RF coil resonator system and method

Abstract

Described embodiments include a subsystem for supplying RF power to an inductively coupled plasma (ICP) torch. The present disclosure relates to some technical aspects of an RF power converter and the design of a load coil and a resonant RF tank circuit for an ICP. The systems and methods described herein counteract RF on the axis due to the symmetry of the applied voltage and the symmetry of the load coil. Thus, RF balancing is achieved by the design without the need to find and adjust the optimal RF voltage ratio. Embodiments also allow for high RF currents and low RF voltages, reducing the risk of RF breakdown outside the torch. Transistors may be used to deliver RF power. Thus, a more compact ICP assembly may be used.

Description

[0001] Related Applications

[0002] This application claims the benefit of priority to 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

[0003] Inductively coupled plasma (ICP) has many applications, ranging from semiconductor processing to waste incineration, material handling and powder handling devices, to analytical instruments such as ICP-MS (ICP mass spectrometry), ICP OES (ICP optical emission spectroscopy), to mass spectrometry cell analysis.

[0004] Mass spectrometry cytometry is becoming a popular tool for flow cytometric analysis of biological samples as well as for bioimaging of tissue samples. The mass spectrometry cytometry principle is based on revealing the concentration of antigens in single biological cells using affinity probes to which elemental tags are attached. Once the cells are labeled, the readout means sending these cells to an inductively coupled plasma ion source, where the elemental tags on each cell are atomized and ionized. The ionized cloud from each cell containing the elemental tag is sampled into the mass spectrometer, where the sequence of clouds for the entire sample is recorded. One benefit of the mass spectrometry cytometry approach is that a large number of probes can be applied and recorded simultaneously in one experiment. More than 40 probes recorded in one experiment have been demonstrated with this technique. Recently, the application of mass spectrometry cytometry has been extended to the field of biological tissue imaging based on immunohistochemistry. This technique is called imaging mass spectrometry cytometry. TM (IMC TM ). In any of these methods, the ICP torch plays a role in converting the biological material into a transient signal of ions derived from the elemental tags.

[0005] ICPs typically operate at frequencies between 1 MHz and 100 MHz and at power levels ranging from 10s of Watts at low pressure to megawatts at atmospheric pressure. Kilowatt-class ICPs operating at atmospheric pressure are used in analytical instruments. The power converter of the ICP takes AC / DC power from a power supply and converts it into RF power. Such converters are typically large, bulky, and relatively expensive units. The power conversion efficiency of the converter may also be low, resulting in the generation of a large amount of waste heat. Disadvantages also include the reliability and reproducibility of the analytical results.

[0006] These and other deficiencies have been identified as techniques such as mass spectrometry cell analysis have been adopted by biologists. These and other needs have been addressed. Summary of the invention

[0007] Embodiments described herein include a subsystem for supplying RF power to an inductively coupled plasma (ICP) torch. The present disclosure relates to some technical aspects of RF power converters and the design of load coils and resonant RF tank circuits for ICP. Due to the symmetry of the applied voltage and the symmetry of the load coils, the systems and methods described herein cancel out the RF on the axis. Therefore, RF balance is achieved by design without the need to find and adjust the optimal RF voltage ratio. Embodiments also allow high RF currents and low RF voltages, reducing the risk of RF breakdown outside the torch. Transistors can be used to deliver RF power. Embodiments can produce compact ICP components.

[0008] In an embodiment, the RF coil resonator may include a plurality of loops. Each of the plurality of loops is connected to other loops of the plurality of loops so that each loop is electrically connected in parallel with the other loops when a voltage is applied to the plurality of loops. The RF coil resonator may also include a power supply electrically connected to the plurality of loops. The power supply may be configured in a circuit to deliver 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.

[0009] In an embodiment, the RF power module may include a DC power supply. The RF power module may also include a plurality of transistors electrically connected to the DC power supply. The RF power module may also include a plurality of gate drivers. Each gate driver in the plurality of gate drivers may be connected to a separate transistor in the plurality of transistors. The RF power module may also include a processor. The processor may be configured to control the plurality of gate drivers to open and close the plurality of transistors so as to convert the DC current from the DC power supply into the RF current.

[0010] Embodiments may include an analytical method using plasma. The method may include applying an RF voltage to a plurality of rings surrounding a tube. The plurality of rings may be electrically connected in parallel. A first phase of the RF voltage may be applied to a first terminal of the plurality of rings. A second phase of the RF voltage may be applied to a second terminal of the plurality of rings. The first phase may be opposite to the second phase. The method may also include igniting a plasma within the tube.

[0011] The nature and advantages of embodiments of the present invention may be better understood with reference to the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 An example of a load coil configuration according to an embodiment of the present invention is shown.

[0013] Figure 2 An example of a load coil configuration according to an embodiment of the present invention is shown.

[0014] Figure 3An example of a load coil configuration with a half-turn coil according to an embodiment of the present invention is shown.

[0015] Figure 4 A system including a full bridge of a resonant circuit driving a load coil and a capacitor module according to an embodiment of the present invention is shown.

[0016] Figure 5 A layout of a load coil, resonant capacitor, inductor, and RF drive circuit is shown according to an embodiment of the present invention.

[0017] Figure 6 An integrated plasma torch module with a compact solid-state RF generator according to an embodiment of the present invention is shown.

[0018] Fig. 7A A loading coil is shown around a tube according to an embodiment of the invention.

