About the FEL
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FEL Applications - Carbon Nanotube
Carbon nanotube synthesis by
NASA and
Jefferson Lab moves from research to production phase
What
began in 2001 as an academic investigation of how to make carbon
nanotubes with
a free-electron laser (FEL) has moved into a new phase. Researchers at
NASA’s
Langley Research Center, Hampton, Va., and the FEL at the Department of
Energy’s Thomas Jefferson National Accelerator Facility are now
producing
high-quality, single-wall carbon nanotubes in quantities sufficient for
testing
in aerospace applications.
Carbon
nanotubes generally measure about one nanometer, one billionth of a
meter, wide
and have stretched to up to one millimeter long. A cousin of the
buckyball, a
single carbon nanotube is essentially a sheet of graphite curled up
into a
cylinder. Nanotubes were discovered in 1991, and it’s thought that they
may
lead to an entirely new generation of materials as strong or stronger
than
steel, but very lightweight.
Laser-synthesized
nanotubes tend to have superior properties to those produced by other
techniques. The raw material can be very pure, and the tubes themselves
are
straight, homogeneous, and defect-free. The problem is making them in
large
quantities. Typical tabletop lasers use tens of watts to make nanotubes
at
around 200 milligrams per hour.
Michael W.
Smith, a staff scientist at NASA Langley Research Center, and his
colleagues
designed a new nanotube synthesis process and apparatus that uses a
custom-made, rod-shaped graphite target. A beam of infrared laser light
at a
wavelength of 1.6 microns from the Jefferson Lab FEL vaporizes layers
of the
spinning target to create a plume of nanotubes. The process has so far
proven
it can make about 100 milligrams per minute; that rate can fill a
coffee cup
with raw material in about 15 minutes. The researchers are increasing
the yield
as research continues.
The Jefferson
Lab FEL's unique laser beam makes nanotubes differently than a
conventional
laser. It emits a series of "ultrafast" infrared laser light pulses
(each pulse lasts less than a picosecond, or one trillionth of a
second) at a
high repetition rate of 9.4 MHz, about 9.4 million flashes a second.
The ultrafast
pulses from the Jefferson Lab FEL directly excite the reactants to form
the
nanotubes, unlike a conventional laser, which heats up a material to
produce
them. Research continues into how the FEL production process differs
from
traditional laser synthesis and how it has facilitated scale-up.
Currently, the
scientists are varying the laser's parameters – including the pulse
structure,
wavelength, power, and spot size – to determine what characteristics
produce
the best carbon nanotubes at the fastest rate. One interesting finding
so far
is that the diameter of the nanotubes can be varied by changing the
laser’s
parameters. Since different applications require different sizes, this
may turn
out to be a big advantage of FEL-synthesized nanotubes.
Initial applications
of the nanotubes at NASA Langley will be in fiber-reinforced materials.
The
research is now focusing on purifying and processing the raw material
and will
soon shift to incorporating nanotubes into palm-sized test pieces. NASA
is
interested in high-strength, lightweight materials that are
multifunctional
(can sense strain, bend and flex themselves, or conduct heat and
electric
charge). In theory, carbon nanotube-reinforced materials can do all of
these,
saving critical weight in a myriad of aero and space applications.
NASA Langley
and DOE Jefferson Lab FEL scientists expect a major announcement in the
next
few months. Institutions affiliated with the research include NASA
Langley
Research Center, Thomas Jefferson National Accelerator Facility
(Jefferson
Lab), National Institute of Aerospace (NIA), The College of William
& Mary
Department of Applied Science and Luna Innovations, Inc.
Contacts:
Kandice Carter
Jefferson Lab
kcarter@jlab.org
301-467-0176 (cell) APS meeting preferred contact
757-269-7263 (office)
<>Marny Skora
NASA Langley Research Center
757-864-3315 (office)
757-344-6111 (cell)