RF Coil Resonator System and Method

Abstract

The described embodiments include a subsystem for supplying RF power to an inductively coupled plasma (ICP) torch. The present disclosure addresses some technical aspects of RF power converters, as well as the design of a load coil and a resonant RF tank circuit for an ICP. The systems and methods described herein cancel the on-axis RF due to the symmetry of the applied voltage and the symmetry of the load coil. Thus, RF balance is achieved by design without the need to find and adjust an optimal RF voltage ratio. The embodiments also enable large RF currents and low RF voltages, reducing the risk of RF breakdown outside the torch. Transistors can be used to supply RF power. As a result, a more compact ICP assembly can be used.

Description

Technical Field

[0001]

[0001] Cross - reference to Related Applications This application claims the benefit of priority of U.S. Provisional Application No. 63 / 353,177, filed on June 17, 2022, the entire contents of which are incorporated herein by reference for all purposes.

Background Art

[0002]

[0002] Regarding inductively coupled plasma (ICP), numerous applications have been found ranging from semiconductor processing to equipment for waste incineration, material treatment, and powder processing, analytical instruments such as ICP - MS (ICP mass spectrometry) and ICP - OES (ICP optical emission spectrometry), and mass cytometry.

[0003]

[0003] Mass cytometry is becoming a common tool for flow cytometry analysis of biological samples as well as biological imaging of tissue samples. The principle of mass cytometry is based on using affinity probes attached with elemental tags to reveal the concentration of antigens in individual biological cells. Once the cells are tagged, the readout consists of sending these cells into an inductively coupled plasma ion source to atomize and ionize the elemental tags on each cell. The ionized cloud from each cell containing the elemental tag is sampled into a mass spectrometer, where the sequence of the cloud of the entire sample is recorded. The advantage of the mass cytometry approach is the large number of probes that can be applied and recorded simultaneously in one experiment. More than 40 probes recorded in one experiment have been demonstrated in this technology. In recent years, the application of mass cytometry has expanded into the field of imaging of biological tissues based on immunohistochemistry. This technology is called Imaging Mass Cytometry (trademark) (IMC (trademark)). In any of these methods, the ICP torch plays a role in converting biological substances into transient signals of ions from elemental tags.

[0004]

[0004] ICP typically operates at frequencies from 1 MHz to 100 MHz and power levels from tens of watts at low pressure to several megawatts at atmospheric pressure. A kilowatt-level ICP operating at atmospheric pressure is used in analytical instruments. The power converter for ICP takes in AC / DC power from a power source and converts it into RF power. This converter is often a large, bulky, and relatively expensive unit. Its power conversion efficiency is also low, which may result in significant generation of waste heat. Drawbacks also include the reliability and reproducibility of the analysis results.

[0005]

[0005] These drawbacks and other drawbacks are recognized when technologies such as mass spectrometry are applied among biologists. To address these needs and other needs.

Summary of the Invention

[0006]

[0006] Embodiments described herein include a subsystem for supplying RF power to an inductively coupled plasma (ICP) torch. The present disclosure addresses some technical aspects of RF power converters, as well as the design of a load coil and a resonant RF tank circuit for ICP. The systems and methods described herein cancel out the on-axis RF due to the symmetry of the applied voltage and the symmetry of the load coil. Thus, RF balance is achieved by design without the need to find and adjust the optimal RF voltage ratio. Embodiments also enable large RF currents and low RF voltages, reducing the risk of RF breakdown outside the torch. Transistors can be used to supply RF power. Embodiments can result in a compact ICP assembly.

[0007]

[0007] In an embodiment, the RF coil resonator can include a plurality of loops. Each loop of the plurality of loops may be connected such that when a voltage is applied to the plurality of loops, it is electrically parallel to other loops of the plurality of loops. Further, the RF coil resonator may include a power supply that electrically communicates with the plurality of loops. The power supply may be in a circuit configured to supply a first phase of RF power to a first terminal of the plurality of loops and a second phase of RF power to a second terminal of the plurality of loops.

[0008]

[0008] In an embodiment, the RF power module may include a DC power supply. Further, the RF power module may include a plurality of transistors that electrically communicate with the DC power supply. Further, the RF power module may include a plurality of gate drivers. Each of the plurality of gate drivers may be connected to a respective one of the plurality of transistors. The RF power module may further include a processor. The processor may be configured to control the plurality of gate drivers to turn on and off the plurality of transistors to convert a DC current from the DC power supply into an RF current.

[0009]

[0009] An embodiment may include an analysis method using plasma. The method can include applying an RF voltage to a plurality of loops around a tube. The plurality of loops may be electrically parallel. A first phase of the RF voltage can be applied to a first terminal of the plurality of loops. A second phase of the RF voltage can be applied to a second terminal of the plurality of loops. The first phase may be opposite to the second phase. The method can further include igniting the plasma inside the tube.

[0010]

[0010] A better understanding of the nature and advantages of embodiments of the present invention can be obtained by referring to the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 8A

Figure 8B

Figure 9

Best Mode for Carrying Out the Invention

[0012]

[0021] Inductively coupled plasmas (ICPs) are used in numerous applications, but the power supply system has several drawbacks, including the cost of the RF generator and the amount of power (on the order of 1 - 2 kW) required to operate the analytical torch. The relatively low efficiency of the RF generator and power supply circuit can lead to even greater power consumption. The ICP power supply circuit can have an efficiency of about 60%. This means that when the RF power to the ICP load coil is 1.5 kW, the circuit consumes an additional 1 kW of power, which is converted to heat and must be removed from the electronic components. A circuit with an RF power supply efficiency of about 90% would be beneficial to users and equipment designers. Such a circuit can simplify thermal management for equipment designers and reduce the cost of electricity and air conditioning for end users. Another drawback is the RF coupling of the drive voltage to the plasma, which can cause secondary discharges between the plasma and another electrode, such as the sampler electrode, as described in U.S. Patent No. 4,501,965. Careful balancing of the RF coil voltage is often required. ICP systems and methods are also described in U.S. Patent Application Publication No. 2021 / 0404968. Another drawback is the high voltage (up to several kV) applied to a normal helical load coil with a series connection of turns. In this configuration, dielectric breakdown can occur between the turns of the coil. Additional insulation can be applied to the coil to avoid dielectric breakdown, but this can cause additional cost and complexity.

