On Oct 13, 3:00 pm, Craig Markwardt
wrote:
Robert Clark writes:
...
Thanks for the informative response. Quite key here is that these are
*non-neutral* plasmas. That means the charges are all of the same
sign, all positive or all negative. In your formula you gave note this
would result in the Bremsstrahlung emissivity being zero since one of
the types of charge would be absent.
Huh? First of all, that equation assumed a Boltzmann equilibrium,
which would not be the case if one conveniently "removed" *all*
electrons.
But is that plausible? No. First, fully ionizing a species like
Xenon would still required effectively heating the atoms to
temperatures of kB T ~ 100 keV. Before one could somehow magically
transfer (just) the ions to the storage tank, the energy would be lost
by thermal bremsstrahlung radiation very quickly. Second, a plasma
made up of positive ions *still* radiates by thermal bremstrahlung, so
one can't just pretend the effect is zero.
However, neither of these issues is the real fatal flaw...
There has been alot of research on non neutral plasmas showing they
can be stored in magnetic/electrostatic traps for several days:
Really? Have you considered how much Coulomb energy is required to
separate the charges even by 1 cm? For even 1 cubic cm of the Xenon
you mentioned, the Coulomb energy is tens of thousands of times larger
than the ionization energy density, at voltages of many tens of
megaVolts. In other words, the "trap" would simply be crushed due to
Coulomb forces. A lab setup with a few thousand ions is far different
from your scenario, which is totally implausible.
You are right it would take quite a bit of energy to create the fully
ionized plasmas and quite alot of energy to separate the electrons.
This is clearly not a means of getting "free" energy such as nuclear,
solar, or fossil fuels. It is only a way of storing it.
According to the web site I linked, the positive ions in their traps
could be stored as long as they want if the magnetic/electrostatic
containment fields are sufficiently uniform:
What is a nonneutral plasma?
"Confinement. Nonneutral plasmas can be confined for long periods of
time using only static electric and magnetic fields. One such
configuration is called a Penning Trap, after the inventor F. M.
Penning. The trap consists of a several cylindrically symmetric
electrodes and a uniform magnetic field applied along the axis of the
trap (see diagram below).
"Axial confinement (for a positive plasma) is provided by positive
voltages applied to the end electrodes, which creates an axial
potential well. Radial confinement is provided by the magnetic field.
The plasma rotates, and the resulting v x B force is radially inward,
balancing the outward electric force caused by the unneutralized
collection of charges.
"If the Penning trap had perfect cylindrical symmetry, the plasma
would be confined forever. However, since there are always small
irregularities in the trap fields that break the cylindrical symmetry,
these irregularities drag on the plasma, slowing down its rotation and
decreasing the confining v x B force. This results in a loss of the
plasma, but these irregularities can be made so small that the plasma
can be confined for days in actual experiments. In addition, a new
technique (called the 'rotating wall') has recently been invented by
our group; it allows us to spin up the plasma, keeping it spinning and
confined in the trap for as long as we wish."
http://www-physics.ucsd.edu/~dhdpla/nnp.html#conf
Since the purpose of much of the research on non neutral plasmas is
toward fusion power, these research teams clearly believe their
containment methods can be ramped up to large amounts of non neutral
plasma.
Here's a report on the containment of a million Beryllium ions for
over 30 minutes:
Phase-Locked Rotation of Crystallized Non-neutral Plasmas by Rotating
Electric Fields.
X.-P. Huang, J. J. Bollinger, T. B. Mitchell, and Wayne M. Itano Time
& Frequency Division, National Institute of Standards and Technology,
325 Broadway, Boulder, Colorado 80303
(Received 29 August 1997)
"We report the precise control of the rotation frequency of strongly
coupled non-neutral plasmas by rotating electric fields. These plasmas
of up to 10^6 9Be1 ions are trapped in a Penning trap and laser cooled
into crystallized structures which undergo a rigid-body rotation.
Bragg diffraction shows that the crystalline lattice can be stable for
longer than 30 min (,108 rotations), and that the plasma rotation can
be phase locked to the applied field without any slip. These
corotating plasmas are in a novel global thermal equilibrium whose
asymmetric surface shape (triaxial ellipsoid) has been measured."
http://tf.nist.gov/general/pdf/1215.pdf
And this reports on containment of a billion ions for a period of
weeks:
Confinement and manipulation of non-neutral plasmas using rotating
wall electric fields.
E. M. Hollmann, F. Anderegg, and C. F. Driscoll.
Physics Department and Institute for Pure and Applied Physical
Sciences, University of California at San Diego, La Jolla, California
92093-0319
(Received 24 February 2000; accepted 17 April 2000)
"A 'rotating wall' perturbation technique enables confinement of up to
3×10^9 electrons or 10^9 ions in Penning-Malmberg traps for periods of
weeks. These rotating wall electric fields transfer torque to the
particles by exciting Trivelpiece-Gould plasma modes with kz[not-
equal]0 and mtheta = 1 or 2. Modes that rotate faster than the plasma
column provide a positive torque that counteracts the background
drags, resulting in radial plasma compression or steady-state
confinement in near-thermal equilibrium states. Conversely, modes that
rotate slower than the plasma provide a negative torque, and enhanced
plasma expansion is observed. The observed Trivelpiece-Gould mode
frequencies are well predicted by linear, infinite-length, guiding-
center theory."
http://link.aip.org/link/?PHP/7/2776/1 [abstract only]
Bob Clark