Fusion Propulsion Opening the Solar System Frontier John F Santarius Lecture 28 Resources from Space NEEP 533/ Geology 533 / Astronomy 533 / EMA 601 University of Wisconsin March 31, 2004 Key Points • D-3He appears to be the fusion fuel of choice for space applications. • D-3He fusion will provide capabilities not available from other propulsion options. • Several configurations appear promising for space propulsion, particularly the field-reversed configuration (FRC), magnetized-target fusion (MTF), spheromak, and spherical torus. • Successful development of D-3He fusion would provide attractive propulsion, power, and materials processing capabilities. JFS 2004 Fusion Technology Institute 2 A Prophecy Whose Time Will Come “The short-lived Uranium Age will see the dawn of space flight; the succeeding era of fusion power will witness its fulfillment.” From the essay “The Planets Are Not Enough” (1961). JFS 2004 Fusion Technology Institute 3 D-3He Fusion Will Provide Capabilities Not Available from Other Propulsion Options 107 Fusion ) s 6 / 10 10 kW/kg m ( y 1 kW/kg t i c o l 5 0.1 kW/kg e 10 v t Nuclear us (fission) Ga s-core fission ha electric x 4 E 10 Nuclear thermal Chemical 103 10-5 10-4 10-3 10-2 10-1 1 10 Thrust-to-weight ratio JFS 2004 Fusion Technology Institute 4 At the Predicted Specific Power, α=1-10 kW/kg, Fusion Propulsion Would Enable Attractive Solar-System Travel • Comparison of trip times and payload fractions for chemical and fusion rockets: Fast human transport Efficient cargo transport 1000 1 900 0.9 ) s 800 0.8 on y Chemical i t a 700 0.7 c d 600 Fusion (1 kW/kg) 0.6 ( Fusion (10 kW/kg) 500 fra 0.5 d me i 400 0.4 t oa l p 300 y 0.3 a Tri 200 P 0.2 100 0.1 0 0 Earth-Mars Earth-Jupiter Earth-Mars Earth-Jupiter (33% payload) (7% payload) (260 days) (1000 days) JFS 2004 Fusion Technology Institute 5 Key Fusion Fuel Cycles for Space Applications D + 3He → p (14.68 MeV) + 4He (3.67 MeV) D + T → n (14.07 MeV) + 4He (3.52 MeV) D + D → n (2.45 MeV) + 3He (0.82 MeV){50%} → p (3.02 MeV) + T (1.01 MeV) {50%} 10-21 L 1 - s 3 -22 m H 10 D-3He t a r D-T p-11B n -23 o 10 i t 3 c He- a 3 e D-D He Re 10-24 1 5 10 50 100 500 Ion temperature keV JFS 2004 Fusion Technology Institute 6 H L Physics Viewpoint: D-3He Fuel Requires High β, nτ, and T† Confinement Power density 1000 1 y t 500 i s n e D-T d r -1 100 e 10 3 w L He:D=1:1 o V 50 p e k n H i 3 o i He:D=1:1 T D-T s u -2 10 f 10 e v 5 i D-D t a l e R -3 1 10 1019 1020 1021 1022 1 10 100 nt m-3s Ion temperature keV † β = plasma pressure/magnetic field pressure τ = energy confinementH L time H L JFS 2004 Fusion Technology Institute 7 D-3He Fuel Could Make Good Use of the High Power Density Capability of Some Innovative Fusion Concepts • D-T fueled innovative concepts become limited by neutron wall loads or surface heat loads well before they reach β or B-field limits. • D-T fueled FRC’s (β~85%) optimize at B ≤ 3 T. • D-3He needs a factor of ~80 above D-T fusion power densities. ¾ Superconducting magnets can Power Density Relative to a reach at least 20 T. D-TFRC with b=85%and B=3T ¾ Fusion power density scales as β2 B4. 2000 1000 x ¾ Potential power-density 1000 100 x 10 x improvement by increasing 1 x 0 β and B-field appears at right. 1 20 0.75 15 0.5 10 b 0.25 5 B T 0 JFS 2004 Fusion Technology Institute 8 H L Engineering Viewpoint: D-3He Fuel and High β Relax Constraints 1 • Reduced neutron flux allows D-T e s D-D ¾Smaller radiation shields a e m l s e r a ¾Smaller magnets l p g r e ¾Less activation n o 3 r ed fa He:D -1 10 =1:2 ¾Easier maintenance o i n s o u r Increased charged-particle fy t • u e Tritium burn on nm flux allows direct energy n fraction = 50% 3 s o He:D i as t conversion to thrust or c =1:1 a r 3He:D=3:1 Ff electricity 10-2 1 10 100 Ion temperature keV H L JFS 2004 Fusion Technology Institute 9 Spacecraft Mass Gains Nonlinearly with Thrust Efficiency • High efficiency increases thrust power and reduces radiator mass. 4 a e L h s t a s m Direct a 3 wt o t conversion η a te i d a g rs r 1−η e 2 n tr eo Thermal e u f w cycle e o s po uy 1 or ol o i o t i t a rf a H Rf 0 0 0.2 0.4 0.6 0.8 1 Thrust efficiency • Doubling efficiency from a thermal cycle’s ~1/3 to direct conversion’s ~2/3 gives 4 times better