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Browsing by Author "Sadowski, Marek"

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    Investigation of plasma compression in the PF-24 device with the use of different Z working gases
    (Institute of Nuclear Physics Polish Academy of Sciences, 2020) Marciniak, Łukasz; Kulińska, Agnieszka; Sadowski, Marek; Szydłowski, Adam
    The work addresses the problem of radiative compression of electron-ion plasma occurrence and conditions during electric discharges in the z-pinch type devices. Also, the issue of the plasma radiative compression influence on the total neutron emission from nuclear fusion of deuterium nuclei is addressed. The plasma radiative compression is the phenomenon which should theoretically appear during high current conducting electric discharges in working gases having relatively high Z atomic number in comparison to deuterium (Z = 1), which are pinched with self-generated magnetic field pressure. When these types of gases are used the X-ray radiation losses during discharge are significant leading to cooling of the plasma, smaller internal pressures and possibly enable the compression to smaller sizes and higher densities. Moreover, the discharges in the mixtures of deuterium with noble gases, in which strong radiative compression has developed, may potentially produce more neutrons from the fusion of deuterium nuclei on average, despite the lower initial D2 pressure. The conducted researches are based on: 54 theoretical discharges, 123 experimental discharges and 123 computed discharges in D2, Ar and D2+Ar mixtures under constant initial total pressure of about 2.9 mbar. The experimental discharges were performed in the plasma-focus PF-24 device, which is a type of dynamic non-cylindrical z-pinch type plasma generator and the nuclear fusion device with magnetic confinement, under the 17 kV of charging voltage and the 16.8 kJ of energy storage. During the experimental part of research 3 diagnostic systems were used: the Rogowski coil, the magnetic probe and the neutron counter. They were used to obtain: the total discharge current trace, the derivative of total discharge current over time trace and the total number of counts, during each experimental discharge. The obtained electric traces and number of counts enabled to determine the 6 different measured parameters describing behavior of plasma during each discharge. On the other hand, the theoretical and computed discharges were performed using the 5-phase Lee model code, which enables simulation of approximately all phases of discharge in any plasma-focus type device. Wherein, the 123 computed discharges have been connected to experimental discharges (123 coupled experimental-computed discharges) using the total discharge current fitting technique. The results obtained using the 5-phase Lee model code enabled to determine the 37 computed parameters and the 6 computed radiative compression indicators describing the behavior of plasma for each investigated discharge. The obtained theoretical results showed strong plasma radiative compression phenomenon occurrence for discharges in the 1.70-4.20 mbar of initial Ar pressures and in x = 50-95% of Ar fraction in the (100-x)D2+xAr mixtures. While for all the theoretical discharges in D2, in 0.50-1.60 mbar and 4.50-5.00 mbar of initial Ar pressures and in x = 1-45% of Ar fractions in the (100-x)D2+xAr mixtures weak or non-existent radiative compression phenonmenon was stated. Moreover, the obtained experimental-computed results showed strong radiative compression phenomenon occurrence for only half of discharges in about 1.2 mbar of Ar. While for all the discharges in D2, the other half of discharges in Ar (also about 1.2 mbar) and in all the discharges in x = 3-60% of Ar fractions in (100-x)D2+xAr mixtures weak or non-existent radiative compression phenomenon was stated. The main reason of this state is to be the too low total X-ray line radiation emission power. The main parameters influencing strong radiative compression occurrence were stated as: the total yield of X-ray line radiation, the initial plasma pinch radius, the initial ion temperature and the initial ion number density. These parameters determine the radiative compression phenomenon occurrence during single discharge including its strength. Thus, they should be more accurate in comparison to the standard indicators used: the reduced Pease-Braginskii current, the radiation depletion time, etc. Also, no increase in the average total yield of fusion neutrons was stated for discharges in 3-60% of Ar fraction in (100-x)D2+xAr mixtures under constant initial pressure. The main reason of this is the decrease in deuterium ion number densities due to the decrease in initial pressures and deuterium fractions and the special changes in electro-kinetics/dynamics of discharges.