the liFE project at the lawrence livermore national laboratory in the Us hopes to turn lessons learned at the national ignition Facility into safe, clean fusion energy Image courtesy of LLNL
energies of 1kJ and beyond, ideal for inertial fusion energy and other emerging applications like laser particle accelerators.’ Researchers at LLNL in the US are taking a
different approach. As part of an in-house project they are also developing a high-power DPSSL whose end application will be as part of the Laser Inertial Fusion Engine (LIFE), a laser-driven fusion power plant that continues the work being carried out at NIF. According to Andy Bayramian, a LIFE
engineer, the DPSSL being developed at LLNL will use Nd:glass and will not be cryogenically cooled. ‘We have used the lessons we learned in developing the Mercury system and our approach will be different to that being used in HiPER’s DiPOLE demonstrator,’ he said. ‘We want to minimise risk so have chosen a well-known material for the gain medium. We also have some concerns about cryogenic cooling and believe that, while it could increase effi ciency, it could also increase cost and delivery time.’ Of the many tasks facing the LIFE laser system, one of them is to reduce the cost and increase effi ciency of diode pulsers. According to Bayramian, current power supplies are limited to ~20Hz, the cost per unit is excessive (~$1/W), and the pulsers are ineffi cient due to operational parameter adjustability, diagnostics, and the need for long cables between pulser and diode array. LIFE engineers have therefore developed a new kind of pulser, named a ‘smart tile’, which is a miniaturised and simplifi ed version of the current pulsers. The central design is based on the following key elements: Remove all processing and adjustability, place the pulser in close contact to the diodes it is driving, and utilise the diode array backplane as the heatsink for
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the pulser. Using a circuit design program, their ‘smart tile’ model indicates these devices should meet performance requirements with a baseline component cost which is 40 times lower in cost and 20 times lower in size while being 15 per cent higher in effi ciency than the existing technologies. These fi gures are important when you consider that an estimated 4.4 million pulsers will be needed for a power plant. Unlike his colleagues across the pond at HiPER, Bayramian does not have concerns about the availability of laser diodes or optics in time for LIFE. ‘The capacity will be there when we need it,’ he said. ‘When NIF started, there was no laser glass and our suppliers built facilities in order to meet our demand. We have been talking to the optics industry and have solicited several white papers on how the industry can increase production and reduce costs. For a separate project, we received a quote for up to 100,000 laser diode bars at a price of $0.30/W. We have likewise solicited diode laser companies and have compiled a white paper with more than 15 diode manufacturers stating that LIFE production rates are possible at price points that meet LIFE requirements.’ This is an order of magnitude lower than
today’s prices for laser diodes which range between $3 and $5 per peak Watt, fully packaged. Most estimates, however, state that the price of
laser diodes needs to come down even further, to something in the region of $0.02/W, before laser- driven fusion can become a commercial reality. This would equate to fi ve to 10 per cent of the total power plant cost, and the cost of electricity would be in the range of $0.06/kWh. But none of this can happen if the laser diode
industry does not invest in its capacity and starts adopting high-volume manufacturing techniques. While all eyes are on NIF, HiPER’s Tyldesley warns: ‘It is really important that our industry, our investment community, and our governments too, don’t sit waiting for fi rst ignition at NIF. Much planning and preparation needs to be done ahead of time so that we can really gear up our efforts once NIF ignites. Sooner or later, the arguments will be accepted and laser energy will come on line. It’s our job in HiPER and other such projects, to make sure it is sooner rather than too late.’ l
LINKS
hilAsE –
www.hilase.cz liFE (Us) –
http://lasers.llnl.gov/ hipEr (UK) –
www.hiper-laser.org ngcEo –
www.ngc.com
MARCH 2011 l ElEctro optics
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