HK1076224A - Plasma catalyst - Google Patents

Description

Plasma catalyst

Cross Reference to Related Applications

This application claims priority from the following U.S. provisional patent applications: no.60/378,693, filed on 8/5/2002, No.60/430,677, filed on 4/12/2002, and No.60/435,278, filed on 23/12/2002, which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates to methods and apparatus for exciting, conditioning and sustaining a plasma from a gas using a plasma catalyst.

Background

It is known to excite a plasma by subjecting the gas to a sufficient amount of microwave radiation. However, plasmas are generally more easily ignited when the gas pressure is substantially below atmospheric pressure. However, the vacuum equipment used to reduce the pressure is expensive and inefficient, wasting energy. Furthermore, the use of such equipment may limit manufacturing flexibility.

Disclosure of Invention

The present invention provides a plasma catalyst for exciting, conditioning and maintaining a plasma. The plasma catalyst may be inert or active. The inert plasma catalyst according to the present invention may comprise any object capable of deforming a local electric field to induce a plasma without adding additional energy. Active plasma catalysts, on the other hand, may include any particle or high energy wave packet capable of delivering a large amount of energy to gaseous atoms or molecules in the presence of electromagnetic radiation to excite at least one electron from the gaseous atoms or molecules. In both cases, the plasma catalyst may improve or relax the environmental conditions required to ignite the plasma.

The invention also provides a method and apparatus for forming a plasma. In one embodiment according to the invention, the method includes flowing a gas into a multi-mode processing chamber and exciting a plasma by subjecting the gas in the chamber to electromagnetic radiation having a frequency of less than about 333GHz in the presence of at least one passive plasma catalyst comprising a material that is at least semi-conductive.

In another embodiment according to the present invention, a method and apparatus are provided for exciting a plasma by subjecting a gas to electromagnetic field radiation having a frequency of less than about 333GHz in the presence of a plasma catalyst comprising a powder.

In another embodiment according to the present invention, other methods and apparatus are provided for forming a plasma using a dual chamber system. The system may include a first excitation chamber and a second chamber in fluid communication with each other. The method may include: (i) subjecting the gas in the first excitation chamber to electromagnetic radiation having a frequency below about 333GHz such that the plasma in the first excitation chamber causes a second plasma to form in the second chamber, and (ii) sustaining the second plasma in the second chamber by subjecting it to additional electromagnetic radiation.

Other plasma catalysts, methods and apparatus for igniting, conditioning and sustaining a plasma are also provided.

Drawings

Other features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, in which like reference characters designate like parts, and wherein:

FIG. 1 shows a schematic diagram of a plasma system according to the present invention;

FIG. 1A shows an embodiment of a partial plasma system for adding a powdered plasma catalyst to a plasma chamber to ignite, condition or sustain a plasma in the chamber in accordance with the present invention;

FIG. 2 shows a plasma catalyst fiber according to the present invention having a concentration gradient of at least one component along its length;

FIG. 3 shows a plasma catalyst fiber according to the present invention having a plurality of components that vary in ratio along its length;

FIG. 4 shows another plasma catalyst fiber according to the present invention, the fiber including an inner core and a coating;

FIG. 5 shows a cross-sectional view of the plasma catalyst fiber of FIG. 4 taken along line 5-5 of FIG. 4, in accordance with the present invention;

FIG. 6 illustrates an embodiment of another portion of a plasma system including an elongated plasma catalyst extending through an excitation port in accordance with the present invention;

FIG. 7 shows an elongated plasma catalyst for use in the system of FIG. 6 according to the present invention

Example (c);

FIG. 8 illustrates another embodiment of an elongated plasma catalyst for use in the system of FIG. 6 in accordance with the present invention; and

FIG. 9 shows an embodiment of a portion of a plasma system for introducing radiation into a radiation chamber in accordance with the present invention.

Detailed Description

The present invention relates to methods and apparatus for igniting, conditioning and maintaining a plasma for various applications, including: heat treatment, synthesis and deposition of carbides, nitrides, borides, oxides and other materials, doping, carburization, nitridation and carbonitriding, sintering, multi-component processing, joining, decrystallization, fabrication and operation of furnaces, waste gas treatment, waste treatment, incineration, purification, ashing, carbon structure growth, hydrogen or other gas production, electrodeless plasma nozzle production, line plasma treatment, sterilization, cleaning, and the like.

The invention can be used for controllable heat generation and plasma-assisted processing to reduce energy consumption and improve heat treatment efficiency and flexibility of plasma-assisted manufacturing.

Accordingly, a plasma catalyst for igniting, regulating and sustaining a plasma is provided. The catalyst may be inert or active. The passive plasma catalyst according to the present invention may comprise any object that induces a plasma by deforming a local electric field (e.g., an electromagnetic field) without applying additional energy to the catalyst, such as applying a voltage to cause an instantaneous discharge. Active plasma catalysts, on the other hand, may be any particle or high energy wave packet capable of transferring sufficient energy to a gaseous atom or molecule in the presence of electromagnetic radiation to cause the gaseous atom or molecule to lose at least one electron.

