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

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

ITER Fueling Needs are Significant 4 m 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. Gas Injectors Pellet Injection ITER Cross Section

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

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

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

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.

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

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

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

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.

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

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

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

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.

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

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

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

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

The End Tritium Pellet