[0013]

[0022] Another drawback of existing ICP equipment is the aging of the RF load coil and the periodic replacement of the coil. The load coil is exposed to a significant amount of heat flux. This heat can raise the temperature of the load coil up to 300°C in air. At this temperature, the outer layer of copper can blacken, and ultimately the load coil deteriorates, requiring periodic replacement. This problem can be overcome using liquid cooling of the load coil, but the RF circuit becomes even more complex. Given the compatibility with the high RF voltage on the load coil, the range of cooling solutions that can be used is often limited.

[0014]

[0023] Typical load coils are usually manufactured by bending copper or silver tubes. Bending the tubes introduces some distortion in the geometric parameters of the coil, resulting in lower accuracy and precision compared to when the coil can be machined from larger parts. Combined with the aforementioned regular replacement of the coil, the inaccuracy of the geometric parameters of the coil limits the reproducibility of the analysis results.

[0015]

[0024] Another drawback of current ICP equipment is the axial RF current on the axis of the plasma. The axial RF current in the plasma can penetrate the vacuum interface of the mass spectrometer and affect the ion signal. U.S. Patent No. 4,501,965 provides one way to solve this problem by using an electrical method that generates RF_A and RF_B voltages at a rate such that their net effect cancels out at a point on the axis just before the sampler orifice. However, experimentation is required to find the appropriate ratio, and the ratio depends on the position and shape of the plasma in the torch and its relationship to the sampler position.

[0016]

[0025] Some ICP equipment has the problem that RF MOSFET transistors require relatively large power to drive their gates. This complicates the drive circuit and increases the overall power loss of the system. Additionally, another problem is that existing triode-vacuum-tube-based RF generators for ICP require a high-voltage DC source for the triode. The high-voltage DC power source is a custom power source and is relatively large and expensive compared to off-the-shelf low-voltage power sources with similar power handling capabilities.

[0017]

[0026] Embodiments of the ICP configurations and methods described herein simplify the RF generator, make the RF circuit of the ICP more efficient in terms of power, suppress the degradation of the load coil, make the load coil mechanically more reproducible, reduce or eliminate the need for RF balancing, and reduce or eliminate the axial RF current.

[0018]

[0027] I. RF coil resonator The embodiments described herein operate the ICP MS load coil using large RF currents and low RF voltages by electrically connecting the turns of the load coil in parallel rather than in series. The low RF voltage can allow heat to escape directly from the individual turns of the RF load coil to its base, thus extending the life of the load coil. The low RF voltage reduces the risk of RF breakdown outside the torch and eliminates the possibility of breakdown between turns. This allows for a reduction in the clearance between mechanical components and enables a more compact assembly. A circuit can create an overvoltage condition to ignite the plasma without the risk of electrical breakdown. The self-ignition of the plasma can simplify the ICP subsystem and make the subsystem more compact. A solid-state circuit can be used for power supply and operation of the resonant tank circuit. The compactness of the ICP torch and electronics facilitates integration with a laser ablation module for ultra-fast transients. The throughput of a laser ablation-based imager is determined by the width of the transient. Thus, among other things, a more compact ICP assembly promotes the advancement of imaging mass spectrometry and Imaging Mass Cytometry (trademark).

[0019]

[0028] The embodiments include several major interconnected components, namely a load coil, a resonant RF tank circuit connected to the load coil, an RF power supply circuit that powers the resonant tank circuit, and the torch itself.

[0020]

[0029] A. Load coil and RF tank circuit Figure 1 shows an example of a configuration 100 of a load coil that provides self - balancing of the on - axis RF potential in a plasma. The load coil 104 is positioned around a virtual tube 108 having a plasma 112. For simplicity, only one turn of the load coil 104 is shown. A plurality of turns of the load coil 104 are possible, and each turn is flat - circular or approximately circular, as in the figure. A first terminal 116 may connect the load coil 104 to phase A 120 of an RF power supply. A second terminal 124 may connect the load coil 104 to phase B 128 of the RF power supply. Capacitor 132 represents the capacitive coupling of phase A between the load coil 104 and the plasma 112. Capacitor 136 represents the capacitive coupling of phase B between the load coil 104 and the plasma 112. Neither capacitor 132 nor capacitor 136 is a physical capacitor.

[0021]

[0030] As a result of symmetry, when the voltages of the RF+A phase and the RF-B phase have the same amplitude, the RF effects cancel each other out, and the on-axis (e.g., the longitudinal axis passing through the center of tube 108) potential of the plasma is zero. Further details about the reasons for RF balance can be found in H. Niu, Fundamental studies of the plasma extraction and ion beam formation processes in inductively coupled plasma mass spectrometry, Dissertation, 1994, pp. 38-40, which is available at doi.org / 10.31274 / rtd-180813-11783. In a typical analytical ICP MS instrument, the load coil has three or four turns arranged as a spiral or helix. These turns can be considered to be connected in series as a set of individual turns. In the spiral arrangement of the turns, only the central turn has the appropriate balance. The outer turns have RF voltages that do not match and do not cancel each other. Therefore, the net balance can generally be achieved only at one position along the axis set in the region just before the sampler. The balance can be achieved for a particular state of the plasma (e.g., plasma power and its distance from the sampler). However, it can be difficult to achieve a good balance over the entire range of operating conditions.