The following commonly owned and concurrently filed U.S. patent applications are hereby incorporated by reference in their entirety: united states patent application

No.10/＿，＿(Atty.Docket No.1837.0008)，

No.10/＿，＿(Atty.Docket No.1837.0009)，

No.10/＿，＿(Atty.Docket No.1837.0010)，

No.10/＿，＿(Atty.Docket No.1837.0011)，

No.10/＿，＿(Atty.Docket No.1837.0012)，

No.10/＿，＿(Atty.Docket No.1837.0013)，

No.10/＿，＿(Atty.Docket No.1837.0015)，

No.10/＿，＿(Atty.Docket No.1837.0016)，

No.10/＿，＿(Atty.Docket No.1837.0017)，

No.10/＿，＿(Atty.Docket No.1837.0018)，

No.10/＿，＿(Atty.Docket No.1837.0020)，

No.10/＿，＿(Atty.Docket No.1837.0021)，

No.10/＿，＿(Atty.Docket No.1837.0023)，

No.10/＿，＿(Atty.Docket No.1837.0024)，

No.10/＿，＿(Atty.Docket No.1837.0025)，

No.10/＿，＿(Atty.Docket No.1837.0026)，

No.10/＿，＿(Atty.Docket No.1837.0027)，

No.10/＿，＿(Atty.Docket No.1837.0028)，

No.10/＿，＿(Atty.Docket No.1837.0030)，

No.10/＿，＿(Atty.Docket No.1837.0032)，

No.10/＿，＿(Atty.Docket No.1837.0033)。

Description of plasma System

FIG. 1 illustrates a plasma system 10 in accordance with an aspect of the present invention. In this embodiment, a cavity 12 is formed in a container located inside a radiation chamber (i.e., an applicator) 14. In another embodiment (not shown), the container 12 and the radiation chamber 14 are one and the same, so that two separate components are not required. The container in which the cavity 12 is formed may include one or more radiation transmissive baffles to improve its thermal insulating properties without the cavity 12 being significantly shielded from radiation.

In one embodiment, the cavity 12 is formed within a container made of ceramic. Since the plasma according to the present invention can reach very high temperatures, ceramics capable of operating at about 3000 degrees Fahrenheit can be used. For example, the ceramic material may comprise 29.8% silicon, 68.2% aluminum, 0.4% iron oxide, 1% titanium, 0.1% calcium oxide, 0.1% magnesium oxide, 0.4% alkali metal by weight, and is Model No. LW-30 sold by New Castle reflectories of Pennsylvania, New Castle. However, one of ordinary skill in the art will recognize that other materials, such as quartz and those other than the ceramic materials described above, may also be used in accordance with the present invention.

In one successful experiment, the plasma was formed in a partially open cavity within a first brick and capped with a second brick. The dimensions of the cavity are about 2 inches by about 1.5 inches. There are at least two holes in the brick in communication with the cavity: one for observing the plasma and at least one for supplying the gas. The size of the chamber depends on the plasma treatment that needs to be performed. In addition, the chamber should at least be configured to prevent plasma from rising/drifting away from the main processing region.

The chamber 12 may be connected via line 20 and control valve 22 to one or more gas sources 24 (e.g., argon, nitrogen, hydrogen, xenon, krypton, etc.) powered by a power source 28. The line 20 may be tubular (e.g., between about 1/16 inches and about 1/4 inches, such as about 1/8 inches). Furthermore, if desired, a vacuum pump may be connected to the chamber to evacuate any unwanted gases generated during plasma processing. In one embodiment, gas may flow into and/or out of the chamber 12 through one or more apertures in the multi-component container. Thus, the ports of the present invention do not require special holes, but can take other forms, such as many small distributed holes.

A radiation leak detector (not shown) is mounted adjacent the source 26 and waveguide 30 and is connected to the safety interlock system, for example, by FCC and/or OSHA (e.g., 5 mW/cm) if a leak exceeding a predetermined safety value is detected²) The radiation (e.g. microwave) power supply is automatically turned off at a prescribed value.

A radiation source 26, powered by a power source 28, introduces radiant energy into the chamber 14 through one or more waveguides 30. It will be appreciated by those skilled in the art that the source 26 may be directly connected to the chamber 12, thereby eliminating the waveguide 30. Radiant energy entering the chamber 12 can be used to excite a plasma within the chamber. The plasma may be substantially sustained and confined within the chamber by applying additional radiation to the catalyst. Furthermore, the frequency of the radiation (e.g. microwave radiation) is considered unimportant in many applications.

The radiant energy is provided by circulator 32 and tuner 34 (e.g., a 3-stub tuner). The tuner 34 serves to minimize reflected energy as a function of changing excitation or processing conditions, particularly after plasma formation, since microwave energy, for example, will be strongly absorbed by the plasma.

As described in more detail below, the location of the radiation-transmissive cavity 12 within the chamber 14 is not critical if the chamber 14 supports multiple modes, particularly when the modes are continuously or periodically mixed. And as described in more detail below, the motor 36 may be coupled to a mode mixer 38 to provide a substantially uniform time-averaged radiant energy distribution within the chamber 14. Also, a window 40 (e.g., a quartz window) may be provided on one wall of the chamber 14 adjacent the chamber 12 to enable a temperature sensor 42 (e.g., an optical pyrometer) to be used to view the process within the chamber 12. In one embodiment, the optical pyrometer output value may increase from 0 volts to within the tracking range value as the temperature increases.

The sensor 42 is capable of generating an output signal as a function of the temperature of an associated workpiece (not shown) in the chamber 12, or any other monitorable condition, and supplying that signal to the controller 44. Dual temperature sensing and heating, as well as automatic cooling rates and airflow control, may also be employed. The controller 44, in turn, is used to control the operation of the power supply 28, which has one output connected to the source 26 and another output connected to the valve 22 that controls the flow of air into the chamber 12.

Although any radiation frequency less than about 333GHz may be used, the present invention achieves similar success with 915MHz and 2.45GHz microwave sources provided by the communications and energy industry (CPI). The 2.45GHz system continuously provides variable microwave energy from about 0.5 kilowatts to about 5.0 kilowatts. A 3-way stub tuner matches the impedance to maximum energy transfer and a bi-directional connector is employed that measures the incident and reflected energy. An optical pyrometer was also used to remotely sense the sample temperature.

