Boost Ratio Regulation Method Based on Coupled Load Resonant under Marx-LTD Architecture

Abstract

The present invention proposes a step-up ratio regulation method based on a coupled load resonance type under the Marx-LTD architecture. By utilizing the characteristic that the load presents capacitive in the field of plasma discharge, a power resistor with adjustable resistance value is connected in series on the high-voltage output branch of the secondary side of the pulse transformer to form an RLC series circuit. By using the RLC series resonance, the capacitive load is coupled, and an output pulse maximum amplitude voltage step-up ratio model of the circuit is established. Based on the parameter relationship of the proposed amplitude gain regulation model, by adjusting the resistance value of the power resistor, it is possible to achieve the compatibility driving effect of the nanosecond pulse power supply for different plasma loads under the Marx-LTD architecture without changing the total number of Marx stages and the number of serially connected LTDs. At the same time, the number of stages of the pre-stage Marx circuit can also be reduced, further improving the overall economy of the power supply.

Description

Technical Field

[0001] The present invention relates to a method for regulating the boost ratio of a coupled load resonance type, and particularly to a method for regulating the boost ratio of a coupled load resonance type based on a Marx-LTD architecture. Background Art

[0002] When uniform discharge of a DBD load in the gas discharge field is required, an external excitation source needs to provide a high-amplitude pulsed output voltage, so as to achieve uniform discharge of the electrodes and ultimately meet the needs of researchers. Since the existing Marx circuit needs a higher-order Marx circuit to achieve high-voltage output, it cannot be better optimized in terms of the volume and economic cost of the power supply. Moreover, the increase in the number of Marx stages will increase the energy loss of the power supply, reduce the energy utilization efficiency of the power supply, and reduce the reliability of the whole machine system. At present, researchers design a nanosecond pulsed power supply with a higher output pulsed voltage, a steeper pulsed front edge, and a higher pulsed repetition frequency by using an architecture combining a Marx circuit and a Linear Transformer Driver (LTD) unit. However, the traditional Marx-LTD hybrid architecture is based on the form of series connection of the secondary sides of multiple LTD transformers to form the amplitude voltage required for plasma electrode load discharge. And there are different plasma loads, and the equivalent load capacitances thereof have large differences, resulting in great distortion of the output voltage amplitude and pulsed front edge of Marx-LTD, unable to ensure reliable driving of the pulsed power supply for plasma loads, and unable to be well applied to the field of plasma discharge applications.

[0003] Currently used boost regulation schemes all have certain defects. As described in Patent CN 211928193 U, its structure has a certain impact on the quality of the output voltage. Although the voltage multiplication is achieved by using the structure of the C-W voltage multiplier circuit, the output voltage ripple of the C-W voltage multiplier circuit is large, and the voltage drop is large. As described in Patent CN 212875687 U, although the combination of LC resonance and the Boost circuit achieves a large-scale DC boost, the structure is complex and there is no good way to flexibly adjust for different loads. As described in Patent CN 1004654489 C, the method of adjusting the capacitance and inductance parameters to adapt to different loads, although overcoming the defects of the PFM control method, has a complex control logic. Each adjustment element (capacitance or inductance) needs to be matched with a controllable switch to form at least one adjustment branch to achieve. And these boost regulation methods cannot instantaneously and effectively adjust to achieve the best pulsed voltage output when facing different plasma capacitive impedance loads. Summary of the Invention

[0004] 1. Technical problems to be solved:

[0005] The existing Marx-LTD hybrid architecture is based on the form of series connection of the secondary sides of multi-stage LTD transformers to form the amplitude voltage required for the discharge of the plasma electrode load. There are different plasma loads, and the equivalent load capacitances vary greatly, resulting in significant distortion of the output voltage amplitude and pulse front of Marx-LTD, making it impossible to ensure the reliable drive of the pulse power supply for the plasma load and unable to be well applied to the field of plasma discharge applications.

[0006] 2. Technical solution:

[0007] To solve the above problems, the present invention provides a boost ratio regulation method based on a coupled load resonance under the Marx-LTD architecture, including the following steps: Step S1: The power supply of the Marx-LTD architecture nanosecond pulse generator uses multi-stage Marx units with parallel inputs and series connection of the secondary sides of the LTD units; Step S2: Connect an adjustable power resistor in series on the secondary side of the LTD in series; through the RLC series connection of the adjustable power resistor, the leakage inductance of the pulse transformer, and the capacitive load, an RLC resonance network is formed; Step S3: Establish a boost ratio model for the maximum amplitude voltage of the output pulse of the Marx-LTD circuit; Step S4: By adjusting the resistance value of the power resistor, realize the boost ratio regulation of the voltage amplitude gain.

