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Control system of neutral particle analyzer in energy sweeping mode
Fusion Engineering and Design 151 (2020) 111412
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Control system of neutral particle analyzer in energy sweeping mode
T
M.B. Dreval*, A.S. Slavnyj IPP NSC Kharkov Institute of Physics and Technology, Kharkov, Ukraine
A R T I C LE I N FO
A B S T R A C T
Keywords: Neutral Particle Analyzer NPA U-3M NPA energy sweeping technique STM-32
For analyzing energy distribution of charge exchange atoms the ion energy sweeping technique is suggested as an alternative to the conventional multichannel Neutral Particle Analyzer (NPA) diagnostics. New electronics for application of the sweeping technique in the presence of mass separation (MS) electromagnet is described. The L/R time constant of the magnet is about 200 ms. Variation of current trough the magnet from zero to 0.3 A during 5 ms is required for energy-sweeping technique implementation in the ion energy range of 0−2 keV. The voltage applied to electrostatic part of NPA should be varied from zero to 500 V (measured energy is 4.5 times higher than the applied voltage). The dependence of the electrostatic voltage on the MS magnet current should correspond to the NPA calibration curve. The problem of simultaneous variation of the voltage at electrostatic part and current in MS magnet in accordance with NPA calibration is solved by means of developed electronics with the use of a STM32F100 microprocessor as a control unit. Square wave pulses of 310 V of variable duration are applied to generate MS magnet current. The IGBT bridge is used as a power unit of the MS magnet. The electrostatic voltage was formed by digital to analog convertor unit of STM32F100 microprocessor. The synchronized output of two control signals is produced by means of the direct memory access unit of the STM32F100 microprocessor.
1. Introduction The Neutral Particle Analyzer (NPA) diagnostics is widely used in fusion devices for measurement of ion energy distribution. Typically conventional NPA consists of a set of channels corresponding to different energies of ions that appear in the NPA via charge exchange of plasma escaping neutrals. The energy sweeping technique can be used as an alternative to the conventional multichannel NPA diagnostic technique. The application of a fast voltage sweep to the NPA electrostatic analyzing plates allows to provide the measurement of the ion energy distributions using single channel NPA hardware. The sweeping technique has important advantages in comparison with multichannel NPAs, namely the NPA design simplicity and higher energy resolution. In addition, it allows to take into account a noise of NPA signal by controlling it in a zero voltage sweeping phase. The idea of NPA energy sweeping and its application were reported from TCV [1] and used in the URAGAN-3 M (U-3 M) stellarator. The U-3 M stellarator is equipped with two passive electrostatic small-angle 30 °CX NPAs similar to that described in Ref [2]. The NPAs can work in configuration without mass separation (as it was used in Ref [2].) or can be equipped with mass separation electromagnet. Simplified schematic of the NPA equipped with MS electromagnet is shown in Fig. 1.
⁎
The NPA energy sweeping technique is routinely used in U-3 M [3]. The fast sweeping rate is required in U-3 M due to short plasma pulse duration. NPA electronics in the U-3 M allow one to measure the ion energy distribution in the 0.1–4.5 keV range (the ion energy is related to the NPA voltage on electrostatic plates Ua as: Ei = 4.5·e·Ua) every 2–5 ms in the low-density U-3 M discharges, where the flux of neutrals is significant [3] (see Fig. 2). Usually, the NPA in U-3 M was not equipped with the mass separation (MS) magnet in the sweeping mode configuration. Meanwhile, the MS part is required for some experimental conditions in a case of presence of different masses in plasma and as the efficient suppressor of parasitic influence of plasma radiation on the NPA measurements (due to geometrical factor). The electrostatic voltage depends on the current through MS magnet via the NPA calibration curve. The calibration curve of our NPA for hydrogen neutrals is shown in Fig. 3. The electrostatic voltage and the MS current should be changed simultaneously and follow to the calibration curve in the case of sweeping mode of NPA operation. We should note, that in present NPA configuration with single NPA detector, only one mass can be separated at fixed stage of the measurement. Substantially different NPA calibration curve is required for different masses. The MS electromagnets of about 10 H are available for our NPA diagnostics. The L/R time of this
Corresponding author. E-mail address: [email protected] (M.B. Dreval).
