IX-5 IX-5 磁気ノズルによる遷音速流の生成と宇宙推進機への応用

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1 PF 6, Dec, 6, Tsukuba IX-5 IX-5 磁気ノズルによる遷音速流の生成と宇宙推進機への応用 Production Production of of a a transonic transonic plasma plasma flow flow in in a a magnetic magnetic nozzle nozzle and and its its application application to to space space propulsion propulsion 犬竹正明 Masaaki Inutake 東北大学工学研究科 TOHOKU UNIV.

2 Outline. Introduction. Experimental devices: MPD arcjet, spectroscopy and Mach probe 3. Plasma flow dynamics in various magnetic channels Choked flow in a uniform field, Supersonic flow in a diverging field, Shock wave in a simple mirror field, Transonic flow and specific heat ratio γ i in a Laval nozzle, Helical-kink instability in a current-carrying plasma jet Plasma detachnent from a magnetic nozzle of a space thruster 5. Summary

3 HAYABUSA s ion engine worked well Image of HAYABUSA ion engine Total weight 5kg, Xe gas 6kg, If chemical, propellant 5kg! Nov 6, 5 Hayabusa spacecraft with four ECR ion engines was successfully landed on the asteroid Itokawa for a sample return mission after.5 year flight. isas.jaxa

4 MPD (Magneto-Plasma-Dynamic) Arcjet Plasma thruster with a larger thrust for a manned Mars mission Self-field acceleration (Anode) Fz=j r B θ j (Cathode) B θ j z j F r =j z B θ j r F (Anode) On-ground test of MPD thruster Space laboratory SFU : 4 ton ISAS, JAXA MPDT on-board test in

5 Electromagnetic Acceleration (a) Self-field acceleration (In the present experiments) (b) With external field to improve the performance and to suppress electrode erosion Blowing Pumping ( pinch) + Swirling (rotation) + Hall acceleration

6 HITOP (HIgh density TOhoku Plasma) Device Length : 3.3m Diameter :.8m Axial B z : ~. T ( Mach probe ) Cathode : mmφ Anode :3mmφ MPD Arcjet Quasi-steady pulse ~ ms Highly-ionized ~ 5-9% Density ~ 8 - ( m -3 ) Ion temperature Ti ~ - 4 ev Electron Te ~ 3 - ev

7 Spectroscopic measurements near the MPD exit Particle Temperature T = m c k λ Δλ e (Doppler Broadening) Flow Velocities u z Δλz sinφ = c, uθ = c λ Δλθ λ (Doppler Shift) Spectrum lines HeI(atom) : nm HeII(ion) : nm

8 Mach probe in the downstream region Ion acoustic Mach number : M i M i = U C s = k B miu ( γ T + γ T ) e e i i Alfvén Mach number : M A j M i = κ j M A = U V A = B U μ m n i i (V A : Alfvén velocity) κ is calibrated by use of spectroscopy. γ I and γ e are assumed. Magnetosonic Mach number : M S M S = V A U + C S Ando et al., J. Plasma & Fusin Reseach, 8 (5)

9 3. Plasma flow dynamics in various magnetic channels Choked flow in a uniform field, Supersonic flow in a diverging field, Shock wave in a simple mirror field, Transonic flow and specific heat ratio γ i in a Laval nozzle, Helical-kink instability in a current-carrying plasma jet Plasma detachnent from a magnetic nozzle of a space thruster Uniform field near the MPDA Gradually divergingfield in the down stream region

10 Flow characteristics near the exit of MPD arcjet in in uniform external field anode He atom He ion Rotational velocity Rotational velocity [km/s] Temperature Temperature [ev] Line intensity Line intensity [a.u.] [a.u.] [ev] [km/s] cathode I d = 7.7 ka, dm/dt =.6 g/s(he), B =. T

11 Saturation of M ii in in a Uniform External Field u z [km/sec] T [ev] 3 HeI(atom) HeII(ion) Flow Energy [ev] Linear increase of flow velocity Steep increase of ion temperature ( ion heating : T i >> T e ) M Discharge Current I [ka] d dm/dt =.6g/s(He), B =kg (uniform) at Z=4cm Saturation of M i at unity ( the flow is choked ) Bernoulli s equation γ Bθ ρu Z + P + = γ μ ( B θ is proportional to I d ) const.

12 Choked flow in a uniform field (B z =.87kG) Uniform magnetic field γ I =5/3 and γ e = are assumed. M iz Axial profile of n e and M iz M iθ M ir measurement region I d = 5.kA, dm/dt =.5g/sec

13 Supersonic flow in a diverging field Diverging magnetic field γ I =5/3 and γ e = are assumed. M iz Axial profile of n e and M i M iθ M ir measurement region I d = 5.kA, dm/dt =.5g/sec

14 Shock Wave and Transonic Flow in a Laval nozzle Shock wave near the mirror midplane Transonic flow in a Laval nozzle Mirror cell Laval nozzle Shock transonic flow l c = 5cm > λ ii ~ cm c/ω pi ~cm Shock thickness = ~3cm M i =?

