Acoustically Driven MTF By Dr. Michel Laberge General Fusion Inc. Vancouver, Canada www.generalfusion.com

1. Acoustically Driven MTF By Dr. Michel Laberge General Fusion Inc. Vancouver, Canada www.generalfusion.com

2. MTF • Leader is Los Alamos National Lab in the US • Inject 10 cm diameter FRC in aluminum tube • Discharge a large capacitor bank into the tube, the magnetic field crushes the tube • Problem for making a power plant. Tube and cable connection destroyed for each shot, neutron exposure of chamber and equipment. High cost of electrical pulse power

3. Linus • Linus concept address these problems • Low cost compressed gas driver • Fully surrounded with thick first wall of liquid PbLi • No hardware replacement • Too slow, ms collapsing time • Plasma confinement time required still too challenging • It is closer to normal MF

4. Acoustically Driven MTF

5. Acoustic MTF • 3 m quasi spherical vessel filled with liquid PbLi • The liquid metal is spun to open a vertical vortex • 2 spheromaks (or FRC’s) are sent from each end • They merge to produce a FRC in the center • 1500 psi steam actuated pistons accelerate to 100 m/s • Impact with vessel generates 20 kBar acoustic wave • The wave focuses to the center generating 5 Mbar • The liquid metal collapses on the D-T plasma • Plasma compressed to thermonuclear conditions • Neutrons heat the liquid metal and re-breed tritium • Heat exchanger produces steam for electricity and for the next shot at a rate of ~0.5 Hz

6. Advantages • Extremely low cost of pneumatic driver, ~3 M$ for 120 MJ of delivered acoustic energy • Easily achieves required repetition rate • Impact produces acoustic pulse of piston thickness/Cs for a steel piston of ~10 cm, time = 40 ms. A good match for a MTF driver • Good acoustic match between steel and PbLi 92% • Fast liner velocity of 2.6 km/s reduces the plasma requirement to achievable specifications • Solves stand-off problem, the energy is delivered through the liquid metal blanket/liner

7. Advantages • Solves first wall problem, 100% coverage by 1.5 m of PbLi stops most neutrons and all other radiation • Low activation and neutron damage of steel structure • Excellent tritium re-breeding ratio • Low tritium solubility in PbLi reduces tritium inventory in a 60 MWe power plant to ~1g, very safe • Solves chamber clean up time problem, no material destroyed in the reactor chamber to be evacuated • Solves price of electricity problem, no liner and transmission line replacement for each shot. Low capital cost of driver.

8. Advantages • Re-circulated power is steam, not electricity, reducing cost of turbo-machinery. • Relatively small power plant size of ~60 MWe reduces cost and time of development • Retains all the nice advantages of the LINUS concept but with a faster liner, reducing plasma size and lifetime requirements

9. ITER ICF LANL LINUS GF

14. Difficulties • Multiple impacts wear pistons • Hot die casting produces 100 000 parts at 300 C at 20 kBar pressure • Not quite enough, but wear is proportional to metal flow (from parts being forged) on the die • With no flow, maybe more pulses are possible • Easy change pistons if not enough impacts for full plant life

15. Difficulties • All pistons need to impact within ~1 ms • Unlikely to be achieved by simple mechanical timing of valve opening • Servo loop control of piston trajectory • All energy from compressed gas, but a small fraction of electrically controlled breaking under servo loop control • Modern commercial linear motion control with servo loop linear motor can control trajectory to 10 mm at speed up to 2 m/s • We need 100 mm at 100 m/s, should be doable with electromagnetic breaking (induction linear motor)

16. Difficulties • 1.5 m of PbLi reduces the neutron flux at the wall by 3 orders of magnitudes • No problem with neutron damage to structure for plant life • Still will activate the structure to a level above safe manual handling • Will need robotic handling for maintenance • At end of plant life, big chunk of steel will need to be stored for ~100 years before release to environment

