Startling amounts of stored energy in fully ionized plasmas.

In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.
Some examples of the amount of ionization energy energy can be found
he

Ionization energies of the elements.
http://en.wikipedia.org/wiki/Ionizat...f_the_elements

You see for hydrogen it's 1312 kilojoules per mole. Since the atomic
weight of hydrogen is 1, this is 1,312,000 joules per gram or 1.3
billion joules per kilo. Note that this amount of energy that needs
to be added to ionize the gas will conversely be released when the
electrons are recombined with the ionized gas. Then this is several
times higher than the maximum energy density of chemical reactions on
a per weight basis such as by chemically oxidizing neutral hydrogen:

Energy density in energy storage and in fuel.
http://en.wikipedia.org/wiki/Energy_..._an d_in_fuel

Other elements can produce even higher amounts. By and large, the
energy density gets higher for the heavier elements. For instance you
can find the total for copper by adding up the amounts given on the
"Ionization energies of the elements" page. You get 4,345,619.4 in kJ/
mol. Then since the atomic weight of copper is 64, this amounts to 68
billion joules per kilo.
On the "Energy density in energy storage and in fuel" page, there is
a huge gap in energy density between the chemical reactions to the
nuclear reactions. Then these "electron recombination" reactions, if
you will, would provide an intermediate level in energy storage
density.
However, for getting these amounts note that the element has to be in
gas form since the energy required to release the electrons from orbit
is different for solids, called the "work function", usually smaller.
So the released amount of energy on recombination would also be
smaller. Then for some elements such as metals you would also have to
supply high heat to get the element in gas form. Then this energy
storage method would probably be better in heavy gases, such as
xenon.
The ionization energy of xenon is incomplete on the "Ionization
energies of the elements" page. A more complete list can be found on
the page:

NIST Atomic Spectra Database Levels Form.
http://physics.nist.gov/PhysRefData/...vels_form.html

by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.
There are table top instruments available for producing and studying
these highly ionized plasmas:

Highly Ionized Plasmas.
http://www.llnl.gov/str/Schneider.html

The problem of course is storing them for long periods. If they
contact the walls of a container then they will lose their ionization.
Some possibilities would be to use Penning or Paul traps used to store
non neutral plasmas for fusion research:

Penning trap.
http://en.wikipedia.org/wiki/Penning_trap

Quadrupole ion trap (Paul trap).
http://en.wikipedia.org/wiki/Paul_trap

The amount of energy available from the ions is so high it's possible
we could siphon off a small portion of them to use their energy to
maintain the containment of the rest.
The Penning trap uses in part magnetic fields and there is a limit to
the number of particles such a trap will contain called the Brillouin
limit depending on the strength of the magnetic field. Since there is
a limit to the strength of *stable* magnetic fields that so far can be
maintained in the range of perhaps 50 T, this puts a severe limit on
the density of fully ionized particles that could be contained.
However, some researchers claim the Brillouin limit can be exceeded:

Confinement Of Pure Ion Plasma In A Cylindrical Current Sheet.
http://www.pppl.gov/pub_report//2000/PPPL-3403.pdf

Even the density achieved here though is still quite low at 4×10^14
particles per cm^3. This is at nanogram levels per cubic centimeter,
milligrams per cubic meter.
Since the Paul trap does not use magnetic fields it is unclear to me
if there is a limit to how many particles it can contain.
There would need to be quite a bit more research on how to contain
these plasmas at high densities if this is to be an energy storage
method in common use on Earth. However, it is possible that they could
be used to provide energy for space missions in deep space where
volume is not as big a concern, only mass. For instance, even at
milligrams per cubic meter this could provide kilograms of storage if
kept within a volume a hundred meters wide. For ion drives that
typically use fuel at rates of milligrams per second this could
provide fuel and the energy to power the drive over several days.

cf.:

From: Robert Clark
Newsgroups: sci.space.policy, sci.astro, sci.physics,
sci.physics.relativity, sci.physics.fusion
Date: Thu, 20 Sep 2007 13:47:28 -0700
Local: Thurs, Sep 20 2007 4:47 pm
Subject: Stored ionized gas for ion drives.
http://groups.google.com/group/sci.s...4c75eb5630f41d


Bob Clark

Robert Clark writes:
In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.
.... remainder deleted ...
by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.
....