As noted above, any radiation having a frequency less than about 333GHz may be used in accordance with the invention. For example, frequencies such as the energy line frequency (about 50Hz to 60Hz) may be employed, although the gas pressure forming the plasma may be reduced to facilitate plasma ignition. Further, any radio frequency or microwave frequency may be used in accordance with the present invention, including frequencies greater than about 100 kHz. In most cases, the gas pressure for these relatively high frequencies need not be reduced in order to excite, condition, or sustain the plasma, thus enabling multiple plasma processes above atmospheric pressure and pressure. The device is controlled by a computer using LabVIEW 6i software, which provides real-time temperature monitoring and microwave energy control. Noise is reduced by smoothing with an average of an appropriate number of data points. Also, to increase speed and computational efficiency, the number of data points stored in the buffer array is limited by shift registers and buffer sizing.

The pyrometer measures about 1cm²For calculating the average temperature. A pyrometer is used to detect the radiation intensity at two wavelengths and to fit these intensity values using planck's law to determine temperature. However, it should be understood that other devices and methods for monitoring and controlling temperature consistent with the present invention also exist and may be used. Control software that may be used in accordance with the present invention is described, for example, in commonly owned and concurrently filed U.S. patent application Ser. No.10/, (Attonney Dorket No.1837.0033), the entire contents of which are incorporated herein by reference.

The chamber 14 has several glass cover ports with radiation shielding and a quartz window for insertion of the pyrometer. There are several ports connected to the vacuum pump and the gas source, although this is not necessary.

The system 10 also includes a closed loop deionized water cooling system (not shown) with an external heat exchanger cooled with tap water. In operation, deionized water cools the magnetron first, then cools the load and unload in the circulator (for the case of magnetron), and finally flows through water channels welded to the outer surface of the chamber to cool the radiant chamber.

Plasma catalyst

The plasma catalyst according to the invention may comprise one or more different substances and may be inert or active. In the case where the gas pressure is lower than, equal to, or greater than atmospheric pressure, the plasma catalyst may ignite, condition, and/or sustain a plasma among other substances.

A method of forming a plasma according to the present invention may include subjecting a gas within a chamber to electromagnetic radiation having a frequency of less than about 333GHz in the presence of an inert plasma catalyst. The passive plasma catalyst according to the present invention includes any object that induces plasma by deforming a local electric field (e.g., electromagnetic field) according to the present invention without applying additional energy to the catalyst, such as by applying a voltage to cause an instantaneous discharge.

The inert plasma catalyst of the present invention may also be a nanoparticle or a nanotube. The term "nanoparticle" as used herein includes any particle that is at least semi-conductive with a maximum physical dimension of less than about 100 nm. Also, doped and undoped, single-walled and multi-walled carbon nanotubes are particularly effective for exciting the plasma of the present invention due to their exceptional electrical conductivity and elongated shape. The nanotubes may be of any suitable length and may be fixed on the substrate in powder form. If fixed, the nanotubes may be randomly oriented on the surface of the substrate or fixed to the substrate (e.g., in some predetermined direction) when the plasma is initiated or sustained.

The inert plasma of the present invention may also be a powder and need not include nanoparticles or nanotubes. For example, it may be formed into fibers, dust particles, flakes, sheets, and the like. In the powder state, the catalyst may be at least temporarily suspended in the gas. By suspending the powder in a gas, the powder can be quickly dispersed throughout the cavity and more easily consumed, if desired.

In one embodiment, a powdered catalyst may be loaded into a chamber and at least temporarily suspended in a carrier gas. The carrier gas may be the same or different from the gas forming the plasma. Furthermore, the powder may be added to the gas before introduction into the chamber. For example, as shown in FIG. 1A, the radiation source 52 may apply radiation to a radiation chamber 55 provided with a plasma chamber 60. The fines source 65 supplies catalyst fines 70 to the gas stream 75. In an alternative embodiment, the powder 70 may be added to the chamber 60 in bulk (e.g., a pile) and then distributed within the chamber in any number of ways, including gas flowing through or over the bulk powder. In addition, the powder may be added to the gas to ignite, condition or sustain the coating plasma by moving, transporting, spraying, sprinkling, blowing or otherwise delivering or distributing the powder into the chamber.

In one experiment, a plasma was excited in a chamber by placing a stack of carbon fiber powder in a copper tube that extended into the chamber. The copper tube shields the powder from the radiation to which it is subjected, despite sufficient radiation being introduced into the chamber, that plasma excitation does not occur. However, once the carrier gas begins to flow into the copper tube, the powder is forced out of the copper tube and into the chamber, thereby exposing the powder to radiation, and the plasma in the chamber is almost instantaneously excited.

The powder catalyst according to the invention is essentially non-combustible, so that it need not include oxygen or burn in the presence of oxygen. As described above, the catalyst may include metal, carbon-based alloy, carbon-based composite, conductive polymer, conductive silicone elastomer, polymer nanocomposite, organic-inorganic composite, and any combination thereof.

Moreover, the powdered catalyst may be substantially uniformly distributed (e.g., suspended in a gas) within the plasma chamber, and plasma excitation may be precisely controlled within the chamber. Uniform excitation is important in some applications, including applications requiring short plasma exposure times, such as in the form of one or more bursts. It also requires a certain time to distribute the powdered catalyst itself evenly throughout the cavity, especially in complex multi-chambered cavities. Thus, in accordance with another aspect of the invention, a powder plasma may be introduced into the chamber through multiple ignition ports to more quickly develop a more uniform catalyst distribution therein (see below).

