Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
  • C08J7/12—Chemical modification
  • C08J7/123—Treatment by wave energy or particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/16—Surface shaping of articles, e.g. embossing; Apparatus therefor by wave energy or particle radiation, e.g. infrared heating
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/08—Ion sources; Ion guns using arc discharge
  • H01J27/14—Other arc discharge ion sources using an applied magnetic field
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
  • B29C35/0866—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using particle radiation
  • B29C2035/0872—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using particle radiation using ion-radiation, e.g. alpha-rays
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/06—Sources
  • H01J2237/08—Ion sources
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/31—Processing objects on a macro-scale
  • H01J2237/3165—Changing chemical properties
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/317—Processing objects on a microscale
  • H01J2237/31701—Ion implantation

Definitions

• This invention relates to a process for treating the surface and near surface regions of a polymer with high intensity pulsed ion beams with sufficient beam fluence to achieve the various effects of cross-linking, pyrolizing, etching or ablating the polymer in the treated areas. More particularly, the ion beam pulses are characterized by pulse widths of less than 10 microseconds per spatially contiguous pulse, beam intensities of 0.01 to 10 J/cm 2 , and ion energies of typically greater than 25 keV.
• This application is a continuation-in-part of co-pending patent application Serial No. 08/153,248 filed November 16, 1993, assigned to assignee of the present invention.
• beams of high energy particles or photons for modifying polymers has been known and practiced for years using sources of particles such as the radiation decay products of radioactive elements (e.g. "Co) and electron beams produced from continuous and pulsed beam sources.
• Typical ion beam polymer treatment uses sources of high energy ions from expensive, research-type accelerators such as linear accelerators (linacs) or Van de Graff accelerators that are expensive, produce very low dose rates and, although useful as diagnostic tools for research, are not suitable for commercial treatment.
• Electron beams typically > 1 MeV electrons
• Photons (10-30 eV) have also been used to treat polymer surfaces by inducing chemical reactions.
• Continuous, high energy photon ( ⁇ ) sources e.g. 60 Co with 1-3.5 MeV photons
• ⁇ 60 Co with 1-3.5 MeV photons
• These techniques have demonstrated the ability of high energy particles at dose levels of order 10-100 Mrad to produce beneficial changes to polymers including improved toughness, resistance to solvents, and increased adhesion, as well as changes in optical density and electrical conductivity.
• the treatment typically extends deep into the material (e.g., the range of 1 MeV electrons is approximately 0.5 cm, the range of MeV photons is » 1 cm). This relatively deep treatment requires large total treatment doses to produce a significant effect. This occurs because of the difficulty in obtaining high fluences of low energy particles using existing treatment methods and the problem of surface heating that results from high continuous irradiation levels.
• reaction products such as free radicals, ionized molecules, and broken bonds, along the regions caused by energy deposition from particles moving through the polymer. Interaction between such reaction products would both increase the rate of the expected chemical reactions within the polymer (such as cross-linking) and enable unusual reactions normally precluded by the relative stability of the carbon-carbon bond.
• the low dose rates available using present technology precludes such interactions, as the density of reaction products is far too low.
• Present techniques also cannot produce dose rates sufficient to produce effective pyrolyzation (removal of hydrogen and oxygen) or etching (removal of material by rapidly heating the surface material beyond the point at which it begins to vaporize) of polymer surfaces without significantly affecting the underlying material.
• high pulsed doses of particles delivered to polymer surface regions can also modify the topology of the near surface region (e.g. by producing a rougher surface texture) in a way that present technology cannot support.
• the limitations of the prior art techniques are surmounted by the present invention.
• the advantages of applying high intensity pulses of particles to the surface and near surface regions of a polymer simultaneously produce a high density of ion track excited regions within the treated region of the polymer while limiting the total energy deposition required for such excitation.
• the invention makes possible effective dispersal of heat produced by the irradiation and a relatively energy-efficient means of irradiation.
• Each spatially contiguous pulse of the ion beam delivers a fluence of typically 0.01 to 10 J/cm 2 of a selectable ion species into the polymer surface in less than 10 microseconds.
