiation effects testing.
Michael Johnson is research coordinator at the 88-Inch Cyclotron. He says, “We
specialize in heavy ion beams, which are used to test for single-event particles
striking electronics in space. These particles cause a loss of functionality, burnout or
other malfunctions.
“For something like an SRAM memory chip, testing will involve writing different
patterns of 1’s and 0’s to chip memory locations while bombarding it with a particle
beam, then reading back the results. If you find something different than what you left
there, you have an upset.
“You can then analyze the number of upsets, the number of beam particles that
struck the chip, and the energy of the beam particles to create models of how these
parts will behave in a satellite.”
“We take accelerated ions from the 88-Inch Cyclotron and deposit varying amounts
of energy into the chips being tested. Beam energies and fluences are then compared
with the cross-section of the event, and plots are generated showing the results. For
example, Single Event Upset (SEU) results are often plotted as SEU cross-section
versus linear energy transfer.”
Most radiation testing is done in the laboratory, but there has been a series of
satellite missions to study radiation effects on components in space. A recent
example is RadFX (Radiation Effects) project by the Institute for Space and Defense
Electronics (ISDE) at Vanderbilt University and the Radio Amateur Satellite
Corporation in the USA. The experiments on the payload monitor single event
upsets in memories, data corruptions that occur because of the natural radiation
environment. The results are being used to evaluate modeling and test capabilities.
“One of our areas of expertise is assessing and predicting radiation-induced
failures before vulnerable microelectronics make it into a system,” explains Professor
Brian Sierawski at the Institute for Space and Defense Electronics.
“The mission of the ISDE is to contribute to the design and analysis of radiation
hardened electronics, develop test methods and plans for assuring radiation
hardness, radiation effects characterization and qualification testing and the
development of solutions to system-specific problems related to radiation effects.
ISDE engineers help to identify radiation-related issues at the device, circuit, and
subsystem/system levels, propose and implement design solutions, and devise and
conduct radiation experiments.
“The current RadFx satellite missions are designed to evaluate the impact of
proton-induced upsets in memories. Modern commercial memories are vulnerable
to ionization from a single proton, which was not a concern for older generations of
microelectroncs. To date, the program has collected over four years of on-orbit data
for the validation of the prediction methods and models,” says Sierawski.
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“The concept of a safe mode – shutting down nonessential
functions while troubleshooting an SEE – is not
applicable for environmental control and life support on
a human spacecraft while the crew are onboard. Multiple
redundancy, hazards- and operational controls are
imperatives for NASA to ensure the safety of the
astronaut crew during missions.”
RADIATION SOURCES
The testing of the effects of radiation and shielding can
use several different approaches, depending on the type
of effects under consideration. Facilities either use
radioactive sources such as Cobalt 60, which emit gamma
rays, or particle beams from particle accelerators which
can be used to generate electrons, protons and heavy ions
for use in testing.
Professor Nigel Bannister, senior lecturer from the
School of Physics and Astronomy at the University of
Leicester says, “If we are interested in how a material or
an electronic component changes its properties over
time because of ionizing radiation, then radioactive
sources and beams of electrons and protons will be used.
“In the case of understanding how microprocessors
are affected, then heavy ion beams and proton beams
are used.”
Bannister’s work is currently focused on the ESA’s
JUICE (JUpiter ICy moons Explorer), a probe which is
planned for launch in 2022 and is scheduled to arrive at
Jupiter in 2029. JUICE will spend at least three years
making detailed observations of the giant gaseous
planet and three of its largest moons, Ganymede, Callisto
and Europa.
“Jupiter’s strong magnetic field traps particles and the
rotation of the planet accelerates these particles to high
energies. This is what forms the radiation environment,
which can damage and destroy electronics and
materials,” says Bannister.
Testing of JUICE’s components consists of exposing
the parts to a representative environment in an
accelerated way. “To execute a TID test, the tested parts
are exposed to photons emitted by the decay of a Cobalt
60 radioactive source. To test against DD, which is a
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