[0019] Figure 7B The operation of an ICP torch according to an embodiment of the present invention is shown.

[0020] Fig. 8A and Figure 8B The simulation results of the current density distribution within the turns of the load coil according to the embodiment of the present invention are shown.

[0021] Fig. 9 is a flow chart of a process associated with an analysis method using plasma according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Although inductively coupled plasma (ICP) is used in many applications, the power delivery system has several disadvantages, including the cost of the RF generator and the amount of power required to operate the analytical torch (in the range of 1 to 2kW). The relatively low efficiency of the RF generator and the power delivery circuit can lead to even higher electrical power consumption. The ICP power delivery circuit can have an efficiency of 60% scale. This means that at 1.5kW RF power entering the ICP load coil, the circuit will consume an additional 1kW of electrical power, which is converted into heat that needs to be removed from the electronic components. A circuit with about 90% RF power transfer efficiency will benefit users and instrument designers. The circuit can simplify thermal management for instrument designers and reduce electricity and air conditioning costs for end users. Another disadvantage is the RF coupling of the drive voltage to the plasma, which can cause secondary discharges between the plasma and another electrode (such as a sampler electrode), as described in U.S. Patent No. 4501965. It is usually necessary to carefully balance the RF coil voltage. ICP systems and methods are also described in U.S. Patent Publication No. 2021 / 0404968. Another disadvantage is the high voltage (up to several kV) applied to the typical spiral load coil, with the coil turns connected in series. In this configuration, electrical breakdown can occur between the coil turns. The coil can be additionally insulated to avoid breakdown, which can result in additional expense and complexity.

[0023] Another disadvantage of existing ICP setups is the aging of the RF load coil and the periodic replacement of the coil. The load coil is subject to a large amount of heat flux. This heat can raise the temperature of the load coil to 300°C in air. At this temperature, the outer layer of copper will turn black and the load coil will eventually degrade, requiring periodic replacement. Liquid cooling of the load coil can be used to overcome this problem, but increases the complexity of the RF circuitry. Considerations of compatibility with the high RF voltages on the load coil generally limit the range of cooling solutions that can be employed.

[0024] Typical load coils are usually manufactured by bending copper or silver tubes. Bending the tube results in some distortion of the coil geometry and is less accurate and precise than coils that can be machined from larger workpieces. Together with the aforementioned periodic coil replacement, the inaccuracy of the coil geometry limits the reproducibility of the analysis results.

[0025] Another disadvantage of existing ICP setups is the axial RF current on the axis of the plasma. The axial RF current in the plasma can penetrate into the vacuum interface of the mass spectrometer and affect the ion signal. U.S. Patent No. 4501965 provides a solution to this problem by using an electrical scheme that generates RF_A and RF_B voltages in a certain ratio so that their net effect cancels at one position on the axis, just in front of the sampler orifice. However, finding the appropriate ratio involves experimentation, and the ratio depends on the position and shape of the plasma in the torch and its relationship to the sampler position.

[0026] Some ICP arrangements have the problem that the RF MOSFET transistors require relatively high power to drive their gates. This complicates the drive circuitry and increases overall system power losses. Additionally, another problem is that existing vacuum tube triode based RF generators for ICP require a high voltage DC source for the triodes. The high voltage DC source is a custom power supply that is relatively large and expensive compared to lower voltage off-the-shelf power supplies of similar power handling capability.

[0027] Implementations of the ICP configurations and methods described herein simplify the RF generator, make the ICP's RF circuit more power efficient, suppress degradation of the load coil and make it more mechanically reproducible, reduce or eliminate the need for RF balancing, and reduce or eliminate axial RF currents.

[0028] I. RF Coil Resonator

[0029] Embodiments described herein use high RF current and low RF voltage to power the load coil of an ICP MS by connecting the load coil turns electrically in parallel rather than in series. The low RF voltage can allow the individual turns of the RF load coil to dissipate heat directly to their base and thereby increase 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 reduced gaps between mechanical parts and more compact assemblies. The circuit can generate an overvoltage condition to ignite the plasma without the risk of electrical breakdown. The spontaneous combustion of the plasma can simplify the ICP subsystem, making the subsystem more compact. Solid-state circuits can be used for power transfer and to power resonant tank circuits. The compactness of the ICP torch and electronics facilitates its integration with laser ablation modules for ultrafast transients. The throughput of a laser ablation-based imager is limited by the width of the transient. Thus, more compact ICP assemblies, among other things, facilitate imaging mass spectrometry and imaging mass spectrometry cell analysis TM progress.

[0030] Embodiments include several main interconnected components: a load coil, a resonant RF tank circuit connected to the load coil, an RF power delivery circuit feeding the resonant tank circuit, and the torch itself.

[0031] A. Load Coil and RF Tank Circuit

[0032] Figure 1 An example of a load coil configuration 100 that results in a self-balancing on-axis RF potential in a plasma is shown. The load coil 104 surrounds a virtual tube 108 having a plasma 112. For simplicity, only one turn of the load coil 104 is shown. Multiple turns of the load coil 104 are possible, where each turn is a flat circle or nearly a circle, similar to the figure. A first terminal 116 can connect the load coil 104 to phase A 120 of an RF power source. A second terminal 124 can connect the load coil 104 to phase B 128 of an RF power source. Capacitor 132 shows capacitive coupling of phase A between the load coil 104 and the plasma 112. Capacitor 136 shows capacitive coupling of phase B between the load coil 104 and the plasma 112. Neither capacitor 132 nor capacitor 136 is a physical capacitor.