• This level of ion fluence produces an ion track density within the polymer sufficient that a substantial percentage of the polymer molecules excited (i.e., broken bonds, free radicals, excited bonding states, etc.) by interaction with the energetic ions can interact directly with other excited polymer molecules, thereby creating an environment for cross-linking and other chemical reactions unlike any conventional environment.
• the relatively thin surface region of the polymer treated by this process is instantaneously raised to a much higher temperature, then flash-cooled by rapid conduction of heat into the underlying regions of the polymer without the adverse effects normally produced by the longer duration heating periods necessarily produced by prior art techniques. Accordingly, the pulsed ion beam process is also useful for etching or ablating away unprotected portions of the polymer surface, pyrolizing of the polymer surface, changing the geometry and topology of the polymer surface, and inducing thermally-activated chemical changes within the polymer.
• Figure 1 is a cut away cross sectional view of a surface of a polymer undergoing irradiation by the pulsed ion beam;
• Figure 2 is a graph plotting normalized density of states as a function of binding energy for Kapton, obtained by using x-ray photoemission spectroscopy, both with and without an oxygen-containing chemical coating, demonstrating the change in oxygen concentration in the Kapton;
• Figure 3 is graph plotting absorbance (measured using Fourier Transform Infrared Spectroscopy) as a function of wavenumber for treated and untreated polycarbonate, again demonstrating the change in chemical composition of the polymer before and after treatment;
• Figure 4 is a microphotograph showing the change in the surface structure of a polypropylene surface after irradiation;
• Figure 5 is a bar chart showing the improved adhesion characteristics of a polycarbonate surface with varying degrees of ion beam irradiation; low « 0.1 J/cm 2 , med. « 0.5 J/cm 2 , high « 1-2 J/cm 2 ;
• Figure 6A is a scanning electron microscope photograph showing an untreated polyethylene surface;
• Figure 6B is a scanning electron microscope photograph showing a similar polyethylene surface (from the same batch as Fig. 6A) after treatment with a 0.5-1.0 J/cm 2 ion beam;
• Figure 7 is a schematic of the RHEPP pulsed power system;
• Figure 7A is a circuit diagram of a pulse compression system utilized in the pulsed power system of Figure 7;
• Figure 7B is a cross sectional view of a pulse forming line element
• Figure 7C is a cross sectional view of the Linear Inductive Voltage Adder (LrVA)
• Figure 8 is a partial cross sectional view of the magnetically-confined anode plasma (MAP) source 25;
• Figure 8A is a modified version of Figure 8 showing the magnetic field lines produced by the fast and slow coils in the MAP source;
• Figure 8B is an expanded view of a portion of Fig. 8 showing the gas inlet valve and the gas inlet channel;
• Figure 8C is a schematic diagram of the electric circuit for the fast coil.
• Figure 9 is a schematic full cross-sectional view of the MAP ion diode.
• IBEST Ion Beam Surface Treatment
• EBEST Electron Beam Surface Treatment
• IBEST uses pulsed power and intense ion beam technology to treat polymer surfaces with very intense, but relatively short, pulses of ions.
• the ability to produce such pulses of ions in single or few pulse bursts at relatively low ( ⁇ 1 Hz) repetition rates has existed for several years but the potential benefits of such pulses have not previously been recognized. This lack of recognition is probably because these techniques could not be developed into commercially viable processes, partially because of a very limited lifetime ( ⁇ 1000 pulses) for key components and partially because of severely limited average power.
• a new capability that enables and adds to the value of this process is the combination of repetitively pulsed power technology as demonstrated by RHEPP I and RHEPP H, developed at Sandia National Laboratories, with repetitive intense ion beam technology as demonstrated by the Magnetically-confined Anode Plasma ion beam system.
• RHEPP/MAP technology is a representative example of this new capability.
• These technologies combine to provide a new, commercially viable method to deliver up to several hundred kW or more of average ion power at tens of keV to MeV ion kinetic energies in intense short duration ( ⁇ 30nsec - ⁇ 10 ⁇ sec) pulses.