[0022]

[0031] Embodiments may include driving ICP in several turns connected in parallel to the same RF source. In such a configuration, all turns of the load coil generate an RF balanced plasma (on-axis), regardless of plasma conditions and elongation. Another advantage of driving several turns in parallel is that the RF voltage required to drive such a system at a given plasma power is reduced. The reduction in the voltage requirements of the load coil facilitates coupling a low-to-medium voltage power transistor to the load. When the turns are connected in parallel, the RF voltage is reduced, but the RF current increases proportionally to maintain the same RF power. This results in a significant reduction in the inductance of the load coil and an increase in the current required to maintain the RF voltage across the load coil. To minimize the impedance reduction effect of the load coil, a capacitor can be placed across the load coil of the present invention. Not all of the current supplied to the plasma is transferred to the plasma. The capacitor can help store some of this excess current and thus forms part of the resonant tank circuit.

[0023]

[0032] FIG. 2 shows an example of a configuration 200 of a load coil having a physical capacitor. The load coil 204 is located around a tube 208 having a plasma 212. For simplicity, only one turn of the load coil 204 is shown. Multiple turns of the load coil 204 are possible. A first terminal 216 may connect the load coil 204 to the A-phase 220 of the RF power source. A second terminal 224 may connect the load coil 204 to the B-phase 228 of the RF power source. A capacitor 232 is connected to both the first terminal 216 and the second terminal 224.

[0024]

[0033] The load coil 204 may act as an inductor, or an inductor (not shown) may be added in series with the load coil 204. The value of the capacitor 232 can be selected to almost cancel out the impedance of the inductor at a preferred operating frequency. Thus, the electrical characteristics of the circuit can be made to be dominated by the resistive losses of the RF energy in the plasma. Without a resonant capacitor, the parasitic inductance of the connecting wires limits the ability of the circuit to circulate a large current through the load coil while applying a low voltage, so this arrangement is beneficial. The capacitor makes it possible to cancel out most of the inductive impedance of the equipment. Most of the remaining impedance is resistive, but a part of the inductive or capacitive impedance can be generated by shifting the RF frequency of the signal above or below the resonant frequency of the equipment. The load coil, together with the inductor and the capacitor, is thought to form part of a resonant RF tank circuit or a resonant tank circuit. The resonant RF tank circuit can play a role in balancing the impedance associated with the resonance of the current passing through the load coil.

[0025]

[0034] Although FIGS. 1 and 2 show only one turn of the load coil, a similar circuit can operate with a load coil having a plurality of turns connected in parallel. The turns can be stacked such that each turn is connected to its dedicated driver, and the drivers can be operated in RF synchronization. The RF model showed that when the load coil includes three turns connected in parallel and the central turn is shielded by the outer turns and the same voltage is applied to all turns, the current in the central turn is less than the current in the outer turns. As a result of this observation, it can be concluded that the central turn does not function as hard as the outer turns. The number of turns of the load coil can be reduced to two, enabling a more compact load coil and torch. Another option may be to generate outer turns having an inductance larger than that of the central turn. This can be achieved by giving the outer turns a larger diameter than the central turn, or by adding parasitic inductance to the feed legs (i.e., terminals) of the outer turns.

[0026]

[0035] Further design variants are available for the resonant circuit. The capacitor 232 can be replaced with two independent capacitors, each independent capacitor being able to connect one side of the load coil to ground. This capacitor arrangement reduces the voltage rating required for the capacitor by half. A DC blocking capacitor can be installed in series with the load coil to block the DC voltage that may be generated from the RF driver. A capacitive divider can be connected to each side of the load coil. The total capacitance of the divider can be selected to cancel out most of the inductive impedance of the load coil. By having a capacitive divider, it is possible to inject RF at a smaller amplitude into the divider and, through the resonance process, increase the amplitude at a second capacitor directly connected to the load coil. Various resonance schemes for impedance conversion are available for changing the impedance of the load coil (in the presence of power dissipation from the plasma) and are described herein (e.g., FIG. 4).

[0027]

[0036] Figure 3 shows another example of the configuration 300 of the load coil. The single loop of the load coil of FIGS. 1 and 2 can be divided into a first half-turn coil 304 and a second half-turn coil 308. The first half-turn coil 304 and the second half-turn coil 308 are located around the plasma 312. The first terminal 316 of the first half-turn coil 304 is connected to the A phase of the RF driver 320. The second terminal 324 of the first half-turn coil 304 is connected to the B phase of the RF driver 328. The first terminal 332 of the second half-turn coil 308 is connected to the A phase of the RF driver 328. The second terminal 336 is connected to the B phase of the RF driver 320. The RF current flows in the clockwise direction as indicated by the arrows 340 and 344. The RF driver 320 and the RF driver 328 can be operated in RF synchronization with each other. Resonance capacitors 348 and 352 cancel out the effect of the low coil inductance, similar to the capacitor 232 of FIG. 2.

[0028]

[0037] In FIG. 3, the half-turn coil requires only a further lower RF voltage and can further improve the balance. The RF power requirement of each individual RF driver is reduced by half. Although a half-turn configuration is shown here, 1 / 3 turn, 1 / 4 turn, or other split-turn configurations are also possible. Two or more disks of half-turns can be arranged along the length of the torch to produce an installation similar to the 3-turn load coil described in FIG. 1.

