Challenges to Developing an ICF-Based Energy Source

1. Challenges to Developing an ICF-Based Energy Source Harold K. Forsen NRC December 17, 2010

2. Long Term Energy Gains • With Driver Efficiency – D • Target Gain – G • Thermal/Electric Conversion Efficiency – T/E • We require: D x G x T/E > 1 to only provide the driver energy, but need the product > 5-10 for a power plant. • Given thermodynamic efficiencies of power plants at about 40%; this means: D x G ~ 2.5 and we need > 13-25 for power plants

3. Long Term Energy GainFESAC – 2004: Driver Efficiency • Heavy Ions • Expected efficiency ~ 25-40%. • Problems with beam focusing, brightness, pulse compression. • Z-Pinches • Efficiencies of 15% stored energy to x-rays – using indirect targets. • Major challenges with transmission line replacement – repetition rate increases. • Lasers • KrF lasers with 7% projected system projected efficiencies and good wavelength, beam uniformity, and brightness. Fluorine handling challenges and foil and final optics lifetime improvements needed. • Diode Pumped Solid State Lasers with efficiencies of 4% and a goal of 7% are projected but requires wavelength shortening and final optics lifetime improvement.

4. DIRECT DRIVE - LASER DRIVERS Simpler targets, Difficult illumination uniformity requirements, Hydrodynamic instabilities, Energy absorption scale length issues, Beam pointing accuracy, target positioning in 3D space, Theory and modeling improvements, Variety of codes available, Several international programs in place, Data sharing. FAST IGNITION – ALL DRIVERS APPLICABLE Two drivers required – igniter and compressor, Difficult igniter requirements, Possibly higher gains. INDIRECT DRIVE – ALL DRIVERS APPLICABLE Increased target complexity, X-ray conversion efficiency, Less demanding beam requirements in pointing and aiming, but target positioning now in 3D space plus yaw and pitch added due to cylinder, Material properties at high densities and pressures, Theory and modeling improvements, Codes have very limited distribution and availability, Severe lack of facilities to verify codes and very low experimental (shot) rates. Long Term Target Energy GainFESAC – 2004 Energy Gain

5. POWER PRODUCTION REQUIREMENTS – REPETITION RATE - R • Assume a 500 MW thermal power plant using Deuterium and Tritium fuel: • Energy released per fusion is 17.6 MeV • Deuterium – Deuterium would be over 4 times less. • Since WATTS = JOULES/ SECOND: 5 x 108 = 1.76 x 107 x 1.6 x 10-19 x R • Thus: R = 1.8 x 1020 fusion events/sec are needed. • Thus far, no laboratory experiment has ever made 1015 neutrons or DT fusion events in a pulse. • Consequently, for such a power plant, an improvement in fusions per pulse of greater than ~3 x 104 at 5 pps are required.

6. Two Metrics on What Remains • One example we have is in recent information from the National Ignition Facility. It can deliver about 3 shots per week or 2 x 10 exp 5 seconds between shots. At a requirement of 5 shots/sec or 0.2 sec between shots, an improvement of 10 exp 6 is needed in repetition rate • A recent single shot delivered a fusion record 3 x 10 exp 14 neutrons or the same number of fusion events. At a requirement of 2 x 10 exp 19 fusion events per shot (at 5 pps) for a 500 MW thermal power plant, an increase of about 10 exp 5 in yield per shot is required. • It also used approximately 1.3 MJ of laser energy to produce less than 1000 Joules of DT fusions, indicating that increases of over 1000 are needed just to produce the laser light. Of course, we have no indication of what kinds of targets or tests were performed. This is only to point out a couple of the challenges we face in ICF fusion which will hopefully will be addressed and met.

7. Perspective on Progress • In early magnetic fusion experiments of the 1950’s and 1960’s, some experiments produced 109 D D neutrons a shot and a few microsecond containment. • In 2020 to 2030, or more than 70 years from the early start of fusion, today there have been thousands of experiments operated worldwide and produced more than tens of million of shots to obtain data – confirming codes. • ITER is anticipated to produce steady state fusion at hundreds of megawatts thermal for a few hundred seconds and at reasonable rates. Point here is that lots of shots have been needed to refine experiments and confirm computer codes and models. Science and technology progress in the fusion business is difficult, expensive, and takes time.

8. Summary & Conclusions • THE SCIENCE MUST BE UNDERSTOOD • Theory, Modeling and Experiments • Concerns about very few groups, lack of rate of available experimental data and limited information sharing – especially with indirect drive targets. • DRIVER EFFICIENCIES MUST BE ADEQUATE • Electric driven sources with very high demands on quality, focusing, timing, pointing and coupling need to be developed. • REPETITION RATES MUST BE GREATLY INPROVED • Given the demands on the above, rate increases will be most challenging • CHAMBER DESIGNS MUST BE ADEQUATE • Ideas abound but until more is known, it is difficult to know what is really needed. • PLANT CONCEPTUAL DESIGNS EVOLVED • Developing concepts to handle the unknowns above yield limited but valuable data on what may be needed and other complexities of the systems. However, continuing improvements in materials, particularly carbon composites, components and nanotechnologies should help equipment, design concepts, availability, reliability and economics. However, concepts of cheap, deliverable, and high rate target manufacturing facilities could also prove useful as well as target replacement concepts.

9. REMEMBER: We really don’t know what we don’t know.