EP2020672B1 - High frequency generator for ion and electron sources - Google Patents

Description

The invention relates to a device for coupling ionization energy into an inductively or inductively-capacitively excited ion or electron source.

In an ion engine, there is a high-frequency plasma to be excited within an isolated vessel, the so-called discharge vessel. A coupling coil for feeding in a high-frequency energy necessary for plasma excitation is wound around the discharge vessel. The plasma is thus inside the coupling coil. If there are changes in status, e.g. Changes in the density or conductivity, the plasma to changes in impedance, this causes detuning of the resonant circuit.

In high-frequency generators operating at a fixed frequency, e.g. 13.56 MHz, the impedance of a coupling network that connects the high-frequency generator to the coupling coil and changes due to plasma states must be compensated for by manual re-determination of an impedance matching network (so-called matchbox) or an actuator. The result of the compensation is that the capacitance of a capacitor of the impedance matching network, e.g. by changing the surface, is suitably adjusted or the inductance of a coil of the impedance matching network is changed by retracting a ferrite. The impedance matching via an impedance matching network can usually not be readjusted very quickly and can only be optimally adjusted over a small frequency load range. Not fast means that readjustment can take seconds. As a result, considerable power losses occur in the impedance matching networks.

The publication DE 199 48 229 C1 discloses a high frequency ion source with a high frequency generator equipped with a PLL control loop and with a high-frequency coil, the high-frequency coil forming a series or parallel resonance circuit with a capacitor.

The publication US 2007/114945 A1 discloses a high-frequency ion source with a high-frequency generator equipped with a PLL control loop and with a high-frequency coil, the high-frequency coil being connected to the high-frequency generator via an impedance network.

It is an object of the present invention to provide a device for coupling ionization energy into an inductively or inductively-capacitively excited ion or electron source for use in an ion engine, which does not have the disadvantages listed above.

This object is achieved by a device with the features of claim 1. Advantageous embodiments result from the dependent patent claims.

A device according to the invention for coupling ionization energy into an inductively or inductively-capacitively excited ion or electron source comprises: a discharge vessel for a gas to be ionized, such as Xe, Kr, Ar, Ne, He, H ₂ , O ₂ , CO ₂ , Cs or Hg; a coupling coil wound around the discharge vessel for feeding in a high-frequency energy necessary for plasma excitation; a coupling capacitor electrically coupled to the coupling coil; and a high-frequency generator electronically coupled to the coupling coil, which together with the at least one coupling capacitor forms a resonance circuit, the high-frequency generator having a PLL control device for automatically adjusting the impedance of the resonance circuit, so that the resonance circuit can be operated at a resonance frequency. According to the invention, it is provided that the at least one coupling capacitor and the coupling coil are connected to the high-frequency generator via a transformer, the transformer being capacitively coupled on the primary side and forming the resonance circuit on the secondary side with the at least one coupling capacitor and the coupling coil. This is useful, for example, in the event that very large impedance adaptations are required.

The coupling coil is connected to the high-frequency generator and forms a series or parallel resonance circuit with the coupling capacitor of the high-frequency generator.

The device according to the invention corrects phase errors of current and voltage in the power output stage of the high-frequency generator by automatically tracking the frequency and phase of the resonant frequency of the load circuit. The control principle is based on the fact that the PLL control circuit continuously compares the phase position of the sinusoidal high-frequency output current and the phase position of the generator output voltage via a digital phase detector and adjusts a phase error that occurs by adjusting the generator frequency via a voltage-controlled oscillator (VCO) to the frequency of the resonance circuit until the phase error Zero is present. Since the response time of the PLL control device is very short (depending on the design <100 µsec), there are no longer lasting phase errors even with rapid changes in the resonance frequencies. The high-frequency generator is therefore adapted to the consumer with the highest possible efficiency. Due to the very fast frequency tracking and the phase adjustment by means of the digital phase comparator, the PLL control device ensures that current and voltage are always in phase and thus the maximum power can be coupled into the plasma via the coupling coil. This can be done without mechanical movement or in any other way. The device according to the invention is characterized by its simplicity and great flexibility and the usability over a wide frequency range.

