| Autor: |
Plewa, J. M., Eichwald, O., Yousfi, M., Wattieaux, G., Cartier, S., Cartier, F., Poulet, F., Bernigaud, V., Ribière, M., Delaunay, R., d'Almeida, T., Maisonny, R. |
| Předmět: |
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| Zdroj: |
Physics of Plasmas; Aug2018, Vol. 25 Issue 8, pN.PAG-N.PAG, 11p |
| Abstrakt: |
A high power electron diode is used to generate an intense high quality pulsed electron beam (2.6 kA, 4 MeV) in order to produce a bremsstrahlung radiation pulse for the first axis of the flash radiography facility named Epure. The plasma created by surface flashover of the velvet cathode provides a zero work function emitter used to produce the space-charge-limited electron beam. In order to optimize the design of diodes and to better understand the plasma dynamics, we have developed a 0D Collisional-Radiative Model (CRM) which describes the time-dependent evolution of the density of the plasma species in three plasma compositions: 100% H, 95% H + 5% C, and 64% H + 31% O + 5% C. The non-equilibrium electron energy distribution functions (EEDFs) are pre-calculated for a large range of electron mean energies for each mixture. EEDFs and cross sections of electron impact processes are then used to tabulate the electron rate coefficients needed to simulate the time-dependent plasma species densities. The evolution of the electron mean energy is estimated through the electron beam current density itself inferred from particle-in-cell calculations experimentally validated. Visible emission spectroscopy measurements were performed in order to investigate the plasma composition, to measure the Hα/Hβ intensity ratio, and to estimate the electron density. It was shown that the electron density in our setup is between 1014 and 1016 cm−3. Experimental results were compared to the 0D CRM. Results from the time-dependent CRM show that for the three studied plasma compositions, maximum electron densities range from 0.9 × 1014 cm−3 to 1.7 × 1014 cm−3 and that the electron energy averaged over the time interval of the electronic beam pulse is about 3.5 eV. An estimate of the electron energy inside the plasma during the relaxation provides values ranging from 0.10 eV to 0.12 eV based on comparison between the calculated and measured Hα/Hβ intensity ratio averaged over 5 μs. Moreover, main reactions involved in the evolution of the electron density were pointed out. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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