[0029]

[0038] The half-turn or split-turn configuration has advantages regarding RF balance. The system can have better symmetry of the RF current in the plasma. The amplitude of the RF voltage in the half-turn is reduced by half. Therefore, the imbalance due to the asymmetry of the actual installation is further attenuated by the reduction of the applied RF voltage.

[0030]

[0039] B. RF Power Supply Embodiments include supplying each phase of RF power to a load coil via a resonant RF tank circuit. An RF triode can be used to generate and supply RF power, but such a power source is large and expensive. Further, an RF triode may only have an efficiency of 60 - 70%. To address the size and cost issues of the RF power supply module for ICP MS, embodiments use a high-frequency power transistor instead of an RF triode. Since an RF transistor operates at a low DC voltage, the power supply for such a transistor can be off-the-shelf rather than custom, which means that in many cases, when the power handled is at the same level, it is cheaper, more compact, and more efficient.

[0031]

[0040] Embodiments include using the principle of a switched-mode power supply (SMPS) at these relatively high frequencies (about 40 MHz) instead of a linear amplifier for RF power. An SMPS is composed of transistors. An SMPS having a transistor as a driver can be configured to operate efficiently with an inductively coupled plasma load. There are many possible configurations for those having similarities with a resonant SMPS topology. The operation of a resonant RF power converter at 40 MHz can be facilitated by high-performance transistors such as gallium nitride (GaN)-based transistors. These transistors require relatively little energy at the input for switching states (on / off). Thus, the drivers for these transistors can be in the form of more commercially available MOSFET drivers and can be directly controlled by a digital signal. This simplifies the design of the control circuit as well as the number of stages and components required for the RF power converter. Further, the SMPS provides greater flexibility in the timing and shape of the control signals used in resonant converters. Further explanation is discussed at the location of resonant conversion.

[0032]

[0041] One embodiment of the RF driver is a resonant converter type driver by soft-switching of transistors. The configurations of RF drivers in the field of resonant converter SMPSs include basic LLC and LCC configurations, as well as more complex configurations (such as LCLC) (however, it is not limited to these). Similarly, in the field of resonant SMPSs, RF drivers can be configured with a number of topologies (such as various arrangements of transistors, capacitors, and inductors). Selections can be made to conform to specific technologies of RF capacitors, or to minimize or reduce the influence of stray inductance, or to reduce power losses in transistors and other components.

[0033]

[0042] A high-performance switching transistor including a GaN transistor can be integrated into the RF driver. The RF driver can be configured as a full-bridge resonant driver (for example, using four transistors), a half-bridge resonant driver (for example, using two transistors with one side grounded), or a flyback resonant driver (for example, using one switching transistor). Multiple transistors can be used in parallel within one switch to expand the power processing range.

[0034]

[0043] FIG. 4 shows a system 400 including a full bridge that drives an RF tank circuit 402 of a load coil and a capacitor module. The RF tank circuit 402 includes impedance matching inductors LA 404 and LB 408, as well as capacitors C1A 412a, C1B 412b, C2A 416a, and C2B 416b. RF power is transmitted from the output of the bridge driver to the resonant load coil circuit by inductors LA 404 and LB 408.

[0035]

[0044] A DC power supply 420 supplies DC power to a transistor that drives an RF tank circuit 402. The RF power is supplied using transistors QA1 424, QA2 428, QB1 432, and QB2 436. Each transistor can have an associated gate driver for turning the transistor on and off. By turning the transistor on and off, it can be made possible for a square wave to pass from the driver to the output of the transistor. Here, a square wave is described for simplicity of explanation. In an actual implementation, it is necessary to consider the rise time and fall time of the transition between the on state and off state of the transistor. These transitions can be made more power-efficient with the help of resonance effects within the tank circuit. The timing of turning the transistor on and off can enable the supply of RF current to the RF tank circuit 402. The transistor may be a GaN MOSFET. A controller can send digital pulses to the gate driver. The digital pulses can have parameters such as duration, frequency, and time delay. Further, the controller can adjust these parameters on the fly to optimize efficiency, or increase the RF voltage, or adapt to changes in plasma conditions.

[0036]

[0045] The impedance matching inductors LA 404 and LB 408 assist in the zero voltage switching operation of the GaN MOSFET. Zero voltage switching is a technique of turning on a power transistor at the instant when the voltage across the transistor is low (close to zero). To further facilitate zero voltage switching under all load conditions, the switching frequency may be modulated to maintain a specific phase relationship between the voltage at the output of the bridge and the voltage between the load coil terminals.

[0037]

[0046] FIG. 5 shows a layout of a MOSFET bridge connection by inductors LA and LB implemented as silver-plated copper bars connecting a load coil 504, resonant capacitors, and bridge terminals to resonant capacitors C1A, C1B, C2A, and C2B. FIG. 5 shows an example of the system 400 of FIG. 4. FIG. 5 shows how an RF drive circuit and a load coil can be miniaturized into one package (module). The inner diameter of the load coil is 22 mm. The length of the load coil is about 2 cm.

[0038]

[0047] FIG. 6 shows an integrated plasma torch module 600 with a small solid-state RF generator. An ICP tube 604 for the plasma torch is sealed against a sampler 608. The ICP tube 604 is surrounded by a load coil 612. The load coil 612 may be the load coil 104 of FIG. 1 or the load coil 204 of FIG. 2. The load coil 612 can be operated by an RF generator 616 that can include the full bridge of FIG. 4. The flow of the coolant is indicated by arrows 620, 624, and 628. The plasma torch module 600 can share liquid cooling for the electronics with liquid cooling for the ICP tube 604 and the sampler 608, enabling a compact cooling system.

