APEX Task I Progress, Status, and Plan

1. APEX Task I Progress, Status, and Plan Presented by Alice Ying APEX Meeting Nov. 3, 2003

2. Progress Since Last APEX Meeting By June, completed the final version of the paper entitled “Exploratory Studies of Flowing Liquid Metal Divertor Options for Fusion Relevant Magnetic Fields in the MTOR Facility” to be published in the APEX FED special issue July-September: • Conducted quantitative measurements of film height profiles over a range of flow conditions • Performed experiments on the effect of transient field ramp-up and down on free surface film flow characteristics (MTOR ramp up time ~ 1 s slightly longer than 0.6 s in NSTX) • Results presented at the SOFE meeting • The 1st generation conducting wall MTOR-NSTX LSM test article retired

3. A 2nd generation MTOR-NSTX LSM conducting wall- test article designed and currently under fabrication • Objectives: • To simulate a complete NSTX representative surface normal field • To investigate whether surface expansion would help reducing film pile-up from MHD drag caused by the surface normal field Experiments will be conducted over the next couple months for a rang of flow conditions Note that the decision on employment of NSTX LSM currently postponed until 2006-2007

4. 45 cm vs 28 cm Top view Side view 8 magnets vs 2 Permanent magnets (8 in place) The new test article features simulation of toroidal expansion as lithium moves from inboard to outboard (a 40% increase in flow area over a 45 cm flow path)

5. MTOR conducting test article size limited by the available gap required to create prototypical field strength • Current test article size of 5 cm wide is narrower than NSTX LSM size of 40 cm wide (if it would be a module) • conductance ratio • Stronger boundary layer effect from gradient toroidal field? The wall is less electrically resistive than the Hartmann layer. • Less MHD drag from surface normal field • Correspondingly, a relevant question concerns whether a mid-wall divider needed in NSTX LSM in order to cut down surface normal field induced toroidal current and the resultant flowing opposing MHD drag. • Effects of simultaneous area expansion with uphill flow C5 cm > C40 cm at same steel thickness Impact of Conducting Wall Test Article Width

6. Power Supply needed to Create Better MTOR-NSTX Field Environments Current size of MTOR-NSTX LSM test article limited by the need of using iron flux concentrator can not adequately resolve pile-up and flow asymmetric issues • Request • A staged power Upgrade to MTOR to achieve full coil current of 3600 A operations (right now coil is operated at 1800 A) • In-house facility power upgrade on-going • Additional need is a power supply system

7. Preface Power upgrade to MTOR was proposed at last November meeting. However, it was not going forward, due to a significant amount of money needed. The estimated total cost was > $400 k including a power upgrade to the lab of $250k and a power supply of $150 to 200 k. What happened since then? The E1 building at UCLA needed to be torn down and switched to the 12.47 kV line through a trench down the alley right in front of our lab. This provided an opportunity for us to bring the 12.47kV line into the lab. The cost was $40k (in stead of $250k) and would be paid by the department. And, we are doing it! Request Details

8. 2.5MW fusion power upgrade piggy-backed of Nanotech building project E1 building to be torn down Fusion Lab spur trench with 2.5 MW of 12.47 KVAC New E1 power trench

9. Request Details (Cont’d) Now, it appears reasonable to ask for a power upgrade to MTOR (to run at its full capacity). What do we need additionally? The biggest amount will be spent on the rectifier power supply, which transforms an input voltage of 12.47kV to an output current of 3664Adc (MTOR full coil current). The quote for this from the SatCon Power Systems Canada Ltd. is $175.5k. There are other miscellaneous costs such as an about $20k for conduit and cable needed in the lab, and a similar cost for cooling system upgrade. However, they may be paid by the school. We hope to proceed and complete this upgrade by mid-2005!

10. Request Details (Cont’d) Specific Request It is requested that the $180k needed for the rectifier power supply system to be shared and paid by the APEX unallocated fund and ALPS the discretionary money. A written request (document 3) will be provided to the ALPS SC for this purpose. For Fy2004 the proposed request is $100k, while the remaining $80k shall be provided in Fy2005.

