[extropy-chat] A ROOM-TEMPERATURE PALM-SIZED NUCLEAR FUSION DEVICE

[John K Clark]

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 729 April 27, 2005  by Phillip F. Schewe, Ben Stein
                                                        
PYROFUSION:
A ROOM-TEMPERATURE, PALM-SIZED NUCLEAR FUSION DEVICE has
been reported by a UCLA collaboration, potentially leading to new
kinds of fusion devices and other novel applications such as
microthrusters for MEMS spaceships.  The key component of the UCLA
device is a pyroelectric crystal, a class of materials that includes
lithium niobate, an inexpensive solid that is used to filter signals
in cell phones.  When heated a pyroelectric crystal polarizes
charge, segregating a significant amount of electric charge near a
surface, leading to a very large electric field there.  In turn,
this effect can accelerate electrons to relatively high (keV)
energies (see Update 564,
http://www.aip.org/pnu/2001/split/564-2.html).
The UCLA researchers (Seth Putterman, 310-825-2269) take this idea
and add a few other elements to it.  In a vacuum chamber containing
deuterium gas, they place a lithium tantalate (LiTaO3) pyroelectric
crystal so that one of its faces touches a copper disc which itself
is surmounted by a tungsten probe.  They cool and then heat the
crystal, which creates an electric potential energy  of about 120
kilovolts at its surface.  The electric field at the end of the
tungsten probe tip is so high (25 V/nm) that it strips electrons
from nearby deuterium atoms. Repelled by the negatively charged tip,
and crystal field, the resulting deuterium ions then accelerate
towards a solid target of erbium deuteride (ErD2), slamming into it
so hard that some of the deuterium ions fuse with deuterium in the
target.  Each deuterium-deuterium fusion reaction creates a helium-3
nucleus and a 2.45 MeV neutron, the latter being collected as
evidence for nuclear fusion.  In a typical heating cycle, the
researchers measure a peak of about 900 neutrons per second, about
400 times the "background" of naturally occurring neutrons.   During
a heating cycle, which could last from 5 minutes to 8 hours
depending on how fast they heat the crystal, the researchers
estimate that they create approximately 10^-8 joules of fusion
energy.  (To provide some perspective, it takes about 1,000 joules
to heat an 8-oz (237 ml) cup of coffee one degree Celsius.)  By
using a larger tungsten tip, cooling the crystal to cryogenic
temperatures, and constructing a target containing tritium, the
researchers believe they can scale up the observed neutron
production 1000 times, to more than 10^6 neutrons per second.
(Naranjo, Gimzewski, Putterman, Nature, 28 April 2005).  The
experimental setup is strikingly simple: "We can build a tiny
self-contained handheld object which when plunged into ice water
creates fusion," Putterman says.
(http://rodan.physics.ucla.edu/pyrofusion )