Liquid purification or separation – Magnetic
Reexamination Certificate
2002-02-28
2003-07-01
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Magnetic
C210S243000, C210S748080, C422S186010, C422S186020, C250S281000, C209S012100, C209S727000, C204S155000
Reexamination Certificate
active
06585891
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to plasma apparatus and processes for use in material separation applications. More particularly, the present invention pertains to apparatus which are capable of separating ions in a plasma according to their respective mass to charge ratio. The present invention is particularly, but not exclusively, useful for separating ions in a plasma according to their respective mass to charge ratios using ponderomotive forces.
BACKGROUND OF THE INVENTION
For applications wherein the purpose is to separate one constituent element from a multi-constituent material, such as a chemical mixture of elements or isotopes, there are several possible ways to proceed. In some instances, mechanical separation may be possible. In others, chemical separation may be more appropriate. When mechanical or chemical processes are not feasible, however, it may happen that separation procedures and processes involving plasma physics may be necessary. To do this, a multi-species plasma needs to be made from the chemical mixture and the resultant ions separated according to their respective mass to charge ratios.
Ion separation can be accomplished in several ways known in the pertinent art. For example, plasma centrifuges and their methods of operation are well known. On the other hand, and not yet so well known, plasma filters and their methods of operation are also useful for this purpose. For example, the invention as disclosed by Ohkawa in U.S. Pat. No. 6,096,220 which issued on Aug. 1, 2000, for an invention entitled “Plasma Mass Filter” and which is assigned to the same assignee as the present invention, is useful for separating ions of different mass to charge ratios. Quite different from the above described techniques, the present invention contemplates the use of ponderomotive forces to separate ions in a multi-species plasma according to their mass to charge ratios.
It is well known that photons carry momentum. When a wave of photons (i.e. an electromagnetic wave) is evanescent in a medium, reflection of the wave occurs. When a photon is reflected from a media, momentum is transferred from the photon to the medium. Importantly, this momentum transfer exerts a force (a ponderomotive force) on the medium. In the case where the medium is a plasma, a force is exerted on the individual particles (ions and electrons) in the plasma. Along these lines, co-pending application Ser. No. 10/086,575 entitled “Ponderomotive Force End Plug For A Plasma Mass Filter” by Tihiro Ohkawa filed concurrently herewith now allowed and which is assigned to the same assignee as the present invention, discloses the use of ponderomotive forces to create an end plug for a plasma chamber. The contents of the co-pending allowed application entitled “Ponderomotive Force End Plug For A Plasma Mass Filter” are hereby incorporated by reference.
In a uniform, stationary magnetic field, the ions and electrons in a plasma will rotate in oppositely directed orbits. If a circularly polarized electromagnetic wave is propagating in the direction of the magnetic field, two distinct polarization modes are possible for the electromagnetic wave; a right-hand polarized mode and a left-hand polarized mode. In the right-hand mode, the electric field of the electromagnetic wave rotates in the same direction as the gyration of the electrons in the stationary magnetic field. In contrast, in the left-hand mode, the electric field of the electromagnetic wave rotates in the opposite direction as the gyration of the electrons in the stationary magnetic field.
Importantly for the present application, a left-hand polarized mode electromagnetic wave having specifically tailored characteristics can impart ponderomotive forces on ions, the direction of which will vary depending on the mass to charge ratio of the ion. Stated differently, for a plasma that contains multiple species of ions, the low-mass ions with the cyclotron frequencies higher than the frequency of the left-hand polarized mode electromagnetic wave are forced to move in one direction while the electrons and the high-mass ions are forced to move in the opposite direction.
To make the plasma dielectric negative, the sum of the ponderomotive forces on all charged particles must be confining (i.e. directed away from the source of the electromagnetic wave). Since each species receives a different force, an electrostatic field build up occurs due to the ambipolar effect. The steady state can be calculated by starting with the contribution &egr;
s
of a single charged particle to the plasma dielectric in the left-hand polarized mode, which is given by:
&egr;
s
={e
2
/m
&ohgr;[−&OHgr;]} [1]
where m is the mass, &ohgr; is the wave frequency and ≠ is the cyclotron frequency of the charged particle including the sign. For convenience, the following convention is used; &ohgr;>0, &OHgr;
i
>0 and &OHgr;
e
<0.
The ponderomotive force, f, on the particle is given by
f={e
2
/m
&ohgr;[−&ohgr;+&OHgr;]}[½][∇
E
2
] [2]
where E is the electric field of the wave. The sign (i.e. direction) of the ponderomotive force is directly related to the sign of the dielectric contribution. The ponderomotive potential U can be defined by
U={e
2
/m&ohgr;[−&ohgr;+&OHgr;]}[E
2
/2]. [3]
The force balance equations for the electrons and the ions are given by
−∇
p
e
−n
e
∇U
e
+e n
e
∇&PHgr;=0
and
−∇
p
i
−n
i
∇U
i
−e n
i
∇&PHgr;=0 [4]
where p is the pressure and &PHgr; is the electrostatic potential.
Consider now a plasma with two ion species [subscript
1
and
2
]. By assuming equal and uniform temperature T, the following equations are obtained:
∇{−
T In n
e
−U
e
+e
&PHgr;}=0
∇{−
T In n
1,2
−U
1,2
−e
&PHgr;}=0 [5]
n
1
+n
2
=n
e
.
By eliminating &PHgr;, the following equations are obtained:
n
1
2
={n
1,0
2
n
e
exp[[
U
2
−2
U
1
−U
e
]/T]{}n
2,0
+n
1,0
exp[
U
2
−U
1
]/T}
−1
n
2
2
={n
2,0
2
n
e
exp[[
U
2
−U
e
]/T]{}n
2,0
+n
1,0
exp[
U
2
−U
1
]/T}
−1
[6]
where the subscript
0
denotes the quantities away from the source of the electromagnetic wave.
The ratio of the densities is given by
n
2
1
=[n
20
10
]exp[−
U
2
+U
1
]/T
[7]
and
[−
U
2
+U
1
]/T={e
2
E
2
/T&ohgr;[&OHgr;
2
−&OHgr;
1
]}[M
1
−1
+M
2
−1
]. [8]
Thus, the concentration of the low-mass ions, M
1
, increases away from the source of the electromagnetic wave.
Since the low-mass ions are not confined, the above equilibrium is fictitious. The equation for the low-mass ions should contain the velocity term
−∇
p
2
−∇{M
2
v
2
2
/2
+U
2
+e
&PHgr;}=0. [9]
The uniform temperature assumption may not be correct but it can be used to see a trend, namely
∇[
T In n
2
+M
2
v
2
2
/2
+U
2
+e
&PHgr;]=0. [10]
The above equation is the same as eq. [5] if U
2
is replaced by U
2
+M
2
v
2
2
/2. The solution given by eq. [6] holds with the substitution. The solution is made self consistent with
n
2
v
2
=&Ggr;
2
=const.
If the magnitude of the ponderomotive potentials for the electrons and the ions are comparable, eq. [10] shows that the unconfined ions stream out at the sound velocity.
Useful results can be obtained by using the concentration ratio given by eq &
Archimedes Technology Group, Inc.
Nydegger & Associates
Reifsnyder David A.
LandOfFree
Plasma mass separator using ponderomotive forces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma mass separator using ponderomotive forces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma mass separator using ponderomotive forces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3095969