This is not really a good method for storing energy. The losses are
too rapid.

In order to maintain (say) Xenon in a fully ionized state, a Boltzmann
equilibrium must be achieved. Removing the last two electrons of
Xenon takes ~40 keV each (ref. X-ray Data Book, xdb.lbl.gov). Thus,
the temperature must be (kB T 40 keV) where kB is the Boltzmann
constant. Let's say kB T = 100 keV, or a temperature of 1 billion Kelvins.
That is hot.

The Bremsstrahlung emissivity of a plasma scales approximately as,
W = 1.4e-34 ne nZ Z^2 T^(0.5) in Joule / s / cm^3
where ne is the electron density, nZ is the ion density, Z
is the atomic number of the ion. (ne and nZ must be in cm^{-3}).
Compare this to your quoted energy density of (200 keV / ion)
= (3.2e-14 Joules / ion), or an energy density of E = 3.2e-14 nZ Joules / cm^3.

Even your "low" density of 4e14 ions/cm^3, the ratio of W / E
is 1/(0.11 msec). In other words, all the internal (and ionization)
energy of the plasma will leak out in less than 1 millisecond by
bremsstrahlung radiation. This is radiation that can't be contained
by any magnetic field or trap, so it is unavoidable.

Not to mention the danger of carrying around a tank of 1 billion
degree plasma...

CM

On Oct 12, 7:56 am, Craig Markwardt
wrote:
Robert Clark writes:
In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.

... remainder deleted ... by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.

...

This is not really a good method for storing energy. The losses are
too rapid.

In order to maintain (say) Xenon in a fully ionized state, a Boltzmann
equilibrium must be achieved. Removing the last two electrons of
Xenon takes ~40 keV each (ref. X-ray Data Book, xdb.lbl.gov). Thus,
the temperature must be (kB T 40 keV) where kB is the Boltzmann
constant. Let's say kB T = 100 keV, or a temperature of 1 billion Kelvins.
That is hot.

The Bremsstrahlung emissivity of a plasma scales approximately as,
W = 1.4e-34 ne nZ Z^2 T^(0.5) in Joule / s / cm^3
where ne is the electron density, nZ is the ion density, Z
is the atomic number of the ion. (ne and nZ must be in cm^{-3}).
Compare this to your quoted energy density of (200 keV / ion)
= (3.2e-14 Joules / ion), or an energy density of E = 3.2e-14 nZ Joules / cm^3.

Even your "low" density of 4e14 ions/cm^3, the ratio of W / E
is 1/(0.11 msec). In other words, all the internal (and ionization)
energy of the plasma will leak out in less than 1 millisecond by
bremsstrahlung radiation. This is radiation that can't be contained
by any magnetic field or trap, so it is unavoidable.

Not to mention the danger of carrying around a tank of 1 billion
degree plasma...

CM

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.
There has been alot of research on non neutral plasmas showing they
can be stored in magnetic/electrostatic traps for several days:

What is a nonneutral plasma?
http://www-physics.ucsd.edu/~dhdpla/nnp.html


Bob Clark

On Oct 12, 7:50 am, Robert Clark wrote:
On Oct 12, 7:56 am, Craig Markwardt



wrote:
Robert Clark writes:
In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.

... remainder deleted ... by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.

...

This is not really a good method for storing energy. The losses are
too rapid.

In order to maintain (say) Xenon in a fully ionized state, a Boltzmann
equilibrium must be achieved. Removing the last two electrons of
Xenon takes ~40 keV each (ref. X-ray Data Book, xdb.lbl.gov). Thus,
the temperature must be (kB T 40 keV) where kB is the Boltzmann
constant. Let's say kB T = 100 keV, or a temperature of 1 billion Kelvins.
That is hot.

