The following narratives will indicate the steps required for each technology application (TA) to reach the starting point of the DEMO conceptual design. Conceptual design of DEMO reactors will depend on one or more TAs successfully achieving technology readiness levels (TRLs) of 6 for each component of that TA “package.” The specific steps are meant to be illustrative of the conditional requirements that DOE should set down in its planning process—requirements that should be regularly updated based on scientific and technological progress.
LASER IFE EVENTS-BASED ROADMAP TO DEMO (TA-1)
In addition to the target gain and laser efficiency demonstrations required before operation of an FTF or design of a DEMO reactor, additional detailed pre-conditions are required for each of three main laser IFE candidate technology applications (TAs).
Indirect Drive Target with Diode-Pumped Laser: Pre-conditions for FTF or DEMO
1a. In the present National Ignition Facility (NIF) indirect drive campaign, if 1 < G < 10 is achieved, there should be a further program of work on NIF to extend the gain well into the reactor-scale range before committing to an FTF or DEMO.
1b. If G < 1 is the final result of the National Ignition Campaign (NIC) and follow-on campaigns after some reasonable period of scientific testing, then other drive approaches should be investigated as planned.
1c. The diode-pumped solid-state laser is optically very similar to the flashlamp-pumped NIF laser and so experiments on NIF will define future expectations for indirect drive with a diode-pumped laser. Assuming G > 10, before commitment to an FTF or DEMO, the following achievements will be necessary simultaneously in one laser IRE device, for instance,
— Energy in the 5 kJ range in the ultraviolet as planned.
— Efficiency >10 percent with 15 percent goal in UV.
— Repetition frequency >5 Hz, with clear technical extension to >15 Hz.
— Life test to >107 pulses, with clear technical extension to >109 pulses using the same medium.
1d. A chamber design with life expectancy of >108 pulses must exist for the indirect-drive threat spectrum and the chamber design to include final optical elements.
1e. Target fabrication must project to the precision and economy required of reactor operation.
Direct-Drive Target with Diode-Pumped Laser: Pre-conditions for FTF or DEMO
As with indirect drive, the diode-pumped laser will be optically very similar to the flashlamp-pumped NIF laser, and so laser performance on the NIF will define future expectations for direct drive with a diode-pumped laser.
Regardless of the outcome on indirect drive, even in the case that reactor-scale gain is achieved (1a above), the NIF laser should be used to study direct-drive targets, as planned.
Polar direct drive (PDD) is an interim approach to spherical direct drive (SDD) that employs the existing NIF beam ports. However, ignition with PDD is uncertain owing to likely laser-plasma instability (LPI) differences between the “equatorial” and the more polar beams. Polar direct drive may be a valid test bed for a preview of spherical direct-drive interactions on the NIF laser.
2a. In event 1b above, with G < 1 in indirect drive at the end of the ignition campaign, NIF should be upgraded as planned for PDD studies (2017) with beam smoothing (estimated $30 million for materials) and employed in a study of PDD physics at reactor plasma-scale size. If modeling of the results with validated codes
points to likely G > 1 with SDD, the NIF should be reconfigured at the earliest opportunity to a true SDD configuration (estimated $300 million).
2b. If 1 < G < 10 is achieved with SDD on the NIF there should be additional work to tune as far as possible to reactor-scale gains.
2c. Until the SDD and ID approaches on the NIF both fail to achieve 1 < G < 10 in item 2b, the diode-pumped solid-state laser should continue to be developed. Before commitment to an FTF or DEMO, assuming G > 10 is achieved, all of the following achievements are needed simultaneously in one DPSSL laser IFE beam line:
— Energy in the 5 kJ range in the ultraviolet as planned.
— Efficiency >10 percent with 15 percent goal in the UV, as planned.
— Repetition frequency >5 Hz, with clear technical extension to >15 Hz.
— Life test to >107 pulse, with clear technical extension to >109 pulses using the same medium.
2d. A chamber design with life expectancy >108 pulses must exist for the direct-drive threat spectrum and the chamber design must include final optical elements. 2e. Target fabrication must project to the precision and economy required of reactor operation.