[0039]

[0048] In a sealed torch facility, the pressure inside the torch can be reduced below atmospheric pressure to initiate an RF discharge with a relatively low RF voltage. This RF discharge can then be changed to a high-pressure ICP plasma by gradually increasing the pressure and plasma power supplied to the torch. This enables self-ignition of the plasma inside the torch without the need for an additional igniter assembly or a large overvoltage of RF required for ignition at atmospheric pressure.

[0040]

[0049] The concept of self-ignition has been experimentally and theoretically verified. The theoretical estimation of the ignition voltage is based on the balance between the energy of electrons received from the electric field and the losses in collisions under the conditions of the present inventors. This is given by the following approximate formula

Number

[0041]

[0050] Furthermore, the pressure inside the torch can be easily made several atmospheres just by controlling the flow of the plasma gas entering and leaving the torch. When operating at pressures above 1 atm, a smaller-scale torch can be used. A smaller-scale torch requires less RF power to maintain the plasma, and due to the compactness of the plasma, a smaller-scale torch can facilitate faster transient phenomena for transient events such as ablation plume recording or single-particle detection in the plasma.

[0042]

[0051] In an embodiment, the sealed torch may be fabricated from ceramic by 3D printing. Other suitable torch materials such as fused silica can be used as well. The sealed torch may be a manifold that includes plasma. Ceramic by 3D printing can enable cooling channels within the ceramic body, as well as plasma gas supply channels and plasma gas removal channels. The ceramic by 3D printing can be selectively metallized (using a mask) to create soldering pads for turns of the load coil and additional RF components such as capacitors and inductors. Thus, ceramic 3D printing technology can further facilitate the integration of the torch and RF electronics into a single plasma module. Such integration can include a sampler at the output of the torch and an injector plate at the input of the torch. The integrated system can enable operation with an injector that is only a few centimeters short. The short injector can be advantageous for the fast transient phenomena of the ablation plume used in Imaging Mass Cytometry™ and imaging mass spectrometry. In comparison, in some commercial systems, the distance between the ablation region and the tip of the injector into the plasma is about 40 cm. The delay in the arrival of the transient phenomena and the spread of the transient phenomena typically increase approximately proportionally to the length of the injector.

[0043]

[0052] C. Operation FIG. 7A shows a photograph of the load coil 704 around the tube. The load coil 704 is machined rather than formed from the tube. Machining enhances the mechanical precision of the coil and thus improves the reproducibility of the analysis results when another coil of the same design is used (e.g., from coil replacement or analysis on different equipment).

[0044]

[0053] FIG. 7B shows a photograph of the operation of the ICP torch. FIG. 7B shows the operation of a solid state RF generator having a sealed torch.

[0045]

[0054] Figures 8A and 8B show the simulation results of the current density distribution within the turns of a load coil having circular turns. The load coil may be a load coil in which turns are connected in parallel as described herein. Figure 8A shows a simplified geometric shape of a simulation including three cylindrically symmetric coil turns simulated in a sufficiently large free space. The x-axis is the radius. The y-axis is the axial direction. Figure 8B is an enlarged graph of the cross-section of the coil turn and the calculated current density at an RF frequency f = 100 kHz. Two different effects are seen. First, the current is located near the surface of the coil. This is the well-known skin effect, and the thickness of the current layer is proportional to f -1 / 2 . Second, the current is shifted towards the inner part of the coil (left side of the figure). When f increases up to a typical operating frequency of 27 MHz, the distribution remains qualitatively the same, but the thickness of the current layer becomes so small (a few micrometers) that it cannot be shown in a photograph at this scale of dimension. For this reason, the illustration is made at a low frequency where the skin effect is prominent. The current flows along the inner surface of the coil, and the small current layer may be able to change the shape of the coil. For example, the coil can potentially be manufactured as a deposition of a thin copper layer on the surface of a ceramic, as described above. A thin layer of conductor in the region of high current density may be sufficient to generate substantially the same RF field using the RF current within these layers.

[0046]

[0055] D. Exemplary System Embodiments include an RF coil resonator. The RF coil resonator can include a plurality of loops. Each loop of the plurality of loops may be geometrically parallel to the other loops of the plurality of loops. Each loop of the plurality of loops can include a flat surface parallel to the closest surface of the adjacent loop. Each loop may be the load coil 104 of FIG. 1 or the load coil 204 of FIG. 2. The plurality of loops may be the load coil 504 of FIG. 5, the load coil 612 of FIG. 6, or the load coil 704 of FIG. 7.

[0047]

[0056] Each loop of the plurality of loops may form a discontinuous circle. The plurality of loops may be configured such that the center of curvature of each loop of the plurality of loops is on the longitudinal axis. The longitudinal axis is perpendicular to each plane including each loop of the plurality of loops. The plurality of loops can include at least 2, 3, 4, 5, 6, 7, 8, or 9 or more loops. The plurality of loops may be odd or even. In some embodiments, there are no other loops in electrical communication with the plurality of loops.

[0048]

[0057] Each loop of the plurality of loops can define an opening. The shape of the opening may be circular. In some embodiments, the opening may not be perfectly circular, but may be more than 60%, 70%, 80%, 90%, 95%, or 99% circular (the percentage is the overall percentage of the circumference of the circle defined by the loop). The opening may include a portion extending from the circular portion of the opening. This portion may be rectangular in shape. The opening may be in the shape of a lollipop with a rod protruding from the circle. The cross-section of each loop may be square, rectangular, or circular. The cross-section may be the portion having the minimum cross-sectional area of the loop.