The Bremsstrahlung emissivity of a plasma scales approximately as,
W = 1.4e-34 ne nZ Z^2 T^(0.5) in Joule / s / cm^3
where ne is the electron density, nZ is the ion density, Z
is the atomic number of the ion. (ne and nZ must be in cm^{-3}).
Compare this to your quoted energy density of (200 keV / ion)
= (3.2e-14 Joules / ion), or an energy density of E = 3.2e-14 nZ Joules / cm^3.

Even your "low" density of 4e14 ions/cm^3, the ratio of W / E
is 1/(0.11 msec). In other words, all the internal (and ionization)
energy of the plasma will leak out in less than 1 millisecond by
bremsstrahlung radiation. This is radiation that can't be contained
by any magnetic field or trap, so it is unavoidable.

Not to mention the danger of carrying around a tank of 1 billion
degree plasma...

CM

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.
There has been alot of research on non neutral plasmas showing they
can be stored in magnetic/electrostatic traps for several days:

What is a nonneutral plasma?http://www-physics.ucsd.edu/~dhdpla/nnp.html

Bob Clark


Interesting.

Each galaxy emits plasma from its center at right-angles to
its disc (being 'blown off its accretion disc' NOT). The central
vortex separates infalling neutrons into negative and positive plasmas
and blows them out in opposite directions.

One kind of non-neutral plasma will be going out
one way, and the other will go out the other way.
The two will eventually re-combine into new stars.

John

Robert Clark writes:
On Oct 12, 7:56 am, Craig Markwardt
wrote:
Robert Clark writes:
In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.

... remainder deleted ... by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.

...

This is not really a good method for storing energy. The losses are
too rapid.

In order to maintain (say) Xenon in a fully ionized state, a Boltzmann
equilibrium must be achieved. Removing the last two electrons of
Xenon takes ~40 keV each (ref. X-ray Data Book, xdb.lbl.gov). Thus,
the temperature must be (kB T 40 keV) where kB is the Boltzmann
constant. Let's say kB T = 100 keV, or a temperature of 1 billion Kelvins.
That is hot.

The Bremsstrahlung emissivity of a plasma scales approximately as,
W = 1.4e-34 ne nZ Z^2 T^(0.5) in Joule / s / cm^3
where ne is the electron density, nZ is the ion density, Z
is the atomic number of the ion. (ne and nZ must be in cm^{-3}).
Compare this to your quoted energy density of (200 keV / ion)
= (3.2e-14 Joules / ion), or an energy density of E = 3.2e-14 nZ Joules / cm^3.

Even your "low" density of 4e14 ions/cm^3, the ratio of W / E
is 1/(0.11 msec). In other words, all the internal (and ionization)
energy of the plasma will leak out in less than 1 millisecond by
bremsstrahlung radiation. This is radiation that can't be contained
by any magnetic field or trap, so it is unavoidable.

Not to mention the danger of carrying around a tank of 1 billion
degree plasma...

CM

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.

CM

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

Robert Clark writes:

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:
....

You seem to be missing the point. If it takes many thousand times as
much energy to separate the charges as it does to ionize them, then
you've built a 99.999% capacitor + 0.001% ion storage device. But
there are much safer and straightforward ways to build a capacitor, so
why bother with the ionization part at all?

CM

On Oct 13, 11:15 pm, Craig Markwardt
wrote:
....
...

You seem to be missing the point. If it takes many thousand times as
much energy to separate the charges as it does to ionize them, then
you've built a 99.999% capacitor + 0.001% ion storage device. But
there are much safer and straightforward ways to build a capacitor, so
why bother with the ionization part at all?

CM


No capacitor or battery or any energy storage method short of
nuclear power offers anywhere near 154 billion joules per kilogram
energy storage.
See the list of energy densities he

Energy density in energy storage and in fuel.
http://en.wikipedia.org/wiki/Energy_..._an d_in_fuel

Bob Clark

Robert Clark writes:

On Oct 13, 11:15 pm, Craig Markwardt
wrote:
....
...

