Spin Polarized Fuel for Increased Fusion Gain Larry Baylor1, William Heidbrink2, Michael Lowry3, G. Wilson Miller4, David Pace5, Andrew Sandorfi3, Sterling Smith5, Mickey Wade5, Xiangdong Wei3, and Xiaochao Zheng4 1Oak Ridge National Laboratory, Oak Ridge, TN 37831 2University of California-Irvine, Irvine, CA 92697 3Thomas Jefferson National Accelerator Facility, Newport News, VA 23606 4University of Virginia, Charlottesville, VA 22904 5General Atomics, San Diego, CA 92186 Presented to the FESAC Transformative Enabling Capabilities Subcommittee Meeting in Rockville, Maryland, USA 31 May 2017 Random Polarization (Typical) Polarizations Aligned along magnetic field

Polarizing & Aligning Spins of Fuel Nuclei Increases Fusion Cross Section and Fusion Gain Q1,2,3 Spin polarization of DT nuclei modifies fusion reaction properties: [Kulsrud PRL 49 1248 (1982)] 50% increase in fusion cross section when spin of both D and T are aligned with the magnetic field Resultant alpha particle velocity distribution is anisotropic Potential impact on alpha confinement and induced torque Predictions show enhanced cross section leads to 75% increase in ITER fusion gain Reactivity further enhanced beyond simple cross section increase by increased alpha heating Polarizations Aligned to B Polarizations Anti-aligned ITER Q vs. cross section enhancement SPF <συ> gain

1) Produce Spin Polarized fuel 2) Inject into Fusion Device Two Basic Steps needed for Application of Spin Polarized Fuel to Future Fusion Devices Q2 1) Produce Spin Polarized fuel 2) Inject into Fusion Device Storage may also be required, depending on available inventory and reprocessing plant design

1) Produce Spin Polarized fuel Production and “Payloading” of Spin-Polarized Fuel Has Been Demonstrated Q6 1) Produce Spin Polarized fuel Jefferson Labs (JLab) routinely makes large (25 cc) HD samples for nuclear physics experiments: Up to ~40% of the deuterium polarized Depolarization time @ liquid He temp ~2 yr JLab and Univ. of Virginia (UVa) have pioneered the filling of ICF pellets with polarized 3He, retaining > 2/3 of the initial polarization Depolarization time @ liquid N2 temp > 5 hr eg. ICF pellet MRI: pellet: empty - full ✔ 3He fill line  

2) Inject into Fusion Device Technology and Physics of Delivery and Heating of Spin-Polarized Fuel Still an Open Question Q6 2) Inject into Fusion Device Pellet injection routinely available on many fusion devices ✔

2) Inject into Fusion Device Technology and Physics of Delivery and Heating of Spin-Polarized Fuel Still an Open Question Q6 2) Inject into Fusion Device Pellet injection routinely available on many fusion devices However, Injection technology to retain spin state during pellet delivery requires substantial development ✔ ?

2) Inject into Fusion Device Technology and Physics of Delivery and Heating of Spin-Polarized Fuel Still an Open Question Q6 2) Inject into Fusion Device Pellet injection routinely available on many fusion devices However, Injection technology to retain spin state during pellet delivery requires substantial development More importantly, Basic prediction that spin polarization is retained as ion is heated to thermonuclear temperatures is untested ✔ ? ?

2) Inject into Fusion Device Success of Spin Polarized Technology Dependent on Both Technology & Physics Variables Q4 2) Inject into Fusion Device Critical design variables: Production: Achievable polarization fraction Retained polarization fraction during “payloading” Rate at which polarized fuel can be produced/”payloaded” Delivery to Plasma Retained polarization fraction during delivery Repetition rate for delivery Within Plasma Retained polarization fraction during heating Required fueling rate ✔ ? ?

Most Critical Uncertainty is Survivability of Polarization in the Fusion Plasma Environment Q5 Many possible depolarization mechanisms have been considered in the literature: eg, Kulsrud et al., Nucl. Fusion 26 (1986) 1443; Gatto, Springer Proc. Phys. 187 (2016) 79 Most mechanisms predicted to have little or no impact over short fusion times Primary exception is depolarization through wall recycling Fortunately, plasma re-fueling from wall recycling is expected to be very small in burning plasma devices ITER modeling affirms this expectation eg, Pacher et al., Nucl. Fusion 48 (2008) 105003; Garzotti et al., Nucl. Fusion 52 (2012) 013002 Reliance on “once-through” nuclei for fusion power production puts spin- polarized fuel on same footing as un-polarized D/T Only way to confirm polarization survival is through a dedicated proof-of-principle experiment

Proof-of-Principle Experiment Takes Advantage of Existing Capabilities in the U.S. Scientific Program Q7 1) Produce Spin-Polarized HD and 3He using methods develop at JLab and UVa 2) Inject into fusion device and measure D-3He fusion by-products D-3He has same nuclear and spin physics as D-T  Results should be directly applicable to polarized D-T reaction

