1. 1 Div. Of Plasma Application & Tech. H 2 Retention and Physical/Chemical Evaporation Problems from the Interactions between ECR Plasma and FLiNaK Molten Salt National Fusion Research Institutes, 113 Gwahangno, Yusung-Gu, Daejeon 305-333, Korea Taihyeop Lho, Yong-Sup Choi, and HyonJae Park PMIF 2011, Julich in Germany / 19 ~21 Sep. 2011

2. 2 CPC : Convergence Plasma research Center CONTENTS of PRESENTATION  Introduction - Objectives  Experimental Setup o Plasma Parameters o Magnetic field structure  Interaction between the plasma and molten salt (FLiNaK) o Ar plasma o H 2 Plasma  Hydrogen retention  Morphology  Future Plan - Research Load Map

3. 3 CPC : Convergence Plasma research Center INTRODUCTION - OBJECTIVES  Molten salts have been suggested as the one of the liquid wall material in a fusion device.  The advantages of the liquid wall materials are heat removal, refreshing wall conditions and more.  Molten salts have low thermal conductivity which indicates low heat transfer to the structure of the device.  In addition, molten salts have low electrical conductivity (~10 2 Ω -1 m -1 ) which is relatively weak MHD effects on the surface flow comparing to the liquid lithium.  The molten salt also have low chemical reactivity and low evaporation.  However, we don’t know about the possibility of molten salts as a plasma facing material.  This research aims on the feasibility test of the possibility.

4. 4 CPC : Convergence Plasma research Center EXPERIMENTAL SET-UP Overall Review on Molten Salt Exp. System ItemsSpec. ChamberD=520 mm H=640 mm B-FieldMagnet Coil Magnet Power 100A max875 G/ 20A MW Freq.2.45 GHz MW Power2kW Max. Turbo sys.1600 lps Backing Pump 1000 lpm Gas ControlMFC, 100 sccm GasAr, H 2 Molten Salt Heater 700 o C max 100 pie FLiNa K ECR Source Process Chamber Pumping System Magnetron Magnet Power Magnetron Power

5. 5 CPC : Convergence Plasma research Center EXPERIMENTAL SET-UP PM Tube To Pumping System To DAS Thermocouple Function Gen. 640 mm Focal Length : 750mm Apeture Ratio : f/9.8 Grating : 1800 Gr/mm Resolution : ~ 0.02 nm Langmuir Probe : ¼ inch one side planar probe 520 mm Resonance Layer 150mm RGA : Stanford Laboratory

6. 6 CPC : Convergence Plasma research Center 174 mm 221mm 25mm 80 mm 91mm 55mm 20mm Molten Salt Probe position 55mm 20 MAGNETIC FIELD STRUCTURE

7. 7 CPC : Convergence Plasma research Center ■ Hydrogen Plasma density, Temperature and potential PLASMA PARAMETERS  Cylindrical Langmuir probe : Diameter 0.5 mm, Length 12 mm  Unmagnetized plasma assumption : Laframboise Analysis  Hygrogen Plasma

8. 8 CPC : Convergence Plasma research Center I.Experiment condition Base pressure: 6 ⅹ 10 -6 Torr Working pressure: 1mTorr, Ar 16 sccm ECR head input current: 17A Microwave input power: 500 watt Initial FLiNaK temp.: 28 ℃ II. Measured by monochromator Measuring range: 300~850 nm Resolution: 0.275 nm 2000 point Interaction between Ar ECR plasma and solid FLiNaK

9. 9 CPC : Convergence Plasma research Center Interaction between Ar ECR plasma and Liquid FLiNaK I.Experiment condition Base pressure: 6 ⅹ 10 -6 Torr Working pressure: 1mTorr, Ar 16 sccm ECR head input current: 17A Microwave input power: 1000 watt Initial FLiNaK temp.: 539 ℃ II. Measured by monochromator Measuring range: 300~850 nm Resolution: 0.275 nm 2000 point

10. 10 CPC : Convergence Plasma research Center  Ar plasma interaction with the molten salt  Heat load by ions and electrons to the molten salt is about 30kW/m 2 MAX  Radial density profile included  ΔT ~ 50 ℃ after plasma load (initial temperature =500 ℃ ) Resonance Layer Molten salt bath NUMERICAL SIMULATION

11. 11 CPC : Convergence Plasma research Center I.Experiment condition Base pressure: 4.3 ⅹ 10 -6 Torr Working pressure: 1mTorr, H 2 46 sccm ECR head input current: 17A Microwave input power: 500 watt Initial FLiNaK temp.: 15 ℃ II. Measured by monochromator Measuring range:300~850 nm Resolution: 0.275 nm 2000point Interaction between H 2 ECR plasma and solid FLiNaK