[0008] The whole machine power supply of the nanosecond pulse power generator is composed of n Marx-LTD units. The input ends of all units share the same DC power supply to charge the energy storage capacitors in the Marx circuit. The secondary sides of the LTD of each unit adopt a series connection structure to superimpose the module voltages.

[0009] The expression of the boost ratio model for the maximum amplitude voltage of the output pulse is:

[0010] where k marx is the boost ratio of the Marx link, k TR is the boost ratio of the pulse transformer, k RLC is the maximum value of the boost ratio from the secondary side voltage of the transformer to the output voltage of the load equivalent capacitance, k fouri is the ratio of the amplitude voltage of the distorted secondary side output voltage of the LTD transformer to the amplitude voltage of the ideal square wave voltage, m is the number of Marx-LTD modules, n is the number of Marx stages, N 1 is the number of turns of the primary side of the transformer, N 2 is the number of turns of the secondary side of the transformer, C load is the capacitive load, R tp_sec is the adjustable power resistor, L lk_sec is the leakage inductance of the secondary side of the LTD pulse transformer. When driving the capacitive load, by connecting an adjustable power resistor R in series on the secondary side of the transformer tp_secThe method couples the load C load , adjust the impedance network structure of the secondary side circuit, so that it can achieve different plasma DBD electrode loads C load Under the conditions, compensate and adjust the boost control of the amplitude voltage of the entire pulse power supply.

[0011] The boost ratio k of the Marx link marx And the boost ratio k of the pulse transformer TR The equation is:

[0012]

[0013] k fouri The numerical range of is: 1 ≤ k fouri ≤ 1.637.

[0014] The maximum value of the boost ratio from the secondary side voltage of the transformer to the output voltage of the load equivalent capacitance is:

[0015]

[0016] The adjustable power resistor should meet the following conditions:

[0017] 3. Beneficial effects:

[0018] The present invention proposes a boost control method of coupled load resonance type, which can, without changing the total number of Marx series and the number of series-connected LTDs, only by connecting a power resistor in series on the secondary side of the series-connected LTD, according to the proposed control design model, easily achieve compensation for the lost boost ratio parameter and pulse voltage rise rate parameter under different plasma load conditions, so as to achieve the compatibility driving effect of the nanosecond pulse power supply under the Marx-LTD architecture, and at the same time reduce the number of stages of the pre-stage Marx circuit, further improving the economic efficiency of the overall power supply design. Description of the drawings

[0019] Figure 1 It is the system architecture diagram of the Marx-LTD nanosecond pulse generator.

[0020] Figure 2 It is the schematic diagram of the single-stage Marx-LTD module circuit.

[0021] Figure 3 It is the equivalent circuit model of the LTD pulse transformer considering non-ideal parameters.

[0022] Figure 4 It is the ideal secondary side square wave waveform of the transformer TR.

[0023] Figure 5 It is the typical diagram of the RLC series circuit.

[0024] Figure 6 is H c (jη) amplitude-frequency characteristic curve.

[0025] Figure 7 is an example diagram of the boost control scheme of the coupled load resonance type.

[0026] Figure 8 is the variation trend of the power resistor with the load capacitance.

[0027] Figure 9 is the high-voltage pulse test waveform diagram when the output pulse voltage of the Marx circuit is 900V.

[0028] Figure 10 is the high-voltage pulse test waveform diagram when the output pulse voltage of the Marx circuit is 3kV.

[0029] Figure 11 is the high-voltage pulse test waveform diagram when the output pulse voltage of the Marx circuit is 2kV. Detailed implementation manner

[0030] The present invention will be described in detail below with reference to the accompanying drawings.