[0049]

[0058] Each loop of the plurality of loops may be connected such that when a voltage is applied to the plurality of loops, it is electrically parallel to the other loops of the plurality of loops. Each loop can have a first terminal, and the first terminal is located at the same end of each loop. The first terminal of the loop may be in direct contact with the first conductive piece. Each loop can have a second terminal, and the second terminal is located at the same end of each loop, but the second terminal is located at an end different from the first terminal. The second terminal of the loop may be in direct contact with the second conductive piece. The first conductive piece and the second conductive piece may not be in contact with each other. The first conductive piece and the second conductive piece may be copper bars. In embodiments, the current reaches all loops simultaneously or almost simultaneously, unlike a plurality of loops connected electrically in series.

[0050]

[0059] The plurality of loops may be machined from a single piece of metal (e.g., copper or silver). For example, parallel slits may be formed in the piece of metal to separate one loop from another. The piece of metal can have holes drilled therein to form circular openings in the plurality of loops.

[0051]

[0060] Each loop of the plurality of loops may be characterized by the same radius of curvature. For example, each of the plurality of openings may have a congruent shape that includes a congruent circular shape.

[0052]

[0061] The discontinuous circle may be the result of a single insulating section, two insulating sections, or three or more insulating sections. For example, a loop having two insulating sections may include both the first half-turn coil 304 and the second half-turn coil 308 of FIG. 3. The capacitor can electrically couple the first terminal to the second terminal. The capacitor may bridge one of each of the insulating sections. The capacitor may be the resonant capacitor 348 or the resonant capacitor 348.

[0053]

[0062] A loop between two other loops may have a smaller radius of curvature than the two other loops. An end loop (i.e., having only one adjacent loop) may be larger than a central loop (i.e., having two adjacent loops).

[0054]

[0063] Each loop of the plurality of loops may include an insulating material (e.g., ceramic) coated with a conductive thin film. In some embodiments, a subset of, but not all of, the plurality of loops may include an insulating material coated with a conductive thin film.

[0055]

[0064] Furthermore, the RF coil resonator may include a power source that is electrically connected to a plurality of loops. When two components are connected by a switch or a transistor, they can be considered to be electrically connected to each other even when the switch or the transistor is in the off position. The power source may be within a circuit configured to supply a first phase of RF power to a first terminal of a plurality of loops and a second phase of RF power to a second terminal of the plurality of loops. The power source may include a DC power source 420. The power source may be a switched-mode power source. The circuit may be an RF supply circuit that supplies power to a resonant RF tank circuit.

[0056]

[0065] The RF coil resonator may include a resonant RF tank circuit that is electrically connected to a plurality of loops. The resonant RF tank circuit may include a capacitor and an inductor. A circuit (e.g., an RF power supply circuit) configured to supply a first phase of RF power to a plurality of loops can supply the first phase of RF power to the plurality of loops via an RF tank circuit including a capacitor and an inductor. The resonant RF tank circuit can include two, three, four, five, six, seven, eight, nine, or ten or more capacitors. The resonant RF tank circuit can include two, three, four, five, six, seven, eight, nine, or ten or more inductors. The resonant RF tank circuit can include an RF tank circuit 402.

[0057]

[0066] The RF power supply circuit may include a transistor for gate-supplying RF power to a plurality of loops. The transistor may include a gallium nitride or silicon carbide transistor. The RF power supply circuit may include one, two, three, four, five, six, seven, eight, nine, or ten or more transistors. The power handling characteristics of the transistor may be from 100 W to 5 kW. To increase the power handling capacity, several transistors can be operated in parallel. The full-bridge operation utilizes four transistors and effectively shares the parasitic power dissipation among the four transistors. The operating frequency can be selected to be higher than the target frequency of the operation of the ICP torch. For example, while the torch can operate at 30 MHz, the transistor may have an operating frequency limit of 100 MHz. The ICP operating frequency can be in the range of several MHz to several hundred MHz. The RF power supply circuit can supply a second phase of RF power to a second terminal. The RF power supply circuit may be part of a circuit that is not a resonant RF tank circuit.

[0058]

[0067] The RF coil resonator can include a tube. The plurality of loops may be arranged around the tube. The tube may be quartz. The tube may be cylindrical. The tube may be at the center inside the plurality of loops.

[0059]

[0068] Some embodiments can include a module including any RF coil resonator described herein and a sampler. The sampler may include a sampler 608. The sampler may be configured to provide a path from the plasma effluent from the plasma ignited and / or sustained by the load coil to flow into a chamber within the sampler. A plasma torch and an RF supply module without a sampler may be smaller than 30 cm in length, 20 cm in width, and 4 cm in depth. An analysis system having the module may further include a detector. The detector may be a detector in a mass spectrometer, an optical detector in an emission spectroscopy system, or other detector.

[0060]

[0069] The RF coil resonator can be used in any analysis method using the plasma described in this specification.

[0061]

[0070] Some embodiments may include an RF power module. The RF power module may include an RF power supply circuit. The RF power module may include a DC power supply. The DC power supply may be any power supply described in this specification, such as the DC power supply 420. Further, the RF power module may include a plurality of transistors in electrical communication with the DC power supply. The plurality of transistors may be any transistors described in this specification.

[0062]

[0071] The RF power module may include a plurality of gate drivers. Each of the plurality of gate drivers may be connected to a respective one of the plurality of transistors. For example, the number of transistors may be equal to the number of gate drivers. The gate driver may be any gate driver described in this specification, such as the gate driver of FIG. 4.

[0063]

[0072] The RF power module may include a processor. The processor may be configured to control the plurality of gate drivers to turn on and off the plurality of transistors to convert the DC current from the DC power supply into an RF current. Instructions for the gate drivers may be stored on a non-transitory computer-readable medium.