12. 12 CPC : Convergence Plasma research Center I.Experiment condition Base pressure: 3.9 ⅹ 10 -6 Torr Working pressure: 1mTorr, H 2 57 sccm ECR head input current: 17A Microwave input power: 500 watt Initial FLiNaK temp.: 539 ℃ II. Measured by monochromator Measuring range: 200~850 nm Resolution: 0.2 nm 3250 point Interaction between H 2 ECR plasma and liquid FLiNaK

13. 13 CPC : Convergence Plasma research Center EDS ANALYSIS - MORPHOLOGY C-K O-K F-K Na-K K-K Base_pt1 3.22 0.36 37.27 0.96 58.19 Base_pt2 1.14 0.92 59.09 9.72 29.13 C-K O-K F-K Na-K K-K Base(18)_pt1 1.51 0.64 53.05 6.35 38.44 Base(18)_pt2 1.10 61.55 8.26 29.08 Base(18)_pt3 1.79 41.38 4.46 52.37 C-KF-KNa-KK-K 4.0457.48.6229.94  EDS analysis before the interaction

14. 14 CPC : Convergence Plasma research Center RGA CALIBRATION  RGA can detect the elements from the molten salt even though without the plasma interaction.  Need RGA calibration for hydrogen retention to find the total amount of hydrogen retention. Time (sec) H 2 Pressure (Torr)

15. 15 CPC : Convergence Plasma research Center 5min RGA DATA – HF MEASUREMENT  The potasium is the main element from the molten salt evaporation.  Hydrogen fluoride formation increase with plasma interaction time.  It is possibly come from the chemical formation of HF. Plasma irradiation time 10min 20min

16. 16 CPC : Convergence Plasma research Center H 2 retention depends on the interaction time with H 2 Plasma  Measured the partial pressure of out-gassed H 2 from the molten salt surface as a reference without plasma interaction.  The difference between the measured lines and reference have been integrated with the time to convert into the total amount of the hydrogen molecules retention. H2 RETENTION - RESULTS

17. 17 CPC : Convergence Plasma research Center Plasma interaction time [sec]30060012002400 Hydrogen Dose into molten Salt [cc] 2.454.99.819.6 H 2 retention of FLiNaK [cc] 11.73.46 Ratio [%] 40.834.7 30.6 Plasma interaction time [sec]30060012002400 Hydrogen Dose into molten Salt [cc] 4.99.819.639.2 H 2 retention of FLiNaK [cc] 11.73.46 Ratio [%] 20.417.3 15.3  Considering on High Energy Neutral Particles by the Charge Exchange in the Pre-sheath  Considering only the ion bombardment on the Molten Salt H 2 RETENTION - RESULTS  Hydrogen retention mainly result from the ion flux into the molten salts.  If the charge exchange which is the high energy neutral particle formation process in the pre-sheath is considered, the retention ratio will be decreased by factor 2.

18. 18 CPC : Convergence Plasma research Center SUMMARY and FUTURE PLANS  Sodium and Potasium are main impurities from the molten salt.  Fluorine forms the Hydrogen fluoride molecules, which is very corrosive, by chemical reaction at the surface of molten salt or in the bulk plasma.  The composition of the molten salt changed with the interaction time and the position of molten salt.  The amount of hydrogen retention in the molten salt is about 30-40% when the charge exchange in the pre-sheath not included.  We need to understand some issues in the near future  The analysis methods to evaluate the composition of the molten salt.  Physical properties, especially viscosity of molten salt, after plasma interaction.  The impurities from the molten salt, quantitatively.  Influence of HF to the structure.

19. 19 CPC : Convergence Plasma research Center 1 2 3 4 1170 mm 1030 mm ECR Helicon Length of Pipe [mm] Vol. [cc] 17001374.4 2500981.7 36001178.1 4400785.4 Total volume [cc]4319.7 Total mass of molten salt [kg]2.1  Roughly request minimum Molten Salt over 4kg  Conceptual design parameters for the flowing system  Helicon and ECR are the candidates of the plasma sources CONCEPTUAL DESIGN OF THE FLOWING SYSTEM 3

20. 20 CPC : Convergence Plasma research Center FUTURE PLANS – ROAD MAP 2012 2015 2018 2020 - 2010  CPC will move to the new site in 2012.  The flowing system of the molten salt will be built.  The linear device will be operated in 2015.  New molten salt, such as FLiBe, FLiNaBe, will be studied from 2018  Molten Salt exp. in a Torus device from 2020 ?