In addition to powder, the inert plasma catalyst according to the present invention may also comprise, for example, one or more micro-or macro-fibers, flakes, needles, threads, strands, filaments, yarns, twines, shavings, splits, chips, woven threads, tapes, whiskers, or any mixture thereof. In these cases, the plasma catalyst may have at least a portion with one physical dimension substantially larger than another physical dimension. For example, the ratio between at least two perpendicular dimensions is at least about 1: 2, and may be greater than about 1: 5 or even greater than about 1: 10.

Thus, the inert plasma catalyst may comprise at least a portion of a relatively thin material compared to its length. Catalyst bundles (e.g., fibers) comprising, for example, a length of graphite tape may also be used. In one experiment, a length of tape having about thirty thousand strands of graphite fibers, each having a diameter of about 2-3 microns, was successfully used. The number of internal fibers and the beam length are not important to exciting, modulating, or maintaining the plasma. For example, satisfactory results were obtained with a length of graphite tape approximately 1/4 inches long. One carbon fiber successfully used in accordance with the present invention is sold under the trademark Magnamite by Hexcel corporation of Salt Lake City, Utah^Model No. AS4C-GP 3K. In addition, silicon carbide fibers have also been successfully used.

The inert plasma catalyst according to another aspect of the present invention may comprise one or more portions such as substantially spherical, annular, conical, cubic, planar, cylindrical, rectangular or elongated.

The inert plasma catalyst comprises at least one material that is at least electrically semiconducting. In one embodiment, the material has strong electrical conductivity. For example, the inert plasma catalyst according to the present invention may include a metal, an inorganic material, carbon, a carbon-based alloy, a carbon-based composite, a conductive polymer, a conductive silicone elastomer, a polymer nanocomposite, an organic-inorganic composite, or any combination thereof. Some possible inorganic materials that may be included in the plasma catalyst include carbon, silicon carbide, molybdenum, platinum, tantalum, tungsten, carbon nitride, and aluminum, although it is believed that other conductive inorganic materials may also be used.

The inert plasma catalyst of the present invention may include one or more additives (conductivity is not required) in addition to one or more conductive materials. As used herein, the additive may include any material that a user desires to add to the plasma. For example, during doping of semiconductors and other materials, one or more dopants may be added to the plasma through a catalyst. See, for example, U.S. patent application Ser. No.10/, (Attonney DorketNo.1837.0026), which is commonly owned and filed concurrently herewith and incorporated herein by reference in its entirety. The catalyst may comprise the dopant itself or it may comprise a precursor material which decomposes to produce the dopant. Thus, the plasma catalyst may include one or more additives and one or more conductive materials in any desired ratio, depending on the final desired plasma composite and the treatment with plasma.

The ratio of conductive component to additive in the inert plasma catalyst varies with the time it is consumed. For example, during excitation, the plasma catalyst may be required to include a greater percentage of conductive components to improve the excitation conditions. On the other hand, if used in sustaining a plasma, the catalyst may include a greater percentage of additives. It is known to those skilled in the art that the composition ratio of the plasma catalyst used to ignite and sustain the plasma may be the same.

The predetermined ratio profile can be used to simplify many plasma processes. In many conventional plasma processes, the composition in the plasma is increased as needed, but such an increase typically requires the programmable device to add the composition according to a predetermined schedule. However, according to the present invention, the composition ratio in the catalyst is variable, and thus the composition ratio of the plasma itself can be automatically changed. That is, the composition ratio of the plasma at any particular time is dependent on the portion of the catalyst that is currently consumed by the plasma. Therefore, the catalyst component ratio may be different at different positions within the catalyst. Also, the composition ratio of the current plasma is dependent on the current and/or pre-depleted catalyst fraction, especially when the gas flow rate through the plasma chamber is slow.

The inert plasma catalyst according to the present invention may be uniform, non-uniform or graded. Also, the ratio of the plasma catalyst components in the entire catalyst may be changed continuously or discontinuously. For example, in fig. 2, the ratio may smoothly change forming a gradient along the length of catalyst 100. Catalyst 100 may include a stream of material having a lower concentration of components in section 105 and a continuously increasing concentration toward section 110.

Alternatively, as shown in FIG. 3, the ratio may be varied discontinuously in each portion of the catalyst 120, for example, including alternating sections 125 and 130 of different concentrations. It should be appreciated that the catalyst 120 may have more than two stages. Therefore, the ratio of the catalyst component consumed by the plasma may be changed in any predetermined form. In one embodiment, when the plasma is monitored and a particular additive has been detected, further processing may be automatically started or ended.

Another method of varying the composition ratio in the plasma being sustained is by introducing multiple catalysts with different composition ratios at different times and at different rates. For example, multiple catalysts may be introduced at approximately the same location or different locations in the cavity. When introduced at different locations, the plasma formed in the chamber will have a concentration gradient of constituents determined by the location of the different catalysts. Thus, the automated system may include a means for mechanically inserting a consumable plasma catalyst before and/or during plasma ignition, regulation, and/or maintenance.

The inert plasma catalyst according to the invention may also be coated. In one embodiment, the catalyst may comprise a substantially non-conductive coating deposited on the surface of a substantially conductive material. Alternatively, the catalyst may comprise a substantially conductive coating deposited on the surface of a substantially non-conductive material. For example, fig. 4 and 5 show a fiber 140 that includes an inner layer 145 and a coating 150. In one embodiment, to prevent oxidation of the carbon, the plasma catalyst includes a nickel-coated carbon core.

A plasma catalyst may also include a multilayer coating. If the coating is consumed during exposure to the plasma, the coating can be continuously introduced into the plasma from the outer coating to the innermost coating, thereby forming a time-release mechanism. Thus, the coated plasma catalyst may comprise any number of materials, as long as a portion of the catalyst is at least electrically semiconducting.