Direct-Drive Target with KrF Laser: Preconditions for FTF or DEMO
There is not an ignition-level facility available at the KrF wavelength of 248 nm with bandwidth of 3 THz. However, calculations presented to the committee based on spherical direct drive predict the lowest energy threshold for ignition to occur with KrF. These calculations are plausible because the LPI threshold of KrF is higher by a factor of 2 compared to 3ω thresholds at 351 nm. This potential benefit of KrF suggests that, if reactor-scale gain of 140 is achieved under heading 2b above, cost-effective power generation could be possible with KrF-driven IFE.
Prior to construction and operation of a 400-500 kJ KrF laser FTF for the exploration of SDD physics with reactor-scale targets at 248 nm, the committee suggests the following preconditions to maximize the chance that power generation by KrF-driven, direct-drive IFE will be cost competitive.
3a. A single-shot 15-25 kJ KrF beamline operates at 0.01 Hz with the desired pulse shape, focal uniformity, and zooming (~20 copies of this beamline would drive the facility).
3b. The NRL Electra repetitive test of a 500 J KrF laser at 5 Hz runs for >107 pulses with efficiency of >6 percent and a clear projection of the same technology to the 15-25 kJ module at >109 pulses.
3c. Experimental evidence validates some aspects of high gain (>140) in 2D(+) calculations that include the most advanced validated models of LPI at 248 nm and incorporate learning from SDD experiments on the NIF.
3d. A chamber design exists that projects to >108 pulses with the threat spectrum of direct-drive targets, to include a plausible final optics design, and that direct drive targets can be injected into the chamber and engaged by the laser at a >5 Hz rate.
3e. Target manufacture projects to mass production at the quality desired for direct drive and within the cost required for power production.
3f. KrF direct-drive laser IFE is estimated to be cost-competitive with other IFE or MFE plant designs.
Note that the NIF can also be upgraded to operate at 4ω in the deep UV if such operation is necessary for testing LPI at the deep UV vs 351 nm.
HEAVY-ION IFE EVENTS-BASED ROADMAP TO DEMO (TA-2)
There are several technical approaches to heavy-ion inertial fusion. Each approach uses a particular kind of accelerator, a particular kind of target, and a particular kind of chamber. The two principal types of accelerators are radio-frequency (RF) accelerators and induction linear accelerators (linacs). Unlike laser fusion, there is nearly a continuum of targets ranging from targets that are fully directly driven to targets that are indirectly driven. Ultimately, the program must determine the optimal point in this continuum, but, in this section, we will simply distinguish between direct drive and indirect drive. As is the case for lasers, the target ignition modes include hot-spot ignition, shock ignition, and fast ignition. Heavy-ion fusion appears to be compatible with several types of chambers, but most power plant studies have adopted chambers with thick liquid walls to minimize radiation damage to materials.
In order to make progress on limited funds there has, for many years, been an informal agreement that the United States would pursue induction linacs while the foreign programs would pursue RF accelerators. In the near term it is not necessary to choose between direct drive and indirect drive. The accelerator requirements for the two cases are similar. The accelerator requirements for fast ignition are quite different. Fast ignition targets require high kinetic energy ions compared to other types of targets. The large RF heavy-ion accelerators in Germany and Russia are designed to produce high kinetic energies. Fast ignition is an important part of some of these foreign programs. Although large future machines such as the Facility for Antiproton and Ion Research (FAIR) in Germany may be able to do some preliminary experiments on fast ignition, they will likely fall short of the required ignition temperature by more than two orders of magnitude. Consequently it
appears difficult to validate ion fast ignition physics. In the remainder of this section the committee considers only the U.S. program—induction linacs and direct or indirect drive.
Pre-conditions for FTF or DEMO
Much of the target information for heavy-ion fusion is based on computer simulations using the codes that are also used for laser and pulsed power fusion. There is also limited experimental information on ion-driven fusion, including heavy-ion energy deposition experiments in cold and laser-heated matter and light-ion-beam-driven hohlraum data up to about 60 eV.1,2 For information on inertial confinement fusion physics, it is currently necessary to rely on classified data and the laser fusion programs, particularly the NIF program. Given this situation, the committee now turns to the pre-conditions needed for a heavy-ion fusion FTF or DEMO:
1a. Laboratory-scale ignition on NIF or elsewhere is necessary. These ignition experiments must be convincingly connected, using state-of-the-art computer simulations and existing ion target data, to the achievement of high gain (G > 30) ion-driven targets. Since the fuel capsules for indirectly driven ion-beam fusion are similar or identical to those for indirectly driven laser fusion, and since ions have driven hohlraums to approximately 60 eV, it is much easier to make a convincing connection for indirect drive than for direct drive.