• Such ion beam pulses are capable of producing the effects described above. These parameters allow low cost (on the order of 1 cent/sq. ft) treatment of high volumes of polymer with long lifetime (» 1000 pulses) systems. This capability is the first of its kind.
• the depth of treatment can be chosen by selecting different ion species and kinetic energies. In many cases it is desirable to treat only the near surface region of a polymer with the object of providing a tougher, scratch and solvent resistant surface with improved adhesive properties. For such surface treatment applications it may only be necessary to treat a near-surface region having a depth of perhaps a few microns. By contrast, a high energy pulsed electron beam system will affect on the order of a few mm before the electrons stop in the polymer. Accordingly, the ability to use high energy pulses of ions and to adjust the ion energy and species to treat only this depth allows us to greatly reduce (typically by factors of up to 1000) the energy needed per unit area while still achieving the desired modification of near surface properties.
• the local dose from a 400 keV ET ion moving through polycarbonate is approximately 1.3 x 10 "10 J/g (1.3 x 10 s rad) per incident ET ion.
• a pulse of 0.25 J of H at 400 keV contains 4 x 10 12 H * ions. This results in a local dose of approximately 50 Mrad delivered in 100 ns for a dose rate of 5 x 10 8 Mrad/second. During this time the temperature of the polymer rises approximately 500 K.
• the radius, r p of effects induced around the ion track (due to ionization, excitation, and the effects resulting from secondary electron formation and their resulting ionization and excitation, and the effects resulting from surrounding region) is approximately 15nm (from Radiation Effects on Polymers, ed. R. Clough and S. Shalably, Ch. 2, p48) for 400 keV ET.
• the temperature increase from a 0.25 J/cm 2 pulse of protons on polycarbonate is about 500 °K, as mentioned above. If one pulse is adequate for the desired treatment, this level of temperature rise is safe for the great majority of polymers. However, if a multi-pulse treatment is necessary, the polymer surface must have time to cool between pulses, or the temperature increase will be much greater, perhaps causing significant problems. Also, if the temperature rise is maintained for too long, the polymer may be damaged. The essential problem here is the extremely low thermal conductivity of some polymers.
• the characteristic timescale for heat to diffuse a length ⁇ in a material is
• the other issue coming out of the thermal timescale analysis concerns the thickness of the polymer near-surface region which may be excited. If there is a reason, a region as thick as —100 ⁇ m may be irradiated. For such a thick layer, the thermal time constant is - 2 milliseconds. Clearly this does not offer either rapid quenching or extremely short exposure to heat, but also does not represent a major limitation to use of pulsed ion beam treatment on polymer surfaces.
• the present invention provides the first capability to achieve high densities of free radicals, even up to conditions in which the effects of reaction products from adjacent ion tracks overlap. This allows an entirely new regime of radiation treatment to be explored in which tne reaction products react more strongly with each other, rather than simply with the polymer.
• the short pulse allows one to easily control and limit the local dose and heating of the surface, allowing it to cool between pulses while still preserving the advantages of the high intensity.
• this technique because of its high intensity, can also modify the surface of polymers by changing the topology of the surfaces.
• Figures 6A and 6B show an example of this modification.
• the holes formed in the surface can be advantageous in various ways, including the ability of deposited films to more easily mechanically adhere to the rough surface. Pyrolyzing and etching by ablation of the surface are also techniques made possible by the high intensities.
• the short pulse nature of this process allcws these effects to be exploited near the surface without affecting the underlying material.
• Fig. 1 shows a cross section of a polymer undergoing irradiation by the process of this invention. The process is described in terms of ion beams, but electron beams and gamma ray beams are also useful in this process.
• the ions 100 from the pulsed ion beam enter into the surface 115 of the polymer 116 down to a depth 117 determined by the species and the kinetic energy of the particular ion used. It is in this upper region between 115 and 117 that the effects of the irradiation are most pronounced.
• the heat created in this region by the ion pulse is very rapidly dissipated into the region of the polymer underlying the interface 117, thereby preventing the adverse effects of longer term heat buildup in the upper region.