According to another embodiment of the invention, the plasma catalyst may be located entirely within the irradiation chamber in order to substantially reduce or prevent radiant energy leakage. In this way, the plasma catalyst is not electrically or magnetically connected to the container comprising the chamber, or any electrically conductive object outside the chamber. This prevents an instantaneous discharge at the ignition port and prevents possible subsequent radiation leakage out of the cavity during ignition and if the plasma is sustained. In one embodiment, the catalyst may be located at the end of a substantially non-conductive extension that extends into the excitation port.

For example, FIG. 6 shows a radiation chamber 160 in which a plasma chamber 165 may be disposed. The plasma catalyst 170 may extend and protrude into the excitation port 175. As shown in FIG. 7, a catalyst 170 according to the present invention may include an electrically conductive tip portion 180 (disposed within the chamber 160) and an electrically non-conductive portion 185 (disposed substantially outside the chamber 160). This configuration prevents an electrical connection (e.g., a flash) between the tip portion 180 and the chamber 160.

In another embodiment as shown in fig. 8, the catalyst is formed from a plurality of electrically conductive segments 190, the plurality of electrically conductive segments 190 being separated by and mechanically connected to a plurality of electrically non-conductive segments 195. In this embodiment, the catalyst can extend through the excitation port between one point in the cavity and another point outside the cavity, but its electrically discontinuous distribution effectively prevents the generation of a momentary discharge and energy leakage.

Another method of forming a plasma according to the present invention includes subjecting a chamber gas to electromagnetic radiation having a frequency of less than about 333GHz in the presence of an active plasma catalyst, producing or including at least one ionized particle.

An active plasma catalyst according to the present invention may be any particle or high energy wave packet capable of transferring sufficient energy to a gaseous atom or molecule to cause the gaseous atom or molecule to lose at least one electron in the presence of electromagnetic radiation. With a source, the ionized particles may be introduced directly into the chamber in the form of a focused or collimated beam, or they may be ejected, sputtered, or otherwise introduced.

For example, FIG. 9 shows radiation source 200 introducing radiation into radiation chamber 205. The plasma chamber 210 may be disposed within the chamber 205 and allow gas flow through the ports 215 and 216. The source 220 may introduce ionized particles 225 into the chamber 210. The source 220 may be protected with a metallic shield through which, for example, ionized particles may pass, but also shields the source 220 from electromagnetic radiation. Source 220 may be water cooled if desired.

Examples of ionizing particles according to the present invention may include x-ray particles, gamma-ray particles, alpha particles, beta particles, neutrons, protons, and any combination thereof. Thus, the ionizing particle catalyst may be charged (e.g., ions from an ion source) or uncharged and may be the product of a radioactive fission process. In one embodiment, the vessel in which the plasma chamber is formed may be wholly or partially permeable to ionized particulate catalyst. Thus, when the radioactive fission source is located outside the cavity, the source may direct the fission product through the vessel to ignite the plasma. To substantially prevent fission products (such as ionized particle catalysts) from causing safety hazards, radioactive fission sources may be located within the radiation chamber.

In another embodiment, the ionizing particle may be a free electron, but it need not be emitted during radioactive decay. For example, electrons may be introduced into the chamber by energizing an electron source (e.g., a metal) so that the electrons have sufficient energy to escape from the source. The electron source may be located within the chamber, adjacent to the chamber, or even on the chamber wall. One of ordinary skill in the art will recognize that any combination of electron sources may be used. A common method of generating electrons is to heat the metal and these electrons can be further accelerated by applying an electric field.

Free energy protons can be used to catalyze the plasma in addition to electrons. In one embodiment, free protons may be generated by ionizing hydrogen and selectively accelerated by an electric field.

One advantage of the active and inert catalyst according to the invention is that the plasma can be catalysed in a substantially continuous manner. For example, a discharge device can only catalyze a plasma when a transient discharge occurs. However, an instantaneous discharge is generally generated by applying a voltage between two electrodes. Generally, the transient discharge is periodically generated and separated by a period in which the transient discharge is not generated. The plasma is not catalyzed during the period when the transient discharge is not generated. Furthermore, for example, electrical discharge devices typically require electrical energy to operate, although the active and inert plasma catalysts according to the present invention do not require electrical energy to operate.

Multimode radiation chamber

The radiation waveguide, cavity or chamber is arranged to support or facilitate propagation of at least one mode of electromagnetic radiation. As used herein, the term "mode" refers to a particular form of any standing or propagating electromagnetic wave that satisfies Maxwell's equations and applicable boundary conditions (e.g., of the cavity). Within the waveguide or cavity, the mode may be any of a variety of possible forms of propagating or stagnant electromagnetic fields. Each mode is characterized by the frequency and polarization of its electric and/or magnetic field vector. The electromagnetic field form of a mode depends on the frequency, index or permittivity and the geometry of the waveguide or cavity.

The Transverse Electric (TE) mode is the mode in which the electric field vector is perpendicular to the direction of propagation. Similarly, the Transverse Magnetic (TM) mode is the mode in which the magnetic field vector is perpendicular to the direction of propagation. Transverse Electromagnetic (TEM) modes are modes where both the electric and magnetic field vectors are perpendicular to the direction of propagation. Hollow metal waveguides generally do not support the standard TEM modes of radiation propagation. Although the radiation appears to propagate along the length of the waveguide, it is so reflected at an angle only by the inner walls of the waveguide. Thus, radiation (e.g., microwaves) has some electric field component or some magnetic field component along the waveguide axis (usually referred to as the z-axis) depending on the mode of propagation.

The actual field distribution in a cavity or waveguide is the superposition of modes therein. Each type of die may be indexed by one or more indices (e.g., TE)₁₀("Tee ee one zero")). The subscripts generally indicate how many "half waves" are contained at the conduit wavelength in the x and y directions. Those skilled in the art will appreciate that the waveguide wavelength is different from that of free space because radiation propagating within the waveguide is reflected at an angle by the inner walls of the waveguide. In some cases, a third subscript may be added to define the number of half waves in the standing wave pattern along the z-axis.