https://doi.org/10.1016/j.fusengdes.2019.111412 Received 21 June 2019; Received in revised form 23 September 2019; Accepted 14 November 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 151 (2020) 111412
M.B. Dreval and A.S. Slavnyj
Fig. 4. Diagram of the NPA power electronics.
load driver should be designed and the calibration curve should be precisely reproduced. Power electronics and microprocessor-based control system of NPA developed for energy sweeping technique with MS magnet is described in our work. 2. Control system and power electronics of NPA with MS
Fig. 1. Scheme of the NPA: 1 – stripping cell, 2 – electrostatic plates, 3 – MS magnet, 4 – ion-electron convertor, 5 – scintillator, 6 – PMT tube.
Due to long L/R duration time of the MS magnet it is difficult to determine desirable waveform of the current. We decide to use square voltage pulses applied to the MS magnet and to work with “self-defined” waveform of the current. This waveform is determined by the pulse duration and properties of the magnet. It should be noted that the MS magnet response is rather different in comparison with an ideal inductance, due to parasitic internal capacitance and iron core with unknown response. However, this is not important in our “self-defined” strategy. The “self-defined” waveforms strategy is used if the time response is the key parameter, for example, in the high voltage devices [4,5]. Simplest design solutions are possible with this strategy, in spite of nonlinear output waveform. The diagram of NPA power electronics required for implementation of our strategy is shown in Fig. 4. The power electronics contains two parts. We use unchanged electrostatic power part from our previous design for sweeping without MS magnet. Most of modern high voltage IGBT and MOSFET can be operated in the linear mode, in spite of the original designs for the switching mode, according to our experience. A very low current consumed by the electrostatic unit of NPA simplifies its design. Single MOSFET transistor IRFBG20 is used as a 1 keV output linear mode transistor in our design. The second part of the power electronics should apply square pulses of rather high voltage for fast generation and dumping of current in the MS unit inductor. The bridge circuit is widely used as an indicative load driver. The IGBT bridge is used as a power unit of MS magnet in our design. One pair of the bridge is used at the current rise stage; another pair applies the reverse voltage for the fast decay of the MS magnet current. Our estimations confirm that the value of bridge voltage of 310 V is enough for sweeping MS inductor current from zero to 0.3 A during 2−5 ms. The advanced control unit is required in order to satisfy NPA calibration dependence between voltage and current at all stages of the energy sweeping operation. The diagram of NPA control unit is shown in Fig. 5. We use STM32F100 microprocessor [6] as a core of the control unit. In spite of low cost it contains all required interfaces, is well documented and simple. In a framework of “self-defined” current waveform in MS unit, a single digital output is used for MS magnet control. The IGBT drivers IR2104 and IR2110 are used for further bridge driving. In order to provide required waveform of electrostatic voltage a digital to analog converter (DAC) is used in the electrostatic part. We use internal DAC available in the STM32 microprocessor. Two direct memory access (DMA) interfaces incorporated in STM32 are used in order to precisely synchronize current and voltage sweeping waveforms. A feed-forward control technique is used since properties of output loads (MS inductor and electrostatic unit properties) are constant in time. Since we cannot control waveform of MS current in our self-defined technique, we should apply controlled waveform to the electrostatic unit in order to
Fig. 2. Waveforms of the NPA sweeping voltage (lower figure), and the raw NPA collector signal.
Fig. 3. NPA calibration curve for hydrogen.
magnet is about 0.2 s. Thus, we need to sweep NPA voltage and current in two orders of magnitude faster than L/R time in order to archive desirable 2−5 ms sweeping time. Two problems have to be solved for application of sweeping technique with the magnet. The high inductive 2
Fusion Engineering and Design 151 (2020) 111412
M.B. Dreval and A.S. Slavnyj
for NPA counting mode of operation). Thus the CX signal is high enough and does not limited the sweeping time. It should be noted, that the shape of voltage sweep in the electrostatic unit is very flexible (due to low capacitance and inductance and high resistance of the electrostatic plates circuit as well as flexible performance of ADC of STM32). The calibration from one mass to another can be, in principal, adjusted during one pulse, from one swiping scan to another. Thus the single detector NPA can, in theory, measure energy distribution of different masses in a single pulse. Although, signal corresponding to different masses can be orders of magnitude different (due to different concentrations of different ions in plasma and substantially different stripping cross-sections). An adjustment of the PMT sensitivity together with the electrostatic voltage shape is required between U-3 M pulses for different mass selection under these conditions.