• This figure also shows another layer of material 112 emplaced above the upper surface 115 of the polymer 116.
• the layer can be one of two different types of materials.
• an H+ beam at 0.4 MeV will have a 5 micron range in polypropylene and cause a temperature increase of 110 K for a 10 Mrad pulse (0.1 J/cm 2 ).
• the resulting ionization and disruption of polymer bonds caused by the ion pulse will form free radicals which then recombine to cross-link the polymer chains within the polymer surface.
• the material 112 is of the appropriate type, such as epoxy or another polymer material, it also will be treated by the ion pulse and bind to the underlying polymer.
• a 30 keV electron beam has a 10 micron range in polypropylene, produces a temperature increase of 112 C for a 10 Mrad pulse (0.2 J/cm 2 ) and produces similar polymer alteration effects to those described above for ion beam irradiation.
• Figure 2 is a graph obtained using the x-ray photoemission spectroscopy diagnostic showing the changes in the polymer chemistry of Kapton (polyimide) under control conditions without irradiation, after being irradiated with a low dose ion beam pulse (a mixed carbon, electron beam at 0.2 - 0.6 MV), and after being irradiated with a low dose beam through a 50 - 100 n thick oxygen-containing coating .
• the graph reveals that the carboxylic acid level of the Kapton has increased with the pulsed ion beam treatment, verifying chemical changes induced by treatment.
• Figure 3 is a graph obtained using Fourier Transform Infrared Spectroscopy showing the chemical signature shift in a polycarbonate before and after treatment with the pulsed ion beam.
• the parameters of the treatment were approximately 0.5 J/cm 2 of mixed IT and C * delivered in an approximately 200 ns pulse.
• Figure 4 is a microphotograph showing the change in surface geometry of a polypropylene surface coated with one micron of copper at the transition between a treated and an untreated region.
• the treatment parameters here were as above. Other tests of this material indicated improved copper adhesion to the polycarbonate in similarly treated areas.
• Figure 5 is a bar chart showing different adhesion strengths as a function of treatment intensity for polycarbonate coated with one micron of copper. A stud was attached to the copper coating and pulled until the copper layer separated from the polycarbonate. The treatment levels were 0.1 J/cm 2 (low), 0.5 J/cm 2 (med.), and 1-2
• Figure 6A is a microphotograph of an untreated polyethylene surface.
• Figure 6B is a microphotograph of the surface after treatment at 0.5 - 1.0 J/cm : to form the uniformly pitted surface shown. This treated surface exhibits increased adhesion characteristics.
• the invention requires a system capable of delivering ion beams of the requisite power and timing over commercially realistic work periods.
• One such system is described in co-pending patent applications serial numbers 08/153,248 filed November 16, 1993, 08/317,948 filed October 4, 1994 and 08/340,519 filed November 16, 1994, which are incorporated herein by reference in their entirety. The discussion that follows is excerpted from these applications to describe the best mode presently known for the practice of this invention.
• This discussion is a description of one system which can be utilized to produce the ion beams for surface treatment of various materials.
• This system has two major subsystems, a pulsed power source and a Magnetically-confined Anode Plasma (MAP) ion diode.
• MAP Magnetically-confined Anode Plasma
• the MAP ion diode when combined with the repetitive high energy pulsed power (RHEPP) source, provides for an ion beam generator system capable of high average power and repetitive operation over an extended number of operating cycles for treating large surface areas of materials at commercially attractive costs.
• the ion beam generator of the present invention can produce high
• the ion beam generator can directly deposit energy in the upper regions of the surface of a material.
• the depth of treatment can be controlled by varying the ion energy and species as well as the pulse length.
• the MAP ion diode can be combined with other power sources where less demanding power demands are present.
• the first of the components in the pulsed ion beam generating system is a compact, electrically efficient, repetitively pulsed, magnetically switched, pulsed power system capable of 10 9 pulse operating cycles of the type described by H. C. Harjes, et al, Pro 8th IEEE Int. Pulsed Power Conference (1991), and D. L. Johnson et al., "Results of Initial Testing of the Four Stage RHEPP Accelerator” pp. 437-440 and C. Harjes et al., "Characterization of the RHEPP 1 ⁇ s Magnetic Pulse Compression Module", pp.