[0031] The nanosecond pulse power generator system architecture proposed by the present invention is based on the Marx-LTD cascade architecture. As Figure 1 shown, the whole machine power supply is composed of n Marx-LTD units. The input ends of all units share the same DC power supply U dc to charge the energy storage capacitor in the Marx circuit. The secondary sides of the LTD of each unit adopt a series connection structure to superimpose the module voltages and improve the amplitude U of the whole machine pulse voltage pulse , that is:

[0032] U pulse = U unit_1_sec + U unit_1_sec +…+ U unit_n_sec = n·U unit_n_sec .

[0033] The schematic diagram of the single-stage Marx-LTD module circuit is as Figure 2 shown. The input U unit_n of the primary side voltage of the LTD transformer is a unipolar nanosecond pulse waveform output by the m-stage Marx unit. The corresponding pulse voltage is output through the LTD isolation. In order to ensure the pulse width parameter of the LTD output voltage pulse, the turn ratio of the LTD transformer is generally set to 1:1. Then there are the following equations:

[0034] U unit_n = mU dc

[0035] U unit_n_sec = U unit_n = mU dc ,

[0036] Combined with Equation (1), the ideal boost ratio parameter k under the Marx-LTD system architecture can be obtained. ideal :

[0037]

[0038] As can be seen from the above equations, the ideal boost ratio between the input voltage amplitude U dc and the output pulse voltage amplitude U pulse of the proposed Marx-LTD topology is related to the number m of cascaded Marx-LTD modules, and is also related to the Marx series number n of the pulse formation corresponding to each module.

[0039] Based on the Marx-LTD architecture, it is proposed to connect an adjustable power resistor in series on the secondary side of the LTD in series to form an RLC resonance network. Under different plasma DBD load driving requirements, by only adjusting the resistance value of this resistor, the compensation function of the output pulse voltage amplitude can be realized, thereby realizing the boost ratio regulation function of the entire pulse power supply, and solving the problem of the loss of the pulse voltage amplitude and pulse voltage edge performance parameters of the nanosecond pulse power supply for different plasma DBD electrode loads.

[0040] Atmospheric pressure discharge plasma DBD electrode loads require a relatively high driving pulse voltage amplitude and a nanosecond-level pulse voltage edge. The Marx-LTD architecture nanosecond pulse generator power supply uses multiple Marx units in parallel input and the LTD units in series on the secondary side, which can ensure that the required plasma DBD electrode load discharge amplitude voltage is realized under the condition of nanosecond-level pulse voltage edge output. It is a nanosecond pulse power supply implementation scheme that can achieve modular integration and has a relatively low cost.

[0041] In some applications of gas discharge to generate low-temperature plasma, strict requirements are imposed on the uniformity of the discharge. By connecting a power resistor in series in the output circuit, the discharge intensity can be restricted, and to a certain extent, the conversion of the discharge to spark discharge can be slowed down, which is beneficial to the uniform and stable discharge.

[0042] Connecting an adjustable power resistor in series at the high-voltage output end of the pulse transformer has a shaping effect on the finally output high-voltage pulse, and can, to a certain extent, eliminate the clutter caused by LC series resonance and reduce the influence of the clutter on the gas discharge characteristics and application effects of the low-temperature plasma.

[0043] For the convenience of circuit model analysis under parasitic parameter conditions, Figure 3An equivalent model of a single-stage LTD transformer under non-ideal parameters is given, and the corresponding output is U pulse The equivalent load capacitance of the DBD load carried is C load . And there is L lk_pre and L lk_sec are the primary and secondary leakage inductances of the LTD pulse transformer respectively. The number of turns of the primary and secondary sides of the transformer are N 1 and N 2 respectively, and there are inter-turn capacitance parameters C tp_pre and C tp_sec respectively, and the equivalent resistance parameters of the windings are R tp_pre and R tp_sec .

[0044] From the above analysis, the voltage boost ratio k of the Marx link marx and the voltage boost ratio k of the pulse transformer TR The equations are as follows:

[0045]

[0046]

[0047] Due to the single-ended square wave pulse voltage waveform output by the Marx cascade unit, the voltage waveform of U unit_x_sec on the secondary side of the ideal transformer TR is still a square wave waveform, as shown in Figure 4 , where T marx is the pulse period output by the Marx unit, and α is the ratio of the square wave pulse width.