[0033] As a result of symmetry, when the RF+A phase and RF-B phase voltages have the same amplitude, the RF effects cancel and the potential on the axis of the plasma (e.g., the longitudinal axis through the center of the tube 108) is zero. More details on the reasons for balancing RF in H. Niu, Fundamental Studies in Plasma Extraction and Ion Beam Formation Processes in Inductively Coupled Plasma Mass Spectrometry, Dissertation, 1994, pp. 38-40, are 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 in a spiral or helix. These turns as a set of individual turns can be considered to be connected in series. For the turns arranged in a spiral, only the middle turn will have proper balance. The outer turns will have RF voltages that do not match each other and do not cancel each other. Therefore, net balance can only be achieved at one position along the axis, which is usually set in the area directly in front of the sampler. Balance can be achieved for specific conditions of the plasma (e.g., plasma power and its distance from the sampler). However, a good balance across the entire range of operating conditions may become difficult.

[0034] Embodiments may include driving the ICP with several turns connected in parallel to the same RF source. In this configuration, each turn of the load coil produces an RF balanced plasma (on the axis) regardless of plasma conditions and elongation. Another benefit 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 reduced voltage requirement on the load coil makes it easier to couple medium and low voltage power transistors to the load. Once the turns are connected in parallel, the RF voltage is reduced, but the RF current is increased proportionally to maintain the same RF power. This results in a fairly low inductance of the load coil, requiring high current to maintain the RF voltage across it. In order 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 current delivered to the plasma will be transferred to the plasma. The capacitor can help store some of this excess current, forming part of a resonant tank circuit.

[0035] Figure 2 An example of a load coil configuration 200 with a physical capacitor is shown. A load coil 204 surrounds a tube 208 with 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 can connect the load coil 204 to phase A 220 of an RF power source. A second terminal 224 can connect the load coil 204 to phase B 228 of an RF power source. A capacitor 232 is connected to the first terminal 216 and the second terminal 224.

[0036] The load coil 204 can act as an inductor, or an inductor (not shown) can also be added in series with the load coil 204. The value of the capacitor 232 can be selected to largely offset the impedance of the inductor at the preferred operating frequency. As a result, the electrical characteristics of the circuit may become dominated by the resistive loss of RF energy in the plasma. This arrangement is beneficial because without the resonant capacitor, the parasitic inductance of the connecting wires will limit the ability of the circuit to circulate high currents in the load coil while applying low voltages. The capacitor allows most of the inductive impedance of the setting to be offset. The remaining impedance is largely resistive, but a portion of the inductive or capacitive impedance can be generated by moving the RF frequency of the signal above or below the resonant frequency of the setting. The load coil, together with the inductor and capacitor, is considered to form a resonant RF tank circuit or part of a resonant tank circuit. The resonant RF tank circuit can be used to balance the impedance associated with the resonance of the current through the load coil.

[0037] Figure 1 and Figure 2Only one turn in the load coil is shown, but a similar circuit can be operated with a load coil of multiple turns connected in parallel. The turns can be stacked so that each turn is connected to its dedicated driver and the driver is operated in RF synchronization. The RF model shows that when the load coil contains three turns connected in parallel, the middle turn is shielded by the outer turn, and for the same voltage applied to all turns, the current in the middle turn is lower than the current in the outer turn. As a result of this observation, one can conclude that the middle turn does not work as hard as the outer turn. The number of turns in the load coil can be reduced to two, which can allow for a more compact load coil and torch. Another option can be to create an outer turn with a higher inductance than the middle turn. This can be achieved by making the outer turn have a larger diameter than the middle turn or by adding parasitic inductance in the feeding branch (i.e., terminal) of the outer turn.

[0038] Additional design variations may be used for the resonant circuit. Capacitor 232 may be replaced with two separate capacitors, each with its load coil side connected to ground. This capacitor arrangement reduces the required voltage rating of the capacitor by a factor of two. A DC blocking capacitor may be installed in series with the load coil to block DC voltages that may originate from the RF driver. A capacitive voltage divider may be connected to each side of the load coil. The total capacitance of the voltage divider may be selected to offset much of the inductive impedance of the load coil. Having a capacitive voltage divider allows lower amplitude RF to be injected into the voltage divider and have the resonant process increase the amplitude on the second capacitor directly connected to the load coil. Various resonant schemes for impedance transformation may be utilized to change the impedance of the load coil (with power dissipation from the plasma) and are described herein (e.g., Figure 4 ).

[0039] Figure 3 Another example of a load coil configuration 300 is shown. Figure 1 and Figure 2 The single loop of the load coil in 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 surround 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 a clockwise direction, as indicated by arrows 340 and 344. The RF driver 320 and the RF driver 328 can operate in RF synchronization with each other. The resonant capacitors 348 and 352 offset the effect of low coil inductance, similar to Figure 2 Capacitor 232 in.

[0040] exist Figure 3 In the example above, the half-turn coil requires even less RF voltage and can further improve balance. The RF power requirement for each individual RF driver is reduced by half. Although a half-turn arrangement is shown here, one-third turn, one-quarter turn, or other fractional turn arrangements are also possible. More than one half-turn disk can be positioned along the length of the torch, creating a similar Figure 1 The three-turn load coil setup is described.