Fig. 5. The diagram of the NPA control system.
3. Summary and conclusions The energy sweeping mode was used for measurement of the energy distribution of charge exchange neutrals every 3−5 ms via singlechannel electrostatic neutral particle analyzer (NPA) in the U-3 M stellarator. The magnetic mass-separation (MS) part of NPA was omitted during these energy-sweeping measurements. The MS part is required for some experimental conditions in a case when different mass ions are present in plasma and for efficient suppression of parasitic influence of plasma radiation on the NPA measurements (due to geometrical factor). New control system and power electronics of the NPA has been developed. This system allows to provide NPA measurement with MS magnet in the energy range of 0−2 keV every 5 ms in U-3 M. The time achieved for one measurement (5 ms) is an order of magnitude less than the L/R time of the NPA mass separation magnet. This fast operation is achieved by application of rather high voltage to the MS magnet. The “self-defined” strategy of the MS current shaping was used. The problem of simultaneous variation of the voltage at electrostatic part and current in MS magnet in accordance with NPA calibration is solved in our work. We use STM32F100 microprocessor as a control unit, the IGBT bridge – as a power unit of MS magnet, the digital to analog convertor unit of STM32F100 microprocessor – for the electrostatic voltage formation, the direct memory access unit of the STM32F100 microprocessor – for synchronized output of two control signals. Square wave 310 V pulses of variable duration are used for control of MS magnet current. Thus, the NPA energy distribution with improved energy resolution and mass separation can be measured by single-channel NPA using developed electronics.
Fig. 6. Evolution of: a) line-averaged plasma density, b) Hα emission, c) signal from NPA detector, d) MS current, and e) electrostatic voltage in typical frametype antenna radio frequency discharge of U-3 M.
satisfy the calibration dependence during all sweeping stages. A sequence of control pulses is stored in the internal memory of STM32 and reproduced after a trigger signal. The corresponding current waveform produced by this sequence is measured. The required for electrostatic unit analog control waveform is calculated on the base of the NPA calibration curve and is stored in the internal memory of STM32 too and reproduced after trigger signal. This method allows simultaneous current and voltage sweeping along the calibration curve in spite of strongly non-linear self-defined current waveform and the non-linear calibration curve shape. An external trigger signal is used for the sweeping cycle synchronization with the U-3 M discharge start. An interrupt technique of STM32 is used for precise synchronization of the sweeping cycle start. An optocoupler is used in the trigger line for suppression of electromagnetic interference between NPA electronics and external power electrons of U-3 M stellarator (for example via ground loops prevention). Operation of the NPA in sweeping modes with MS magnet in U-3 M are illustrated by Fig.6. The NPA sweeping along the calibration curve is produces from 12 to 45 ms of the discharge. At the initial stage of the NPA sweeping at 5−12 ms, required for initial MS current rising, the calibration dependence is not satisfied. The MS current and electrostatic voltage does not follow to the calibration curve at this initial stage. No NPA signal is consequently observed at this stage (as it is seen from Fig.6). A modification of the NPA detector signal dependence on the sweeping voltage concerns time evolution of the ion energy distribution in U-3 M. We should note, that the strong CX flux produced in typical frame-type radio frequency antenna discharges of U-3 M [3] allows analog operation of the NPA photomultiplier. The analog mode of operation of the NPA photomultiplier is used in the detector section (in spite of usual
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We would like to thank R.O. Pavlichenko for giving the line integrated electron density data, Yu.K. Mironov for providing data of Hα diagnostics and V.S. Voitseny for useful discussions. References [1] [2] [3] [4] [5] [6]
3
A.N. Karpushov, et al., Rev. Sci. Instrum. 77 (2006) 033504. V.V. Afrosimov, et al., Sov. Phys.—Tech. Phys. 5 (1961) 1378. M. Dreval, A.S. Slavnyj, Plasma Phys. Control. Fusion 53 (2011) 065014. T. Onchi, et al., Ieee Trans. Plasma Sci. 44 (2) (2016) 195. T. Onchi, et al., Fusion Eng. Des. 89 (2014) 2559. The STM32F100 Microprocessors Family Specification Available at: https://www.st. com/en/microcontrollers-microprocessors/stm32f100-value-line.html.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Control system of neutral particle analyzer in energy sweeping mode
T
M.B. Dreval*, A.S. Slavnyj IPP NSC Kharkov Institute of Physics and Technology, Kharkov, Ukraine
A R T I C LE I N FO
A B S T R A C T
Keywords: Neutral Particle Analyzer NPA U-3M NPA energy sweeping technique STM-32
