PhD abstract
The work of this PhD thesis is dedicated to developing a standard measurement system to ensure the SI traceability of High Pulsed Power in the Nanosecond and Subnanosecond domain (HPPNS). This traceability is mandatory for the accurate and precise measurements of the voltage waveforms which constitutes the key element of systems based on high pulsed power. A calibration system has been developed for the characterization of high voltage pulses of amplitudes up to 500 kV with rise times as low as few hundreds of picoseconds.
The developed HPPNS measurement system consists of four components: The voltage divider, the termination load, the high-voltage connectors, and the transition cones. The voltage divider is the central component of this measurement system as it permits the analysis of HPPNS waveforms through a calibrated oscilloscope by lowering the voltage amplitudes of the HPPNS waveforms to adequate levels that could be measured through an oscilloscope and without waveform deformation. Some voltage dividers of the scientific literature have been discussed and compared. The voltage divider designed through analytical and numerical calculations has a high value of the division ratio which is relatively constant as a function of frequency up to at least 2 GHz, together with a linear phase response. However, its performances in terms of measuring accurately and precisely the incident HPPNS waveforms depend also on the characteristics of the transmission line termination load since the reflections from an inadequately matched line termination load could lead to the misunderstanding of the measured waveform at the output of the divider. A 50 Ω line termination load is developed and characterized. It has high insulation properties for voltage amplitudes up to 500 kV and a maximum reflection coefficient of -27 dB as a function of frequencies up to 2 GHz.
The characterization of the complete HPPNS measurement system was carried out in two steps. Firstly, the HPPNS measurement system was characterized at low levels of input power by two different methods, namely, VNA characterization and characterization through a SI traceable high frequency attenuation measurement method. The results obtained from these two methods were compared to the CST modelling results and all of these results were found to be in good agreement with each other. These characterizations demonstrated that the developed HPPNS measurement system possesses a high division ratio of around 85 dB, a bandwidth of 2 GHz, and a linear phase response. Furthermore, a 7 GHz bandwidth commercial attenuator was added at the output of the divider and this whole system was re-characterized by both low power methods. The results obtained are as follows: almost 110 dB of division ratio, a bandwidth of 2 GHz and a linear phase response. In the second characterization step, this system was tested at high power levels through a Marx generator. Different high voltage waveforms of voltage peaks as high as 300 kV and rise times as low as 420 ps were successfully measured through this system and an uncertainty budget is drafted. The measurement uncertainties for these high voltage measurements were calculated to be 3.4 % for the voltage peaks and 87 ps for the temporal parameters.
Key words
high pulsed power, measurement standard, voltage divider, calibration, measurement uncertainty
PhD thesis
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