[0041] The half-turn or fractional-turn arrangement has advantages for RF balance. The system can have better RF current symmetry in the plasma. The amplitude of the RF voltage over the half-turn is reduced by a factor of 2. Therefore, balance defects due to asymmetry of the actual setup will be further attenuated by the reduced RF voltage applied.

[0042] B.RF Power Delivery

[0043] Embodiments include delivering a phase of RF power to a load coil through a resonant RF tank circuit. RF triodes can be used to generate and deliver RF power, but such power sources are large and expensive. In addition, the efficiency of RF triodes may be only 60% to 70%. To address the size and cost of the RF power delivery module to the ICP MS, embodiments use high frequency power transistors instead of RF triodes. Because RF transistors operate at low DC voltages, the power supply for such transistors can be generic rather than custom, which generally means cheaper, more compact and more efficient for the same power handling level.

[0044] Embodiments include using the principles of a switched mode power supply (SMPS) at these relatively high frequencies (about 40 MHz) instead of a linear amplifier for RF power. SMPSs are made of transistors. SMPSs with transistors as drivers can be configured to operate efficiently with inductively coupled plasma loads. There are many possible configurations similar to resonant SMPS topologies. The operation of a resonant RF power converter at 40 MHz can be facilitated by high performance transistors such as those based on gallium nitride (GaN). These transistors require a relatively small amount of energy at the input to switch states (on / off). Therefore, the drivers for these transistors can be in the form of more commercial MOSFET drivers and can be directly controlled by digital signals. This simplifies the design of the control circuit and the number of stages and components required for the RF power converter. SMPS also provides greater flexibility in the timing and shape of the control signals used in the resonant converter. More will be discussed in the resonant conversion section.

[0045] An embodiment of the RF driver is a resonant converter type driver with soft switching of transistors. RF driver configurations in the field of resonant converter SMPS include (but are not limited to) basic LLC and LCC configurations, as well as more complex configurations (e.g., LCLC). Similarly, in the field of resonant SMPS, the RF driver can be configured in a variety of topologies (e.g., different arrangements of transistors, capacitors, and inductors). Selections can be made to suit a particular technology of RF capacitors, or to minimize or reduce the effects of stray inductance, or to reduce power losses in transistors and other components.

[0046] High performance switching transistors including GaN transistors can be integrated into RF drivers. The RF driver can be configured as a full-bridge resonant driver (e.g., with four transistors), a half-bridge resonant driver (e.g., one side grounded, with two transistors), or a flyback resonant driver (e.g., with one switching transistor). Multiple transistors can be used in parallel in a switch to increase the power handling range.

[0047] Figure 4 A system 400 is shown of a full bridge including an RF tank circuit 402 driving a load coil and capacitor module. The RF tank circuit 402 includes impedance matching inductors LA 404 and LB 408 and capacitors C1A 412a, C1B 412b, C2A 416a, and C2B 416b. RF power is transferred from the output of the bridge driver to the resonant load coil circuit by means of inductors LA 404 and LB 408.

[0048] The DC power supply 420 delivers DC power to the transistors that drive the RF tank circuit 402. RF power is delivered using transistors QA1 424, QA2 428, QB1 432, and QB2 436. Each transistor may have an associated gate driver to turn the transistor on and off. Turning the transistor on and off may allow a square wave to pass from the driver to the output of the transistor. For purposes of illustration, the square wave is described as simplified here. In actual implementations, the rise and fall times of the transitions between the on and off states of the transistor need to be considered. With the help of the resonant effect in the tank circuit, these conversions can be made more power efficient. The timing of the opening and closing of the transistor may allow RF current to be passed to the RF tank circuit 402. The transistor may be a GaN MOSFET. The controller may send digital pulses to the gate driver. The digital pulses may have parameters such as duration, frequency, and time delay. The controller may also adjust these parameters on the fly to optimize efficiency or increase the RF voltage or adapt to changes in plasma conditions.

[0049] Impedance matching inductors LA 404 and LB 408 assist in zero volt switching operation of the GaN MOSFET. Zero volt switching is a technique that turns on a power transistor when the voltage across the power transistor is low (close to zero). To further facilitate zero volt switching under all load conditions, the switching frequency can be modulated so as to maintain a certain phase relationship between the voltage at the output of the bridge and the voltage between the load coil terminals.

[0050] Figure 5 Shown is a layout of a load coil 504, a resonant capacitor and a MOSFET bridge connection by means of inductors LA and LB implemented as silver plated copper strips connecting the bridge terminals to the resonant capacitors CIA, C1B, C2A and C2B. Figure 5 Shown from Figure 4 An example of a system 400 is shown. Figure 5 Shows how to miniaturize the RF drive circuit and the load coil into one package (module). The inner diameter of the load coil is 22 mm. The length of the load coil is about 2 cm.

[0051] Figure 6 An integrated plasma torch module 600 with a compact solid-state RF generator is shown. An ICP tube 604 for the plasma torch is sealed relative to a sampler 608. The ICP tube 604 is surrounded by a load coil 612. The load coil 612 may be Figure 1 The load coil 104 or Figure 2 The load coil 204. The load coil 612 can be powered by an RF generator 616, which can include Figure 4 The cooling liquid flow is shown 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 sampler 608, allowing for a compact cooling system.

