Liquid purification or separation – Processes – Using magnetic force
Reexamination Certificate
2002-04-02
2004-05-04
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Processes
Using magnetic force
C210S748080, C210S787000, C210S175000, C210S222000, C210S223000, C210S243000, C210S512100, C422S186010, C422S186020, C209S012100, C209S727000, C204S156000, C096S001000, C096S002000, C096S003000, C095S028000
Reexamination Certificate
active
06730231
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to devices and methods for separating and segregating the constituents of a multi-constituent material. More particularly, the present invention pertains to devices for efficiently initiating and maintaining a multi-species plasma in one portion of a chamber and then separating the ions in the multi-species plasma according to their respective mass to charge ratios in a second portion of the chamber. The present invention is particularly, but not exclusively, useful as a high-throughput filter to separate the high-mass particles from the low-mass particles in a plasma chamber having two, axially opposed plasma injectors.
BACKGROUND OF THE INVENTION
There are many reasons why it may be desirable to separate and segregate a multi-constituent material into its separate constituents. One such application where it may be desirable to separate a multi-constituent material is in the treatment and disposal of hazardous waste. For example, it is well known that of the entire volume of nuclear waste, only a small amount of the waste consists of radionuclides that cause the waste to be hazardous. Thus, if the radionuclides can somehow be separated from the non-hazardous ingredients of the nuclear waste, the handling and disposal of the radioactive components can be greatly simplified and the associated costs reduced.
Indeed, many different types of devices, which rely on different physical phenomena, have been proposed to separate mixed materials. For example, settling tanks which rely on gravitational forces to remove suspended particles from a solution and thereby segregate the particles are well known and are commonly used in many applications. As another example, centrifuges which rely on centrifugal forces to separate substances of different densities are also well known and widely used. In addition to these more commonly known methods and devices for separating materials from each other, there are also devices which are specifically designed to handle special materials. A plasma centrifuge is an example of such a device.
As is well known, a plasma centrifuge is a device which generates centrifugal forces to separate charged particles in a plasma from each other. For its operation, a plasma centrifuge necessarily establishes a rotational motion for the plasma about a central axis. A plasma centrifuge also relies on the fact that charged particles (ions) in the plasma will collide with each other during this rotation. The result of these collisions is that the relatively high-mass ions in the plasma will tend to collect at the periphery of the centrifuge. On the other hand, these collisions will generally exclude the lower mass ions from the peripheral area of the centrifuge. The consequent separation of high-mass ions from the relatively lower mass ions during the operation of a plasma centrifuge, however, may not be as complete as is operationally desired, or required.
Apart from a centrifuge operation, it is well known that the orbital motions of charged particles (ions) in a magnetic field, or in crossed electric and magnetic fields, will differ from each other according to their respective mass to charge ratio. Thus, when the probability of ion collision is significantly reduced, the possibility for improved separation of the particles due to their orbital mechanics is increased. For example, U.S. Pat. No. 6,096,220, which issued on Aug. 1, 2000 to Ohkawa, for an invention entitled “Plasma Mass Filter” and which is assigned to the same assignee as the present invention, discloses a device which relies on the different, predictable, orbital motions of charged particles in crossed electric and magnetic fields in a chamber to separate the charged particles from each other. In the filter disclosed in Ohkawa '220, the magnetic field is oriented axially, the electric field is oriented radially and outwardly from the axis, and both the magnetic field and the electric field are substantially uniform both azimuthally and axially. As further disclosed in Ohkawa '220, this configuration of fields causes ions having relatively low-mass to charge ratios to be confined inside the chamber during their transit of the chamber. On the other hand, ions having relatively high-mass to charge ratios are not so confined. Instead, these larger mass ions are collected inside the chamber before completing their transit through the chamber. The demarcation between high-mass particles and low-mass particles is a cut-off mass M
c
which is established by setting the magnitude of the magnetic field strength, B
0
, the positive voltage along the longitudinal axis, V
axis
, and the radius of the cylindrical chamber, “a”. M
c
for this configuration can then be determined with the expression:
M
c
=ea
2
(
B
0
)
2
/8
V
axis
.
In the filter disclosed in Ohkawa '220, a multi-species plasma is introduced into one end of a cylindrical chamber for interaction with the crossed electric and magnetic fields. As further disclosed in Ohkawa '220, the fields can be configured to cause ions having relatively high-mass to charge ratios to be placed on unconfined orbits. These ions are directed toward the cylindrical wall for collection. On the other hand, ions having relatively low-mass to charge ratios are placed on confined orbits inside the chamber. These ions transit through the chamber toward the ends of the chamber. It can happen, however, that some low-mass ions, as they undergo separation, are directed toward the end where the multi-species plasma is being introduced into the chamber. This allows the low-mass ions to be re-mixed with the multi-species plasma, lowering the separation efficiency of the plasma mass filter.
One way to overcome the end loss described above is to use a tandem plasma mass filter. Specifically, U.S. Pat. No. 6,235,202, which issued on May 22, 2001 to Ohkawa, for an invention entitled “Tandem Plasma Mass Filter” and which is assigned to the same assignee as the present invention, discloses a device wherein the feed material is introduced midway between the ends of a cylindrical plasma chamber. After separation in the plasma chamber, the light ions are collected at both ends of the cylindrical chamber. Because a plasma needs to be created near the center of the plasma chamber, the tandem mass filter requires a high density vapor jet or some other injector to introduce vapor into the chamber. Once the vapor is introduced into the chamber, an r-f antenna or some other mechanism is required to heat and ionize the vapor. The present invention reduces the end loss problem in a different way than the tandem plasma mass filter. Specifically, the present invention contemplates maintaining a multi-species plasma in one portion of a plasma chamber and then separating the ions in the multi-species plasma according to their respective mass to charge ratios in a second portion of the chamber. Because of the location of the second portion of the chamber and the configuration of the crossed electric and magnetic fields, the ions are not directed toward the first portion of the chamber during separation, and there is little re-mixing of separated ions.
In light of the above, it is an object of the present invention to provide devices for efficiently initiating and maintaining a multi-species plasma in one portion of a plasma chamber and then separating the ions in the multi-species plasma according to their respective mass to charge ratios in a second portion of the chamber. It is another object of the present invention to provide an efficient, high-throughput filter to separate the high-mass particles from the low-mass particles with little or no re-mixing of separated ions. It is yet another object of the present invention to provide a filter to separate the high-mass particles from the low-mass particles in a plasma chamber that accommodates two, axially opposed plasma injectors. Yet another object of the present invention is to provide devices and methods for separating and segregating the constituents of a multi-co
Archimedes Technology Group, Inc.
Nydegger & Associates
Reifsnyder David A.
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