Inductively Coupled Plasmas Supported by Laser Plasmas for High Enthalpy Flow

1. Inductively Coupled Plasmas Supported by Laser Plasmas for High Enthalpy Flow University of Tokyo O Takayoshi Inoue Susumu Uehara Kimiya Komurasaki Yoshihiro Arakawa

2. Next decade of the space exploration http://www.nap.edu/ • Report produced by “SSEDS” “New Frontiers in the Solar System： An Integrated Exploration Strategy” THE NATIONAL ACADEMIES PRESS, Washington DC, 2003. “Venus In Situ Explorer” is one of the prioritized missions

3. Venus probe Sever environment around the probe Heat flux ~ 104 W/cm2 Specific enthalpy ~ 44 MJ/kg Stagnation pressure ~ 0.7 MPa • Pioneer Venus ( 1978 ) [B.Laub, and E.Venkatapathy; Proceedings of International Workshop on Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science, Lisbon, 2003] Thermal Protection System (TPS) is a single-point-failiure subsystem • TPS performance evaluation • Development of new TPS material

4. Need in Ground Facility Atmospheric constituent of Venus Inductively Coupled Plasma (ICP) wind tunnel 96 % CO2 (H2O, SO2….) ・electrodeless ・less contamination State of development of ICP wind tunnels Power leveloperation pressure NAL/ JAXA (Japan) 100-kW IPG 1 ~ 50 　 kPa IRS ( Stuttgart Univ.) 350-kW IPG3 ~ 2 kPa von Karman Inst. 1-MW IPG3 .5 ~ 10 kPa 100-kW IPG4 1 ~ 100 kPa Mars (Current target) Venus (Next target) Higher pressure of 0.7 MPa

5. Objectives • To clarify the characteristics of • Inductively Coupled Plasma with pressure of more than 1 atm • Development of an ICP generator • Operational condition • Stability • A proposal to stabilize the ICP by using a Laser plasma

6. ICP generator RFpower supply 1.2 kW [13.56 MHz] Impedance Matching Network ICP discharge chamber Tangential flow injection ring Load coil 5 turns – 30 mm in diam. Work gas Argon

7. Atmospheric ICP generation I Set the mass flow rate to 0 g/s and the RF power output to 500 W resulting capacitively coupled plasma generation. II Gradually increased the mass flow rate and pressure coming to about 1 atm the mode transition occurred . III Once the ICP were produced, the flow rate, the pressure and RF power could be adjusted without inductive-capacitive mode transition. I II III

8. ICP instability • Video images RF power 750 W , Argon

9. Operational condition • Tangential flow effect Min. mass flow rate Pressure regulation gas : 0 g/s Tangential flow injection bores 　 2 bores 1 mm in diam. p/2 to the axis No contribution of Axial flow to the stable ICP generation

10. Operational condition • Maximum mass flow rate • Dependent on the RF power • Decrease with the pressure • Minimum mass flow rate • Independent of the RF • power • Increase with the pressure Instabilities in a high power operation in a low mass flow rate operation have been reported.

11. Tangential flow stabilization Buoyancy force Analogy with the planer geometry Stable Stable Buoyancy force Buoyancy force Gravity Centrifugal force Unstable

12. Injection rings • Diameter of the bores f Type I 2 mm Type II 1 mm Type III 0.7 mm

13. Effect of the coil location Min. mass flow rate Tangential flow injection bores 　 2 bores 1 mm in diam. p/2 to the axis The decay of tangential flow lead to the increase in the mass flow rate.

14. Injection rings • Injection angle Type IV has the angle of p/4 to the axis

15. Oscillation 15 Hz 17 Hz 34 Hz 51 Hz Light emission 68 Hz Reflected power 32 Hz CCD images

16. Oscillation frequency • Frequency v.s. Mass flow rate Strong relation between the frequency and the mass flow rate

17. Interim summary Experimental investigation on Inductively Coupled Plasmas stability were conducted , and can be summarized as follows; • ICP was stably generated with 0.1 ~ 0.4 MPa atmospheres by using 1.25 kW RF power source. • Stably operational condition became limited with the increase in the pressure. • Tangential flow injection has the essential role in the stable ICP generation though the design of the injection ring affects the operational conditions of ICPs.

18. Stable ICP generation w/o tangential flow

19. Stabilization using LASER PLASMA Requirement for the stabilization There should be some mechanisms which keep the ICP geometry axisymmetric

20. Experimental setup Specifications Condensing lens Material ZnSe Focal length 210 mm F-number 6.3 CO2 TEM00 Laser Wage length 10.6 mm Max. power 2 kW

21. Fundamental experiment Laser Lens Ignition rod LSP Focal point Coil Laser 700 W + RF 700W Laser 700 W + RF 0W

22. Fundamental experiment Laser Lens Ignition rod LSP Focal point Coil

23. Fundamental experiment Laser Lens Laser 700 W + RF 700W CCD images Ignition rod LSP Zoom of the discharge torch Focal point Laser Gas Coil Laser 700 W + RF 0W Absorbed laser power 300 W Stabilization w/o tangential flow was successfully demonstrated

24. Double tube configuration

25. LSP in the double tube configuration LSP generation limit • LSP was sustained in the inner tube stably • Operational condition was improved

26. ICP generation in the double tube configuration Z~45mm Z~30mm Z ~ 40 mm Also in the double tube configuration, ICP was generated stably w/o tangential flow injection

27. Summary • Tangential flow injection has the essential role in the stable atmospheric ICP generation though the design of the injection ring affects the operational conditions of ICPs. • By using Laser plasma, atmospheric ICP can be generated stably. • Double tube configuration enable to control the flow parameters of the LSP and ICP independently.

28. Next issues In this study…. • Modeling of the stabilization is not enough • No production of the free jet. • No discussion in terms of the enthalpy and the efficiency. Efforts should be directed to… • Establishment of an analytical model of the stability. • Acceleration of the flow by a Laval nozzle. • Evaluation of the performance of the Atmospheric ICPG and its relation with the stability

29. Other researches Herdrich, G., et.al., @ IRS J.Thermophyscs Heat Trans., Vol16, 448, 2002