[0052] In a sealed torch setup, the pressure in the torch can be reduced to below atmospheric pressure to ignite an RF discharge with a relatively low RF voltage. This RF discharge can then be turned into a high pressure ICP plasma by gradually increasing the pressure and plasma power supplied to the torch. This allows for self-ignition of the plasma in the torch without the need for additional igniter components or the large overvoltage of the RF required for ignition at atmospheric pressure.

[0053] The self-ignition concept was demonstrated experimentally and theoretically. Under our conditions, the theoretical estimate of the ignition voltage is based on the balance of the electron energy received from the electric field and the energy lost in collisions. This yields the following approximate formula:

[0054]

[0055] Where E is the threshold electric field for ignition, E ionis the ionization energy of the Ar atom, e is the absolute value of the electron charge, λ is the mean free path of the electron, and δ is the fraction of energy transferred from the electron to the Ar atom in a collision, δ≈2.7﹒10 -5 Because λ is inversely proportional to pressure, reducing the Ar pressure to well below atmospheric pressure can achieve autoignition using a low voltage RF generator. Experimentally, autoignition can occur at pressures below about 3 Torr, which can be achieved in a sealed torch by evacuating the sampler orifice.

[0056] Furthermore, the pressure within the torch can be easily brought to several atmospheres simply by controlling the flow of plasma gas entering and leaving the torch. When operating at pressures above 1 atmosphere, smaller scale torches can be used. Smaller scale torches can consume less RF power to maintain the plasma, and due to the compactness of the plasma, smaller scale torches can facilitate faster transients of transient events, such as ablation plume recording or single particle detection in the plasma.

[0057] In an embodiment, a sealed torch may be manufactured from ceramic via 3D printing. Other suitable torch materials, such as fused silica, may also be used. The sealed torch may be a manifold that contains the plasma. 3D printed ceramics may allow for cooling channels in the ceramic body as well as plasma gas supply channels and plasma gas removal channels. 3D printed ceramics may be selectively metallized (using a mask) to create turns of load coils and pads for additional RF components such as capacitors and inductors. Thus, ceramic 3D printing technology may further facilitate the integration of torches and RF electronics into a single plasma module. Such integration may include a sampler on the output end of the torch and an injector plate on the input end of the torch. The integrated system may allow operation with a short injector of only a few centimeters. Short injectors are useful for imaging mass spectrometry cell analysis. TM Fast transients of the ablation plume used in imaging mass spectrometry can be advantageous. In contrast, in some commercial systems, the distance between the ablation region and the injector tip into the plasma is on the order of 40 cm. The delay in transient arrival and the broadening of the transient typically scales nearly proportionally with the length of the injector.

[0058] C. Operation

[0059] Fig. 7A A photograph of a load coil 704 surrounding a tube is shown. The load coil 704 is machined rather than formed from the tube. Machining improves the mechanical precision of the coil and therefore improves the reproducibility of the analysis results when different but similarly designed coils are used (e.g., by replacing the coil or by analysis on a different instrument).

[0060] Figure 7B Photographs showing the operation of the ICP torch. Figure 7BThe operation of a solid-state RF generator with a sealed torch is shown.

[0061] Fig. 8A and Figure 8B Simulation results of current density distribution within turns of a load coil having circular turns are shown.The load coil may be a load coil having turns connected in parallel as described herein. Fig. 8A A simplified geometry of the simulation is shown, which consists of three cylindrically symmetric coil turns simulated in a sufficiently large empty space. The x-axis is the radius. The y-axis is the axial direction. Figure 8B Here is a zoomed in cross section of a coil turn and the calculated current density at RF frequency f = 100 kHz. Two different effects can be seen. First, the current is localized close to the surface of the coil. This is the well-known skin effect, where the thickness of the current layer is proportional to f. -1 / 2 proportional. Second, the current is transferred to the interior of the coil (the left side in the figure). If f is increased to the typical operating frequency of 27 MHz, the distribution remains qualitatively the same, but the thickness of the current layer becomes so small (a few microns) that the current layer becomes too thin to be shown in the picture at this size scale. Therefore, the illustration is done at lower frequencies where the skin effect is easily noticed. The current flows on the inner surface of the coil, and the small current layer can allow the coil geometry to be modified. For example, the coil can potentially be manufactured as a deposition of a thin copper layer on a ceramic surface, as described previously. The thin layers of conductor in the high current density areas can be sufficient to produce almost the same RF field using the RF currents in these layers.

[0062] D. Example System

[0063] Embodiments include an RF coil resonator. The RF coil resonator may include a plurality of loops. Each of the plurality of loops may be geometrically parallel to other loops in the plurality of loops. Each of the plurality of loops may include a flat surface parallel to a nearest surface of an adjacent loop. Each loop may be Figure 1 The load coil 104 or Figure 2 The load coil 204 in the multiple loops can be Figure 5 The load coil 504, Figure 6 7 , or the load coil 612 in FIG. 7 .

[0064] Each of the plurality of rings may form a discontinuous circle. The plurality of rings may be configured such that the center of curvature of each of the plurality of rings is located on the longitudinal axis. The longitudinal axis is orthogonal to each plane including each of the plurality of rings. The plurality of rings may include at least 2, 3, 4, 5, 6, 7, 8, 9 or more rings. The plurality of rings may be an odd number or an even number. In an embodiment, there are no other rings electrically connected to the plurality of rings.

