U.S. BACKGROUND IN ITER FUELING SYSTEMS AND FUTURE CONTRIBUTIONS

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1 U.S. BACKGROUND IN ITER FUELING SYSTEMS AND FUTURE CONTRIBUTIONS S.K. Combs, 1 L.R. Baylor, 1 B.E. Chapman, 2 P.W. Fisher, 1 M.J. Gouge, 1 M. Greenwald, 3 T.J. Jernigan, 1 W.A. Houlberg, 1 P.B. Parks, 4 J.M. Pfotenhauer, 2 G.L. Schmidt, 5 and D.A. Rasmussen 1 1 Oak Ridge National Laboratory 2 University of Wisconsin 3 Massachusetts Institute of Technology 4 General Atomics 5 Princeton Plasma Physics Laboratory U.S. ITER FORUM May 8-9, 2003 University of Maryland University College Aldelphi, Maryland USA

2 Outline Brief description of ITER fueling system and schedule Why pellet fueling is crucial for ITER Background of U.S. in fueling R&D and experiments Contributions of U.S. during ITER CDA and EDA New technical challenges Benefits to U.S. Fusion Program Summary 2

3 ITER Fueling Systems Requirements and Present Design Plasma Density(n GW ) Fuel Isotope DT Burn Rate Gas Fueling Rate (torr-l/s) Pellet Fueling Rate (torr-l/s) Pulse length (s) Pellet (90%T/10%D) Unknown Up to (375 for 90%T/10%D) Up to 3000 Gas injection system Supplies H 2, D 2, T 2, DT, Ar, Ne, and He via a gas manifold Makes use of conventional gas handling hardware and requires minimal R&D Pellet injection system Supplies H 2, D 2, and DT pellets: 3 to 6 mm diam (50 to 7 Hz, respectively) Only at pre-conceptual design level and significant R&D support still needed 3

4 ITER Fueling System Diagram and Pellet Injection System Design Criteria Pellet Injection System Two centrifuge injectors for redundancy (also supports coincident impurity injection) Steady-state operation Screw extruders for pellet production and supply Each injector assembly housed in cask (~6 m L x 4 m H x 3 m W) Pellets delivered through single guide tube connected through a divertor port to plasma chamber Includes a diagnostic/control and data acquisition system 4

5 Tentative Schedule & Cost for ITER Pellet Injector Design Conceptual Design Prelim. Design PDR Final Design FDR Direct R&D Extruder Mockup Centrifuge rotor prototype Guide/Capture tube prototype Fabrication Let contracts Fabricate injector parts Assemble injector Laboratory Test Ready to install on ITER Costs shown are recent U.S. estimates and have lots of assumptions Costs are if U.S. does it all, but this could be an international collaborate effort R&D will have general benefits to U.S. 5

6 Pellet Injection Will Be Crucial for Effective Core Fueling in ITER as Shown in Fueling Source Profile Comparison with DIII-D (Gas and Pellets in H-mode) D m -3 s HFS Pellet LFS Pellet V+1 Pellet Recycle Gas DIII-D r ITER 0.1 HFS Pellet Gas Fueling 0.01 LFS Pellet Efficiency Gas < 1% Gas puff fueling in ITER will be much less effective in core fueling than in DIII-D; the pellet profiles are from PRL (P. Parks) calculations using a 10-mm pellet extrapolated to 1 Hz operation; a gas fueling rate of ~1000 torr-l/s is used in the ITER case using a B2-Eirene slab calculation (L. Owen and A. Kukushkin) r 6

7 U.S. DOE Office of Fusion Energy Science Has Sponsored Plasma Fueling R&D Program for Over 25 Years Developing Technology for Fusion Experiments 7

8 Pellet Sizes Tested in U.S. Program Are Relevant for Fueling Applications on Any Present Experimental Fusion Device and Future Fusion Reactors 8