For analyzing energy distribution of charge exchange atoms the ion energy sweeping technique is suggested as an alternative to the conventional multichannel Neutral Particle Analyzer (NPA) diagnostics. New electronics for application of the sweeping technique in the presence of mass separation (MS) electromagnet is described. The L/R time constant of the magnet is about 200 ms. Variation of current trough the magnet from zero to 0.3 A during 5 ms is required for energy-sweeping technique implementation in the ion energy range of 0−2 keV. The voltage applied to electrostatic part of NPA should be varied from zero to 500 V (measured energy is 4.5 times higher than the applied voltage). The dependence of the electrostatic voltage on the MS magnet current should correspond to the NPA calibration curve. The problem of simultaneous variation of the voltage at electrostatic part and current in MS magnet in accordance with NPA calibration is solved by means of developed electronics with the use of a STM32F100 microprocessor as a control unit. Square wave pulses of 310 V of variable duration are applied to generate MS magnet current. The IGBT bridge is used as a power unit of the MS magnet. The electrostatic voltage was formed by digital to analog convertor unit of STM32F100 microprocessor. The synchronized output of two control signals is produced by means of the direct memory access unit of the STM32F100 microprocessor.
1. Introduction The Neutral Particle Analyzer (NPA) diagnostics is widely used in fusion devices for measurement of ion energy distribution. Typically conventional NPA consists of a set of channels corresponding to different energies of ions that appear in the NPA via charge exchange of plasma escaping neutrals. The energy sweeping technique can be used as an alternative to the conventional multichannel NPA diagnostic technique. The application of a fast voltage sweep to the NPA electrostatic analyzing plates allows to provide the measurement of the ion energy distributions using single channel NPA hardware. The sweeping technique has important advantages in comparison with multichannel NPAs, namely the NPA design simplicity and higher energy resolution. In addition, it allows to take into account a noise of NPA signal by controlling it in a zero voltage sweeping phase. The idea of NPA energy sweeping and its application were reported from TCV [1] and used in the URAGAN-3 M (U-3 M) stellarator. The U-3 M stellarator is equipped with two passive electrostatic small-angle 30 °CX NPAs similar to that described in Ref [2]. The NPAs can work in configuration without mass separation (as it was used in Ref [2].) or can be equipped with mass separation electromagnet. Simplified schematic of the NPA equipped with MS electromagnet is shown in Fig. 1.
⁎
The NPA energy sweeping technique is routinely used in U-3 M [3]. The fast sweeping rate is required in U-3 M due to short plasma pulse duration. NPA electronics in the U-3 M allow one to measure the ion energy distribution in the 0.1–4.5 keV range (the ion energy is related to the NPA voltage on electrostatic plates Ua as: Ei = 4.5·e·Ua) every 2–5 ms in the low-density U-3 M discharges, where the flux of neutrals is significant [3] (see Fig. 2). Usually, the NPA in U-3 M was not equipped with the mass separation (MS) magnet in the sweeping mode configuration. Meanwhile, the MS part is required for some experimental conditions in a case of presence of different masses in plasma and as the efficient suppressor of parasitic influence of plasma radiation on the NPA measurements (due to geometrical factor). The electrostatic voltage depends on the current through MS magnet via the NPA calibration curve. The calibration curve of our NPA for hydrogen neutrals is shown in Fig. 3. The electrostatic voltage and the MS current should be changed simultaneously and follow to the calibration curve in the case of sweeping mode of NPA operation. We should note, that in present NPA configuration with single NPA detector, only one mass can be separated at fixed stage of the measurement. Substantially different NPA calibration curve is required for different masses. The MS electromagnets of about 10 H are available for our NPA diagnostics. The L/R time of this
Corresponding author. E-mail address: [email protected] (M.B. Dreval).
https://doi.org/10.1016/j.fusengdes.2019.111412 Received 21 June 2019; Received in revised form 23 September 2019; Accepted 14 November 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 151 (2020) 111412
M.B. Dreval and A.S. Slavnyj
Fig. 4. Diagram of the NPA power electronics.
load driver should be designed and the calibration curve should be precisely reproduced. Power electronics and microprocessor-based control system of NPA developed for energy sweeping technique with MS magnet is described in our work. 2. Control system and power electronics of NPA with MS
Fig. 1. Scheme of the NPA: 1 – stripping cell, 2 – electrostatic plates, 3 – MS magnet, 4 – ion-electron convertor, 5 – scintillator, 6 – PMT tube.