[0065] Each of the plurality of rings may define a hole. The shape of the hole may be circular. In embodiments, the hole may not be completely circular, but may be more than 60%, 70%, 80%, 90%, 95% or 99% circular (the percentage being the total percentage of the circumference of the circle defined by the ring). The hole may include a portion extending from the circular portion of the hole. The shape of the portion may be rectangular. The hole may be in the shape of a lollipop, with a stick protruding from the circle. The cross-section of each ring may be square, rectangular or circular. The cross-section may be the portion of the ring with the smallest cross-sectional area.

[0066] When a voltage is applied to the plurality of rings, each of the plurality of rings may be electrically connected in parallel to the other rings in the plurality of rings. Each ring may have a first terminal, wherein the first terminal is at the same end of each ring. The first terminal of the ring may directly contact the first conductive member. Each ring may have a second terminal, wherein the second terminal is at the same end of each ring, but the second terminal is at a different end than the first terminal. The second terminal of the ring may directly contact the second conductive member. The first conductive member and the second conductive member may not contact each other. The first conductive member and the second conductive member may be copper strips. In an embodiment, unlike the plurality of rings electrically connected in series, the current reaches all the rings at or about the same time.

[0067] The plurality of rings may be machined from a single sheet of metal (e.g., copper or silver). For example, the metal sheet may have parallel slits formed therein that separate one ring from another. The metal sheet may have holes drilled therein to form circular holes in the plurality of rings.

[0068] Each of the plurality of rings may be characterized by the same radius of curvature.For example, the plurality of holes may each have congruent shapes, including congruent circular shapes.

[0069] The discontinuous circle may be the result of a single insulating segment, two insulating segments, three insulating segments, or more insulating segments. For example, a ring with two insulating segments may include Figure 3 The capacitor may electrically couple the first terminal to the second terminal. The capacitor may bridge one of each insulating section. The capacitor may be a resonant capacitor 348 or a resonant capacitor 348.

[0070] A ring between two other rings may have a smaller radius of curvature than the two other rings.A ring at the ends (ie, having only one adjacent ring) may be larger than a ring in the middle (ie, having two adjacent rings).

[0071] Each of the plurality of rings may include an insulating material (eg, ceramic) coated with a conductive film. In some embodiments, a non-complete subset of the plurality of rings may include an insulating material coated with a conductive film.

[0072] The RF coil resonator may also include a power supply in electrical communication with the plurality of loops. If two components are connected with a switch or transistor, they may be considered to be in electrical communication with each other even when the switch or transistor is in an off position. The power supply may be in a circuit configured to deliver 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. The power supply may include a DC power supply 420. The power supply may be a switch mode power supply. The circuit may be an RF transfer circuit that delivers power to the resonant RF tank circuit.

[0073] The RF coil resonator may include a resonant RF tank circuit electrically connected to the plurality of loops. The resonant RF tank circuit may include a capacitor and an inductor. A circuit configured to deliver a first phase of RF power to the plurality of loops (e.g., an RF power transfer circuit) may deliver the first phase of RF power to the plurality of loops via an RF tank circuit comprising capacitors and inductors. The resonant RF tank circuit may include 2, 3, 4, 5, 6, 7, 8, 9, 10 or more capacitors. The resonant RF tank circuit may include 2, 3, 4, 5, 6, 7, 8, 9, 10 or more inductors. The resonant RF tank circuit may include an RF tank circuit 402.

[0074] The RF power transfer circuit may include transistors to gate the transfer of RF power to multiple rings. The transistors may include gallium nitride or silicon carbide transistors. The RF power transfer circuit may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more transistors. The power handling characteristics of the transistors may be from 100W to 5kW. Several transistors may be operated in parallel to increase the power handling capability. Full-bridge operation utilizes four transistors, which effectively shares the parasitic power dissipation between the four transistors. The operating frequency may be selected to be higher than the target operating frequency of the ICP torch. For example, the torch may operate at 30MHz, while the operating frequency of the transistor is limited to 100MHz. The ICP operating frequency may be in the range of a few MHz to several hundred MHz. The RF power transfer circuit may transfer the second phase of the RF power to the second terminal. The RF power transfer circuit may be a portion of the circuit that is not a resonant RF tank circuit.

[0075] The RF coil resonator may include a tube. A plurality of rings may be arranged around the tube. The tube may be quartz. The tube may be cylindrical. The tube may be centered within the plurality of rings.

[0076] Embodiments may include a module including any RF coil resonator and a sampler as described herein. The sampler may include a sampler 608. The sampler may be configured to provide a path for a plasma effluent from a plasma ignited and / or maintained by a load coil to flow into a chamber in the sampler. A plasma torch plus RF supply module without a sampler may be less than 30 cm long, 20 cm wide, and 4 cm deep. An analysis system with a module may also include a detector. The detector may be a detector in a mass spectrometer, an optical detector in a light emission spectroscopy system, or other detectors.

[0077] The RF coil resonator may be used in any of the analytical methods using the plasma described herein.

[0078] Embodiments may include an RF power module. The RF power module may include an RF power transfer circuit. The RF power module may include a DC power supply. The DC power supply may be any power supply described herein, including DC power supply 420. The RF power module may also include a plurality of transistors electrically connected to the DC power supply. The plurality of transistors may be any transistor described herein.

[0079] The RF power module may include a plurality of gate drivers. Each gate driver of the plurality of gate drivers may be connected to a separate transistor 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 herein, including Figure 4 Those in .