• FIG. 7 A block diagram of a power system produced according to the teachings of the present application is shown in Figure 7. From the prime power input, several stages of magnetic pulse compression and voltage addition are used to deliver a pulsed power signal of up to 2.5 MV, 60 ns FWHM, 2.9 kJ pulses at a rate of 120 Hz to an ion beam source for this particular system.
• the power system converts AC power from the local power grid into a form that can be used by an ion beam source 25.
• the power system comprises a motor 5 which drives an alternator 10.
• the alternator 10 delivers a signal to a pulse compression system 15 which has two subsystems, a l ⁇ s pulse compressor 12 and a pulse forming line 14.
• the pulse compression system 15 provides pulses to a linear inductive voltage adder (LIVA) 20 which delivers the pulses to the ion beam source 25.
• LIVA linear inductive voltage adder
• the alternator 10 is a 600 kW, 120 Hz alternator. In the unipolar mode, it provides 210 A rms at a voltage' of 3200 V rms with a power factor of 0.88 to the magnetic switch pulse compressor system 15.
• the alternator is driven by a motor connected to the local 480V power grid.
• the particular alternator used herein was designed by Westinghouse Corporation and fabricated at the Sandia National Laboratories in Albuquerque, New Mexico. It is described in detail in a paper by R- M. Calfo et al., "Design and Test of a Continuous Duty Pulsed AC Generator" in the Proceedings of the 8th IEEE Pulsed Power Conference, pp. 715-718, June, 1991, San Diego, California.
• This reference is incorporated herein in its entirety.
• This particular power system was selected and built because of its relative ease in adaptability to a variety of loads.
• Other power sources may be used and may indeed be better optimized to this particular use.
• a power supply of the type available for Magna-Amp, Inc. comprising a series of step-up transformers connected to the local power grid feeding through a suitably-sized rectifier could be used.
• the present system however has been built and performs reasonably well.
• the pulse compression system 15 is separated into two subsystems, one of which is a common magnetic pulse compressor 12 composed of a plurality of stages of magnetic switches (i.e., saturable reactors) the operation of which is well known to those skilled in the art.
• This subsystem is shown in more detail in Fig. 7A.
• the basic operation of each of the stages is to compress the time width (transfer time) of and to increase the amplitude of the voltage pulse received from the preceding stage. Since these are very low loss switches, relatively little of the power is wasted as heat, and the energy in each pulse decreases relatively little as it moves from stage to stage.
• the specific subsystem used herein is described in detail by H. C.
• the PFL is a triaxial water insulated line that converts the input LC charge waveform to a flat-top trapezoidal pulse with a design 15 ns rise/fall time and a 60 ns FWHM.
• the construction and operation of this element is described in detail by D. L. Johnson et al. "Results of Initial Testing of the Four Stage RHEPP Accelerator", 9th IEEE International Pulsed Power Conference, pp.437-440, Albuquerque, NM, June, 1993. This paper is also incorporated by reference in its entirety.
• a cross sectional view of the PFL is shown in Figure 7B.
• the pulse compression system 15 can provide unipolar, 250 kV, 15 ns rise time, 60 ns full width half maximum (FWHM), 4 kJ pulses, at a rate of 120 Hz, to the linear inductive voltage adder (L ⁇ VA) (20).
• the pulse compression system 15 should desirably have an efficiency >80% and be composed of high reliability components with very long lifetimes ( ⁇ 10 9 -10 10 pulses).
• Magnetic switches are preferably used in all of the pulse compression stages, MS1- MS5, because they can handle very high peak powers (i.e., high voltages and currents), and because they are basically solid state devices with a long service life.
• the five compression stages used in this embodiment as well as the PFL 14 are shown in Fig. 7A.
• the power is supplied to the pulse compression system 15 from the alternator 10 and is passed through the magnetic switches, MS1-MS5, to the PFL 14.
