div. of plasma application & tech

1 Div. Of Plasma Application & Tech.

H2 Retention and Physical/Chemical Evaporation Problems from the Inter-actions between ECR Plasma and FLi-

NaK 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 CPC : Convergence Plasma research Center

CONTENTS of PRESENTA-TION

Introduction - Objectives Experimental Setup o Plasma Parameters o Magnetic field structure Interaction between the plasma and molten salt (FLiNaK) o Ar plasma o H2 Plasma Hydrogen retention Morphology Future Plan - Research Load Map


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, re-freshing 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 (~102 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 evapo-ration. 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.


EXPERIMENTAL SET-UPOverall Review on Molten Salt Exp. System

Items Spec.Chamber D=520 mm

H=640 mmB-Field Magnet CoilMagnet Power

100A max 875 G/ 20A

MW Freq. 2.45 GHzMW Power 2kW Max.Turbo sys. 1600 lpsBacking Pump

1000 lpm

Gas Con-trol

MFC, 100 sccm

Gas Ar, H2

Molten Salt Heater

700 oC max 100 pie

FLi-NaK

ECR Source

Process Cham-ber

Pump-ing Sys-tem

Magnetron

Magnet Power

Mag-netron-Power


EXPERIMENTAL SET-UP

PM Tube

To Pumping Sys-tem

To DAS

To DASThermocou-

ple

Function Gen.

640 mm

Focal Length : 750mmApeture Ratio : f/9.8Grating : 1800 Gr/mmResolution : ~ 0.02 nm

Langmuir Probe : ¼ inch one side planar probe

520 mm

Resonance Layer

150mm

RGA : Stanford Labora-tory


174 mm

221mm25m

m

80 mm

91mm

55mm 20m

m

Molten Salt

Probe position

55mm

20

MAGNETIC FIELD STRUCTURE


-150 -100 -50 0 50

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06 -8cm -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8

I sat[A

]

Vbias

[V]

Cylinderical ProbeD0.25, L12mm

■ Hydrogen Plasma density, Temperature and potential

-10 -8 -6 -4 -2 0 2 4 6 8 10

5

10

15

20

25

Vp Te

Position from center [cm]-10 -8 -6 -4 -2 0 2 4 6 8 10

0.0

1.0m

2.0m

3.0m

4.0m

5.0m

6.0m

7.0m

I sat(@

-100

V)[V

]

Position from center [cm]-10 -8 -6 -4 -2 0 2 4 6 8 10

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

Laframboise plot

N[#

/cm

3 ]

Position from center [cm]

PLASMA PARAMETERS

Cylindrical Langmuir probe : Diameter 0.5 mm, Length 12 mm Unmagnetized plasma assumption : Laframboise Analysis Hygrogen Plasma


I. Experiment condition Base pressure: 6ⅹ10-6 TorrWorking pressure: 1mTorr, Ar 16 sccmECR head input current: 17AMicrowave input power: 500 wattInitial FLiNaK temp.: 28 ℃

II. Measured by monochromatorMeasuring range: 300~850 nmResolution: 0.275 nm2000 point

300 400 500 600 700 800

7800

8000

8200

8400

8600

8800

9000

9200

9400

Ar

K I696.5

Na I588.99

Em

issi

on in

tens

ity (a

rb.)

Wavelength (nm)

Ar 1mTorr 500watt, 17A

K I404.7

Ar

Interaction between Ar ECR plasma and solid FLiNaK


Interaction between Ar ECR plasma and Liquid FLiNaK

I. Experiment condition Base pressure: 6ⅹ10-6 TorrWorking pressure: 1mTorr, Ar 16 sccmECR head input current: 17AMicrowave input power: 1000 wattInitial FLiNaK temp.: 539 ℃



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 ℃)

Resonance Layer

Molten salt bath

NUMERICAL SIMULATION


I. Experiment condition

Base pressure: 4.3ⅹ10-6 TorrWorking pressure: 1mTorr, H2 46 sccmECR head input current: 17AMicrowave input power: 500 wattInitial FLiNaK temp.: 15 ℃

II. Measured by monochromator Measuring range: 300~850 nmResolution: 0.275 nm2000point

300 400 500 600 700 800

10000

15000

20000

25000

30000

35000

H656.4H

486.3

Li I610.4

Na I568.8

K I404.7

K I766.6769.9

Li I670.9

Em

issi

on in

tens

ity (a

rb.)