[0080] The RF power module may include a processor. The processor may be configured to control a plurality of gate drivers to turn on and off a plurality of transistors to convert DC current from a DC power source into RF current. Instructions for the gate drivers may be stored on a non-tangible computer readable medium.

[0081] The RF power module may include a plasma load coil. The plasma load coil may be electrically connected to a DC power supply. The plasma load coil, a plurality of transistors, and a DC power supply may be arranged such that an RF current generated from a processor controlling a plurality of gate drivers is delivered to the plasma load coil. The plasma load coil may be any load coil described herein.

[0082] The RF power module may include a capacitor and an inductor. The capacitor, inductor, multiple transistors and a DC power supply may be arranged so that an RF current generated from a processor controlling multiple gate drivers is passed to the inductor. The capacitor or inductor may be any of those described herein. The RF power module may include multiple capacitors and / or multiple inductors.

[0083] II. Example Method

[0084] Fig. 9 is a flow chart of an example process 900 associated with an analytical method using plasma. In some implementations, Fig. 9 One or more process blocks of may be performed by an RF coil resonator (eg, load coil configuration 100, load coil configuration 200, load coil configuration 300, and / or plasma torch module 600). In some implementations, Fig. 9 One or more process blocks of may be performed by another device or group of devices separate from or including the RF coil resonator. Additionally or alternatively, Fig. 9 One or more process blocks of 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 .

[0085] At block 910, process 900 may include applying an RF voltage to a plurality of rings surrounding a tube. The plurality of rings may be electrically connected in parallel. A first phase of the RF voltage may be applied to a first terminal of the plurality of rings. A second phase of the RF voltage may be applied to a second terminal of the plurality of rings. The first phase may be opposite to the second phase. For example, the first phase may be a negative phase of the second phase. The plurality of rings may be any of the plurality of rings described herein, including Figure 5 The load coil 504, Figure 6 The load coil 612 in FIG. 7 or the load coil 704 in FIG. 7. Each loop may be Figure 1 The load coil 104 or Figure 2 The load coil 204 in.

[0086] Applying the RF voltage includes applying a power in the range of 0.10 to 20 kW. The RF voltage can be 100 V to 6 kV. The voltage can be applied at a frequency of 900 kHz to 100 MHz, including 27.12 MHz and 40 MHz. The RF voltage can be applied using a power supply, circuit or other electronic components described herein. A gas pressure for igniting the plasma can be applied before applying the RF voltage.

[0087] At block 920, process 900 may include igniting a plasma within the tube. In an embodiment, igniting the plasma does not include applying a voltage to an electrode within the tube. Igniting the plasma may be performed at a pressure in the range of 0.5 to 20 torr. The pressure of the plasma may be increased (e.g., to 0.5 to 20 atm), which may be a pressure associated with typical analytical conditions. Analytical data generated by the plasma may be acquired, including any analytical data described herein.

[0088] Process 900 includes flowing a first gas through a plasma to form a second gas including plasma effluent. Process 900 may include flowing a sample and the first gas through a plasma to form a second gas. Process 900 may also include flowing the second gas to a detector for analysis. The detector may be any detector described herein.

[0089] Process 900 may include additional implementations, such as any single implementation or any combination of implementations described below and / or in combination with one or more other processes described elsewhere herein.

[0090] although Fig. 9 Example blocks of process 900 are shown, but in some implementations, process 900 may include Fig. 9 More blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in the process 900. Additionally or alternatively, two or more blocks of process 900 may be performed in parallel.

[0091] III. Implementation Methods

[0092] Implementations may include the following.

[0093] Embodiment 1: A method for analysis using plasma, the method comprising: applying an RF voltage to a plurality of rings surrounding a tube, wherein: the plurality of rings are electrically connected in parallel, a first phase of the RF voltage is applied to a first terminal of the plurality of rings, a second phase of the RF voltage is applied to a second terminal of the plurality of rings, and the first phase is opposite to the second phase; and igniting a plasma within the tube.

[0094] Embodiment 2: The method of embodiment 1, wherein applying the RF voltage comprises applying a power in a range of 100 W to 5 kW.

[0095] Embodiment 3: The method according to embodiment 1, wherein the RF voltage is 100 V to 6 kV.

[0096] Embodiment 4: The method of Embodiment 1, wherein igniting the plasma does not include applying a voltage to electrodes within the tube.

[0097] Embodiment 5: The method of embodiment 1, wherein igniting the plasma is at a pressure in the range of 0.5 to 20 Torr.

[0098] Embodiment 6: The method of embodiment 1 further comprises: flowing the first gas through the plasma to form a second gas including plasma effluents.

[0099] Embodiment 7: The method of embodiment 6, further comprising: flowing the sample and the 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 method described herein.

[0100] Embodiment 8: An RF coil resonator, the RF coil resonator comprising: a plurality of loops, wherein: when a voltage is applied to the plurality of loops, each of the plurality of loops is electrically connected in parallel to the other loops in the plurality of loops, each of the plurality of loops is geometrically parallel to the other loops in the plurality of loops, each of the plurality of loops forms a discontinuous circle, the plurality of loops are configured such that a center of curvature of each of the plurality of loops is located on a longitudinal axis, and the longitudinal axis is orthogonal to each plane including each of the plurality of loops; and a power source in electrical communication with the plurality of loops, the power source in a circuit configured to deliver 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 RF coil resonator described herein.