• the PFL is connected to the linear induction voltage adder (LTVA) 20 described below.
• the second and third magnetic switches, MS2 and MS3, are separated by a step-up transformer Tl as shown.
• Switch MS6 is an inversion switch for the PFL.
• the pulse forming line (PFL) element 14 is shown in schematically in Fig. 7A and in cross section in Fig. 7B.
• MS6 in Fig. 7A corresponds to the inversion switch 302 shown in Fig. 7B located on the input side of the tri-axial section 314 of the PFL.
• Output switches 304 and charging cores 306 are also shown.
• the regions 310 are filled with deionized water as the dielectric.
• the interior region 308 is filled with air and oil coiling lines, not shown, for the output switches 304.
• the output of the PFL is fed in parallel to each of the individual LIVA stages 20, with the positive component flowing through conductors 316 and the shell 318 of the PFL serving as ground.
• the positive conductors 316 are connected to each of the LIVA stages.
• the LIVA (20) is preferably liquid dielectric insulated. It is connected to the output of the PFL and can be configured in different numbers of stages to achieve the desired voltage for delivery to the ion beam source.
• the LIVA 20 can deliver nominal 2.5 MV, 2.9 kJ, pulses at a rate of 120 Hz to the ion beam source 25 when configured with 10 stages of 250 kV each.
• the LIVA was configured with four stages of 250 kV each, such that the LIVA delivered a total of 1.0 MV to the ion beam source.
• this voltage can be increased or decreased by changing the number of stages in the LIVA to match the particular material processing need.
• the nominal output pulse of the LIVA 20 is the same as that provided to it by the PFL, namely, trapezoidal with 15 ns rise and fall times and 60 ns FWHM (full width half maximum).
• Figure 7C shows a cross section of the four stage LIVA.
• the four stages, 320, 322, 324, and 326, are stacked as shown and fed the positive pulses from the PFL via the cables 321, 323, 325, and 327.
• the stages are separated by gaps 330 and surrounded by transformer oil for cooling.
• the output from each of the LIVA stages adds to deliver a single total pulse to the ion beam source shown here schematically as 25 which is located within a vacuum chamber 332, shown in partial view.
• the outside shell of the LIVA is connected to ground.
• the power system P ( Figure 7) as described, can operate continuously at a pulse repetition rate of 120 Hz delivering up to 2.5 kJ of energy per pulse in 60 ns pulses.
• the specific power system described here can deliver pulsed power signals of about 20-1000 ns duration with ion beam energies of 0.25-2.5 MeV.
• the power system can operate at 50% electrical efficiency from the wall plug to energy delivered to a matched load.
• the power system P uses low loss pulse compression stages incorporating, for example, low loss magnetic material and solid state components, to convert AC power to short, high voltage pulses.
• the ability to produce voltages from 250 kV or less to several MV by stacking voltage using a plurality of inductive adders incorporating low loss magnetic material is a principle feature when high voltages are needed, although it is also possible to use a single stage pulse supply, eliminating the need for the adder.
• the power system can operate at relatively low impedances ( ⁇ 100 ⁇ ) which also sets it apart from many other repetitive, power supply technologies, such as transformer-based systems. This feature allows high treatment rates and the treatment of large areas (5 to more than 1000 cm 2 ) with a single pulse so as to reduce edge effects occurring at the transition between treated and untreated areas.
• the second component of the pulsed ion beam system is the MAP ion beam source 25 (shown in Figure 8).
• the MAP ion beam source is capable of operating repetitively and efficiently to utilize the pulsed power signal from the power system efficiently to turn gas phase molecules into a high energy pulsed ion beam. It can also be operated in the single shot mode, as necessary for a particular application.
• a precursor of the ion beam source is an ion diode described generally by J. B.
• the ion beam source 25 is a magnetically-confined anode plasma (MAP) source.
• Figure 8 is a partial cross-sectional view of one symmetric side of the ion beam or MAP source 25.
• the ion beam or MAP source 25 produces an annular ion beam K which can be brought to a broad focus symmetric about the axis X-X 400 shown.
