Hot electron studies in the Minimafios ECR ion source

Abstract

The experimental data obtained by three different measurements related to the hot electron population involved in ion stripping in an electron cyclotron resonance ion source (ECRIS), i.e., electron cyclotron emission, bremsstrahlung x-ray radiation, and diamagnetism are presented and shortly discussed. The volume-averaged electron energy essentially depends upon the working pressure, and does not vary much with the rf power, at least above 200 W. The main effect of increasing the rf power is to raise the electron density.

Investigation of the density and temperature of electrons in a compact 2.45 GHz electron cyclotron resonance ion source plasma by x-ray measurements

“…Although one would expect a positive relationship of the temperature with microwave power, it is known that the high-energy electrons are pushed into the loss cone of the magnetic confinement by the microwave field and thus the hot electrons are lost [14]. Such a flat response with increasing microwave power, above an initial rise, has been observed in other ECR sources, though at higher electron temperatures because of the higher microwave frequencies used in these sources [8,9]. The second result is that the electron temperature amounts to about T e ≈ 2 keV for all four gases.…”

“…Note that this electron temperature is in good agreement with recent measurements of T e1 ranging from 3 to 5 keV from [6,7,15], considering that that group used a 7.25 GHz ECR ion source. In addition to this hot electron population a second population is typically found with electron temperatures T e2 in the range of 25-80 keV [6][7][8][9]15]. Given the much higher temperature of the second population, the hot population with T e1 is often referred to as the 'warm' electron population.…”

“…To the best of our knowledge nobody has ever measured the electron temperature and density in such a small and compact 2.45 GHz ECRIS. Of course there exist values from several ECRIS models and measurements from comparable sources, but these sources are not that compact or work at higher frequencies [5][6][7][8][9].…”

Correlation of bremsstrahlung and energy distribution of escaping electrons to study the dynamics of magnetically confined plasma

“…These studies can be characterised based on whether or not the obtained results provide spatially and/or temporally resolved information, as well as based on the origin of the measured bremsstrahlung (plasma emission, thick target radiation induced by escaping electrons). Techniques resulting to volume integrated and time averaged results have been used most widely to probe the general plasma properties [6][7][8][9][10][11][12][13][14][15][16], but there has been also significant development in the use of spatially [17,18] and temporally [19] resolved methods. However, unambiguous de-convolution of either thick-target (wall) or plasma bremsstrahlung spectra to obtain the electron energy distribution (EED) of the escaping or confined electrons is seemingly impossible despite some notable efforts [13,20,21].…”

Upgrades and developments related to stable ion beams injectors at INFN-LNL

“…The position giving the best yield was found to be at around 5 cm from the plasma, by applying -700 V to the sputtering rod: figure 4 shows the charge states distribution obtained in this condition. By comparing the performances with those reported in [6], it can be seen that the The results described above convinced us to start the procedure for the authorization to employ Uranium. In the meantime, further experiments will be carried out in 2023 to further validate the results and to test slightly different target geometries.…”