The procedure according to the invention for optimal impedance and power matching thus consists in comparing the power emitted by the high-frequency generator via a PLL control loop (PLL = phase locked loop) to resonance and phase error zero and transmitting it to the plasma. The transmission of power with a zero phase error means that current and voltage in the resonant circuit are in phase and therefore none Reactive currents flow. This means that no reactive power losses can occur, which means that switching losses are almost eliminated.

To carry out the automatic impedance matching of the resonance circuit, current and voltage are detected in the resonance circuit and fed to the PLL control device as control variables.

The high-frequency generator is characterized by the fact that operation with resonance and optimum phase adjustment is possible. Only sinusoidal currents flow through the PLL control device, both in the high-frequency generator and in the resonance circuit and thus in the coupling coil. The sinusoidal current allows a high efficiency of the high frequency generator and is therefore also at high operating frequencies, i.e. Frequencies above 0.5 MHz, between 90 and 95%.

A device according to the invention with a high-frequency generator with PLL control always works at the resonant frequency of the coupling network of the ion or electron source. The coupling network of the invention is formed by the resonance circuit comprising a coupling coil and a coupling capacitor. This means that the high-frequency generator follows all frequency changes regardless of a frequency detuning and a frequency bandwidth quality by the PLL control. The power adjustment of the high-frequency generator takes place in the microsecond range and leads through the exact phase adjustment of current and voltage in switching elements of the high-frequency generator and the resonance circuit to an almost loss-free switching and an optimal power coupling into the plasma.

A device according to the invention is therefore particularly suitable for the high-frequency energy supply of ion sources (TWK) and electron sources (NTR) with inductive excitation and for applications in which the lowest energy consumption is important.

According to one embodiment, the PLL control device carries out a frequency and / or phase control for impedance matching of the resonance circuit. The power control of the high-frequency generator can be carried out by setting an input DC voltage and an input current of the high-frequency generator. The high-frequency generator is thus characterized in that it generates a high-frequency output voltage from a direct voltage source that can be controlled in voltage and current strength. This AC voltage source is connected to a resonance circuit, including the coupling coil necessary for inductive coupling and the additional coupling capacitor.

The high-frequency generator of the device according to the invention is connected to the coupling coil without the intermediary of an impedance matching network, a so-called matchbox. The coupling of the high-frequency generator with PLL control nevertheless allows the electrical energy to be coupled directly into the plasma of the ion or electron source over a large power and frequency range.

The resonance circuit, which is formed from the coupling coil and coupling capacitor, can optionally be designed as a series or parallel resonance circuit. The impedance is adjusted by including the coupling coil and the design coupling capacitances between the plasma and the discharge vessel and the corresponding supply lines to the series or parallel / resonance circuit, with the PLL-controlled high-frequency generator automatically regulating the frequency and phase.

In a further embodiment, the coupling coil can have a center tap to which the high-frequency generator is connected. This allows the coupling coil to be cooled by supplying a cooling medium without the interposition of isolators, since the coil ends of the coupling coil are at a reference potential. As a cooling medium is preferred Water used. The ground potential can serve as a reference potential, for example.

In a further embodiment, the coupling coil can be arranged between two or more coupling capacitors. It is expedient if the resonant circuit which forms forms a resonance frequency which lies within the so-called lock frequency of the PLL control device. The high frequency generator guides the frequency e.g. by means of a voltage controlled oscillator (VCO = Voltage Controlled Oscillator) and a digital phase comparison of current and voltage in the resonance circuit until the phase error becomes zero.

A device for detecting current and voltage is expediently provided in the resonance circuit, which is coupled to the PLL control device in order to supply the measured current and the measured voltage as control variables.

A further embodiment of the invention provides that the at least one coupling capacitor is arranged in the high-frequency generator or outside it (as an external component).

It can further be provided that the coupling coil is grounded on one side or operated in isolation from a ground potential.

A further embodiment provides that the coupling coil and the plasma form a transformer, the plasma representing a secondary winding of the transformer.

The high-frequency generator comprises a power output stage, which can optionally be designed as one of the variants listed below: half-bridge class D output stage; Full bridge class D power amplifier; Push-pull power amplifier; Class E power amplifier; Class F power amplifier; Class C power amplifier The selection of which power output stage is provided in the high-frequency generator essentially depends on the required frequency and power range. The impedance matching to the coupling resonance circuit takes place in all cases via a frequency phase control using the PLL control device.

