Number Of Fast Ions Research Articles

Laser-plasma debris from a rotating cryogenic–solid-Xe target

We investigate the characteristics of laser plasma debris that is responsible for damaging optics. The debris is composed of fast ions, neutral particles, and fragments, and originates from a solid Xe target on a rotating drum that we developed as an extreme ultraviolet (EUV) source. The ice fragments appear to be a problem most notably with solid Xe targets; however, we find that the damage induced by Xe ice fragments can be avoided by simply reducing the laser pulse energy. We find the number of fast neutral particles to be an order of magnitude less than the number of ions, and we clarify that the plasma debris is primarily composed of fast ions. In addition, we find that the number of fast ions having a few dozen keV of energy decreases when using the rotating target compared with the rest target. We attribute this to a gas curtain effect from the Xe gas localized at the rotating target surface. We estimate the sputtering rate of the Mo/Si mirror, which is caused primarily by the fast ions, to be 104 nm/1x10(6) shots at 190 mm from the source plasma and at an 11.25 degree angle from the incident laser beam. Up to the 1x10(6) shots exposure, remarkable degradation of the mirror reflectivity is not observed though the sputtering damages the mirror. Mitigation of the ions by using gas and/or magnetic fields will further improve the mirror lifetime. By comparing with a liquid jet Xe target, we conclude that the sputtering rate per conversion efficiency when using the solid Xe targets on the rotating drum is the same as that when using the liquid Xe targets. The high conversion efficiency of 0.9% in the rotating drum solid Xe target makes this technique useful for developing laser plasma EUV sources.

"Cooperativity blockage" in the mixed alkali effect as revealed by molecular-dynamics simulations of alkali metasilicate glass.

The relaxation dynamics of a complex interacting system can be drastically changed when mixing with another component having different dynamics. In this work, we elucidate the effect of the less mobile guest ions on the dynamics of the more mobile host ions in mixed alkali glasses by molecular-dynamics (MD) simulations. One MD simulation was carried out on lithium metasilicate glass with the guest ions created by freezing some randomly chosen lithium ions at their initial locations at 700 K. A remarkable slowing down of the dynamics of the majority mobile Li ions was observed both in the self-part of the density-density correlation function, Fs(k,t), and in the mean-squared displacements. On the other hand, there is no significant change in the structure. The motion of the Li ions in the unadulterated Li metasilicate glass is dynamically heterogeneous. In the present work, the fast and slow ions were divided into two groups. The number of fast ions, which shows faster dynamics (Levy flight) facilitated by cooperative jumps, decreases considerably when small amount of Li ions are frozen. Consequently there is a large overall reduction of the mobility of the Li ions. The result is also in accordance with the experimental finding in mixed alkali silicate glasses that the most dramatic reduction of ionic conductivity occurs in the dilute foreign alkali limit. Similar suppression of the cooperative jumps is observed in the MD simulation data of mixed alkali system, LiKSiO3. Naturally, the effect found here is appropriately described as "cooperativity blockage." Slowing down of the motion of Li ions also was observed when a small number of oxygen atoms chosen at random were frozen. The effect is smaller than the case of freezing some the Li ions, but it is not negligible. The cooperativity blockage is also implemented by confining the Li metasilicate glass inside two parallel walls formed by freezing Li ions in the same metasilicate glass. Molecular-dynamics simulations were performed on the dynamics of the Li ions in the confined glass. Slowing down of the dynamics is largest near the wall and decreases monotonically with distance away from the wall.

Selective Acceleration of NBI-injected Fast Ions by Ion Cyclotron Wave in a Tokamak Plasma

The acceleration of NBI-injected fast ions by ICRF waves has been studied in the TORIUT-5 tokamak. The velocity distribution of fast ions has been measured by a neutral-particle analyzer. The number of fast ions with energies higher than the injected energy is found to be increased by the ICRF acceleration effect. The experiment is consistent with numerical simulations.

Free expansion of a plasma with two electron temperatures

A theory for the free expansion of a plasma with two electron temperatures is presented. It is shown that in the case of a laser-produced plasma expansion the ions separate into a fast and a slow component, and that the number of fast ions is particularly sensitive to the hot to cold electron temperature ratio. If the electron temperature ratio is ≳ 10 then the quasi-neutral self-similar solution breaks down. The regions in the rarefaction expansion where the quasi-neutrality assumption fails are discussed.

Results of the dutch cosmic ray expedition 1933: IX. The ionisation-balance for cosmic rays on the ocean

Summary In the following pages the results are given of the measurements of the number and the average life of ions, and of the number of charged and uncharged condensation-nuclei in the air on the open sea. The number of fast ions was constantly recorded with the aid of an Ebert-aspirator combined with an electrometer-triode. We watched the diurnal variation in Bandoeng, the influence of our approach to the coast, of fog and of rain and we tried to determine the mobility-spectrum. The average of all the measurements of ions caught in the aspirator was 213 ions per cc of air. Following Schweid1er's “Method II” the “half-value voltage” was determined; as an average we find H = 0.80 Volt, corresponding to an average life ϑ = 63 sec. Calculation of the ionisation on the ocean from the balance (see preceding paper) gives as an average q = 2,0 J, in sufficient agreement with the value q between 1,8 and 2,1 J, due to cosmic radiation only.