1b. In addition to the current uncertainties in target physics, there are also uncertainties in accelerator physics, at least for the high current beams needed for fusion. To address these uncertainties it is necessary to show that NDCX-II, the ion induction linac currently coming on line at the Lawrence Berkeley National Laboratory (LBNL), meets its designs goals and that its performance matches theory and simulation. A result of these experiments should be a validation of the accelerator and beam physics codes at increasing intensity.
1c. Transport of driver-scale beam charge density in magnetic quadrupoles without serious degradation of beam quality (ability to be focused) must be demonstrated and provide further validation for beam transport codes. This can be done by restarting and upgrading the existing HCX accelerator at LBNL.
1d. Ion sources, magnetic quadrupole arrays, high-gradient insulators, high-voltage pulsers (similar to those needed for the KrF and pulsed power approaches
1 T.A. Mehlhorn, 1997, Intense ion beams for inertial confinement fusion, IEEE Transactions on Plasma Science 25(6): 1336-1356.
2 M.S. Derzon, G.A. Chandler, R.J. Dukart, D.J. Johnson, R.J. Leeper, M.K. Matzen, E.J. McGuire, T.A. Mehlhorn, A.R. Moats, R.E. Olson, and C.L. Ruiz, 1996, Li-beam-heated hohlraum experiments at particle beam fusion accelerator II, Physical Review Letters 76: 435-438.
to IFE), and magnetic materials for induction cores must be further developed to demonstrate adequate cost, reliability, durability, voltage gradient, and efficiency. These components must be assembled into induction acceleration units in an IRE. Pulsing these units at 10 Hz for 3 years will give a total of approximately 109 shots of reliability and durability testing.
1e. It is necessary to produce a complete design of a final focusing system that rigorously meets all known requirements associated with beam physics and shielding. This focusing system must be integrated with a credible chamber design.
1f. The successful completion of items 1a through 1e leads to a major decision point, the decision to proceed with the construction of a 10-kJ to 100-kJ accelerator, the initial step of an FTF. This accelerator must validate the performance of scaled hohlraums and/or adequate hydrodynamic stability for directly driven ion targets. If the estimated cost of this facility is greater than a few hundred million dollars, item 1d has failed to demonstrate adequate cost since the cost of this facility would not extrapolate to acceptable cost for a full-scale driver.
1g. If the intermediate accelerator described in 1f successfully validates the target physics for direct and/or indirect drive and if credible target fabrication techniques and a credible chamber have been successfully demonstrated, there is enough information to make a decision to construct a full-scale accelerator driver. This driver must demonstrate an efficiency-gain product ≥10. At this point, enough information would be available to proceed to an FTF. To minimize the cost of performing the demonstration of efficiency and gain, the driver would be built initially without all the power supplies necessary for high repetition rate. It would be upgraded to drive an FTF by adding more power supplies.
PULSED POWER IFE EVENTS-BASED ROADMAP TO DEMO (TA-3)
There are two technology applications (TAs) to pulsed power (PP) IFE at present. One involves magnetic implosion of magnetized, laser-preheated fusion fuel on a ~100 ns timescale and goes by the name of Magnetized Liner Inertial Fusion, or MagLIF. Other unpublished approaches that would use ~100 ns pulsed power to implode fusion fuel are also under consideration. The other TA, called Magnetized Target Fusion, or MTF, is related to MagLIF through the use of PP technology and magnetic implosion as the driver approach but is otherwise quite distinct: The implosion timescale is more than 10 times longer, the length scale is more than 10 times larger, the magnetic configuration is different (MTF seeks to compress a field-reversed configuration because of the longer timescale) and the plasma density is 100-1,000 times lower. In a broad IFE program including PP IFE, there would be one down-select based on physics and technology between the shorter and longer pulse PP IFE TAs.