Class D and class E output stages are preferably used as output stages for the high-frequency generator, which are characterized by a maximum current flow angle of 180 ° in the switching elements of the output stages (with bipolar or MOSFET transistors). If class D power amplifiers without PLL control are used in connection with resonance circuits, even the smallest frequency phase detunings, depending on the circuit quality of the resonance circuit, lead to considerable reactive currents, both capacitive or inductive, depending on the direction of the phase frequency detuning . The consequence of this is very high current loads on the output stage and consequently high losses in the output stages and coupling networks. The losses occur in the form of reactive current losses. They lead to a sharp drop in the power transmitted to the consumer. By using the PLL control the problems mentioned, i.e. Phase errors in the output stages, even with class D, class E and class F output stages, completely avoided. The use of the PLL control enables the full performance utilization of these output stage types, i.e. a current flow angle of 180 °.

The high-frequency generator can be used to set a resonance frequency in the range from 0.5 MHz to 30 MHz. The power coupled into the high-frequency generator is in the range from 1 W to 10 kW. The load impedance coupled to the high frequency generator is in a range from 0.1 ohm to 1 ohm or in a range from 1 ohm to 50 ohms.

In a further embodiment, the discharge vessel of the device according to the invention has a gas inlet and an outlet arranged opposite it with at least two extraction grids, each with a multi-hole mask, which serves as an electrical lens for focusing the ion beams to be extracted. The extraction is carried out by an electric field that can be applied to the extraction grid. The discharge vessel is made of a non-conductive Material with low high-frequency losses, such as quartz, ceramic, Vespel or boron nitride. The discharge vessel serves as a discharge space for the gas to be ionized.

According to a further embodiment, the coupling coil comprises a single-layer or a multi-layer or a bifilar winding. The coupling coil is arranged around the discharge vessel or within the discharge vessel. The coupling coil is cylindrical, conical, spherical or partially conical with a cylindrical transition body wound around the discharge vessel.

Fig. 1

eine schematische Darstellung einer erfindungsgemäßen Vorrichtung zur Einkopplung von Ionisationsenergie in eine Ionen- oder Elektronenquelle;

Fig. 2

ein elektrisches Ersatzschaltbild der erfindungsgemäßen Vorrichtung;

Fig. 3

ein vereinfachtes erfindungsgemäßes Ersatzschaltbild der erfindungsgemäßen Vorrichtung;

Fig. 4

ein Prinzipschaltbild einer als Halbbrücke ausgeführten Endstufe eines Hochfrequenzgenerators mit einem Serienresonanzkreis;

Fig. 5

ein Prinzipschaltbild einer als Vollbrücke ausgestalteten Endstufe eines Hochfrequenzgenerators mit einem Serienresonanzkreis;

Fig. 6

eine schematische Darstellung der in einer erfindungsgemäßen Vorrichtung notwendigen Komponenten;

Fig. 7

die zeitlichen Verläufe von Strom und Spannung an einem Ausgang des Hochfrequenzgenerators;

Fig. 8

ein elektrisches Schaltbild zweier möglicher Ankopplungen von Koppelspulen an einen Hochfrequenzgenerator;

Fig. 9

eine beispielhafte Darstellung der Ankopplung einer Koppelspule über einen Zusatz-Transformator an den Hochfrequenzgenerator;

Fig. 10

eine Darstellung von Frequenzbandbreite und Resonanzkreisgüte bzw. Frequenzverstimmung sowie Phasengang einer lonenquelle bei verschiedenen Plasmazuständen;

Fig. 11

ein elektrisches Ersatzschaltbild einer Vorrichtung mit einem Hochfrequenzgenerator, der eine Klasse-D-Halbbrücke mit PLL-Regelung aufweist;

Fig. 12

ein elektrisches Ersatzschaltbild einer Vorrichtung mit einem Hochfrequenzgenerator, der eine Klasse-D-Vollbrücke mit PLL-Regelung aufweist;

Fig. 13

ein elektrisches Ersatzschaltbild einer Vorrichtung mit einem Hochfrequenzgenerator, der eine Klasse-E-Endstufe mit PLL-Regelung aufweist;

Fig. 14

ein elektrisches Ersatzschaltbild einer Vorrichtung mit einem Hochfrequenzgenerator, der eine Klasse-D-Halbbrücke mit PLL-Regelung und zusätzlicher transformatorischer Aufwärtsanpassung aufweist; und

Fig. 15

eine schematische Darstellung einer Impedanztransformation am Ausgang des Hochfrequenzgenerators.

