- Email: [email protected]
Glow discharges in superatmospheric CO2-N2-He gas mixtures in a Lamberton-Pearson device
Volume 55A, number 5
PHYSICS LEUERS
29 December 1975
GLOW DISCHARGES IN SUPERATMOSPHERIC C02-N2-He GAS MIXTURES IN A LAMBERTON-PEARSON DEVICE Ch. HOMANN and H. HUBNER Inrtitut fur Plasmaphysik, Technische UniversitIt Hannover, D 3000 Hannover, Germany Received 28 October 1975 Glow discharges were produced in C02-N2-He-mixtures at pressures up to 3 at using a set-up of the LambertonPearson type. Input energies of more than 400 J 1~at~were attained.
The operation of CO2 laser amplifiers at pressures above 1 at results not only in the storage of higher energy densities as a consequence of the larger number density of CO2 molecules but also in a larger amplification of subnanosecond pulses because of the overlap of rotational levels. As to the experimental devices self.sustained discharges working with auxiliary discharges are much easier to realize than non-self-sustained discharges using electron beams. On comparing double discharge techniques known today [1—3]to devices of the Lamberton-Pearson type the latter are the simplest ones because a synchronization of several discharges is not necessary. Since no results have been published about this type for pressures above 1 at we studied the conditions of igniting glow discharges for this discharge type at pressures of several atmospheres. The experimental set-up is shown in fig. 1. The length of the Chang-shaped [4] electrodes is 34 cm, their width is 7.5 cm, and the electrode distance is 1.906 ±0.003 cm. The two trigger wires T (tungsten, 0.1 mm in diameter) are fastened at a distance of 7.5 cm to one another and are located symmetrically to the main electrodes. The discharges are fired with the capacitances C listed in fig. 1. The charging voltages U go up to 40 kV. Before filling with the gas mixture the discharge tube is evacuated to about 3 X 10—2 torr. The gas mixture consists of C02, N2, and He. Sometimes the gas is doped by an addition of xylene or tripropylamine. Thetorr volume themaximum apparatuspressure is 10 1, the rate 10—2 1 s1,ofthe 3 at.leakage The glow discharges are identified by side-on and end-on photographs of the discharge and by the measurement of the electric current which must be over-
6
•~
“Cc C
III iI~IlftI
L
CT
Cc
~
/
U Fig. 1. Electrical circuit. C storage capacitors, 9, 20, 40, 200 nF; Cc coupling capacitors 400 pF; T Trigger wires (0.1 mm diameter); U charging voltage.
The discharge current is measured by use of the Faraday rotation of a 5-mW-He-Ne-laser beam in an ap. propriate glass rod embedded in the collector insulation. Rise times of less than 10 ns and sensitivities of 0.17 mV/kA are realized. The peak currents are in the range of 5-kA, full width at half maximum is about 300 ns. Both values depend on gas composition and pressure. The photographs show that the glow discharge fills a volume of V 0.19 1. The end-on photographs show that the light intensity decreases from the trigger wires to the middle of the discharge volume. Furthermore the photographs show that the band of constricted discharges from the wires to the sides of the main electrodes mentioned by [5, 6] also exist at higher pressures. The maximum pressure p at which glow discharges can be fired in at least 9 out of 10 shots is measured as a function of the pressure of He when CO2 : N2 = 1:1.2/V Theand parameters are the C. input E the capacitance Theenergy resultsdensity are shown = CU in fig. 2. As it can be expected p increases with increasing amounts of helium and by the addition of a doping. A variation of the amount of xylene or tripropylamine shows for a mixture CO 2 : N2 : He 1: 1: 1 with
damped. 287
Volume 55A, number S
PHYSICS LEfl’ERS
C(nFIED/1]
9 ~ 9 ~ 20 50 ~0 90
btl
200 ~80~ 1-
29 December 1975
not deteriorated when 6 torr oxygen are added to the 3% along their whole length. The intensity of the discharge, however, is greater in regions of higher electric field strength when this variation is above 2%. gas mixture or when the electrode distance varies for The authors wish to thank W. Bötticher for many helpful discussions.
2N2~11 i-
50
60
70
80
f%He]
References
Fig 2. Maximum pressure p as a function of He-amount in laser-gas for different input energy densities. *with doping
C = 9 nF and E = 53 J/l that the maximum pressure p for glow ignition cannot be increased further when 1/8 of the saturation pressure of the doping vapor is attained. FortheparametersCo2:N2:Herl:1:8,C9nF, p = 1.2 at, and E = 33.6 JIl, i.e. well below the attainable maximum pressure the quality of the discharge is
288
11] A.J. Alcock, K. Leopold and M.C. Richardson, Appi. Phys. Lett. 23 (1973) 562. 121 A.J. Alcock and A.C. Walker, App!. Phys. Lett. 25 (1974) 299. [3] M. Blanchard, J. Gilbert, F. Rheault, J.L. Lachambre, R. Fortin and R. Tremblay, J. Appi. Phys. 45 (1974) 1311. [4] T.Y. Chang, Rev. Sci. Instr. 44 (1973)405. [5] H.M. Lamberton and P.R. Pearson, Electron. Lett. 7 (1971)141. [6] P.R. Pearson and H.M. Lamberton, IEEE J. Quant. Electr. QE-8 (1972) 145.