[0101] The specific details of a particular embodiment may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments related to each individual aspect or specific combinations of these individual aspects.

[0102] The above description of example 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 form described, and many modifications and variations are possible in light of the above teachings.

[0103] In the foregoing description, for the purpose of explanation, many details have been set forth in order to provide an understanding of various embodiments of the present technology. However, it is apparent to those skilled in the art that certain embodiments may be practiced without some of these details or with additional details.

[0104] Having described several embodiments, those skilled in the art will recognize that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. In addition, many well-known processes and elements have not been described in order to avoid unnecessarily obscuring the invention. Furthermore, the details of any particular embodiment may not always be present in variations of that embodiment, or may be added to other embodiments.

[0105] Where a numerical range is provided, it is understood that, unless the context clearly dictates otherwise, each intervening value between the upper and lower limits of the range is also specifically disclosed, to one-tenth of the unit of the lower limit. Each smaller range between any specified value or intervening value in the specified range and any other specified value or intervening value in the specified range is contemplated. The upper and lower limits of these smaller ranges may be independently included or excluded within the range, and each range in which one, none, or both limits are included within the smaller range is also included within the invention, subject to any specifically excluded limits within the specified range. Where a specified range includes one or both limits, ranges excluding one or both of those included limits are also included.

[0106] As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "a method" includes a plurality of such methods, and reference to "a capacitor" includes reference to one or more capacitors and their equivalents known to those skilled in the art, and so forth. The present invention has now been described in detail for purposes of clarity and understanding. However, it should be understood that certain changes and modifications may be practiced within the scope of the appended claims.

[0107] All publications, patents, and patent applications cited herein are hereby incorporated by reference for all purposes. No admission is made that any is prior art.

Claims

1. An RF coil resonator, the RF coil resonator comprising: Multiple rings, where: Each of the plurality of loops is connected to other loops of the plurality of loops so that each loop is electrically connected in parallel with the other loops when a voltage is applied to the plurality of loops; and A power source is in electrical communication with the plurality of rings, the power source being configured in circuitry to deliver a first phase of RF power to first terminals of the plurality of rings and a second phase of RF power to second terminals of the plurality of rings.

2. The RF coil resonator according to claim 1, wherein: Each ring in the plurality of rings is geometrically parallel to the other rings in the plurality of rings.

3. The RF coil resonator according to claim 1 or 2, wherein: The plurality of rings are arranged such that a center of curvature of each of the plurality of rings is located on a longitudinal axis, and The longitudinal axis is orthogonal to each plane including each ring of the plurality of rings.

4. The RF coil resonator according to claim 1, wherein: Each ring of the plurality of rings includes a planar surface that is parallel to a nearest surface of an adjacent ring.

5. The RF coil resonator according to claim 1 or 3, wherein: Each ring of the plurality of rings is characterized by a same radius of curvature.

6. The RF coil resonator according to any one of claims 1 to 5, wherein: Each of the plurality of rings forms a discontinuous circle.

7. The RF coil resonator according to claim 6, wherein: The discontinuous circle is caused by a single insulating section. 8 . The RF coil resonator of claim 7 , further comprising a capacitor electrically coupling the first terminal to the second terminal.

9. The RF coil resonator according to claim 6, wherein: The discontinuous circle is caused by two insulating sections.

10. The RF coil resonator of claim 9, further comprising two capacitors, wherein: Each of the two capacitors bridges one of the two insulating sections.

11. The RF coil resonator of claim 1 , further comprising: A tube, wherein the plurality of rings are disposed around the tube.

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

13. The RF coil resonator of claim 1, wherein: The plurality of rings includes at least three rings.

14. The RF coil resonator according to claim 13, wherein: The ring between two other rings has a smaller radius of curvature than the two other rings.

15. The RF coil resonator of claim 1, wherein: The power supply is a switch mode power supply.

16. The RF coil resonator of claim 1 , further comprising: capacitors, and Inductor, where: The circuit is configured to deliver the first phase of the RF power to the plurality of loops through the capacitor and the inductor.

17. The RF coil resonator of claim 1, wherein: The circuit includes transistors to gate delivery of RF power to the plurality of rings.

18. The RF coil resonator of claim 1, wherein: Each of the plurality of rings includes a ceramic coated with a conductive film.

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

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

21. An RF power module, comprising: DC power supply; a plurality of transistors in electrical communication with the DC power source; a plurality of gate drivers, each gate driver of the plurality of gate drivers connected to a separate transistor of the plurality of transistors; as well as A processor; wherein: The processor is configured to control the plurality of gate drivers to open and close the plurality of transistors to convert DC current from the DC power source into RF current.

22. The RF power module of claim 21, wherein: The conversion of the DC current to the RF current utilizes a resonant conversion technique.

23. The RF power module of claim 21, further comprising: A plasma loading coil, wherein: The plasma load coil is in electrical communication with the DC power supply, and The plasma load coil, the plurality of transistors, and the DC power supply are arranged such that the RF current generated from the processor controlling the plurality of gate drivers is delivered to the plasma load coil.

24. The RF power module according to claim 21 or 23, further comprising: capacitors, and Inductor, where: The capacitor, the inductor, the plurality of transistors and the DC power supply are arranged such that the RF current generated from the processor controlling the plurality of gate drivers is passed to the inductor.

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

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