You seem to be missing the point. If it takes many thousand times as
much energy to separate the charges as it does to ionize them, then
you've built a 99.999% capacitor + 0.001% ion storage device. But
there are much safer and straightforward ways to build a capacitor, so
why bother with the ionization part at all?

CM


No capacitor or battery or any energy storage method short of
nuclear power offers anywhere near 154 billion joules per kilogram
energy storage.
....

OK, and given that it takes tens of thousands of times *more* energy
density than the ionization energy density in order to overcome the
Coulomb forces, how exactly do you plan on building your storage
device? It seems you've just proved my point.

CM

On Oct 11, 9:10 pm, Robert Clark wrote:
In researching the amount of energy required to ionize gas for ion
drives I was surprised by the total amounts of energy that would be
required to *fully* ionize the gas. This amount of energy is quite
large, actually huge, and so for actual ion drives the gas is only
minimally ionized.
Some examples of the amount of ionization energy energy can be found
he

Ionization energies of the elements.http://en.wikipedia.org/wiki/Ionizat...f_the_elements

You see for hydrogen it's 1312 kilojoules per mole. Since the atomic
weight of hydrogen is 1, this is 1,312,000 joules per gram or 1.3
billion joules per kilo. Note that this amount of energy that needs
to be added to ionize the gas will conversely be released when the
electrons are recombined with the ionized gas. Then this is several
times higher than the maximum energy density of chemical reactions on
a per weight basis such as by chemically oxidizing neutral hydrogen:

Energy density in energy storage and in fuel.http://en.wikipedia.org/wiki/Energy_...ity_in_energy_...

Other elements can produce even higher amounts. By and large, the
energy density gets higher for the heavier elements. For instance you
can find the total for copper by adding up the amounts given on the
"Ionization energies of the elements" page. You get 4,345,619.4 in kJ/
mol. Then since the atomic weight of copper is 64, this amounts to 68
billion joules per kilo.
On the "Energy density in energy storage and in fuel" page, there is
a huge gap in energy density between the chemical reactions to the
nuclear reactions. Then these "electron recombination" reactions, if
you will, would provide an intermediate level in energy storage
density.
However, for getting these amounts note that the element has to be in
gas form since the energy required to release the electrons from orbit
is different for solids, called the "work function", usually smaller.
So the released amount of energy on recombination would also be
smaller. Then for some elements such as metals you would also have to
supply high heat to get the element in gas form. Then this energy
storage method would probably be better in heavy gases, such as
xenon.
The ionization energy of xenon is incomplete on the "Ionization
energies of the elements" page. A more complete list can be found on
the page:

NIST Atomic Spectra Database Levels Form.http://physics.nist.gov/PhysRefData/...vels_form.html

by typing in for example Xe 53 to get the last (54th) electron
ionization energy. However, not every ionization level for xenon is
given on this page either. After a web search, I found the total
amount of energy required to fully ionize xenon is about 200 keV.
Since 1 eV is about 100 kJ/mol , this is about, 2 x 10^10 J/mol. Since
the atomic weight of xenon is 130 this comes to 154 million joules per
gram, 154 billion joules per kilo.
...

This report gives the total ionization energy for uranium as 762.9
keV:

Electron Emission Following the Interaction of Slow Highly Charged
Ions with Solids.
http://www.osti.gov/bridge/servlets/...ble/301182.pdf

Since 1 eV is about 100 kJ/mol and the atomic weight of uranium is
238, this amounts to 320 billion joules per kilogram. Other elements
with high total ionization energies are given in Fig. 1 in this
report.
To put this in perspective, the energy density of hydrogen burned
with oxygen is 140 million joules per kilo of hydrogen. So the
electron recombination reaction of uranium results in more than 2000
times the energy per kilogram.
The space shuttle external tank contains about 100,000 kg of hydrogen
and 600,000 kg of oxygen. Then the energy content here would be
equivalent to only 50 kg of fully ionized uranium. (Note this is *not*
a nuclear reaction.) And the oxygen also would not be required.
Note this is only in regards to the energy content. It does not
consider how the thrust would be generated.


Bob Clark