• slow (1ms rise time) magnetic field coils 414 produce magnetic flux S (as shown in Fig. 8A) which provides the magnetic insulation of the accelerating gap between the cathodes 412 and the anodes 410.
• the anode electrodes 410 also act as magnetic flux shapers.
• the slow coils 414 are cooled by adjacent water lines, not shown, incorporated into the structure 30 supporting the cathodes 412 and the slow coils 414.
• the main portion of the MAP structure shown in this Figure is about 18 cm high and wide.
• the complete MAP ion diode can be visualized as the revolution of the cross- sectional detail of Fig. 8 about the central axis 400 of the device to form a cylindrical apparatus. A full cross sectional view appears in Fig. 9.
• the ion beam or MAP source 25 operates in the following fashion: a fast gas valve assembly 404 located in the anode assembly 35 produces a rapid (200 ⁇ s) gas puff which is delivered through a supersonic nozzle 406 to produce a highly localized volume of gas directly in front of the surface of a fast driving coil 408 located in an insulating structure 420.
• the nozzle is designed to prevent any transverse flow of non-ionized gas into the gap between the anodes 410 and cathodes 412.
• the fast driving coil 408 is fully energized from the fast capacitor 150, inducing a loop voltage of 20 kV on the gas volume, driving a breakdown to full ionization, and moving the resulting plasma toward the anode electrodes 410 in about 1.5 ⁇ s or less, to form a thin magnetically- confined plasma layer.
• the gas can be effectively pre-ionized by placing a small ringing capacitor
• the bias field capacitor 180 drives a greater than 1 microsecond risetime current in the fast coil before the main capacitor pulse begins. This allows adjustment of the field configuration produced by the fast capacitor current.
• the fast capacitor 150 drives a 1 microsecond risetime pulse in the fast coil.
• the preionizer capacitor 160 causes the voltage across the fast coil to ring with a much less than 1 microsecond period, inducing a large oscillating electric field in the gas to be ionized, leading to partial ionization of the gas.
• the rising magnetic field produced by the fast coil 408 pushes the ionized gas away from the fast coil, stagnating it against the preexisting magnetic field from the slow coil 414.
• the fast coil is then fully energized as described above to completely breakdown the gas into the plasma. After this pulse the field collapses back into the fast coil which is connected to a resistive load which is in turn connected to a heat sink, not shown.
• a heat sink not shown.
• cooling channels in the supporting structure are used, but other solutions are possible and relatively straightforward. In this manner heat build up in the fast coil is avoided.
• the fast coils 408 have been redesigned from the reference fast coils in several ways as well as the heat sinking mentioned above.
• the gap between the fast coil and the anode electrodes 410 has been reduced with the result that the amount of necessary magnetic energy has been decreased by over 50%.
• the lower energy requirement permits repetitive use at higher frequencies and reduces the complexity of the feed system voltages for the fast coils.
• the design of the new flux-shaping anode electrode assembly has also contributed to these beneficial results.
• the pulsed power signal from the power system is then applied to the anode assembly 35, accelerating ions from the plasma to form an ion beam K.
• the slow (S) and fast (F) magnetic flux structures, at the time of ion beam extraction, are shown in Figure 2A.
• the definite separation between the flux from the fast coil from the flux from the slow coil is shown therein. This is accomplished by the flux-shaping effects of the anodes 410 and also by the absence of a slow coil located in the insulating structure 420 as was taught in the earlier MAP reference paper.
• the slow coils in the present MAP ion diode are located only in the cathode area of the MAP. This anode flux shaping in conjunction with the location of slow coils in the cathode assembly is different from that shown in the MAP reference paper and permits the high repetition rate, sustained operation of the MAP diode disclosed herein.
• FIG. 8B is a detailed view of the gas valve assembly 404 and the passage
• the passage 425 which conducts the gas from the valve 404 to the area in front of the fast coil 408.
• the passage 425 has been carefully designed to deposit the gas in the localized area of the fast coil with a minimum of blow-by past this region.
• the details of the cross sections of the passage 425 were designed for supersonic transport of the gas puff. The design was done with readily available gas flow computer programs and is within the skill in the art.
