1. Lithium Free-Surface Flow and Wave Experiments H.Horiike 1), H.Kondo 1), H.Nakamura 2), S.Miyamoto 1), N.Yamaoka 1), T.Muroga 3) 1) Graduate School of Engineering, Osaka University, Osaka, Japan 2) Japan Atomic Energy Agency, Ibaraki, Japan 3National Institute for Fusion Science, Gifu, Japan e-mail : horiike@nucl.eng.osaka-u.ac.jp Based on the paper FT/P5-35 for 21st IAEA Fusion Energy Conference 16 - 21 October, Chengdu, China

2. 2 Introduction ItemSpecificationRemarks Deuterium beam energy / current 40MeV / 250mA 125mA nominal x 2 beams Averaged heat flux1 GW/m 2 Beam deposition area on Li jet 0.2 m x 0.05 m Jet width / thickness0.26 m / 0.025 m Jet velocity15 m/srange: 10 - 20 m/s Nozzle geometryDouble-reducerbased on Shima’s model Nozzle contraction ratio 104 x 2.5 Curvature of back wall 0.25 m Wave amplitude of Li-free surface ~ 1 mm Flow rate of Li130 l/s Inlet Temperature of Li 250 o C Vacuum pressure10 -3 Paat Li free surface Materials RAF steel or 316SS (back wall) Back Ground IFMIF ( International Fusion Materials Irradiation Facility ) - Liquid Li Target Aim of this study Investigation of the flow dynamics - Surface fluctuation of the target - Measurement technique - Engineering issues Reference from IFMIF Home Page http://insdell.tokai-sc.jaea.go.jp/IFMIFHOME/i_target_en.html

3. 3 Outline of Osaka Univ. Li Loop Void separation tank Electro-Magnetic Pump Free-Surface Test Section Dump tankLi Ingot ALIP type EMP < 700 l/min In a pit Li inventory : 420 litter In a pit 1/2.5 scaled model of IFMIF Li target Main loop : Test section, Void separation tank, EMP and EMF. The total length : 40 m Daughter loop : Cold Trap, EMP and EMF

4. 4 Outline of Free-Surface Test Section Viewing ports and Shutter Nozzle and Flow Channel Nozzle Shima’s model ×2 ( Two convergent sections ) Hight : 10mm, Width : 70mm ( 1/2.5 scale ) made of SS304 Straight Flow Channel Viewing ports

5. 5 Electro-Contact Probe apparatus Electro-Contact Probe Fluctuations were measured on Li free surface with using an Electro-Contact Probe apparatus ・ Two needles mechanically fixed move together, but electrically independent ・ Electric motor cylinder to move the needles : 0.1 mm step Set on the second viewing port (on the beam axis) 175 mm from the nozzle needle 1 : 16 mm from the side wall needle 2 : 35 mm (at the center of flow) Detection circuit

6. 6 Measured Time Series Signals at 10 m/s Center of flow (c) 10.74mm (b) 11.04mm (a)11.44mm from wall Probes were moved with 0.1mm step, while recording voltage signals. - Recording time : 20 sec - Sampling freq : 48 kHz ( using PCM recorder) Higher than the Li free surface contacts were rare ( almost no contact) Middle of the surface contacts made frequently Lower than the Li free surface contacts were rare ( almost contact ) No contact contact Schematic of contacts

7. 7 Contact frequency : Number of changes between contact and no-contact per unit time (a) 5m/s(b) 10m/s(c) 15m/s Contact frequency and contact time rate were defined and calculated statistically from electric signals Shapes of Li surface waves Contact time rate : The quotient of total contact period divided by recording time

8. 8 Average thickness and max wave amplitude Average thickness of the flow Height at maximum contact frequency ( = center of the fluctuation ) - in the lower velocity of 1 to 5 m/s, the thickness shows a peak at ~ 4m/s - in the velocity 5 to 10 m/s, the thickness continuously increased gradually. - in thr velocity of more than 11 m/s, the thickness decreased to 10mm which equals the depth of nozzle throat. Amplitude of the fluctuation defined as half height between “no contact” and “full contact”. - the amplitude increased with flow velocity - in the velocity more than 12 m/s, the amplitude seems to be saturated. - the amplitude was 2 mm at 15 m/s.

9. 9 Visual observation of the surface (a) 2 m/s(b) 3 m/s(c) 5 m/s (d) 7 m/s(e) 10 m/s(f) 15 m/s Stroboscopic photography of the Li surface at 175mm downstream from the nozzle exit (second viewing port)

10. 10 Boundary layer thickness along the nozzle wall and at the nozzle exit Nozzle coordinate Momentum thickness Transition to turbulent Momentum thickness    along the nozzle was calculated [1] 1. velocity distribution along the nozzle wall ( potential model ) 2. Development of laminar boundary layer ( method of Waltz ) 3. Transition to turbulent ( Re  > 420 ) 3. Development of turbulent boundary layer ( method of Buri ) 4. Relaminarization ( acceleration parameter K ) Boundary layer thickness  at the nozzle exit was estimated from the momentum thickness [1] K. Itoh et al., “Free-surface shear layer instabilities on a high-speed liquid jet”, Fusion Technol. 37 (2000) 74-88 D 

11. 11 Non-dimensional amplitude Experimental results of the amplitude was summarized to non-dimensional form, non-dimensional amplitude : A/  against Weber number : We Weber number was defined as where T: surface tension,  : density, U 0 : mean velocity The non-dimensional amplitude was well predicted by square of We It is noted that the saturation above We of 5.5 is observed..

12. 12 Summary As a result, - Time series signals were represented by contact frequency. - Waves of Gaussian like profiles were observed. - Average thickness of the flow, and maximum amplitude of surface fluctuation were plotted as a function of the velocity. - The amplitude was described by non-dimensional form of We number. This showed that the amplitude was well predicted by square of We number, and it began to saturate above velocity of 12-13m/s. Experiment study on IFMIF liquid Li target was carried out with using a 1/2.5 scale test channel. Surface fluctuation of the target flow was measured by electro- contact probe apparatus.