The invention is explained in more detail below with reference to the figures. Show it:

Fig. 1

a schematic representation of a device according to the invention for coupling ionization energy into an ion or electron source;

Fig. 2

an electrical equivalent circuit diagram of the device according to the invention;

Fig. 3

a simplified equivalent circuit diagram according to the invention of the device according to the invention;

Fig. 4

a schematic diagram of a half-bridge designed final stage of a high frequency generator with a series resonance circuit;

Fig. 5

a schematic diagram of a power amplifier designed as a full bridge of a high frequency generator with a series resonance circuit;

Fig. 6

a schematic representation of the components required in a device according to the invention;

Fig. 7

the time profiles of current and voltage at an output of the high-frequency generator;

Fig. 8

an electrical circuit diagram of two possible couplings of coupling coils to a high-frequency generator;

Fig. 9

an exemplary representation of the coupling of a coupling coil via an additional transformer to the high-frequency generator;

Fig. 10

a representation of frequency bandwidth and resonance circuit quality or frequency detuning and phase response of an ion source in various plasma states;

Fig. 11

an electrical equivalent circuit diagram of a device with a high frequency generator having a class D half bridge with PLL control;

Fig. 12

an electrical equivalent circuit diagram of a device with a high-frequency generator having a class D full bridge with PLL control;

Fig. 13

an electrical equivalent circuit diagram of a device with a high-frequency generator which has a class E output stage with PLL control;

Fig. 14

an electrical equivalent circuit diagram of a device with a high-frequency generator, which has a class D half bridge with PLL control and additional transformer upward adjustment; and

Fig. 15

is a schematic representation of an impedance transformation at the output of the high frequency generator.

Fig. 1 shows a schematic representation of a device according to the invention for coupling ionization energy into an ion or electron source. A gas tank 1, in which a gas to be ionized is stored under high pressure, is coupled to a filling and drainage area 2 via a line. The filling and drainage area 2 is coupled to a flow control unit 3 via a further line. This has two outputs. A first outlet is connected to an inlet 6 of a discharge vessel 4 for ionizing the gas. A second output of the flow control unit 3 is connected to a neutralizer 10. The discharge vessel 4 consists of a non-conductive material that has only low radio frequency (HF) losses. The discharge vessel 4 can consist, for example, of quartz, a ceramic, Vespel or boron nitride. The discharge vessel 4 serves as a discharge space for the gas to be ionized, for example Xe, Kr, Ar, Ne, He, H ₂ , O ₂ , CO ₂ , Cs or Hg.

An isolator 14 and a flow limiter 15 are located at the inlet 6 of the discharge vessel 4. A coupling coil 5 is arranged around a cylindrical section of the discharge vessel 4, which is coupled to the inlet 6. The coupling coil 5 can consist of a single-layer, multi-layer or bifilar winding, which is wound both around and inside the discharge vessel. The shape of the winding of the coupling coil is arbitrary. It can be cylindrical, conical, spherical or partially conical with a cylindrical transition body. The discharge vessel 4 with the coupling coil 5 surrounding it and the neutralizer 10 are surrounded by an engine housing 21.

The coupling coil 5 is connected to a high-frequency generator 16, which generates a high-frequency output voltage from a DC voltage source that can be controlled in voltage and current strength. Together with a coupling capacitor (not shown) provided in the high-frequency generator 16, the coupling coil 5 forms a resonance circuit. The high-frequency generator, which is a field coupling on inductive or combined inductive and capacitive Base can be used in the frequency range from 0.5 MHz to 30 MHz. The efficiency of the high-frequency generator can be achieved in the range between 90 and 95%.

At least two, preferably two or three, extraction grids 8 are arranged at an outlet 7 of the discharge vessel 4, each of which has at least one multi-hole mask. The extraction grids 8 serve as an electrical lens for focusing the ion beams to be extracted. The extraction is carried out by an electric field, which is applied to the extraction grid 8. For this purpose, the extraction grids 8 are connected to an accelerator 18 and a plasma holder 17 (also called a plasma holder), which have different potentials. While the plasma receiver 17 has the function of an anode and generates a voltage of +1200 V, the accelerator 18 provides a voltage of -250 V. A retarder 19 is also connected to the extraction grid. The reference number 9 denotes the direction of the ejection of the positively charged ion beam e + from the extraction grid 8. The positively charged ion beam is compensated at the output of the discharge vessel 4 by means of negatively charged electrons in order to prevent the device from being electrically charged. Reference number 13 denotes the direction of ejection of electrons e-, these being ejected from the neutralizer 10.