• the gas valve flapper 426 is operated by a small magnetic coil 428 which opens and closes the flapper 426 upon actuation from the MAP control system.
• the flapper valve is pivoted on the bottom end 427 of the flapper.
• the coil 428 is mounted in a high thermal conductivity ceramic support structure 429 which is in turn heat sinked to other structure, not shown.
• the gas is delivered to the valve from a plenum 431 behind the base of the flapper.
• the plenum 431 should be visualized as being connected to a larger plenum located at the central core of the complete MAP ion diode as shown in Fig. 9.
• the vacuum in the nozzle 406 rapidly draws the gas into the MAP once the flapper 426 is opened.
• the function of the nozzle is to produce a directed flow of gas only in the direction of flow and not transverse to it. Such transverse flow would direct gas into the gap between the anode and the cathode which would produce detrimental arcing and other effects.
• the vacuum recovery within the MAP allows sustained operation up to and above 100 Hz.
• the magnetic geometry is fundamentally different from previous ion diodes.
• Prior diodes produced rotating beams that were intended for applications in which the ion beam propagates in a strong axial magnetic field after being generated in the diode.
• the present system requires that the ion beam be extracted from the diode to propagate in field-free space a minimum distance of 20-30 cm to a material surface.
• the magnetic configurations of previous ion diodes are incapable of this type of operation because those ion beams were forced by the geometries of those diodes to cross net magnetic flux and thus rotate. Such beams would rapidly disperse and be useless for the present purposes.
• the modifications include: the elimination of a slow coil on the anode side of the diode and its associated feeds, better control over the magnetic field shaping and contact of the anode plasma to the anode electrode structure through use of the partially field- penetrable electrodes, the elimination of the separate pre-ionizer coil from the prior ion diodes, the circuit associated with the fast coil to provide "bias" current to adjust the magnetic field to place the anode plasma surface on the correct flux surface to eliminate beam rotation and allow optimal propagation and focusing of the beam, and the redesign of the gas nozzle to better localize the gas puff which enables the fast coil to be located close to the diode gap which in turn reduces the energy requirements and complexity of the fast coil driver.
• the plasma can be formed using a variety of gas phase molecules.
• the system can use any gas (including hydrogen, helium, oxygen, nitrogen fluorine, neon, chlorine and argon) or vaporizable liquid or metal (including lithium, beryllium, boron, carbon, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, and potassium ) to produce a pure source of ions without consuming or damaging any component other than the gas supplied to the source.
• the ion beam K propagates 20-30 cm in vacuum ( ⁇ 10 '3 ) to a broad focal area (up to 1000 cm 2 ) at the target plane 195, shown in Fig. 3, where material samples are placed for treatment and can thermally alter areas from 5 cm 2 to over 1000 cm 2 .
• the ion beam or MAP source 25 is capable of operating at repetitive pulse rates of 100 Hz continuously with long component lifetimes >10 6 .
• the ion beam or MAP source 25, according to the principles of the present invention draws ions from a plasma anode rather than a solid dielectric surface flashover anode used in present single pulse ion beam sources.
• Use of a flashover anode typically introduces a variety of contaminants to the surface of the material, often with detrimental results.
• One of the significant advantages of using the improved MAP source disclosed herein is that one has precise control over the components in the ion beam by controlling the composition of the gas source.

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• 1996
  • 1996-01-23 RU RU96121341/04A patent/RU2154654C2/ru active
  • 1996-01-23 WO PCT/US1996/000872 patent/WO1996023021A1/en not_active Application Discontinuation
  • 1996-01-23 CA CA002186101A patent/CA2186101A1/en not_active Abandoned
  • 1996-01-23 IL IL11687796A patent/IL116877A/xx not_active IP Right Cessation
  • 1996-01-23 JP JP8522969A patent/JPH09511016A/ja active Pending
  • 1996-01-23 EP EP96910295A patent/EP0751972A4/de not_active Withdrawn
  • 1996-01-23 AU AU53529/96A patent/AU5352996A/en not_active Abandoned

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