For a given radiation frequency, the dimensions of the waveguide can be chosen small enough that it can support one propagation mode. In this case, the system is referred to as a single mode system (e.g., a single mode radiator). TE in rectangular single-mode waveguides₁₀The modes are usually dominant.

As the size of the waveguide (or cavity to which the waveguide is connected) increases, the waveguide or radiator can sometimes support additional higher order modes, forming a multi-mode system. When multiple modes can be supported simultaneously, the system is often denoted as being highly modeled (highly modeled).

A simple single mode system has a field distribution including at least one of a maximum and/or a minimum. The maximum magnitude depends largely on the amount of radiation applied to the system. Thus, the field distribution of a single mode system is strongly varying and substantially non-uniform.

Unlike a single mold cavity, multiple mold cavities can support several propagating modes simultaneously, which when superimposed form a mixed field distribution pattern. In this form, the field becomes spatially blurred and therefore the field distribution does not generally exhibit the same intensity type of minimum and maximum field values within the cavity. In addition, as described in more detail below, a mode mixer may be used to "mix" or "redistribute" the modes (e.g., using mechanical motion of a radiation reflector). Such redistribution is expected to provide a more uniform time-averaged field distribution within the cavity.

A multi-die cavity according to the present invention can support at least two dies, and can support more than two dies. Each mode has a maximum electric field vector. Although there may be two or more modes, only one mode dominates and has a larger magnitude of the maximum electric field vector than the other modes. As used herein, a multi-cavity may be any cavity in which the ratio between the first and second modulus stages is less than about 1: 10, or less than about 1: 5, or even less than about 1: 2. One of ordinary skill in the art will appreciate that the smaller the ratio, the more dispersed the electric field energy between the modes and thus the more dispersed the radiant energy within the cavity.

The distribution of the plasma in the cavity is very dependent on the distribution of the applied electromagnetic radiation. For example, in a purely single mode system there may only be one location of an electric field maximum. Therefore, a strong plasma can only be generated at this one location. In many applications, such a strongly localized plasma can undesirably cause non-uniform plasma processing or heating (i.e., local overheating and under-heating).

Whether single or multiple cavities are used in accordance with the present invention, one of ordinary skill in the art will recognize that the cavity in which the plasma is formed may be completely closed or semi-closed. For example, in certain applications, such as in a plasma-assisted furnace, the cavity may be completely sealed. See, for example, U.S. patent application Ser. No.10/, (Attonney Dorket No.1837.0020), which is commonly owned and filed concurrently herewith and incorporated herein by reference in its entirety. In other applications, however, it may be desirable to flow gas through the chamber, so that the chamber must be opened to some degree. In this way, the flow rate, type and pressure of the flowing gas may change over time. This is desirable because certain gases such as argon, which facilitate plasma formation, are more easily excited but are not needed in subsequent plasma processing.

Mold mixing

In many applications, it is desirable to include a uniform plasma within the chamber. However, since microwave radiation may have a longer wavelength (e.g., tens of centimeters), it is difficult to obtain a uniform distribution. As a result, according to one aspect of the present invention, the radiation modes within the multimode cavity may mix or redistribute over a period of time. Since the field distribution within the cavity must satisfy all of the boundary conditions set by the inner surface of the cavity (if metallic), these field distributions can be changed by changing the position of any portion of the inner surface.

According to one embodiment of the invention, the movable reflective surface is located within the radiation chamber. The shape and movement of the reflective surface will jointly change the inner surface of the cavity during the movement. For example, an "L" shaped metal object (i.e., a "mode mixer") when rotated about an arbitrary axis will change the position or orientation of the reflective surface within the cavity, thereby changing the radiation distribution therein. Any other asymmetrically shaped object may be used (in rotation), but symmetrically shaped objects will work as well, as long as relative movement (such as rotation, translation or a combination of both) causes some change in the position and orientation of the reflective surface. In one embodiment, the die mixer may be a cylinder that rotates about an axis other than the longitudinal axis of the cylinder.

Each of the multiple mold cavities has at least one maximum electric field vector, but each vector appears periodically within the cavity. In general, the maximum is fixed, assuming that the frequency of the radiation is constant. However, by moving the mode mixer so that it interacts with the radiation, it is possible to move the position of the maximum. For example, the mode mixer 38 can be used to optimize the field distribution within the chamber 14 in order to optimize plasma excitation conditions and/or plasma sustaining conditions. Thus, once the plasma is activated, the position of the mode mixer can be changed to shift the position of the maximum for uniform time-averaged plasma treatment (e.g., heating).

Thus, according to the present invention, mode mixing may be used during plasma ignition. For example, when using conductive fibers as a plasma catalyst, it is known that the orientation of the fibers can strongly influence the minimum plasma excitation conditions. For example, it is reported that catalysts rarely improve or relax these conditions when such fibers are oriented at an angle greater than 60 ° to the electric field. However by moving the reflective surface into or close to the cavity, the electric field distribution can be significantly altered.

Mode mixing can also be achieved by injecting radiation into the emitter chamber, for example, through a rotating waveguide joint mounted within the emitter chamber. The rotary joint may be mechanically moved (e.g., rotated) in order to efficiently emit radiation in different directions within the radiation chamber. As a result, varying field patterns can be generated within the radiator chamber.

