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
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

4. 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

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 cm3/s can be achieved at ~ 3 rpm.

8. 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

9. 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

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

17. Metal Bellows Pump
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