17. Difficulties • Liquid PbLi will shoot at high velocity into plasma formation hardware • Hollow hardware sending plasma into a funnel with a smaller hole into reactor vessel • Exiting liquid metal goes trough and into a catching system • Super heated PbLi vapor coming out after the liquid may condensate on plasma equipment surfaces • PbLi vapor needs to be pumped out quickly

18. Difficulties • Pb is a very high Z element • If some gets in the plasma, that would lead to excessive radiation loses • Possible solution is to inject a layer of pure Li on the inside surface of vortex • Then need some Li Pb separation system adding complexity

19. Difficulties • Energy released vaporize some PbLi • Produce a outgoing shock in liquid • Will require strong, thick walled vessel to take the cycling load for plant life • On the plus side, the shock may push pistons back. No need for re-circulated power

20. Plasma Formation • Spheromaks require less voltage (~20 kV) and longer electrical pulse (~10 ms). Easier pulse power technology could be extended to reliable high repetition rates (solid state switch?) • Not demonstrated at 1017 cm-3. Impurities from electrodes at higher current density may be a problem. Maybe forming the spheromak at low density, accelerate and compress it to 1017 cm-3. • Spheromaks collision turns magnetic energy into ions heating just prior to compression, good.

21. Plasma Formation • FRC demonstrated at almost 1017 cm-3 in FRX. High voltage (~100 kV), fast discharge (~2 ms) electrical pulses are technologically harder. It may be difficult to achieve good reliability especially at high repetition rates. • FRC may require guiding magnetic field, difficult to achieve in our reactor geometry. • Less plasma heating is generated during merging. • What should we build? Your opinion please.

22. Small 1 D Hydro Simulation Initial pre-formed plasma • Density: 1.2 x 1017 cm-3 • Temperature: 100 eV • Diameter: 40 cm • Magnetic Field: 7 Tesla Compressed plasma • Density: 1.2 x 1020 cm-3 • Temperature: 25 keV • Diameter: 4 cm • Magnetic Field: 666 Tesla

23. 1 D Hydro Simulation • Kinetic energy of pistons: 120 MJ • Radial compression: 9.76 • Energy transferred to plasma: 14 MJ (12%) • Fusion Yield: 704 MJ • Energy Gain: 5.9 • Maximum liner velocity: 2.6 km/s • Peak plasma pressure: 4.7 Mbar • FWHM of peak density: 6.9 ms • Substantial Alpha particles heating

24. Small Scale Experiment

29. Experimental Results • 30 capacitors discharge in 30 aluminum foil spirals covering the inside of a 16 cm diameter sphere • The sphere is filled with water, 40 kJ of electrical energy vaporizes the foils and sends a 22 kJ acoustic wave towards the sphere center • A 29 mm diameter, 0.75 mm thick lithium tube is mounted in the center of the sphere • A small 500 J capacitor discharges between coaxial electrodes at the base of the tube forming a z pinch in 10 torr of deuterium

30. Experimental Results • It forms a plasma estimated to be 3x1016 cm-3 and 7 eV • The acoustic wave compresses the tube with the plasma in it and neutrons are detected outside the sphere • The signals in the two liquid scintillators arrive at the time of maximum compression • No signal is detected in hydrogen plasma

31. 5 ms 10 ms 0 ms t=0 ms t=5 ms t=10 ms

32. 15 ms 20 ms 25 ms t=15 ms t=20 ms t=25 ms

33. 30 ms 35 ms 40 ms t=30 ms t=35 ms t=40 ms

34. Deuterium

35. Deuterium

36. Deuterium

37. Deuterium

38. Hydrogen

39. Hydrogen

40. Hydrogen

41. Experimental Results • Hydrogen and Deuterium shots where alternated • Signal corresponds to a small neutron yield of ~2000 neutrons/shot • Signal from two ~1 liter scintillation counters placed just outside the sphere