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ITER Pellet Fueling System – Vacuum Technology

Learn about the vacuum technology utilized in the ITER Pellet Injection System (PIS) to meet the significant fueling needs of the ITER plasma volume. Discover the challenges, configurations, and R&D efforts related to pellet injection for deep fueling and high efficiency in ITER. Explore the requirements, design, and development of the Pellet Injector Prototype and the use of tritium-compatible vacuum pumps.

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ITER Pellet Fueling System – Vacuum Technology

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  1. ITER Pellet Fueling System – Vacuum Technology L. R. Baylor, S. K. Combs, T.D. Edgemon, S. J. Meitner, D.A. Rasmussen, S. Maruyama*, Oak Ridge National Laboratory *ITER Organization Presentation for: OLAV III 14-July-2011, ORNL

  2. Contents Why Pellet Injector for ITER ITER Pellet Injection System Configuration Challenges and Present R&D Vacuum Technology for PIS

  3. ITER Fueling Needs are Significant • ITER plasma volume is 840 m3 and scrape-off layer is ~30 cm thick. This compares to 20 m3 and ~ 5 cm for DIII-D. • ITER is designed to operate at high density (> 1x 1020 m-3) in order to optimize Q. • Gas to be introduce from 4 ports on outside and 6 in the divertor region • Inside wall pellet injection planned for deep fueling and high efficiency. Reliability must be very high. • ITER will require significant fueling capability to operate at high density for long durations. • Gas fueling will be limited by poor neutral penetration. • Fusion burn fraction is small ~ 1%, thus high fueling rate and fuel must be recirculated. 4 m Gas Injectors Pellet Injection ITER Cross Section

  4. Simplified ITER Fuel Cycle Flow Diagram Cryo-Viscous Compressor PE PE CVC TCP DS TCP TCP PE CVC TCP TEP Plasma FCV TCP CVC TCP ISS TCP CVC TCP Roughing Pump System Pellet/Gas Injectors SDS Tritium Building Pellet Injector

  5. Pellet Injector Design Requirements Maximum Fuelling Rate to Plasma • H2, D2 and DT pellet : 120 Pa m3/s (~1 bar-L/s) • T2 (90%T/10%D) pellet : 110 Pa m3/s • Impurity pellet (Ar, Ne, N2) : 10 Pa m3/s Number of Injectors (Upgraded Configuration) • Core fuelling : 2 injectors (D2 and T2) • Edge fuelling for ELM control : 1 injector (TBD) Injection Frequency • 16 Hz max. for core fuelling and ELM control • 10 Hz max. for impurity injection Pellet Speed • Reference : 300 m/s Hydrogen, Deuterium and Tritium Pellets

  6. Contents Why Pellet Injector for ITER ITER Pellet Injection System Configuration Challenges and Present R&D Vacuum Technology for PIS

  7. How to Make Solid Tritium • A twin-screw extruder is being developed for continuous D2 and T2 solid formation for the ITER pellet injection system. • A precooler and liquefier uses the ITER supercritical 4.5 K He (4 bar) to precool and liquefy the fuel gas. • Liquid fuel would enter the extruder kept at the triple point temperature (~20K) on top and cooled to ~14K at the nozzle end. • Volume of extruder would be 25 cm3 and hold ~7.7gm T2 = 80,000 Ci = 4000 Pa-m3 = 40 bar-L. 1.5 cm3/s can be achieved at ~ 3 rpm.

  8. Schematic of ITER Pellet Injector Ar/Ne/N2 0.9 bar Vacuum Guard Impurity P 1-3 bar V3 3 Vextr = 25 cm P P ~ 40 bar-L ITER P Guide Tube Selector 30 bar Q2 = 30 mbar-L/s 2nd stage ballast tank P ~ 0.1 mbar QE = 250 mbar-L/s Q1 = 300 mbar-L/s 500 L/s P 30 bar V2 P P 30 bar 3 L/s P Fuel D2/T2 0.9 bar Compressor V1 6000 m3/h 120 m3/h 1000 L/s P Compressor 6000 m3/h D2 0.9 bar 180 m3/h Propellant P 300 mbar-L/s at ~1 bar ITER Vacuum PIS Cask

