New flowing afterglow apparatus, Cryo-FALP, was built to study ternary Collisional-Radiative Recombination (CRR) of Ar+ ions with electrons in He/Ar afterglow plasma at temperatures 40–200 K. The ...obtained ternary recombination rate coefficient at 57 K is KCRR = (3 ± 1) × 10−17 cm6 s−1. It is the first time that the KCRR was measured below 77 K. The measured temperature dependence KCRR ~ T(−4.5 ± 0.4) is in a good agreement with theoretical prediction.
The energy-resolved rate coefficient for the dissociative recombination (DR) of H(3)(+) with slow electrons has been measured by the storage-ring method using an ion beam produced from a ...radiofrequency multipole ion trap, employing buffer-gas cooling at 13 K. The electron energy spread of the merged-beams measurement is reduced to 500 microeV by using a cryogenic GaAs photocathode. This and a previous cold- measurement jointly confirm the capability of ion storage rings, with suitable ion sources, to store and investigate H(3)(+) in the two lowest, (J,G) = (1,1) and (1,0) rotational states prevailing also in cold interstellar matter. The use of para-H(2) in the ion source, expected to enhance para-H(3)(+) in the stored ion beam, is found to increase the DR rate coefficient at meV electron energies.
Utilizing different ratios of para to ortho H{sub 2} in normal and para enriched hydrogen, we varied the population of para-H{sub 3}{sup +} in an H{sub 3}{sup +} dominated plasma at 77 K. Absorption ...spectroscopy was used to measure the densities of the two lowest rotational states of H{sub 3}{sup +}. Monitoring plasma decays at different populations of para-H{sub 3}{sup +} allowed us to determine the rate coefficients for binary recombination of H{sub 3}{sup +} and ortho-H{sub 3}{sup +} ions: {sup p{alpha}}{sub bin}(77 K)=(1.9{+-}0.4)x10{sup -7} cm{sup 3} s{sup -1} and {sup o{alpha}}{sub bin}(77 K)=(0.2{+-}0.2)x 10{sup -7} cm{sup 3} s{sup -1}.
We attempted to compare several probe theories that described collection of charged particles by Langmuir probe at elevated pressures. We used stationary afterglow environment with well-defined ionic ...composition to measure the electron density as a function of time. Afterglow plasma has the advantage that probability of secondary electron emission from probe surface when the probe works in positive ion acceleration regime is negligible and hence the probe data are more dependable. Since estimation of the rate of recombination required knowledge of absolute values of plasma density, we were able, in case of the ions the rate of recombination of which was known, to calculate the electron density, which corresponded to the known rate of recombination. Consequently we were able to compare apparent electron density calculated from the probe data using different theories with the “reference” electron density that we obtained from the known rate of recombination. Up to several mbar pressure the differences between the “reference” value of electron density and value calculated using the collisionless theories of electron collection by Langmuir probe stay within reasonable error limits.
Results of an experimental study of binary recombination of para- and ortho-Formula ions with electrons are presented. Near-infrared cavity-ring-down absorption spectroscopy was used to probe the ...lowest rotational states of Formula ions in the temperature range of 77-200 K in an Formula-dominated afterglow plasma. By changing the para/ortho abundance ratio, we were able to obtain the binary recombination rate coefficients for pure Formula and Formula. The results are in good agreement with previous theoretical predictions.
The segmented hollow-cathode discharge arrangement is used the first time to excite the 224 nm Ag II laser transition. Quasi-continuous output power of 45 mW is obtained during the 300 ...{/content/PL5CRTPGA5NCELH6/xxlarge956.gif}s current pulses at optimal discharge conditions (10 hPa of He+4% Ar buffer gas) for discharge current of 3 A. No power saturation is observed up to this current value. An average output power of 0.75 mW is reached using pulse repetition frequency of 190 Hz. The longitudinal mode structure of the TEM00 transversal mode is measured by means of a scanning confocal Fabry--Perot interferometer. Two-mode operation is found to be dominant at high current values. Attempts and suggestions are made to prolong the lifetime of the laser tube.
Recombination rate coefficients of protonated and deuterated ions KrH
+, KrD
+, XeH
+ and XeD
+ were measured using Flowing Afterglow with Langmuir Probe (FALP). Helium at 1600
Pa and at temperature ...250
K was used as a buffer gas in the experiments. Kr, Xe, H
2 and D
2 were introduced to a flow tube to form the desired ions. Because of small differences in proton affinities of Kr, D
2 and H
2 mixtures of ions, KrD
+/D
3
+ and KrH
+/H
3
+ are formed in the afterglow plasma, influencing the plasma decay. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The obtained rate coefficients,
α
KrD+(250
K)
=
(0.9
±
0.3)
×
10
−8
cm
3
s
−1 and
α
XeD+(250
K)
=
(8
±
2)
×
10
−8
cm
3
s
−1 are compared with
α
KrH+(250
K)
=
(2.0
±
0.6)
×
10
−8
cm
3
s
−1 and
α
XeH+(250
K)
=
(8
±
2)
×
10
−8
cm
3
s
−1.
Experimental studies of the electron energy distribution function “EEDF” under well defined conditions in flowing afterglow plasma, using a Langmuir probe are reported. The EEDF is measured in He
2
+
...and Ar
+
dominated plasmas and in XeH
+
and XeD
+
dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is observed. The mechanism of energy balance in afterglow plasma is discussed.
The results of measurements in low temperature Ar super(+) dominated afterglow plasma are presented. The study was realized using Cryo-FALP apparatus operable in temperature range 77 - 300 K and at ...pressures 200 - 2000 Pa. We have observed decay of electron number density due to collisional radiative recombination (CRR). The measured ternary recombination rate coefficient of CRR of Ar super(+) ions with electrons and its temperature dependence are in good agreement with theoretical predictions of T super(-4.5) dependence.
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