The neutralizer 10 comprises a cathode heater 11 and a neutralization unit 12. An electrode of the cathode heater 11 is connected to an electrode of the neutralization unit 12. A respective other electrode of the cathode heater 11 and the neutralization unit 12 is coupled to the neutralizer 10. There is, for example, a potential difference of 9 V between the electrodes of the cathode heater 10, while there is a potential difference of 15 V between the electrodes of the neutralization unit 12.

A simple electrical equivalent circuit diagram of the invention is shown in Fig. 2 shown. In the electrical equivalent circuit diagram, this is in addition to the invention Device takes into account the plasma located in the discharge vessel. The coupling coil 5 and the plasma operate in the simplified sense like a transformer (reference number 36), the plasma corresponding to a secondary winding 37 of the transformer 36. The primary winding is formed by the coupling coil 5. Resistors 35 and 38 represent line resistances. The coupling capacitor, which forms the resonance circuit with the coupling coil 5, is identified by the reference symbol 22. Parasitic components (resistor 35 and capacitor 46) are contained in the resonant circuit. The parasitic capacitor 46 represents, for example, capacitances of a (coaxial) cable and of output transistors. With short line lengths and frequencies below 3 MHz, the capacitance of the parasitic capacitor 46 can be neglected. A high-frequency generator 16 is connected to the feeding voltage source, so that the input voltage Uin and the input current Jin are present. On the output side, the high-frequency generator 16 is connected to the coupling capacitor 22. The high-frequency generator is also identified in the figures with RFG (Radio Frequency Generator).

Fig. 3 shows a simplified equivalent circuit diagram of the device according to the invention. The high-frequency generator 16 is connected to the feeding voltage source, so that the input voltage Uin and the input current Jin are present. On the output side, the high-frequency generator 16 is connected in series to the coupling coil 5 via the coupling capacitor 22. The resistor 35 represents a line resistance. In simple terms, this means that the coupling coil 5, which is usually wound around the discharge vessel, is connected to the coupling capacitor to form a series or parallel resonance circuit.

Fig. 6 shows a schematic representation of the components necessary in a device according to the invention. The invention is characterized in that the high-frequency generator 16 generates a high-frequency output voltage from a direct voltage source (energy supply 33) that can be controlled in voltage and current strength. The high frequency generator 16 will be included the coupling coil 5 required for inductive coupling and an additional resonance capacitor, the so-called coupling capacitor 22, are connected to form a resonance circuit. For optimal impedance and power matching, the power generated by the high-frequency generator 16 is transmitted via a frequency- and phase-controlled control loop, adjusted for resonance and zero phase errors. This can, for example, the temporal courses of current and voltage at the output of the high frequency generator Fig. 7 be removed. The upper (rectangular) curve shows the voltage U, the middle (sine) curve the current I and the lower one the control of the output stage. In the figure above, the current is also shown to clarify the phase equality. Zero phase error means that current and voltage in the resonant circuit are in phase and therefore no reactive currents flow. This means that no reactive power losses can occur, which virtually eliminates switching losses. By operating with resonance and optimum phase adjustment, produced by a PLL control device, only sinusoidal currents flow both in the switching elements of the high-frequency generator 16 and in the resonance circuit and thus in the coupling coil 5. The sinusoidal current allows switching elements to be switched in the zero current crossing. A high degree of efficiency in the range of 90 to 95% can thus be achieved.