Mode mixing can also be achieved by flexible waveguides injecting radiation into the radiation chamber. In one embodiment, the waveguide may be fixed within the chamber. In another embodiment, the waveguide may extend into the chamber. The position of the end of the flexible waveguide may be continuously or periodically moved (e.g., bent) in any suitable manner in order to inject radiation (e.g., microwave radiation) into the chamber in different directions and/or locations. This movement can also cause mode mixing and contribute to more uniform plasma processing (e.g., heating) on a time-averaged basis. Alternatively, such movement may be used to optimize the location of the excited plasma or other plasma-assisted processes.

If the flexible waveguide is rectangular, simple twisting of the open end of the waveguide will rotate the direction of the electric and magnetic field vectors of the radiation within the radiator chamber. Thus, periodic twisting of the waveguide can cause mode mixing and rotation of the electric field, which can be used to assist in exciting, conditioning or sustaining the plasma.

Thus, even if the initial direction of the catalyst is perpendicular to the electric field, the reorientation of the electric field vector can change the null direction to a more efficient direction. One skilled in the art will recognize that the mode mixing may be continuous, periodic, or pre-programmed.

In addition to plasma excitation, mode mixing may be used to reduce or create (e.g., tune) a "hot spot" within the chamber during subsequent plasma processing. When the microwave cavity supports only a few digital-to-analog (e.g., less than 5), one or more local electric field maxima may create "hot spots" (e.g., within the cavity 12). In one embodiment, these hot spots may be arranged to coincide with one or more separate but simultaneous plasma excitations or treatments. Thus, a plasma catalyst may be placed at one or more of these excitation or subsequent processing locations.

Multiple position excitation

Multiple plasma catalysts at different locations may be used to ignite the plasma. In one embodiment, multiple fibers may be used to ignite the plasma at different points within the chamber. Such multi-point excitation is particularly beneficial when uniform plasma excitation is required. For example, substantially uniform transient striking and re-striking of the plasma may be improved when the plasma is conditioned at high frequencies (i.e., tens of hertz or higher), or ignited in a larger space, or both. Alternatively, when a plasma catalyst is used at multiple points, the plasma may be continuously ignited at different locations within the plasma chamber using the plasma catalyst by selectively introducing the catalyst into these different locations. In this way, a plasma excitation gradient can be controllably formed within the chamber, if desired.

Moreover, in a multi-cavity, the random distribution of catalyst at multiple locations in the cavity increases the likelihood of: the at least one fiber or any other inert plasma catalyst according to the present invention is optimally oriented along the electric lines of force. However, even if the catalyst is not optimally oriented (not substantially aligned with the electric lines of force), the excitation conditions are improved.

Furthermore, since the catalyst powder may be suspended in the gas, it is believed that having each powder particle has the effect of being located at a different physical location within the chamber, thereby improving the excitation uniformity within the chamber.

Dual chamber plasma excitation/sustaining

The dual chamber arrangement according to the present invention can be used to ignite and sustain a plasma. In one embodiment, the system includes at least a first excitation chamber and a second chamber in fluid communication with the first chamber. To excite the plasma, the gas in the first excitation chamber is selectively subjected to electromagnetic radiation having a frequency of less than about 333GHz in the presence of a plasma catalyst. In this way, the proximity of the first and second cavities may cause a plasma formed in the first cavity to ignite a plasma in the second cavity, which may be sustained with additional electromagnetic radiation.

In one embodiment of the invention, the first chamber may be very small and arranged primarily or solely for plasma excitation. In this way, less microwave energy is required to ignite the plasma, making ignition easier, especially when using a plasma catalyst according to the present invention.

In one embodiment, the first cavity is substantially a single mold cavity and the second cavity is a multiple mold cavity. The electric field distribution within the cavity can vary dramatically when the first cavity supports only a single mode, resulting in one or more precisely located electric field maxima. This maximum is generally the first location for plasma ignition, which is taken as the ideal point for placement of the plasma catalyst. It will be appreciated, however, that when a plasma catalyst is used, the catalyst need not be located at the maximum of the electric field and, in most cases, need not be oriented in a particular direction.

In the foregoing embodiments, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not intended to suggest that more features are claimed in the claims than are expressly recited in each claim. Rather, as the following claims recite, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus the following claims are hereby incorporated into this detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

Claims (48)

1. A method of forming a plasma, comprising:

flowing a gas into a multi-mode processing chamber; and

exciting the plasma by subjecting the gas in the cavity to electromagnetic radiation having a frequency below about 333GHz in the presence of at least one inert plasma catalyst comprising a material that is at least electrically semi-conductive.

2. The method of claim 1, wherein the material comprises at least one of a metal, an inorganic material, carbon, a carbon-based alloy, a carbon-based composite, a conductive polymer, a conductive silicone elastomer, a polymer nanocomposite, an organic-inorganic composite, and any combination thereof.

3. The method of claim 2, wherein the material is in the form of at least one of a nanoparticle, a nanotube, a powder, a dust, a flake, a fiber, a sheet, a needle, a thread, a strand, a filament, a yarn, a twine, a shaving, a sliver, a chip, a woven fabric, a tape, a whisker, and any combination thereof.

4. The method of claim 3, wherein the material comprises carbon fiber.

5. The method of claim 1, wherein the material comprises carbon and is in the form of at least one of nanoparticles, nanotubes, powder, dust, flakes, fibers, sheets, needles, threads, strands, filaments, yarns, twines, shavings, slivers, chips, braided threads, tapes, whiskers, and any combination thereof.

6. The method of claim 1, wherein the material comprises at least one nanotube.

7. The method of claim 1, wherein the material is at least partially coated with a second material.

8. The method of claim 1, wherein the at least one inert plasma catalyst comprises a plurality of elongated conductive strips distributed at different locations in the chamber.

9. The method of claim 8, wherein the radiation has power lines, wherein each elongated strip has a longitudinal axis, and wherein the longitudinal axes are not substantially aligned with the power lines.