PHYSICS LEUERS
29 December 1975
GLOW DISCHARGES IN SUPERATMOSPHERIC C02-N2-He GAS MIXTURES IN A LAMBERTON-PEARSON DEVICE Ch. HOMANN and H. HUBNER Inrtitut fur Plasmaphysik, Technische UniversitIt Hannover, D 3000 Hannover, Germany Received 28 October 1975 Glow discharges were produced in C02-N2-He-mixtures at pressures up to 3 at using a set-up of the LambertonPearson type. Input energies of more than 400 J 1~at~were attained.
The operation of CO2 laser amplifiers at pressures above 1 at results not only in the storage of higher energy densities as a consequence of the larger number density of CO2 molecules but also in a larger amplification of subnanosecond pulses because of the overlap of rotational levels. As to the experimental devices self.sustained discharges working with auxiliary discharges are much easier to realize than non-self-sustained discharges using electron beams. On comparing double discharge techniques known today [1—3]to devices of the Lamberton-Pearson type the latter are the simplest ones because a synchronization of several discharges is not necessary. Since no results have been published about this type for pressures above 1 at we studied the conditions of igniting glow discharges for this discharge type at pressures of several atmospheres. The experimental set-up is shown in fig. 1. The length of the Chang-shaped [4] electrodes is 34 cm, their width is 7.5 cm, and the electrode distance is 1.906 ±0.003 cm. The two trigger wires T (tungsten, 0.1 mm in diameter) are fastened at a distance of 7.5 cm to one another and are located symmetrically to the main electrodes. The discharges are fired with the capacitances C listed in fig. 1. The charging voltages U go up to 40 kV. Before filling with the gas mixture the discharge tube is evacuated to about 3 X 10—2 torr. The gas mixture consists of C02, N2, and He. Sometimes the gas is doped by an addition of xylene or tripropylamine. Thetorr volume themaximum apparatuspressure is 10 1, the rate 10—2 1 s1,ofthe 3 at.leakage The glow discharges are identified by side-on and end-on photographs of the discharge and by the measurement of the electric current which must be over-
6
•~
“Cc C
III iI~IlftI
L
CT
Cc
~
/
U Fig. 1. Electrical circuit. C storage capacitors, 9, 20, 40, 200 nF; Cc coupling capacitors 400 pF; T Trigger wires (0.1 mm diameter); U charging voltage.
The discharge current is measured by use of the Faraday rotation of a 5-mW-He-Ne-laser beam in an ap. propriate glass rod embedded in the collector insulation. Rise times of less than 10 ns and sensitivities of 0.17 mV/kA are realized. The peak currents are in the range of 5-kA, full width at half maximum is about 300 ns. Both values depend on gas composition and pressure. The photographs show that the glow discharge fills a volume of V 0.19 1. The end-on photographs show that the light intensity decreases from the trigger wires to the middle of the discharge volume. Furthermore the photographs show that the band of constricted discharges from the wires to the sides of the main electrodes mentioned by [5, 6] also exist at higher pressures. The maximum pressure p at which glow discharges can be fired in at least 9 out of 10 shots is measured as a function of the pressure of He when CO2 : N2 = 1:1.2/V Theand parameters are the C. input E the capacitance Theenergy resultsdensity are shown = CU in fig. 2. As it can be expected p increases with increasing amounts of helium and by the addition of a doping. A variation of the amount of xylene or tripropylamine shows for a mixture CO 2 : N2 : He 1: 1: 1 with
damped. 287
Volume 55A, number S
PHYSICS LEfl’ERS
C(nFIED/1]
9 ~ 9 ~ 20 50 ~0 90
btl
200 ~80~ 1-
29 December 1975
not deteriorated when 6 torr oxygen are added to the 3% along their whole length. The intensity of the discharge, however, is greater in regions of higher electric field strength when this variation is above 2%. gas mixture or when the electrode distance varies for The authors wish to thank W. Bötticher for many helpful discussions.
2N2~11 i-
50
60
70
80
f%He]
References
Fig 2. Maximum pressure p as a function of He-amount in laser-gas for different input energy densities. *with doping
C = 9 nF and E = 53 J/l that the maximum pressure p for glow ignition cannot be increased further when 1/8 of the saturation pressure of the doping vapor is attained. FortheparametersCo2:N2:Herl:1:8,C9nF, p = 1.2 at, and E = 33.6 JIl, i.e. well below the attainable maximum pressure the quality of the discharge is
288
11] A.J. Alcock, K. Leopold and M.C. Richardson, Appi. Phys. Lett. 23 (1973) 562. 121 A.J. Alcock and A.C. Walker, App!. Phys. Lett. 25 (1974) 299. [3] M. Blanchard, J. Gilbert, F. Rheault, J.L. Lachambre, R. Fortin and R. Tremblay, J. Appi. Phys. 45 (1974) 1311. [4] T.Y. Chang, Rev. Sci. Instr. 44 (1973)405. [5] H.M. Lamberton and P.R. Pearson, Electron. Lett. 7 (1971)141. [6] P.R. Pearson and H.M. Lamberton, IEEE J. Quant. Electr. QE-8 (1972) 145.