Proof-of-Principle Experiments Will Require Deployment and/or Development of Several New Capabilities Q7 Production/Transport of Spin-Polarized D and 3He Field a 3He polarizer/pellet diffuser at fusion confinement facility Develop method to transport polarized HD pellet from JLab to facility Delivery to plasma Retrofit existing pellet injection system with Holding field to maintain polarization while waiting for injection Small guide field down launch tube to help sustain polarization SQUID detector to measure actual polarization injected RF spin flipper to achieve aligned/anti-aligned configuration Measuring Impact Develop and deploy diagnostics optimized for fast protons or alphas (fusion products of D/3He) Develop high performance H plasmas Minimize background D-3He fusion production

Preparatory steps for a SPF test experiment - optimize filling pellets with polarized 3He Q6 • R&D at Univ of Virginia and Jefferson Lab • On-line MRI while filling ICF pellets with polarized 3He • In-pellet polarization maintained > 5 hr at LN2 temperatures  develop at UVa/JLab; install at DIII-D Interface with cryo-injection gun 3He polarizer t(s): 30 90 210 300 540 900

Preparatory steps for a SPF test experiment - optimize loading pellets with HD and polarizing Q7 Pellets would be filled at JLab with HD gas, frozen to a solid, and polarized Existing NP techniques used for maximize D polarization Develop fill & handling systems compatible with both NP equipment and cryo-injection guns Large NP targets are transported ~ 1 km while polarized to experimental hall  Need equipment to ship ~4000 km to DIII-D

Key Observables Identified as Quantity and Poloidal Distribution of Energetic Proton Fusion Products P(3He) = 65%; P(D) = 40% ψ 0o +90o -90o +45o -45o DIII-D specific detailed tracking calculation Definitive Signal: • ~30% change expected at several wall locations • distinctive dependence on poloidal angle (ψ)

Further Developments are Needed for Utilizing Spin Polarized DT in an ITER-class Device Q7 If proof-of-principle experiments are successfully, deployment on ITER-class device will require development of: Regular and automated production of high polarization fraction DT pellets at sufficient rate for fueling a burning plasma device Current methods produce ~1021 ions/sec with ~60% polarization purity for D  Need another order of magnitude higher for ITER fueling needs Technology to deliver spin-polarized tritium Could be easier than deuterium Tritium handling may necessitate extra procedures Methods to increase produced/retained polarization fraction Production process Diffusion process if using ICF shells Pellet delivery process

Development of Spin Polarized Fusion Offers Potential for Improved Reactor Efficiency and U.S. Leadership Full polarization of DT fuel leads to significant improvement in performance 50% increase in fusion cross section is roughly equivalent to 25% improvement in confinement (assuming t ~ P-0.5) Opportunity for the U.S. to be a world leader in impactful R&D U.S. is a world leader in producing spin-polarized D and 3He Some interest worldwide in spin-polarized fusion but very few R&D activities Required technical steps are full of opportunities to conduct state-of-the-art R&D Developed technology should be transferable to all confinement concepts (magnetic and potentially also inertial) Spin Polarized Fusion => Transformative, Enabling, and Compelling R&D

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spin-dependent 3He+D  α+p (or T+D  α+n) angular distributions • polar (pitch) angles relative to local magnetic field direction • neglecting interference terms (good to ~ 2-3 %) θ  angle integrated cross section :

• net fractional polarization loss: Polarization dilution from Hyperfine Splitings (HFS) in partially ionized states at injection • g.s. of all fuels (DT, HD, 3He, …) have 2 electrons paired to 1s  no nuclear int. • after injection, a partially-ionized state with 1 electron will exist for ~ 10 ms, during which there will be level mixing and a degree of dilution of nuclear pol • net fractional polarization loss:  3He has the largest hyperfine splitting, AHFS = -8.66565 GHz  mean ΔP/P for 3He, averaged over the DIII-D plasma field region and weighted by particle density = 1 %  HFS ~ 1/B2  irrelevant in ITER, due to higher magnetic fields

Secondary Reactions • use H-plasma heated with H neutral beams • simulations follow secondary reactions to estimate background yields: 3He + D a α + p (Q = +18.3 MeV) E(p) ~ 15 MeV 9 D + D a 3He+n (Q = + 3.3 MeV) 9 D + D a T + p (Q = + 4.0 MeV) E(p) ~ 3 MeV 9 D + T a α + n (Q = +17.6 MeV) • 15 MeV protons from 3He + D a α + p provide a unique signature that is easily separated • 2-step (D + D a 3He) + D wrt primary 3He + D is suppressed by n(D) / [n(D)2xn(D)], which is negligible