As already explained, the control loop is formed by the coupling coil 5 and the coupling capacitance 22, which in the exemplary embodiment of FIG Fig. 6 is arranged inside the high-frequency generator 16. In an alternative embodiment, not shown, the coupling capacitor 22 could also be designed as an external component. Two resistors 35 and 40, which represent line resistances, are also connected in the resonance circuit. The coupling capacitor 22 is coupled via a line to a power stage (output stage) 24, the current flowing in this line being detected by a current measuring device 23. The output stage 24 is designed, for example, as a class D output stage and is controlled by a control circuit 25, which comprises a flip-flop 47 and driver stages 48, 49. The driver stages 48, 49 drive Via transformers, output stages 52, 53 of the output stage 24. The control circuit 25, in turn, is connected to a PLL control device 34. This includes a voltage-controlled oscillator 26 (VCO = Voltage Controlled Oscillator), a filter 27 coupled to it and a digital phase comparator 28 coupled to the filter 27. The PLL control device 34 is coupled to the external power supply 33 via an input filter 31. The output stage 24 is also connected to the power supply 33 via an input filter 32. The PLL control device 34, more precisely the digital phase comparator 28, receives as input signal a current measured by the current measuring device 23, which is amplified by a signal amplifier 29. Furthermore, a voltage present at the output of the output stage 24 is fed via an additional signal amplifier 30 to an input of the digital phase comparator 28. Power can be adjusted in the microsecond range by the exact phase matching of current and voltage in the switching elements of the control circuit 25 and the resonance circuit and leads to an almost loss-free switching of the output stage 24 and thus an optimal power coupling into the plasma introduced into the discharge vessel 4.

Such a high-frequency generator with PLL control is therefore particularly suitable for the high-frequency energy supply of ion sources (TWK) and in electron sources (NTR) with inductive excitation as well as for applications in which the lowest energy consumption is important.

As an output stage in the high-frequency generator 16, the invention enables the use of half-bridges in connection with a PLL frequency and phase control as well as a resonance circuit coupling. In the embodiment of the Fig. 4 A series resonance circuit is shown, which can work in the frequency and power range from 600 kHz to 14 MHz or 1 W to 3 kW. The output stage 24 designed as a half bridge is connected between a supply and a reference potential connection and comprises, in a known manner, two switching elements 44 connected in series with one another with their load paths, in the exemplary embodiment in the form of MOSFETs. These are controlled by the control circuit 25. The coupling capacitance 22 is coupled to a node 38, which is in each case connected to a main connection of the switching elements 44. A resistor 45 of the resonance circuit, which represents a coil resistance, is connected to reference potential, for example ground. The switching elements 44 are controlled by the control circuit 25, which is connected to an energy supply that is variable in current and voltage.

Fig. 5 shows a further basic circuit diagram of an output stage 24 of the high-frequency generator designed as a full bridge. A power amplifier designed as a full bridge is suitable for a frequency range from 600 kHz to 5 MHz and a power range from 2 kW to 10 kW. In a known manner, the output stage 24 each comprises two half-bridge branches connected in parallel, which are connected between a supply and a reference potential connection and each comprise two switching elements 44 connected in series with their load paths in the form of MOSFETs. The resonance circuit, comprising the coupling coil 5, the coupling capacitor 22 and the line resistor 35, is connected to a node 39 of a first half bridge and a node 41 of a second half bridge of the output stage 24. Furthermore, a smoothing capacitor 54 is connected in parallel with the energy supply 33.

For the sake of clarity, the Fig. 4 and 5 neither the control circuit for controlling the switching elements 44 nor the PLL control device for adjusting the frequency and phase are shown.

Fig. 8 represents an electrical circuit diagram of possible coupling of coupling coils to a high-frequency generator. A coupling of the high-frequency generator 16 to the ion or electron source can take place via simple series resonance circuits or parallel resonance circuits in connection with a PLL phase control. Likewise, the coupling can take place via a series / parallel resonance circuit, the coupling coil 5 being a center tap owns (left half of the Fig. 8 ). Their two free ends can each be connected to a reference potential, in the exemplary embodiment ground. A capacitor 55 is connected in parallel. For the sake of simplicity, the PLL frequency / phase control is not shown. The resonance circuit also includes the coupling capacitor 22 and the line resistor 35. A voltage supplied to the PLL control loop is tapped via the resistor 35, these points being identified by v. The current supplied to the PLL control loop as a controlled variable is tapped at the point marked I. In the right half of the Fig. 8 A representation is selected in which the coupling coil 5 is arranged between two coupling capacitors 22a and 22b. Both ends of the coupling coil 5 are connected capacitively. The line resistance is not shown. Also not shown is the PLL frequency phase control provided according to the concept of the invention and the high frequency generator. The coupling described increases the efficiency of the high-frequency generator and the efficiency of the ion or electron source considerably. No reactive currents occur in either module, which means that the power loss decreases. Through an optimized choice of the number of turns of the coil, both an optimal plasma coupling and optimal operating parameters (operating voltage and current) of the high-frequency generator can be achieved.