[0048] This square wave pulse voltage waveform passes through C tp_sec , R tp_pre and L lk_sec for filtering. The square wave waveform can be Fourier decomposed to solve its fundamental amplitude, and then the amplitude voltage ratio k of the distorted output U pulse to the input square wave U unit_x_sec can be derived: fouri :

[0049]

[0050] However, since the ratio α of the pulse width of the nanosecond pulse output to the entire period is very small, the amplitude voltage boost ratio k fouri is almost 1 here.

[0051] Analyze with the most basic RLC series resonance circuit as shown in Figure 5 , the input AC signal is u S , and the goal is to solve the voltage on the series resonance capacitor C and the input voltage u SThe ratio of the maximum amplitude is the boost ratio parameter model of the series resonance unit.

[0052] As Figure 5 shown, u S is a variable-frequency AC power supply. Under its excitation, the inductive reactance and capacitive reactance in the return current change with the frequency. Therefore, the voltage and current in the circuit also change accordingly. Since the frequency characteristics of the inductor L and the capacitor C are opposite and directly subtracted, when the frequency reaches a certain specific value, the inductive reactance and capacitive reactance cancel each other out, that is, LC resonates. At this time, the resonance point frequency f 0 should satisfy:

[0053]

[0054] When LC is in series resonance, the quality factor Q of the resonance circuit is defined in engineering as:

[0055]

[0056] Keep the amplitude of the input voltage u S unchanged. In order to compare the performance differences in the frequency responses of RLC series circuits with different parameters, the output voltage is taken as the ratio of its input voltage at the resonance point, and the frequency is also represented by the ratio η to the resonance frequency. In this way, the differences in the characteristics of different parameters can be compared on the same relative scale. That is:

[0057]

[0058] In the boost control scheme of the coupled load resonance type proposed in the present invention, the main concern is the relationship between the voltage across the load in the loop and the input voltage, which is reflected in Figure 3 as the relationship between the voltage of the capacitor C and the input voltage u S . Therefore, when the capacitor voltage is used as the output variable, its network function H C (jη) can be expressed as:

[0059]

[0060] We want the amplitude-frequency characteristic curve of the above function, so we must find its extreme points. The extreme conditions of H C (jη) are:

[0061]

[0062] Three extreme points can be obtained: And find their corresponding extreme values respectively.

[0063] At this time,

[0064]

[0065] At this time,

[0066]

[0067] At this time,

[0068]

[0069] According to the above analysis, draw the amplitude-frequency characteristic curve of H C (jη) as shown in Figure 4 the figure.

[0070] Denote the step-up ratio of the resonant circuit as k, then:

[0071]

[0072] According to the amplitude-frequency characteristic curve of H C (jη), we can draw the conclusion that at when, k reaches its maximum value at

[0073] After analyzing the principle of the RLC series resonant circuit clearly, the following will specifically describe the examples applicable to the step-up regulation scheme of the coupled load resonance type proposed by the present invention.

[0074] Based on the modulus expression relationship between the voltage on the resonant capacitor of the series resonant circuit and the maximum amplitude of the input voltage, applied to the working condition of the LTD pulse transformer connected to the DBD capacitive electrode load, where the capacitor of the RLC series resonance is C load , because the turn ratio of the TR is generally very small, the inter-turn capacitance parameter C tp_sec of the secondary side is very small and can be ignored, as shown in Figure 7 the figure. For different equivalent C load of the plasma electrode load, it will vary within a large range, and the corresponding parameter expressions of the RLC series resonance are substituted.

[0075] In the field of plasma discharge, the capacitive load C load , the leakage inductance L lk_sec of the secondary side of the pulse transformer, and the resistance R tp_sec cooperate to form an RLC series circuit. Its purpose is to adjust the resistance value of the power in the circuit to couple the capacitive load, and combined with the principle of RLC series resonance, establish a voltage amplitude gain model to obtain further voltage boost.

[0076] From the working principle of the RLC series resonant circuit, we can easily obtain that the maximum value of the boost ratio from the secondary voltage of the transformer to the output voltage of the load equivalent capacitance is:

[0077]

[0078] Also, because the quality factor of the resonant circuit is:

[0079]

[0080] Substituting into the above formula, we get:

[0081]

[0082] Combined with the monotonicity of the function, we can obtain:

[0083]

[0084] Due to the limited number of turns of the primary and secondary windings of the transformer, the corresponding winding additional resistance is very small and can be almost ignored. The present invention proposes to increase the boost ratio by additionally connecting an adjustable power resistor R tp_sec in series on the secondary side. tp_sec Then, by adjusting the resistance value of R load , the amplitude voltage value on the load capacitance C RLC can be conveniently increased, that is, the value of k

[0085] is increased.

