1. 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 Thomas Jefferson National Accelerator Facility, Newport News, VA University 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

2. 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 (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

3. 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

4. 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 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 liquid N2 temp > 5 hr
eg. ICF pellet MRI:
pellet: empty full ✔
3He fill line  

5. 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 ✔

6. 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 ✔ ?

7. 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 ✔ ? ?

8. 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 ✔ ? ?

9. Most Critical Uncertainty is Survivability of Polarization in the Fusion Plasma EnvironmentQ5
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) ; Garzotti et al., Nucl. Fusion 52 (2012)
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

10. 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

11. 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

12. Preparatory steps for a SPF test experiment - optimize filling pellets with polarized 3HeQ6
• 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):

13. Preparatory steps for a SPF test experiment - optimize loading pellets with HD and polarizingQ7
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

14. 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)

15. Further Developments are Needed for Utilizing Spin Polarized DT in an ITER-class DeviceQ7
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

16. 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

17. extras

18. 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 :

19. • 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 = 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

20. Secondary Reactions • use H-plasma heated with H neutral beams
• simulations follow secondary reactions to estimate background yields:
3He + D a α + p (Q = MeV) E(p) ~ 15 MeV
9 D + D a 3He+n (Q = MeV)
9 D + D a T + p (Q = MeV) E(p) ~ 3 MeV
9 D + T a α + n (Q = 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