Wavelength (nm)

1mTorr 500watt, 17A

Na I589.3

Interaction between H2 ECR plasma and solid FLiNaK


I. Experiment condition Base pressure: 3.9ⅹ10-6 TorrWorking pressure: 1mTorr, H2 57 sccmECR head input current: 17AMicrowave input power: 500 wattInitial FLiNaK temp.: 539 ℃


200 300 400 500 600 700 800

10000

15000

50000

55000

60000

K I766.6769.9

Li I670.8H

486.1

Na I589.3

Na I568.8

H I434

H 486.1

H I410.4

Na I330.4

Em

issi

on in

tens

ity (a

rb.)

Wavelength (nm)

1mTorr, liquid 500watt, 17A

K I344.8

Interaction between H2 ECR plasma and liquid FLiNaK

685 690 695 700 705 710 715

15000

20000

25000

30000

35000

F I712.7

F I703.7F I

690.2

Em

issi

on in

tens

ity [a

rb.]

Wavelength [nm]

F I685.6


EDS ANALYSIS - MORPHOLOGY

C-K O-K F-K Na-K K-KBase_pt1 3.22 0.36 37.27 0.96 58.19Base_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-K F-K Na-K K-K4.04 57.4 8.62 29.94

EDS analysis before the interac-tion


RGA CALIBRATION

39600 39900 40200 40500 40800 41100 41400 41700

-2.0x10-8

-1.5x10-8

-1.0x10-8

-5.0x10-9

0.0

5.0x10-9

1.0x10-8

1.5x10-8

Pres

sure

[Tor

r]

Time [s]

F HF Li Na K

H2 inlet0 500 1000 1500 2000

1E-8

1E-7

1E-6

H2

A

H2

0.0 0.5 1.0 1.5 2.00.0

5.0x10-8

1.0x10-7

1.5x10-7

2.0x10-7

2.5x10-7

3.0x10-7

H2 P

r[Tor

r]

Flow [sccm]

Equation y = a + b*xWeight No WeightinResidual Sum of Squares

9.34314E-17

Adj. R-Square 0.99792Value Standard Erro

B Intercept 2.82072E- 2.43053E-9B Slope 1.25287E- 2.33262E-9

Pr=2.8e-8+1.25e-7*Flow

RGA can detect the elements from the molten salt even though without the plasma interaction.

Need RGA calibration for hydro-gen retention to find the total amount of hydrogen retention.

Time (sec)

H2 P

ress

ure

(Torr)


25100 25200 25300 25400 25500 25600 25700 25800-2.0x10-8

0.02.0x10-8

4.0x10-8

6.0x10-8

8.0x10-8

1.0x10-7

1.2x10-7

1.4x10-7

1.6x10-7

1.8x10-7

2.0x10-7

Pres

sure

[Tor

r]

Time [s]

F HF Li Na K

Plasma interaction region

17400 17600 17800 18000 18200 18400 18600 18800-2.0x10-8

0.0

2.0x10-8

4.0x10-8

6.0x10-8

8.0x10-8

1.0x10-7

1.2x10-7

Pres

sure

[Tor

r]

Time [s]

F HF Li Na K


29000 30000 31000 32000

0.0

3.0x10-8

6.0x10-8

9.0x10-8

1.2x10-7

1.5x10-7

1.8x10-7

2.1x10-7

2.4x10-7

2.7x10-7

Pres

sure

[Tor

r]

Time [s]

F HF Li Na K


5min

RGA DATA – HF MEASUREMENT

The potasium is the main element from the molten salt evaporation .

Hydrogen fluoride forma-tion increase with plasma interaction time.

It is possibly come from the chemical formation of HF.

Plasma irradiation time



10min

20min


H2 retention depends on the interaction time with H2 Plasma

1 10 100 10001E-8

1E-7

1E-6

H2 plasma

exposure time (1mTorr)

Pr H

2 [Tor

r]

Time[sec]

ref 5min 10min 20min 40min

w/o plasma

0 1000 2000 3000 4000 5000

0

1

2

3

4

5

640min

20min

10min

Out

gass

ed H

2 [cc]

Time[sec]

5min

Measured the partial pressure of out-gassed H2 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


Plasma interaction time [sec] 300 600 1200 2400

Hydrogen Dose into molten Salt [cc] 2.45 4.9 9.8 19.6

H2 retention of FLiNaK [cc] 1 1.7 3.4 6

Ratio [%] 40.8 34.7 34.7 30.6

Plasma interaction time [sec] 300 600 1200 2400Hydrogen Dose into molten Salt [cc] 4.9 9.8 19.6 39.2

H2 retention of FLiNaK [cc] 1 1.7 3.4 6Ratio [%] 20.4 17.3 17.3 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

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.


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 in-cluded.

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.


1

2

3

4

1170 mm

1030 mm

ECR

Helicon

Length of Pipe [mm] Vol. [cc]1 700 1374.4 2 500 981.7 3 600 1178.1 4 400 785.4 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


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 ?

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