[0064]

[0073] The RF power module may include a plasma load coil. The plasma load coil may be in electrical communication with the DC power supply. The plasma load coil, the plurality of transistors, and the DC power supply may be arranged such that an RF current generated from the control of the plurality of gate drivers by the processor is supplied to the plasma load coil. The plasma load coil may be any load coil described in this specification.

[0065]

[0074] The RF power module may include a capacitor and an inductor. The capacitor, inductor, plurality of transistors, and DC power supply may be arranged such that an RF current generated from the control of a plurality of gate drivers by a processor is supplied to the inductor. The capacitor or inductor may be any of those described herein. The RF power module may include a plurality of capacitors and / or a plurality of inductors.

[0066]

[0075] II. Exemplary Method FIG. 9 is a flowchart of an exemplary process 900 related to an analysis method using plasma. In some embodiments, one or more process blocks of FIG. 9 may be performed by an RF coil resonator (e.g., configuration 100 of the load coil, configuration 200 of the load coil, configuration 300 of the load coil, and / or plasma torch module 600). In some embodiments, one or more process blocks of FIG. 9 may be separate from the RF coil resonator or may be performed by another device or group of devices that may include the RF coil resonator. In addition to, or alternatively to, this, one or more process blocks of FIG. 9 may be performed by one or more components of the plasma torch module 600, such as the ICP tube 604, the sampler 608, or the load coil 612.

[0067]

[0076] In block 910, process 900 may include applying an RF voltage to a plurality of loops around the tube. The plurality of loops may be electrically parallel. A first phase of the RF voltage may be applied to a first terminal of the plurality of loops. A second phase of the RF voltage may be applied to a second terminal of the plurality of loops. The first phase may be opposite to the second phase. For example, the first phase may be negative of the second phase. The plurality of loops may be any of the plurality of loops described herein, such as the load coil 504 of FIG. 5, the load coil 612 of FIG. 6, or the load coil 704 of FIG. 7. Each loop may be the load coil 104 of FIG. 1 or the load coil 204 of FIG. 2.

[0068]

[0077] Applying an RF voltage includes applying power in the range of 0.10 to 20 kW. The RF voltage may be from 100 V to 6 kV. The voltage can be applied at a frequency in the range of 900 kHz to 100 MHz, such as 27.12 MHz and 40 MHz. The application of the RF voltage may be performed using the power supply, circuit, or other electronic components described herein. Before applying the RF voltage, a gas pressure for plasma ignition may be applied.

[0069]

[0078] In block 920, process 900 can include igniting the plasma within the tube. In some embodiments, plasma ignition does not include applying a voltage to an electrode inside the tube. Plasma ignition may be at a pressure in the range of 0.5 to 20 Torr. The plasma pressure can be increased (e.g., up to 0.5 to 20 atm), which can be a pressure associated with typical analysis conditions. Analytical data obtained from the plasma, such as any of the analytical data described herein, can be acquired.

[0070]

[0079] Process 900 includes flowing a first gas through the plasma to form a second gas that includes a plasma effluent. Process 900 may include flowing a sample and a first gas through the plasma to form a second gas. Process 900 may further include flowing the second gas to a detector for analysis. The detector may be any detector described herein.

[0071]

[0080] Process 900 can include additional embodiments, such as any single embodiment or any combination of embodiments described below and / or in relation to one or more other processes described elsewhere in this specification.

[0072]

[0081] FIG. 9 shows exemplary blocks of process 900, but in some embodiments, process 900 may include additional blocks, fewer blocks, different blocks, or blocks in a different arrangement compared to the blocks shown in FIG. 9. Additionally, or alternatively, two or more of the blocks of process 900 may be executed in parallel.

[0073]

[0082] III. Embodiments Embodiments can include the following.

[0074]

[0083] Embodiment 1: An analysis method using plasma, comprising applying an RF voltage to a plurality of loops around a tube, the plurality of loops being electrically parallel, a first phase of the RF voltage being applied to a first terminal of the plurality of loops, a second phase of the RF voltage being applied to a second terminal of the plurality of loops, the first phase being opposite to the second phase, and igniting the plasma in the tube.

[0075]

[0084] Embodiment 2: The method according to Embodiment 1, wherein applying the RF voltage includes applying power in the range of 100 W to 5 kW.

[0076]

[0085] Embodiment 3: The method according to Embodiment 1, wherein the RF voltage is 100 V to 6 kV.

[0077]

[0086] Embodiment 4: The method according to Embodiment 1, wherein igniting the plasma does not include applying a voltage to an electrode inside the tube.

[0078]

[0087] Embodiment 5: The method according to Embodiment 1, wherein igniting the plasma is at a pressure in the range of 0.5 to 20 Torr.

[0079]

[0088] Embodiment 6: The method according to Embodiment 1, further comprising flowing a first gas through the plasma to form a second gas containing plasma effluent.

[0080]

[0089] Embodiment 7: The method according to embodiment 6, further comprising flowing a sample and a first gas through a plasma to form a second gas, and flowing the second gas to a detector for analysis. Embodiments 1 to 7 may be combined with any of the methods described herein.

[0081]

[0090] Embodiment 8: A plurality of loops, each loop of the plurality of loops being connected to other loops of the plurality of loops so as to be electrically parallel when a voltage is applied to the plurality of loops, each loop of the plurality of loops being geometrically parallel to other loops of the plurality of loops, each loop of the plurality of loops forming a discontinuous circle, the plurality of loops being configured such that the center of curvature of each loop of the plurality of loops is located on the longitudinal axis, the longitudinal axis being orthogonal to each plane including each loop of the plurality of loops, a plurality of loops, and a power source electrically connected to the plurality of loops, the power source in a circuit configured to supply a first phase of RF power to a first terminal of the plurality of loops and a second phase of RF power to a second terminal of the plurality of loops. Embodiment 8 may be any of the RF coil resonators described herein.

