balance between these different philosophies. Balance is achieved by the exercise of subjective judgment that may vary depending on the development stage of IFE, the personal experience of the researchers, and even the political philosophy of government administrations. It is important that the competition between these two approaches not interfere with the best use of the NIF facility for IFE development.

The pre-ignition roadmap described in this report is meant to be an example of the kind of contingency planning that the committee believes DOE should undertake across TAs, with the advice and review of the Inertial Fusion Energy Scientific Advisory Committee, as recommended above. If at any time ignition is reached for any TA, the roadmap would shift from pre-ignition to post-ignition.

Ignition hopes and efforts have been focused primarily on indirect drive on the NIF. Even though ignition was not reached by the end of FY2012, it will be a number of years (approximately 2017) before alternative approaches, such as direct drive in the form of a polar direct drive configuration, could be tested on the NIF. This should give ample time to understand why the model predictions of indirect drive’s performance were invalid and to try new approaches with indirect drive using the current NIF configuration, should new understanding warrant them.

With ignition not having been achieved with laser-indirect drive, a commitment would be warranted to build the optics and other components for a polar direct drive option on the NIF, recognizing that the completed system could not be operational for 4 or more years.10 As a first step, it would be appropriate to measure the extent of laser-plasma instabilities and experiment with beam smoothing, both of which are precursor activities that can be done before installing polar direct drive (2017, at the earliest). Deciding on the balance of these experiments and experiments appropriate for understanding the failure of indirect drive to achieve ignition by the end of the NIC could be informed by the ISAC, identified in Recommendation 4-5. Note that even if ignition is reached with indirect drive before 2017, a decision to build the polar drive option would be warranted to explore opportunities for higher gain. And, modification of NIF to polar direct drive would not foreclose future experiments with indirect drive, although some setup time would be required to switch configurations.

If polar direct drive on NIF should show promise that direct drive might well reach ignition, construction of a spherical direct drive system for the NIF would be

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17 companies, with annual budgets around $15 million. Through it, sufficient progress was made in developing repetitively pulsed DPSSL and KrF lasers to give confidence that both concepts were worth considering for IFE. Progress was also made on target launching and tracking, final mirror optics, frozen tritium behavior, first wall materials issues, magnetic diversion to protect the first wall, and systems studies. See http://aries.ucsd.edu/HAPL.

10 LLNL, 2012, Polar Drive Ignition Campaign Conceptual Design, LLNL TR-553311, submitted to NNSA in April and revised and submitted to NNSA by LLE in September 2012.



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