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

Creating atomic iodine Electric discharge – most popular Electric discharge – most popular Chemical reactions Chemical reactions I 2 thermal dissociation (>1200 ˚K) I 2 thermal dissociation (>1200 ˚K) Carroll et al 1999 Proc. of the Int. Conf. on Lasers '99, p. 69.

History First experiments with CW COIL: CW discharges with I 2 as the precursor in He carrier, RF and microwave discharges. Power enhancement at low [I 2 ], no enhancement at optimal [I 2 ], incomplete I 2 dissociation. Endo et al Jpn.J.Appl.Phys. 39, 468; Wakazono et al Proc. SPIE. v. 3574, 290

Recent history DC discharge generation of iodine atoms in supersonic COIL resulted in increase of I 2 dissociation rate. DC discharge generation of iodine atoms in supersonic COIL resulted in increase of I 2 dissociation rate. Barmashenko et al Appl. Phys. Lett., 2007, 90, Chemical technique of iodine atom generation and experiments with the supersonic COIL. No improvement in chemical efficiency. Chemical technique of iodine atom generation and experiments with the supersonic COIL. No improvement in chemical efficiency. Špalek et al Proc. SPIE. v. 5777, 181.

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

CH 3 I as a precursor Vapor: 400 Torr at room temperature Vapor: 400 Torr at room temperature Successfully used in laser experiments before Successfully used in laser experiments before Vagin et al Quant. Electron DC discharge is less stable with I 2 DC discharge is less stable with I 2 I+I+M  I 2 +M I+I+M  I 2 +M M k, cm 6 /c; 350 K Ar 5.3  10 ‑ 33 CH 3 I 2.5  10 ‑ 31 I2I2I2I2 1.8  10 ‑ 30

I recombination in the presence of CH 3 I and I 2 P Ar – 20 Torr [I]+2[I 2 ] – cm -3 [CH 3 I] – cm -3 [I 2 ] – according to initial degree of dissociation

CH 3 I as a precursor Ar found to be the best carrier for a DC glow discharge ~50% of iodine was extracted out of CH 3 I Ar found to be the best carrier for a DC glow discharge ~50% of iodine was extracted out of CH 3 I Mikheyev et al Quant. Electron. 32, 1 80%[I]+20%[I 2 ] at the outlet of the glow discharge generator 80%[I]+20%[I 2 ] at the outlet of the glow discharge generator Azyazov et al Quant. Electron. 39, 84

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/CH 3 I dc glow discharge Plasma Sources Science and Technology 19 (2010)

Experiment: CH 3 I as a precursor Decay rates of COIL active medium with dependence on [I*] at the I* peak Decay rates of COIL active medium with dependence on [I*] at the I* peak The rate of [O 2 ( 1  )] removal was ~30% smaller, with iodine produced from CH 3 I. 50%[I]+50%[I 2 ] mixture injected The rate of [O 2 ( 1  )] removal was ~30% smaller, with iodine produced from CH 3 I. 50%[I]+50%[I 2 ] mixture injected Mikheyev et al Proc. SPIE V.6346, 63460J Mikheyev and Azyazov J. Appl. Phys., 104,

Coaxial DC discharge iodine generator with a segmented cathode 670 Ω each - + Ar/CH 3 I Stainless steel Thermo stabilized at 350 ˚K

DC discharge iodine generator with a segmented cathode

Iodine output In a good agreement with the model predictions I discharge – 2 A

COIL with the DC discharge iodine generator and the centrifugal SOG Flow rates, mmole/s: Cl 2 – 6.5; Primary He – 11; Secondary Ar – 3.5; CH 3 I – H 2 O/O 2 – Pressure in the resonator – 8 Torr. Teflon iodine duct and rake-type injector

O 2 ( 1 ∆) + iodine flows With iodine generated in the electric discharge generator With I 2 without electric discharge

COIL power output Dependence of laser output upon iodine flow rate

Conclusions The cw COIL operation with external production of iodine atoms in CH 3 I/Ar dc glow discharge has been demonstrated for the first time. The cw COIL operation with external production of iodine atoms in CH 3 I/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. 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 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. The products of methyl iodide dissociation have little or no adverse effect on COIL performance.