Evaluating Hydrogen Retention and Evaporation Challenges in ECR Plasma - FLiNaK Molten Salt Interactions

1. H2 Retention and Physical/Chemical Evaporation Problems from the Interactions between ECR Plasma and FLiNaK Molten Salt TaihyeopLho, Yong-Sup Choi, and HyonJae Park National Fusion Research Institutes, 113 Gwahangno, Yusung-Gu, Daejeon 305-333, Korea PMIF 2011, Julich in Germany / 19 ~21 Sep. 2011 Div. Of Plasma Application & Tech. 1

2. CONTENTS of PRESENTATION • Introduction - Objectives • Experimental Setup • o Plasma Parameters • o Magnetic field structure • Interaction between the plasma and molten salt (FLiNaK) • oAr plasma • o H2 Plasma • Hydrogen retention • Morphology • Future Plan - Research Load Map

3. 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 conductivitywhich indicates low heat transfer to the structure of the device. • In addition, molten salts have low electrical conductivity (~102Ω-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. EXPERIMENTAL SET-UP • Overall Review on Molten Salt Exp. System Magnetron ECR Source Process Chamber Magnet Power MagnetronPower Pumping System

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

6. 174 mm MAGNETIC FIELD STRUCTURE 80 mm 221mm 91mm 25mm 55mm 20mm 55mm Probe position 20 MoltenSalt

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

8. Interaction between Ar ECR plasma and solid FLiNaK Experiment condition Base pressure: 6ⅹ10-6Torr 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

9. Interaction between Ar ECR plasma and Liquid FLiNaK Experiment condition Base pressure: 6ⅹ10-6Torr 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. NUMERICAL SIMULATION Resonance Layer Molten salt bath • Ar plasma interaction with the molten salt • Heat load by ions and electrons to the molten salt is about 30kW/m2 MAX • Radial density profile included • ΔT ~ 50℃ after plasma load (initial temperature =500 ℃)

11. Interaction between H2 ECR plasma and solid FLiNaK Experiment condition Base pressure: 4.3ⅹ10-6Torr Working pressure: 1mTorr, H2 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

12. Interaction between H2 ECR plasma and liquid FLiNaK Experiment condition Base pressure: 3.9ⅹ10-6Torr Working pressure: 1mTorr, H2 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

13. EDS ANALYSIS - MORPHOLOGY • EDS analysis before the interaction

14. 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. H2 Pressure (Torr) Time (sec)

15. RGA DATA – HF MEASUREMENT Plasma irradiation time Plasma irradiation time 10min 5min Plasma irradiation time 20min • 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.

16. H2 RETENTION - RESULTS H2 retention depends on the interaction time with H2 Plasma • Measured the partial pressure of out-gassed H2from 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.

17. H2 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. • Considering only the ion bombardment on the Molten Salt • Considering on High Energy Neutral Particles by the Charge Exchange in the Pre-sheath

18. 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. CONCEPTUAL DESIGN OF THE FLOWING SYSTEM • Roughly request minimum • Molten Salt over 4kg • Conceptual design parameters • for the flowing system ECR Helicon 2 1170 mm 1 3 • Helicon and ECR are the • candidates of the plasma sources 3 4 1030 mm

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