9 DIII-D Pellet Injection System Developed/Supported in the U.S. Fueling Program and Used to Study Improved Mass Deposition with HFS Injection Three-barrel repeating pneumatic injector (machine gun like) Straight guide tubes ( 4 m) Three independent standard low-field-side (LFS) injection tubes: 135º port Curved guide tubes ( 12.5 m) Two independent vertical injection tubes: 0º (V+3) and 60º (V+1) ports Two independent HFS injection tubes on inner wall: 45º upper and lower ports Great flexibility in injection ports and range of possible experiments Massive gas puff system for disruption mitigation studies has been developed and successfully tested on DIII-D, and this technique appears scalable to ITER and is closely related to the fueling system 9

10 During the ITER CDA and EDA ( ), the U.S. Was Responsible for ITER Fueling System Design and R&D Technology Highlights Tritium injector design and testing with ITER-size (up to 8 mm) DT and T pellets and cumulative T amounts of a few 10s of grams Development of innovative high-field-side launch technology and experiments (experimental studies for DIII-D, JET, LHD, and FIRE) Demonstration of high-throughput/steady-state hydrogen ice supply approaching the full ITER pellet fueling design value Physics Highlights (Supported by U.S. Theory Program) Developed isotopic tailoring concept with DT pellets key to operating ITER with minimal tritium inventory (Gouge et al.) Significant progress on international pellet injection database to better understand the physics of pellet penetration and ablation (Baylor et al.); this is being extended to alternative injection locations as part of the ITPA effort Russian Federation (R.F.) is the other ITER participant that has expressed strong interest in the pellet fueling subsystem, and an arrangement where responsibility would be shared between the U.S. and R.F. is an option 10

11 In Tritium Pellet Experiments at TSTA, U.S. Obtained Unique Data and Experience with T 2 & DT Directly Relevant for ITER Design and Operations Tritium Extrusion ( 8 mm) 11

12 New Technical Challenges Systems must be able to operate reliably in tritium environment and be readily maintained Throughput requirements are significantly greater than achieved in experiments to date Continuous screw extruders (I. Viniar, R.F.) are assumed in the ITER baseline design, but these have only achieved flow rates that are a factor of ~5-10 lower than that required Highest ice flow rates to date (~67% of ITER design value) were achieved at ORNL using a prototype with three large volume extruders operating in sequence (Combs et al.) Centrifuges in the ITER design have not achieved the overall reliability objective (~100% intact pellets); pneumatic injectors can more easily meet reliability requirements, but have a gas load issue Significant R&D effort still required before final design; development and testing program will be needed to validate proposed ITER pellet injector design and to modify it as needed Evolution of the system may permit new technologies such as supersonic gas jet, high-speed vertical injector, and inner bore injector 12

13 Benefits to the U.S. Fusion Program U.S. has been recognized as world leader in pellet fueling for decades, and key role in ITER fueling activity would help maintain R&D capabilities in this unique scientific field/technology Lead to improved fueling systems for present and planned U.S. experiments Result in better understanding of the details of fueling physics Increased international collaboration opportunities (e. g., on JET and DIII-D) for testing of advanced or prototypical pellet injectors Major U.S. participation in fueling physics experiments on ITER will be much more likely if the U.S. is responsible for the fueling system Increased opportunities for graduate students; for example, collaboration with J.M. Pfotenhauer at University of Wisconsin on advanced cryogenic cooling systems for pellet injectors 13

14 SUMMARY Success of ITER relies largely on the ability to operate the plasma at high density with good confinement; pellet fueling is the primary mechanism to provide the necessary deep fueling U.S. had the lead role in ITER fueling during the CDA and EDA and is in an excellent position to resume that role, with a particularly strong interest in the pellet fueling system U.S. has the proven capability to develop, design, and construct the entire ITER fueling system as a turnkey item U.S. could share responsibility for ITER fueling with R.F. and possibly other international collaborators ITER fueling tasks will be relatively low cost compared to other major systems, and U.S. can realize a fairly low cost/benefit ratio 14