[0082]

[0091] The specific details of particular embodiments can be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present invention. However, other embodiments of the present invention can be directed to particular embodiments relating to each individual aspect or to particular combinations of these individual aspects.

[0083]

[0092] The foregoing description of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms described, and many modifications and variations are possible in light of the above teachings.

[0084]

[0093] In the above description, for the purpose of explanation, numerous details have been described to provide an understanding of various embodiments of the present technology. However, it will be apparent to those skilled in the art that certain embodiments may be practiced without some of these details or with additional details.

[0085]

[0094] Although several embodiments have been described, those skilled in the art will recognize that various modifications, alternative configurations, and equivalents can be used without departing from the spirit of the present invention. Further, to avoid unnecessarily obscuring the present invention, some well-known processes and elements have not been described. Additionally, the details of any particular embodiment do not always exist in variations of that embodiment and may be added to other embodiments.

[0086]

[0095] When a range of values is presented, each value intervening between the upper and lower limits of that range is also specifically disclosed to the extent of one-tenth of the unit of the lower limit, unless the context clearly dictates otherwise. Each smaller range between any of the recited values or intervening values within the recited range and any other recited value or intervening value within the recited range is included. The upper and lower limits of these smaller ranges may be individually included in or excluded from the range, and each range that includes either, neither, or both of these smaller ranges is also included in the present invention, subject to any specifically excluded limits within the recited range. When the recited range includes one or both of the limits, ranges excluding one or both of those included limits are also included.

[0087]

[0096] As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a method" includes a plurality of such methods, reference to "the capacitor" includes reference to one or more capacitors and equivalents thereof known to those skilled in the art, and so on. The present invention has been described in detail for purposes of clarity and understanding. However, it will be understood that certain changes and modifications may be made within the scope of the appended claims.

[0088]

[0097] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None of them are admitted to be prior art.

Claims

1. A plurality of loops, each loop of the plurality of loops being connected to other loops of the plurality of loops so as to be electrically parallel when a voltage is applied to the plurality of loops; and a power source electrically connected to the plurality of loops, the power source in a circuit configured to supply a first phase of RF power to a first terminal of the plurality of loops and a second phase of RF power to a second terminal of the plurality of loops An RF coil resonator comprising.

2. The RF coil resonator according to claim 1, wherein each loop of the plurality of loops is geometrically parallel to other loops of the plurality of loops.

3. The plurality of loops are configured such that the center of curvature of each loop of the plurality of loops is located on the longitudinal axis, the longitudinal axis being perpendicular to each plane including each loop of the plurality of loops, The RF coil resonator according to claim 1 or 2.

4. The RF coil resonator according to claim 1, wherein each loop of the plurality of loops has a flat surface parallel to the closest surface of an adjacent loop.

5. The RF coil resonator according to claim 1 or 3, wherein each loop of the plurality of loops has the same radius of curvature.

6. The RF coil resonator according to any one of claims 1 to 5, wherein each loop of the plurality of loops forms a discontinuous circle.

7. The RF coil resonator according to claim 6, wherein the discontinuous circle is the result of a single insulating section.

8. The RF coil resonator according to claim 7, further comprising a capacitor that electrically couples the first terminal to the second terminal.

9. The RF coil resonator according to claim 6, wherein the discontinuous circle is the result of two insulating sections.

10. The RF coil resonator according to claim 9, further comprising two capacitors, each capacitor of the two capacitors bridging one of the two insulating sections.

11. A tube further comprising, The RF coil resonator according to claim 1, wherein the plurality of loops are arranged around the tube.

12. The RF coil resonator according to claim 1, wherein the first terminal faces the second terminal.

13. The RF coil resonator according to claim 1, wherein the plurality of loops includes at least three loops.

14. The RF coil resonator according to claim 13, wherein a loop between two other loops has a radius of curvature smaller than that of the two other loops.

15. The RF coil resonator according to claim 1, wherein the power supply is a switched-mode power supply.

16. A capacitor, and an inductor further comprising, The circuit of the RF coil resonator according to claim 1, wherein the circuit is configured to supply the first phase of the RF power to the plurality of loops via the capacitor and the inductor.

17. The RF coil resonator according to claim 1, wherein the circuit comprises a transistor for gating the supply of RF power to the plurality of loops.

18. The RF coil resonator according to claim 1, wherein each loop of the plurality of loops comprises a ceramic covered with a conductive thin film.

19. A module comprising the RF coil resonator according to any one of claims 1 to 18 and a sampler.

20. A system comprising the module according to claim 19 and a detector.

21. A DC power supply, a plurality of transistors electrically connected to the DC power supply, a plurality of gate drivers each connected to a different one of the plurality of transistors, a processor further comprising, The processor is configured to control the plurality of gate drivers to turn on and off the plurality of transistors to convert a DC current from the DC power supply into an RF current. RF power module.

22. The conversion of the DC current into an RF current in the RF power module according to claim 21 utilizes resonance conversion technology.

23. A plasma load coil further comprising, The plasma load coil is electrically connected to the DC power supply, The plasma load coil, the plurality of transistors, and the DC power supply are arranged such that the RF current generated from the control of the plurality of gate drivers by the processor is supplied to the plasma load coil. The RF power module according to claim 21.

24. A capacitor, and an inductor further comprising, The capacitor, the inductor, the plurality of transistors, and the DC power supply are arranged such that the RF current generated from the control of the plurality of gate drivers by the processor is supplied to the inductor. The RF power module according to claim 21 or 23.

25. The RF power module according to claim 21, wherein the plurality of transistors are gallium nitride transistors.

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