15 Axial profiles of plasma parameters Shock region throat Langmuir probe Mach probe data Electrostatic energy analyzer γ e = γ i =5/3 Langmuir probe T e is almost constant γ e =

16 -D isentropic flow in in a Laval nozzle When the nozzle wall varies gradually, Mach number M, flow velocity U, temperature T and mass density ρ of compressible media are changed dm M du U + = = M ( γ ) M dα ( Μ ) A da A dt T dρ ρ = ( γ ) M M = M M da A da A Mach number M increases when a plasma passes through a Laval nozzle. Mach number M becomes unity at the nozzle throat. The value of ion specific heat ratio influences spatial evaluation of a Mach number.

17 Evaluation of ion specific heat ratio γ i Axial profiles of M i is best-fitted to-d isentropic model. t =.3ms Fitted well It was confirmed that M i = at the throat. ( Sonic Black Hole)

18 Near the the MPDA exit exita converging magnetic nozzle is is effectively formed formeddue due to to strong strong diamagnetic effect. effect. B (external)=87g, He plasma 4 3 anode Bz:5 (G) cathode Br: (G) B j :5 (A/cm z ) j : (A/cm r ) Z (cm) j The flow is choked in the downstream uniform field region.

19 Plasma Rotation and Potential formation u θ [km/s] u θ [km/s] He atom He ion B =.5[T] B =.[T] Cathode 5 Applied Field B [G] Anode X [cm] 5 Flow energy [ev] The u θ increases linearly with the plasma radius in the core region rigid rotation Rotational velocity increases with the increase of applied-field strength. ExB drift is not dominant in the plasma rotation Q V E B E Equation of motion for a rotating plasma B θ p + j θb Z j zb θ = u m i n ; p = p i + p r r Generalized Ohm s law (radial component) en p en r e ( E u B u B ) = ηj + ( j B j B ) = r + θ Z z θ r θ Z z θ e

20 Schematic Steady Electromagnetic of flow patterns Acceleration near in the an MPD MPDA Arcjetexit (A) Applied field ( B z +B r ) Current flow ( j r +j z ) J r flows across B ( not force-free) (B) Helical field ( B z +B θ ) with a variable-pitch (C) Ion flow pattern ( u z +u θ ) U i flows across B ( UxB: back emf, Hall term) en TOHOKU UNIV. en p r e ( E u B u B ) = ηj + ( j B j B ) = r + θ Z z θ r θ Z z θ

21 Collimated Instabilities Helical in in Jet an from MPD an Plasma MPD Arcjet Flow Plasma behavior in axial direction Schematic helically-twisted plasma column From the phase difference of azimuthal and axial probe array signal, the plasma has twisted structure and it rotates in the same direction of the twist. TOHOKU UNIV.

22 Dependence on on Curvature of of Magnetic Field Lines The instability appears even in uniform or diverging magnetic field without any bad curvature of the magnetic field line. The instability seems to be related to the current flowing in the plasma. TOHOKU UNIV.

23 Density profile of the collimated helical jet The jet is not so much diffused even with a large helical axis rotation. Analogous to astrophysical jet?

24 Astrophysical Jet Active Galactic Nuclei (AGN) Radio Jet Large scale jet is formed from a small core region and twisted structure (wiggles) is observed. MHD simulation of the AGN jet The twisted structure is formed in a jet rotating azimuthally by helicalkink instability. Ref: D.L.Meier, et.al., Science, 9()84. Ref: M.Nakamura,et.al., New Astronomy, 6 () 6.

25 Summary Summary () Mechanism of electro-magnetic acceleration : Self-field MPDA : Bernoulli equation? Partly yes Applied-field MPDA : modified Bernoulli equation? Not yet () Mach number limitation and ion heating near MPDA exit: Choked flow in the effectively converging nozzle due to strong diamagnetic effect of a high beta plasma? Yes Shock heating or adiabatic compression heating? Not yet = const. + + μ γ γ ρ θ B P U Z ( ) const. = z Z Z u u B B B P u u μ μ γ γ ρ θ θ θ θ

26 (3) Energy conversion through a magnetic nozzle : Isentropic conversion from subsonic to supersonic flow possible? Yes How high is the specific heat ratio γ i? γ i =. -. depending on the ionization degree (4) Higher velocity by ICRF wave heating : (not shown) Alfvén wave one-path heating of a fast flowing plasma possible? Yes Perp-para particle energy conversion according to magnetic moment μ = const.? Yes (5) Helical-kink instability and its control: yes (6) Plasma detachment from a magnetic filed line : (in future) Can super-alfvénic flow tear away the field line? Steadily or intermittently? Charge separation?