11. The goal was to quantity the film height variation- A set of three induction probes are used to determine the film thickness at three stations, that span the length of the channel Some Specific Details on Recent Experimental Study

12. Experiment Details • Test section at zero inclination (NSTX 21.5o, M-TOR 1.85o) • Flow from inboard towards outboard • Three different inlet nozzle velocity ranges • Range A (1.2-1.3 m/s) (NSTX 5.3 m/s @ 2mm) • Range B (1.7-1.8 m/s) (NSTX 7.0 m/s @ 2mm) • Range C (2.2-2.3 m/s) (NSTX 9.6 m/s @ 2mm) • Four Scenarios • No magnetic field • Toroidal field only (electromagnetic coils) • Surface normal field only (permanent magnets) • Combined Toroidal and Surface normal fields

13. At the lowest range of velocity, the flow was nearly completely stopped Inlet velocity ~ 1.1 m/s to 1.2 m/s (toroidal field adjusted) With both surface normal and toroidal fields

14. Experiment Details • Three stream-wise measurement stations • Station 1 : 2 cm from inlet nozzle (strong toroidal component) • Station 2 : 14 cm from inlet nozzle (gradient location, near NSTX strike point) • Station 3 : 26 cm from inlet nozzle (strong surface normal component) • Span-wise off-centering (Three configurations) • A 4 s voltage signal from the inductive probes was sampled using a digital oscilloscope. This technique also captures the fluctuations in the flow, the standard deviation of the 10,000 digitized voltage points can give an idea of the surface fluctuations.

15. Inductive probe traces at a particular location for the four different magnetic field scenarios Station 2 (surface normal field ~ 0.04 T) Centered location Velocity range B No Field Toroidal field Only Surface Normal Only Combined SNT

16. Spanwise Film Height Characteristics for Different Operating Conditions ~ 7.0 m/s Li at 2mm film height ~ 5.3 m/s Li at 2mm film height Pile-up due to wall wetting ~ 9.7 m/s Li at 2mm film height 30% reduction in velocity when toroidal field on Station 1 All Velocity Ranges All Scenarios Toroidal Field : 1.08 T Surface Normal Field : 0.01 T

17. Spanwise Film Height Characteristics for Different Operating Conditions ~ 7.0 m/s Li at 2mm film height ~ 5.3 m/s Li at 2mm film height ~ 9.7 m/s Li at 2mm film height Station 2 All Velocity Ranges All Scenarios Toroidal Field : 0.86 T Surface Normal Field : 0.04 T SN gradient : 0.025 T/cm

18. Asymmetric effect Spanwise Film Height Characteristics for Different Operating Conditions ~ 7.0 m/s Li at 2mm film height ~ 5.3 m/s Li at 2mm film height ~ 9.7 m/s Li at 2mm film height Station 3 All Velocity Ranges All Scenarios Toroidal Field : 0.7 T Surface Normal Field : 0.3 T

19. Inferences • It appears possible to establish liquid metal film flow on a conducting substrate under NSTX outboard divertor magnetic field conditions • Under the simulated conditions, the film flow is uneven with significant stream-wise and span-wise variations • The toroidal field is the strongest at the inlet nozzle, and it affects the flow in the loop as a whole • Surface normal field effects are significant towards the end of the flow channel, the surface normal field has local effects on the flow, under the present spatial distribution of magnetic fields and the flow configuration

20. Inferences (Cont’d) • The toroidal field creates the minimum span-wise variation in the film thickness • The toroidal field modifies the surface structure significantly, 2-D column type structures are observed at regions of strong toroidal field, surface normal field effect on the surface characteristics is not that profound • The effect of toroidal field ramp up and ramp down on the film flow behavior seems benign, though this fact needs to be further quantified

21. Implications for the NSTX LSM application • The current experiments show a significant pile up of the liquid towards the outboard (attributed mainly to the strong surface normal field present) • The maximum increase in the film thickness for the three velocity ranges at the outboard is as follows • Range A : X 6.2 (corresponding to 5.3 m/s of lithium flow at 2 mm initial film height) • Range B : X 4 (~7.0 m/s of lithium flow) • Range C : X 3.5 (~9.7 m/s of lithium flow) • Fluid pile up is very sensitive to the local surface normal field, NSTX scaled surface normal field at the outboard is less than the current M-TOR outboard surface normal value • The NSTX LSM will have a much larger toroidal extent, than the current test article used at M-TOR (expected to reduce MHD effects)

22. Summary: Power Supply needed to Create Better MTOR-NSTX Field Environments • Request • A staged power Upgrade to MTOR to achieve full coil current of 3600 A operations (right now coil is operated at 1800 A) • In-house facility power upgrade on-going • Additional need is a power supply system Specific It is requested that the $180k needed for the rectifier power supply system to be shared and paid by the APEX unallocated fund and ALPS the discretionary money. A written request (document 3) will be provided to the ALPS SC for this purpose. For Fy2004 the proposed request is $100k, while the remaining $80k shall be provided in Fy2005.