Due to long L/R duration time of the MS magnet it is difficult to determine desirable waveform of the current. We decide to use square voltage pulses applied to the MS magnet and to work with “self-defined” waveform of the current. This waveform is determined by the pulse duration and properties of the magnet. It should be noted that the MS magnet response is rather different in comparison with an ideal inductance, due to parasitic internal capacitance and iron core with unknown response. However, this is not important in our “self-defined” strategy. The “self-defined” waveforms strategy is used if the time response is the key parameter, for example, in the high voltage devices [4,5]. Simplest design solutions are possible with this strategy, in spite of nonlinear output waveform. The diagram of NPA power electronics required for implementation of our strategy is shown in Fig. 4. The power electronics contains two parts. We use unchanged electrostatic power part from our previous design for sweeping without MS magnet. Most of modern high voltage IGBT and MOSFET can be operated in the linear mode, in spite of the original designs for the switching mode, according to our experience. A very low current consumed by the electrostatic unit of NPA simplifies its design. Single MOSFET transistor IRFBG20 is used as a 1 keV output linear mode transistor in our design. The second part of the power electronics should apply square pulses of rather high voltage for fast generation and dumping of current in the MS unit inductor. The bridge circuit is widely used as an indicative load driver. The IGBT bridge is used as a power unit of MS magnet in our design. One pair of the bridge is used at the current rise stage; another pair applies the reverse voltage for the fast decay of the MS magnet current. Our estimations confirm that the value of bridge voltage of 310 V is enough for sweeping MS inductor current from zero to 0.3 A during 2−5 ms. The advanced control unit is required in order to satisfy NPA calibration dependence between voltage and current at all stages of the energy sweeping operation. The diagram of NPA control unit is shown in Fig. 5. We use STM32F100 microprocessor [6] as a core of the control unit. In spite of low cost it contains all required interfaces, is well documented and simple. In a framework of “self-defined” current waveform in MS unit, a single digital output is used for MS magnet control. The IGBT drivers IR2104 and IR2110 are used for further bridge driving. In order to provide required waveform of electrostatic voltage a digital to analog converter (DAC) is used in the electrostatic part. We use internal DAC available in the STM32 microprocessor. Two direct memory access (DMA) interfaces incorporated in STM32 are used in order to precisely synchronize current and voltage sweeping waveforms. A feed-forward control technique is used since properties of output loads (MS inductor and electrostatic unit properties) are constant in time. Since we cannot control waveform of MS current in our self-defined technique, we should apply controlled waveform to the electrostatic unit in order to
Fig. 2. Waveforms of the NPA sweeping voltage (lower figure), and the raw NPA collector signal.
Fig. 3. NPA calibration curve for hydrogen.
magnet is about 0.2 s. Thus, we need to sweep NPA voltage and current in two orders of magnitude faster than L/R time in order to archive desirable 2−5 ms sweeping time. Two problems have to be solved for application of sweeping technique with the magnet. The high inductive 2
Fusion Engineering and Design 151 (2020) 111412
M.B. Dreval and A.S. Slavnyj
for NPA counting mode of operation). Thus the CX signal is high enough and does not limited the sweeping time. It should be noted, that the shape of voltage sweep in the electrostatic unit is very flexible (due to low capacitance and inductance and high resistance of the electrostatic plates circuit as well as flexible performance of ADC of STM32). The calibration from one mass to another can be, in principal, adjusted during one pulse, from one swiping scan to another. Thus the single detector NPA can, in theory, measure energy distribution of different masses in a single pulse. Although, signal corresponding to different masses can be orders of magnitude different (due to different concentrations of different ions in plasma and substantially different stripping cross-sections). An adjustment of the PMT sensitivity together with the electrostatic voltage shape is required between U-3 M pulses for different mass selection under these conditions.