Although the power-plant ideas presented by the proponents of MagLIF and MTF differ, the challenges are the same: high yield per pulse in a liquid wall chamber at a repetition rate of order 0.1 Hz; the chamber must be commercially viable and long-lived; and delivery of the current to the target must be accomplished reliably with standoff. Generically, the latter challenge is addressed with recyclable transmission lines (RTLs), and the chamber is assumed to be a thick liquid wall chamber that must recover “completely” to its undisturbed state in the ~10 s between pulses.
MagLIF Approach: Pre-conditions for FTF or DEMO
Up to now, all “data” on MagLIF is from computer simulations. A substantial systematic experimental campaign is planned each year for 5 years to validate the computer simulations and to determine if the goal of scientific breakeven can be achieved on the existing 27 MA Z-machine at Sandia. Scientific breakeven is defined as fusion energy out (using D-T fuel) equals energy delivered to the fuel.
1a. If scientific breakeven is achieved and predictive validity of the design code(s) is demonstrated, results should be compared with other existing results. If one is clearly making more progress than the other, a down-select might be made by the end of the 5-year period based on code predictions of which will be the most favorable approach for IFE. Here the committee assumes that it is unnecessary to take into account differences in reactor technology to do this down-selection. However, if there are significant differences, the necessary engineering design tasks should be carried out during the 5-year period. The conceptual design of a gain >1 facility should be developed. If possible, that facility should be designed to be upgradeable to a high gain facility (FTF) rather than requiring a completely new facility.
1b. If scientific breakeven is achieved but predictive capability is not achieved, experiments and theoretical research must continue before any decision is made to go for an IFE ignition facility. However, the National Nuclear Security Administration (NNSA) may decide to initiate preparations for a single-shot-ignition and high-gain facility depending on mission requirements.
1c. If scientific breakeven is not achieved and the reasons are not understood, MagLIF’s place in the broad IFE program should be reconsidered in light of progress on other TAs.
1d. PP technology must have favorable long lifetime and high efficiency projections as well as low maintenance and repair cost expectations for MagLIF to proceed to an FTF, although a single-shot high-gain facility might still be of interest to NNSA.
1e. A conceptual chamber design with life expectancy of >107 pulses must exist for the 0.1 Hz, 10 GJ yields presently favored by PP IFE proponents, or the approach must be reoptimized at a different rep-rate and yield per pulse. Additionally,
engineering projections for use of RTLs must be favorable and proof-of-principle experiments for their use in a PP system must be successful before an FTF design is undertaken.
MTF approach to PP IFE: Preconditions for FTF or DEMO.
Laboratory experiments on the Shiva Star (operating at 4.5 MJ) capacitor bank deliver up to 12 MA of current to a 10 cm diameter, 30 cm long, 1 mm thick aluminum (Al) cylinder. Assuming success of integrated experiments in which field reversed configuration plasmas are injected into the Al cylinder and then imploded, explosively driven experiments are to follow. Computer simulations are carried out using the Mach2 MHD code.
2a. The Shiva Star experiments are expected to achieve >1019/cm3, 3-5 keV, ~1 cm diameter plasmas confined in a 300-500 T (peak field) field-reversed plasma configuration in ~3 years. Success here would lead to the explosively driven implosion experiments, which could achieve breakeven. The success of the explosively driven experiments together with demonstrated predictive capability would make MTF a competitor at the time of PP IFE down-selection in about 5 years. “Predictive capability” means that the enhancement of yield due to the presence of magnetic field in the initial plasma should be understood in detail in spite of poor diagnostic access.
2b. If scientific breakeven is achieved but predictive capability is not achieved, experiments and theoretical research must continue before any decision is made to go for an IFE ignition facility.
2c. If scientific breakeven is not achieved and the reasons are not understood, MTF’s place in the broad IFE program should be reconsidered in light of progress on other TAs.
2d. PP technology must have favorable long life-time and high efficiency projections as well as low maintenance and repair cost expectations in order for MTF to go on to an FTF, although a single-shot high-gain facility might still be of interest to NNSA.
2e. A conceptual chamber design with life expectancy of >107 pulses must exist for the 0.1 Hz, 5 GJ yields presently favored by MTF proponents. Additionally, engineering projections for use of RTLs must be favorable, and proof-of-principle experiments for their use in a PP system must be successful before an FTF design is undertaken.
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