Fig. 9 shows an exemplary schematic representation of the coupling of a coupling coil via an additional transformer 42 to the high-frequency generator 16. The additional transformer 42 enables additional transformer impedance matching, in particular in the frequency and power range from 600 kHz to 5 MHz or 1 W to 1 kW possible. The additional transformer 42 has a center tap in the exemplary embodiment. A capacitor 54 connected downstream of the high-frequency generator 16 is used for decoupling the DC voltage of the additional transformer 42.

Fig. 10 shows a representation of frequency bandwidth and resonance circuit quality or frequency detuning and phase response of an ion source at different Plasma states. The different quality curves of the resonance circuit are caused by different impedances of the plasma due to different degrees of ionization. The steepest curve in the lower graphic has the greatest quality and the smallest bandwidth. The illustration illustrates that the control loop according to the invention reacts to the most varied of grades and stably engages. The curves given in the upper half of the figure show that a change in the plasma impedances results in ion currents of different phase positions, which are compensated for by the phase locked loop.

Fig. 11 shows a further block diagram, which shows the use of the PLL control device for controlling the high-frequency generator. In the example, the output stage 24 is designed as a class D half bridge, the resonance circuit being coupled to the node 39. A current measuring device 23 is provided between the node 39 and a resistor 35. Resistor 35 represents a line resistance. Resistor 45, connected in series, represents a coil resistance. A voltage is tapped between the node 39 and a reference potential. This voltage and a current measured by the current measuring device 23 are fed to the inputs of a phase comparator 28. The output voltage applied to the phase comparator 28 is filtered and fed to the input of the voltage-controlled oscillator 26. This control voltage is changed by the phase comparator, which functions as an error amplifier, until there is frequency and phase equality at its inputs. A flip-flop 47 drives driver stages 48, 49, which drive or drive output stages 52, 53 via transformers 50, 51.

Fig. 12 shows a device with a high frequency generator having a class D full bridge with PLL control. The resonance circuit is designed as a series resonance circuit. The other components and their wiring correspond to the description Fig. 11 .

In Fig. 13 A device with a high frequency generator is shown, which has a class E output stage with PLL control. The resonance circuit is designed as a series resonance circuit and comprises the coupling capacitor 22, the coupling coil 5 and the line resistance 35 and the coil resistance 45. The use of a class E output stage circuit for the high-frequency generator with PLL frequency and phase control and resonance circuit coupling, in particular a series / Parallel resonance circuit including the coupling coil is preferably used in the frequency and power range from 600 kHz to 30 MHz or 1 W to 500 W. The coil 56 is part of the class E amplifier and is many times larger than the coil 5. It serves as an energy store when the output stage 52 is blocked. The other components and their wiring correspond to the description Fig. 11 .

Fig. 14 shows an electrical equivalent circuit diagram of a device with a high-frequency generator, which has a class D half-bridge with PLL control and additional transformer upward adaptation. For this purpose, a transformer 57 and a capacitor 58 are connected to the output of the output stages 52, 53. The capacitor 58 is connected in a known manner to a center tap of the transformer 57. The other components and their wiring correspond to the description Fig. 11 .

Finally shows Fig. 15 an embodiment of a possible capacitive impedance transformation, which can be used in all amplifier classes (class C, class D, class E, class F). With such an impedance transformation, it is possible to vary the impedance of the plasma or an input impedance Zi of the resonance circuit and thus to optimize the efficiency, the frequency range and the voltage range (for thrust resolution). Resistor 38 represents the resistance of the plasma. A capacitor 59 can be connected in parallel with the resistor 38. The resistor 60 and the capacitor 61 connected in parallel represent elements of the high-frequency generator. The capacitors 22, 61 represent resonance capacitors, the coil 5 is the coupling coil.

The advantage of all the variants described is that the energy generated by the high-frequency generator can be coupled directly into the plasma of the ion or electron source over a large power and frequency range without an impedance matching network. The core of the power adjustment is the inclusion of the coupling coil, design-related coupling capacities between the plasma and the housing of the discharge vessel, as well as the cabling to a series or parallel resonance circuit, and the automatic frequency and phase control of the high-frequency generator.