Fig. 5. The diagram of the NPA control system.
3. Summary and conclusions The energy sweeping mode was used for measurement of the energy distribution of charge exchange neutrals every 3−5 ms via singlechannel electrostatic neutral particle analyzer (NPA) in the U-3 M stellarator. The magnetic mass-separation (MS) part of NPA was omitted during these energy-sweeping measurements. The MS part is required for some experimental conditions in a case when different mass ions are present in plasma and for efficient suppression of parasitic influence of plasma radiation on the NPA measurements (due to geometrical factor). New control system and power electronics of the NPA has been developed. This system allows to provide NPA measurement with MS magnet in the energy range of 0−2 keV every 5 ms in U-3 M. The time achieved for one measurement (5 ms) is an order of magnitude less than the L/R time of the NPA mass separation magnet. This fast operation is achieved by application of rather high voltage to the MS magnet. The “self-defined” strategy of the MS current shaping was used. The problem of simultaneous variation of the voltage at electrostatic part and current in MS magnet in accordance with NPA calibration is solved in our work. We use STM32F100 microprocessor as a control unit, the IGBT bridge – as a power unit of MS magnet, the digital to analog convertor unit of STM32F100 microprocessor – for the electrostatic voltage formation, the direct memory access unit of the STM32F100 microprocessor – for synchronized output of two control signals. Square wave 310 V pulses of variable duration are used for control of MS magnet current. Thus, the NPA energy distribution with improved energy resolution and mass separation can be measured by single-channel NPA using developed electronics.
Fig. 6. Evolution of: a) line-averaged plasma density, b) Hα emission, c) signal from NPA detector, d) MS current, and e) electrostatic voltage in typical frametype antenna radio frequency discharge of U-3 M.
satisfy the calibration dependence during all sweeping stages. A sequence of control pulses is stored in the internal memory of STM32 and reproduced after a trigger signal. The corresponding current waveform produced by this sequence is measured. The required for electrostatic unit analog control waveform is calculated on the base of the NPA calibration curve and is stored in the internal memory of STM32 too and reproduced after trigger signal. This method allows simultaneous current and voltage sweeping along the calibration curve in spite of strongly non-linear self-defined current waveform and the non-linear calibration curve shape. An external trigger signal is used for the sweeping cycle synchronization with the U-3 M discharge start. An interrupt technique of STM32 is used for precise synchronization of the sweeping cycle start. An optocoupler is used in the trigger line for suppression of electromagnetic interference between NPA electronics and external power electrons of U-3 M stellarator (for example via ground loops prevention). Operation of the NPA in sweeping modes with MS magnet in U-3 M are illustrated by Fig.6. The NPA sweeping along the calibration curve is produces from 12 to 45 ms of the discharge. At the initial stage of the NPA sweeping at 5−12 ms, required for initial MS current rising, the calibration dependence is not satisfied. The MS current and electrostatic voltage does not follow to the calibration curve at this initial stage. No NPA signal is consequently observed at this stage (as it is seen from Fig.6). A modification of the NPA detector signal dependence on the sweeping voltage concerns time evolution of the ion energy distribution in U-3 M. We should note, that the strong CX flux produced in typical frame-type radio frequency antenna discharges of U-3 M [3] allows analog operation of the NPA photomultiplier. The analog mode of operation of the NPA photomultiplier is used in the detector section (in spite of usual
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We would like to thank R.O. Pavlichenko for giving the line integrated electron density data, Yu.K. Mironov for providing data of Hα diagnostics and V.S. Voitseny for useful discussions. References [1] [2] [3] [4] [5] [6]
3
A.N. Karpushov, et al., Rev. Sci. Instrum. 77 (2006) 033504. V.V. Afrosimov, et al., Sov. Phys.—Tech. Phys. 5 (1961) 1378. M. Dreval, A.S. Slavnyj, Plasma Phys. Control. Fusion 53 (2011) 065014. T. Onchi, et al., Ieee Trans. Plasma Sci. 44 (2) (2016) 195. T. Onchi, et al., Fusion Eng. Des. 89 (2014) 2559. The STM32F100 Microprocessors Family Specification Available at: https://www.st. com/en/microcontrollers-microprocessors/stm32f100-value-line.html.