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COIL operation with iodine atoms generated in a glow discharge

COIL operation with iodine atoms generated in a glow discharge. P.A. Mikheyev , V.N. Azyazov , M.V. Zagidullin , N.I. Ufimtsev , N.A. Khvatov , A.I. Voronov. Samara Branch of P.N. Lebedev Physical Institute, Russia. Motivation. I 2 dissociation consumes ~10% of singlet oxygen molecules.

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COIL operation with iodine atoms generated in a glow discharge

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  1. COIL operation with iodine atoms generated in a glow discharge P.A. Mikheyev, V.N. Azyazov, M.V. Zagidullin, N.I. Ufimtsev, N.A. Khvatov, A.I. Voronov. Samara Branch of P.N. Lebedev Physical Institute,Russia

  2. Motivation • I2 dissociation consumes ~10% of singlet oxygen molecules. • I2 molecules are fast I* quenchers. • If iodine atoms are used instead of molecules it could increase COIL chemical efficiency up to 40% Madden et al 1998. Proc. of the Int. Conf. on Lasers '98. Carroll et al 1999. Proc. of the Int. Conf. on Lasers '99, p. 69.

  3. Creating atomic iodine • Electric discharge – most popular • Chemical reactions • I2 thermal dissociation (>1200 ˚K) Carroll et al 1999 Proc. of the Int. Conf. on Lasers '99, p. 69.

  4. History First experiments with CW COIL: CW discharges with I2 as the precursor in He carrier, RF and microwave discharges. Power enhancement at low [I2], no enhancement at optimal [I2], incomplete I2 dissociation. Endo et al 2000. Jpn.J.Appl.Phys. 39, 468; Wakazono et al 1998. Proc. SPIE. v. 3574, 290

  5. Recent history • DC discharge generation of iodine atoms in supersonic COIL resulted in increase of I2 dissociation rate. Barmashenko et al 2007. Appl. Phys. Lett., 2007, 90, 161122. • Chemical technique of iodine atom generation and experiments with the supersonic COIL. No improvement in chemical efficiency. Špalek et al 2004. Proc. SPIE. v. 5777, 181.

  6. I2 dissociation and recombination • 50-80% I2 dissociates in MW & RF discharges, decreases with [I2] Endo et al 2000. Jpn.J.Appl.Phys. 39, 468 Quillen and Schall 2003. COIL R&D Workshop, Stuttgart Due to residual [I2] the rates of recombination I+I+M  I2+M (buffer gas) I+I+I2  2I2 may be comparable at ~350 ˚K

  7. CH3I as a precursor • Vapor: 400 Torr at room temperature • Successfully used in laser experiments before Vagin et al 1995. Quant. Electron. 25 746. • DC discharge is less stable with I2 • I+I+M  I2+M

  8. I recombination in the presence of CH3I and I2 PAr – 20 Torr [I]+2[I2] – 1016 cm-3 [CH3I] – 1016 cm-3 [I2] – according to initial degree of dissociation

  9. CH3I as a precursor • Ar found to be the best carrier for a DC glow discharge ~50% of iodine was extracted out of CH3I Mikheyev et al 2002. Quant. Electron. 32, 1 • 80%[I]+20%[I2] at the outlet of the glow discharge generator Azyazov et al 2009. Quant. Electron. 39, 84

  10. Output of the electric discharge iodine generator A V Demyanov, I V Kochetov, A P Napartovich, V N Azyazov and P A Mikheyev Study of iodine atoms production in Ar/CH3I dc glow discharge Plasma Sources Science and Technology19 (2010) 025017

  11. Experiment: CH3I as a precursor • Decay rates of COIL active medium with dependence on [I*] at the I* peak • The rate of [O2(1)]removal was ~30% smaller, with iodine produced from CH3I. 50%[I]+50%[I2] mixture injected Mikheyev et al 2006. Proc. SPIE V.6346, 63460J Mikheyev and Azyazov 2008. J. Appl. Phys., 104, 123111

  12. - Ar/CH3I + Stainless steel Coaxial DC discharge iodine generator with a segmented cathode 670 Ω each Thermo stabilized at 350 ˚K

  13. DC discharge iodine generator with a segmented cathode

  14. Iodine output Idischarge – 2 A In a good agreement with the model predictions

  15. COIL with the DC discharge iodine generator and the centrifugal SOG Flow rates, mmole/s: Cl2 – 6.5; Primary He – 11; Secondary Ar – 3.5; CH3I – 0.1-0.2. H2O/O2 – 0.15. Pressure in the resonator – 8 Torr. Teflon iodine duct and rake-type injector

  16. O2(1∆) + iodine flows With I2 without electric discharge With iodine generated in the electric discharge generator

  17. COIL power output Dependence of laser output upon iodine flow rate

  18. Conclusions • The cw COIL operation with external production of iodine atoms in CH3I/Ar dc glow discharge has been demonstrated for the first time. • Four times increase of laser output was observed in experimental conditions unfavorable for a conventional COIL due to high water content and increased pressure in the resonator. • The results prove that a substantial amount of iodine atoms had been transported to the injection point. • The products of methyl iodide dissociation have little or no adverse effect on COIL performance.

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