Claims (21)

1. Device for coupling ionisation energy into an ion or electron source, which is excited inductively or inductively-capacitively, and which comprises

   - a discharge vessel (4) for a gas to be ionized,

   - a coupling coil (5), which is wound around the discharge vessel (4) for feeding a high-frequency energy, which is required for plasma excitation,

   - a coupling capacitor (22), which is electrically coupled to the coupling coil (5),

   - a high-frequency generator (16), which is electrically coupled to the coupling coil (5) and which forms together with the at least one coupling capacitor (22) a resonant circuit, the high-frequency generator (16) including a PLL controller (34) for automatic impedance matching of the resonant circuit, so that the resonant circuit can be driven at a resonant frequency,

   wherein
   the at least one coupling capacitor (22) and the coupling coil are connected to the high-frequency generator via a transformer (42), wherein on the primary side the transformer (42) is capacitively coupled to the high-frequency generator and on the secondary side forms the resonant circuit with the at least one coupling capacitor (22) and the coupling coil (5), characterized in that the high-frequency generator (16) is connected to the coupling coil without interposing an impedance matching network.
2. Device according to claim 1, characterized in that a frequency and/or phase control for impedance matching of the resonant circuit is carried out by the PLL controller (34).
3. Device according to claim 1 or 2, characterized in that the power control of the high-frequency generator (16) can be performed by adjusting an input direct voltage (Uin) and an input current (Jin) of the high-frequency generator (16).
4. Device according to any one of the previous claims, characterized in that the resonant circuit is a series or parallel resonant circuit.
5. Device according to any one of the previous claims, characterized in that the coupling coil (5) has a centre tap (41), to which the high-frequency generator (16) is attached.
6. Device according to any one of the previous claims, characterized in that the coupling coil (5) is disposed between two or more coupling capacitors (22a, 22b).
7. Device according to any of the preceding claims, characterized in that a device for detecting current and voltage in the resonant circuit is provided, which is coupled to the PLL controller (34) in order to feed the measured current and the measured voltage as controlled variables thereto.
8. Device according to any one of the previous claims, characterized in that the at least one coupling capacitor (22) is disposed in the high-frequency generator (16) or outside the high-frequency generator (16).
9. Device according to any one of the previous claims, characterized in that the coupling coil (5) is grounded unilaterally.
10. Device according to any one of the previous claims, characterized in that the coupling coil (5) is attached insulated from a reference potential via the resonant circuit.
11. Device according to any one of the previous claims, characterized in that the coupling coil (5) and the plasma form a transformer, the plasma representing a secondary winding of the transformer.
12. Device according to any one of the previous claims, characterized in that the high-frequency generator (16) comprises a power output stage (24).
13. Device according to claim 12, characterized in that the power output stage (24) is optionally configures as one of the variants listed below:

    - half bridge Class D output stage;

    - full bridge class D output stage;

    - push pull output stage;

    - output stage of class E;

    - output stage of class F;

    - output stage of class C.
14. Device according to any one of the previous claims, characterized in that a resonant frequency in set in a range of 0.5 MHz to 30 MHz by the high-frequency generator (16).
15. Device according to any one of the previous claims, characterized in that the power that is coupled into the high frequency generator (16) is in a range of 1 W to 10 kW.
16. Device according to any one of the foregoing claims, characterised in that the load impedance, which is coupled to the radio frequency generator (16), is in a range of 0.1 ohm to 1 ohm or in a range of 1 ohm to 50 ohm.
17. Device according to any one of the previous claims, characterized in that the discharge vessel (4) includes a gas inlet (6) and an outlet (7), which are arranged opposite each other, with at least two extraction grids (8), each of which has one multi-apertured mask, which serves as an electric lens for focusing the ion beams that are to be extracted.
18. Device according to claim 17, characterised in that an electric field can be applied to the extraction grids (8).
19. Device according to any one of the previous claims, characterized in that the coupling coil (5) comprises a single layered or a multi-layered or a bifilar winding.
20. Device according to any of the previous claims, characterized in that the coupling coil (5) is disposed around the discharge vessel (4) or inside the discharge vessel.
21. Device according to any of the previous claims, characterized in that the coupling coil (5) is wound about the discharge vessel of the corresponding shape in a cylindrical, conical, spherical or partially conical manner with a cylindrical transition body.

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