Hard X-ray emission by clusters in an intense femtosecond laser field during collective recombination

Collisional recombination in strongly coupled plasmas

“…The Killian-Rolston experiment [9] is the first where the collisional recombination rate is measured for SCP. It is discovered that only about 20% of ions recombined for 10 2 μs in the plasma with the electron number density 10 10 cm −3 and temperature 1 K. It gives the estimation of the recombination rate as 2.3 × 10 −6 τ −1 e in agreement with the value 2.6×10 −6 τ −1 e which follows from (5). This comparison is only of qualitative value, since some subsequent theoretical and experimental papers on ultracold plasmas [24][25][26] have shown that the electron temperature varies during the evolution of the plasma and the electron Coulomb coupling parameter rapidly (within the first microsecond) goes to about = 0.2.…”

“…Another argument is figure 1(b) which shows that the energy region adjoining to the ionization limit is the bottleneck for the collisional recombination as is mentioned above. Since the one-step jump across the 'gap' becomes the limiting recombination mechanism for SCP, the dependence of the recombination rate is supplemented by the additional exponential terms in (5) which can be interpreted as a probability for an electron to overcome the 'gap'. Two effects can be distinguished.…”

“…It is well studied for ideal plasmas [1,2]. It is also essential for strongly coupled plasmas (SCP) in a cluster [3][4][5], latent track [6][7][8] and ultracold [9][10][11] cases when multiple ionization is included (ions with charge Z > 1). Different approximations are used to analyze the influence of nonideality on the recombination [12][13][14][15][16][17][18][19][20].…”

X-ray generation by electron photo-recombination in charged atomic clusters formed in intense femtosecond laser pulses

“…According to our results [14,15], for a uniformly charged cluster the maximum photo-recombination cross section is…”

“…(1) the remaining electrons concentrate in the central region of the cluster: this leads to a neutral cluster core; a positive charged surface region consists only of positive atomic ions; this assumption corresponds to a statistical equilibrium of the electron cloud; (2) the remaining electrons are distributed uniformly within the whole charged cluster ball because of their high velocities (non-equilibrium distribution). In [14,15], we considered photo-recombination of ejected electrons into the charged cluster, considering using as a quantum-mechanical potential well, the second assumption about uniform electron distribution inside the cluster.…”