[0086]

[0087] As Figure 8 shown, each curve represents the variation trend of the resistance value of the power resistor connected in series in the loop when driving different electrode loads (with different equivalent capacitances) under the same leakage inductance of the transformer while ensuring that the boost ratio remains unchanged. The three different curves correspond to the variation trends under different leakage inductances.

[0088] Based on the above principle analysis, we can obtain the model expression of the boost ratio of the maximum amplitude voltage from input to output pulse as: where k marx is the boost ratio of the Marx link, k TR is the boost ratio of the pulse transformer, k RLC is the maximum value of the boost ratio from the secondary voltage of the transformer to the output voltage of the load equivalent capacitance, k fouri is the ratio of the amplitude voltage of the distorted secondary output voltage of the LTD transformer to the amplitude voltage of the ideal square wave voltage, m is the number of Marx-LTD modules, n is the number of Marx stages, N 1 is the number of turns of the primary side of the transformer, N 2is the number of turns on the secondary side of the transformer, C load is a capacitive load, R tp_sec is an adjustable power resistor, L lk_sec is the leakage inductance of the secondary side of the LTD pulse transformer.

[0089] When driving a capacitive load, by connecting an adjustable power resistor R in series on the secondary side of the transformer tp_sec to couple the load C load , the impedance network structure of the secondary side circuit is adjusted, so that the boost regulation of the amplitude voltage of the entire pulse power supply can be achieved under different plasma DBD electrode loads C load .

[0090] To verify the effectiveness of the proposed solution of the present invention, taking the combination of the Marx circuit and the transformer as an example, the analysis is verified by building an experimental platform. Since the boost regulation scheme of the coupled load resonance type designed by the present invention mainly aims at the electrodes in the gas discharge field, and its load characteristic is a capacitive load, therefore, in the high-voltage pulse output test experiment in this paper, a 100 pF high-voltage capacitor is used to replace the actual discharge electrode load, and a linear pulse transformer with multiple turns ratios is used for the experiment. The turns ratio of the pulse transformer is set to K br_TR = 2, and the amplitude of the output pulse voltage across the capacitor is observed under different input voltages, different leakage inductances of the linear pulse transformer, and different series resistance values.

[0091] Figure 8 is the test waveform under the conditions of a pulse repetition frequency of 100 Hz and an input voltage of the high-voltage DC unit of 300 V. In the figure, CH 1 is the maximum amplitude of the pulse output voltage of a multi-turn ratio linear pulse transformer in the first stage: U pulse = 2.8 kV, CH 2 is the maximum amplitude of the output pulse voltage of the pre-stage Marx circuit: U Marx = 900 V. At this time, L lk_sec = 10 μH, C load = 100 pF, R tp_sec = 600 Ω.

[0092] Therefore, the experimental test value of the total boost ratio of the transformer from the primary side to the output voltage through two boosts, namely coil boost and resonant boost circuit, can be obtained from the input voltage on the primary side of the transformer, that is, the maximum amplitude of the output pulse voltage U Marx of the pre-stage Marx circuit and the maximum amplitude of the pulse output voltage U pulse of the transformer as:

[0093]

[0094] Figure 10 is at Figure 9Under the experimental conditions, without changing other variables, only increasing the input voltage of the high-voltage DC unit to 1000V, at this time, the maximum amplitude of the output pulse voltage of the pre-stage Marx circuit: U Marx = 3kV, and the maximum amplitude of the pulse output voltage of the transformer U pulse = 8.6kV.

[0095] Calculate the total voltage boost ratio obtained from the experimental test as:

[0096]

[0097] Figure 8 and Figure 9 The experimental conditions of and are the same except for the input voltage, so they have the same quality factor Q, resulting in the same voltage boost ratio through resonance voltage boost.

[0098]

[0099] It is known that the turn ratio of the pulse transformer is set as K br_TR = 2, so the calculated value of the total voltage boost ratio from the primary side of the transformer to the output voltage of the transformer is:

[0100] K tot = K br_TR ×K br_LC = 2×1.667 = 3.335.