10. The method of claim 1, wherein the plasma catalyst comprises at least one conductive component and at least one additive in a ratio, the method further comprising sustaining the plasma, wherein the sustaining comprises:

introducing additional electromagnetic radiation into the cavity; and

allowing the catalyst to be consumed by the plasma, whereby the plasma comprises the at least one additive.

11. The method of claim 10, wherein the ratio is different at different portions of the catalyst, and wherein the allowing step comprises allowing different portions of the catalyst to be consumed by the plasma at different times such that the plasma comprises a varying ratio of the conductive component to the at least one additive.

12. The method of claim 1, wherein the multi-mode cavity is configured to support at least a first mode and a second mode of the radiation, each mode having a maximum electric field vector in the cavity, each of the vectors having an order of magnitude, and wherein a ratio between the first mode order and the second mode order is less than about 1: 10.

13. The method of claim 12, wherein the ratio is less than about 1: 5.

14. The method of claim 13, wherein the ratio is less than about 1: 2.

15. The method of claim 14, wherein the multi-mode cavity is configured to support at least a first mode and a second mode of the radiation, each mode having at least one largest electric field vector at a location in the cavity, the method further moving each of the locations by mode mixing.

16. The method of claim 1, wherein the exciting comprises exciting the plurality of plasma catalysts at different locations in the cavity.

17. The method of claim 1 wherein said cavity is located in a radiation chamber and said catalyst is located entirely within said chamber such that said catalyst is substantially electrically non-conductive with said chamber and electrically non-conductive with electrically conductive objects located outside said chamber.

18. The method of claim 1, wherein the catalyst is located at an end of a substantially non-conductive extension that passes through an excitation port formed in the radiation chamber.

19. The method of claim 1, wherein the catalyst comprises a plurality of discontinuous segments separated by and mechanically connected to a plurality of non-conductive segments, wherein during excitation, the catalyst extends through an excitation port within the cavity between one location within the cavity and another location outside the cavity.

20. The method of claim 1, wherein the exciting comprises exciting the plasma while the catalyst is suspended within the chamber.

21. A method of forming a plasma comprising exciting a plasma by subjecting a gas to electromagnetic radiation having a frequency of less than about 333GHz in the presence of a plasma catalyst comprising a powder.

22. The method of claim 21, wherein the subjecting step occurs within a chamber, the method further comprising flowing a gas into the chamber.

23. The method of claim 21, wherein the step of subjecting the gas to radiation occurs in a chamber located within the chamber.

24. The method of claim 23, wherein the chamber is a multi-mode chamber.

25. The method of claim 21, further comprising introducing the powder into the radiation with a carrier gas.

26. The method of claim 21, further comprising introducing the powder into the radiation using a technique that at least transiently suspends the powder in the cavity, the technique being at least one of feeding, gravity feeding, conveying, spraying, blowing.

27. The method of claim 21, further comprising introducing the powder into a cavity through a plurality of firing ports.

28. The method of claim 21, wherein the exciting comprises exciting the plasma while the powder is in suspension.

29. The method of claim 21, wherein the plasma catalyst comprises a non-combustible material.

30. The method of claim 29, wherein the plasma catalyst comprises at least one of a metal, an inorganic material, carbon, a carbon-based alloy, a carbon-based composite, a conductive polymer, a conductive silicone elastomer, a polymer nanocomposite, and an organic-inorganic composite.

31. A method of forming a plasma comprising subjecting a gas within a chamber to electromagnetic radiation having a frequency of less than about 333GHz in the presence of an active plasma catalyst comprising at least one ionic particle.

32. The method of claim 31, wherein the at least one ionizing particle comprises a beam of particles.

33. The method of claim 31, wherein the particle is at least one of an x-ray particle, a gamma ray particle, an alpha particle, a beta particle, a neutron, and a proton.

34. The method of claim 31, wherein the at least one ionizing particle is a charged particle.

35. The method of claim 31, wherein the ionizing particle comprises a radioactive fission product.

36. The method of claim 35, wherein a cavity is formed in the vessel that is at least partially transmissive to the product, the method further comprising positioning a radioactive fission source outside the cavity such that the source introduces the fission product into the cavity through the vessel.

37. The method of claim 35, wherein the vessel and the radioactive fission source are within a radiation chamber, and wherein the chamber includes material that substantially prevents the product from escaping the chamber.

38. The method of claim 35, further comprising disposing a radioactive fission source within the cavity, wherein the source produces the at least one fission product.

39. The method of claim 31, wherein the ionizing particle is a free electron, the method further comprising generating the electron by exciting an electron source.

40. The method of claim 39, wherein the energizing step comprises heating the electron source.

41. The method of claim 31, wherein the particles comprise mobile protons, the method further comprising generating the mobile protons by ionizing hydrogen.

42. The method of claim 31, wherein the cavity is at least partially open, allowing the gas to flow in.

43. A method of forming a plasma in a system having at least a first excitation chamber and a second chamber in fluid communication with the first chamber, the method comprising:

subjecting the gas in the first excitation cavity to electromagnetic radiation having a frequency of less than about 333GHz, such that the plasma in the first cavity causes a plasma to form in the second cavity; and

the second plasma is sustained by subjecting it to additional electromagnetic radiation.

44. The method of claim 43, wherein the exposing comprises exposing the gas to the radiation in the presence of a plasma catalyst.

45. The method of claim 43, wherein the first cavity is smaller than the second cavity.

46. The method of claim 45, wherein the first cavity is substantially a single mold cavity and the second cavity is a multi-mold cavity.

47. The method of claim 46, wherein the second cavity is highly molded.

48. The method of claim 44, wherein the plasma catalyst comprises carbon fiber.