  9. ITER PIS Development Items Extruder Gas gun mechanism Vacuum Guard Ar/Ne/N2 0.9 bar P Selector 1-3 bar Impurity V3 3 Vextr = 25 cm P P ~ 40 bar-L ITER P Guide Tube Selector Fuel recirculation 30 bar Q2 = 30 mbar-L/s 2nd stage ballast tank P ~ 0.1 mbar QE = 250 mbar-L/s Q1 = 300 mbar-L/s 500 L/s P 30 bar V2 P P 30 bar 3 L/s P Fuel Compressor V1 6000 m3/h D2/T2 0.9 bar 120 m3/h 1000 L/s P Compressor 6000 m3/h D2 0.9 bar 180 m3/h P 300 mbar-L/s at ~1 bar Propellant Propellant recirculation ITER Vacuum

  10. Contents Why Pellet Injector for ITER ITER Pellet Injection System Configuration Challenges and Present R&D Vacuum Technology for PIS

  11. Pellet Extruder R&D at ORNL • A twin screw extruder looks very promising for providing sufficient ice for the ITER pellet injection system. • Works on the same principle as a screw vacuum pump • A prototype twin screw extruder with a throughput of ~20% of ITER requirements has been successfully built and demonstrated. • New R&D task to develop pellet injector prototype, in which gas gun accelerator prototype and propellant gas recovery scheme will be added is underway.

  12. Pellet Injector Prototype Liquefier Extruder Cryocooler To plasma chamber Gas gun mechanism

  13. Contents Why Pellet Injector for ITER ITER Pellet Injection System Configuration Challenges and Present R&D Vacuum Technology for PIS

  14. Vacuum Pumps Present a Materials Challenge • Tritium compatible vacuum pumps are needed throughout the fuel cycle. They must be oil free. • Tritium (H3) beta decays with a half life of 12 yrs – destroys Teflon and other elastomers and contaminates lubricants. • The types of dry (oil free) pumps we have looked at in some detail are: • Mikuni Piston Pump • Normetex scroll pumps • Metal Bellows • Turbo pumps • Cryopumps – modifications needed, epoxy for charcoal adhesion • NEG – getter pumps • Fluitron – diaphragm compressor

  15. Mikuni Piston Pump • Piston pump developed for JAERI and tested at LANL TSTA. Reliable performance (S. Willms) Fus. Tech. 19 (1991) 1663, Fus. Eng. Des. 28 (1995) 357. • Smaller version also built and tested at JAERI • A prototype pump is being built by Mikuni who was the original designer/fabricator.

  16. Normetex Scroll Pumps http://www.ecovenant.net/pumps/NormetexScrollPumps.html

  17. Metal Bellows Pump http://www.metalbellows.com/Products/compressor-pump.html • Uses double bellows to isolate the process fluid. • Combined in series or parallel • Easy maintenance • Long life • Well known and reliable • Subsidiary of Senior Aerospace

  18. Continuous Cryopump “Snail Pump” • Snail pump developed for possible use in ITER for divertor pumping and pellet injector pumping. • 2004 test at LANL was successful (> 120,000 L/s pumping speed measured for D2). (C. Foster and S. Willms) • Precooled inlet line used to compress helium for pumping with turbopumps. • Foster (CAF, Inc. SBIR reported at SOFE 2005) Snail pump under test at LANL in 2004

  19. Snail Pump Operating Principle LHe • The Snail Pump is a continuously regenerating cryopump, i.e. a high throughput pumping scheme • Developed at ORNL, but commercialized by CAF, Inc. (C. Foster) under an SBIR DOE project. • Prototypes of this pump have been developed with tests at LANL achieving > 120,000 L/s pumping speed for D2(S. Willms, C. Foster, et al.) • Helium pumping can be achieved by precooling the incoming gas and pumping it with conventional turbo pumps. Inlet Exhaust to blower Snail in operation

  20. The End Tritium Pellet

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