[0101] Analysis Figure 9 and Figure 10 The experimental results and theoretical calculations show that the voltage boost ratios of the experiment and the calculation are basically the same, partially proving the effectiveness of the coupled load resonance type voltage boost regulation proposed in the present invention.

[0102] In order to fully prove the effectiveness of the proposed solution in the present invention, under the conditions of a pulse repetition frequency of 100Hz, an input voltage of the high-voltage DC unit of 1000V, and a load C load = 100pF, a two-stage linear pulse transformer with a multi-turn ratio is adopted, and the leakage inductance change is: L lk_sec = 26μH, and the resistance value is changed: R tp_sec = 1000Ω. The waveforms shown in Figure 10 are measured. In the figure, CH 1 is the maximum amplitude of the pulse output voltage of the transformer: U pulse = 15.5kV, and CH 2 is the maximum amplitude of the output pulse voltage of the pre-stage Marx circuit: U Marx = 2kV. The experimental value and the theoretical calculation value of the voltage boost ratio from the primary side of the pulse transformer to the output voltage of the transformer are calculated respectively, and it is found that the two are basically the same.

[0103] Theoretical calculation value:

[0104]

[0105]

[0106] Experimental calculated value:

[0107]

[0108] There is a small error between the above experimental theoretical value and the calculated value, but they are basically the same. The final experimental test results verify the feasibility of the boost regulation scheme of the coupled load resonance type proposed by the present invention.

Claims

1. A step-up ratio regulation method based on a coupled load resonance under the Marx-LTD architecture, including the following steps: Step S1: The power supply of the Marx-LTD architecture nanosecond pulse generator uses multiple Marx units with parallel inputs and series connections on the secondary side of the LTD units; Step S2: Connect a variable power resistor in series on the secondary side of the LTD in series: Through the RLC series connection of the variable power resistor, the leakage inductance of the pulse transformer, and the capacitive load, an RLC resonance network is formed; Step S3: Establish a boost ratio model for the maximum amplitude voltage of the output pulse of the Marx-LTD circuit; Step S4: By adjusting the resistance value of the power resistor, the boost ratio control of the voltage amplitude gain is achieved. The overall power supply of the nanosecond pulse generator is composed of n Marx-LTD units. The input terminals of all units share the same DC power supply to charge the energy storage capacitors in the Marx circuit. The secondary sides of the LTDs of each unit adopt a series connection structure to superimpose the module voltages. The expression of the boost ratio model for the maximum amplitude voltage of the output pulse is: where k marx is the boost ratio of the Marx section, k TR is the boost ratio of the pulse transformer, k RLC is the maximum value of the boost ratio from the voltage on the secondary side of the transformer to the output voltage of the load equivalent capacitor, k fouri is the ratio of the amplitude voltage of the distorted voltage on the secondary side of the LTD transformer to the amplitude voltage of the ideal square wave voltage. m is the number of Marx-LTD modules, n is the number of Marx stages, N 1 is the number of turns of the primary side of the transformer, N 2 is the number of turns of the secondary side of the transformer, C load is the capacitive load, R tp_sec is the variable power resistor, L lk_sec is the leakage inductance of the secondary side of the LTD pulse transformer. When driving the capacitive load, by connecting a variable power resistor R tp_sec in series on the secondary side of the transformer to couple the load C load , the impedance network structure of the secondary side circuit is adjusted, so that it is possible to achieve compensation and adjustment of the boost control of the amplitude voltage of the entire pulse power supply under different plasma DBD electrode load C load conditions.

2. The step-up ratio regulation method based on a coupled load resonance under the Marx-LTD architecture according to claim 1, characterized in that: Boost ratio k of the Marx section marx and the boost ratio k of the pulse transformer TR The equation is as follows:

3. The step-up ratio regulation method based on a coupled load resonance under the Marx-LTD architecture according to claim 1, characterized in that k fouri The numerical range of fouri k is: 1 ≤ k ≤ 1.

637.

4. The step-up ratio regulation method based on a coupled load resonance under the Marx-LTD architecture according to claim 1, characterized in that: The maximum value of the step-up ratio from the secondary side voltage of the transformer to the output voltage of the load equivalent capacitor is:

5. The step-up ratio regulation method based on a coupled load resonance under the Marx-LTD architecture according to claim 1, characterized in that : The adjustable power resistor shall meet the following conditions:

Images