power per unit waste heat. JFS 2004 Fusion Technology Institute 10 Predicted Specific Power of D-3He Magnetic Fusion Rockets is 1-10 kW/kg • Prediction based on reasonably detailed magnetic fusion rocket studies. Specific Power First Author Year Configuration (kW/kg) Borowski 1987 Spheromak 10.5 Borowski 1987 Spherical torus 5.8 Santarius 1988 Tandem mirror 1.2 Bussard 1990 Riggatron 3.9 Teller 1991 Dipole 1.0 Nakashima 1994 Field-reversed configuration 1.0 Williams 2003 Spherical torus 8.7 Thio 2002 Magnetized-target fusion 50 Emrich 2000 Gasdynamic mirror 130 Wessel 2000 Colliding-beam FRC 1.5 JFS 2004 Fusion Technology Institute 11 Generic Fusion Rocket Model Supports 1-10 kW/kg • Rationale for this performance published by J.F. Santarius and B.G. Logan, “Generic Magnetic Fusion Rocket,” Journal of Propulsion and Power 14, 519 (1998). Features of the model are: ¾ Cylindrical geometry ¾ Main mass contributors: radiation shields, magnets, refrigerators, and radiators ¾ Heat flux limit of 5-10 MW/m2 ¾ Neutron wall load limit of 20 MW/m2 ¾ Radiators reject 5 kW/kg ¾ Low temperature superconducting magnet He refrigerators require 1000 kg/kWrejected ¾ Low-mass radiation shield (LiH with 10% Al structure) ¾ Magnet mass calculated by virial theorem and by winding-pack current density limit (50 MA/m2); larger value used ¾ Development of high-temperature superconductors should reduce the power-plant mass. Reduced refrigerator mass for magnet coolant Reduced shielding, because more magnet heating can potentially be tolerated before quenching JFS 2004 Fusion Technology Institute 12 Earliest D-3He Reactor Design Was a Fusion Rocket G.W. Englert, NASA Glenn Research Center New Scientist (1962) “If controlled thermonuclear fusion can be used to power spacecraft for interplanetary flight it will give important advantages over chemical or nuclear fission rockets. The application of superconducting magnets and a mixture of deuterium and helium-3 as fuel appears to be the most promising arrangement.” JFS 2004 Fusion Technology Institute 13 Conventional Tokamaks Have Large Mass JFS 2004 Fusion Technology Institute 14 EFBT Toroidal Fusion Rocket J. Reece Roth, NASA Lewis, 1972 JFS 2004 Fusion Technology Institute 15 Spherical Torus Space Propulsion • ST’s give high β, implying Princeton Plasma Physics Lab NSTX experiment high power density. • Crucial problems are recirculating power and providing thrust from a toroidal configuration. • Martin Peng has suggested helicity ejection, and the concept will be tried on NSTX. JFS 2004 Fusion Technology Institute 16 Plasma-Jet Magnetized-Target Fusion Allows Liner Standoff from Target Plasma gun Based on NASA MSFC figures Plasma jet Arrows indicate flow direction Plasma liner Magnetized target plasma • An approximately spherical • The jets merge to form a distribution of jets is launched spherical shell (liner), towards the compact toroid at imploding towards the center. the center of a spherical vessel. JFS 2004 Fusion Technology Institute 17 The MTF Explosion/Implosion Process Involves a Complicated Mixture of Shock Waves • Red=target; Purple=plasma jet; Green=buffer plasma 0.05 Case 030313_02 mt=4.38 mg; Dt=5.0 cm 0.04 mj=0.2 g; Dj=2.4 cm mb=2.0 g; Db=22.1 cm vj=125 km s; vb=125 km s L 0.03 m H ê ê u i d a r e n o 0.02 Zs 0.01 0 0 0.5 1 1.5 2 Time ms JFS 2004 Fusion Technology Institute 18 H L Conversion of Fusion Energy into Thrust -4 -1 -5 -3 -2 4 5 0 1 2 3 -4 Reversed Conical -2 Theta Compressed Main Pinch magnetic flux Coils 0 Expanding plasma Fusion front burst 2 • Fusion produces a high-temperature plasma, which can be used to push against a magnetic field to produce thrust directly. • Direct conversion of the fusion energy into thrust is important in realizing the benefits of fusion for propulsion. NASA MSFC RevolutionaryRevolutionary AerospaceAerospace SystemsSystems ConceptsConcepts (RASC)(RASC) FY02FY02 StudyStudy ProposalProposal GroupGroup 22 –– HHumanuman ExplorationExploration OctoberOctober 2,2, 20012001 BeyondBeyond MarsMars RASC/HOPE MTF Engine Configuration Reversed Conical Plasma Gun Theta Pinch (Approx. 56 in. long x 9.5 in. dia.) Theta Pinch Gun (48 plcs) (Located 180 deg. Apart) (2 plcs) Structural Ring Stiffener (12 in.