ionic propulsion
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8/12/2019 Ionic Propulsion
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Lattice-Boltzmann Models of Ion
Thrusters
Dr. Jacques C. Richard
richard@aero.tamu.edu
And
Prerit Shah
Prerit_aggie@neo.tamu.edu
Texas A & M University
College Station, TX 77845, USA
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Lattice-Boltzmann Method (LBM) & Ion Thrusters
! Complement Discrete Simulation Monte-Carlo (DSMC) models for faster computation
of critical ion thruster parameters
!
Use LBM to model plasma flow in thruster! Compare results with experimental data and
DSMC predictions
! Identify plasma flow characteristics that lead
to thruster component erosion; e.g.,grids
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Outline
! Ion thrusters (see Gallimore, 2004)
Basic physics of operation
Issues of interest: lifetime/erosion
! Why try LBM?
! LBM & Ion thrusters
! Some results
! Summary, conclusion & future work
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Ion thrusters are the most efficient EP devices at converting input power to thrust and are
used both as primary propulsion and for station-keeping on commercial and scientific
spacecraft.Key issues include grid erosion and thrust density limitations from space-charge effects.
Xe+Xee-Xe
e-Xe+
Xe+
DischargePlasma
Ion Beam
Propellant Feed
e-
e-
Xe
Xe
Hollow Cathode Neutralizer
Anode
DischargeHollow
Cathode
Permanent Magnets
Acceleration Grid
Screen Grid
e-
Ion Thrusters
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Ion thruster concept (Gallimore, 2004)
!Electrons are emitted from dischargecathode assembly (DCA)
! DCA electrons (Primary) areaccelerated by local sheath to highvoltage (>15 eV)
! Primaryelectrons create ions viaimpact ionization with neutrals
! Ionization process starts with one
Primaryand one neutral - results in 2Maxwellian electrons and one ion
! Ions are attracted to ion optics (Screengrid) via electric field
! Ions are accelerated through optics(Screen & Accel grids) - ion beamneutralized by neutralizer cathode
! Accel grid negative to prevent electron
backstreaming! Note: While Maxwellianelectrons
outnumber Primaries10:1, the latteraccount for most of the ionization inthe discharge chamber.
Ion Thrusters Basics
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Solar Electric Propulsion NASAs EvolutionaryXenon Thruster (NEXT) [5-10 yr. deployment time]
-NEXT is the follow-on to NSTAR used on DS1 and
slated for DAWN (2006 launch)-NEXT represents a 4x improvement in thrust and
power and a 25% increase in Isp (from 3280 to 4100
s) over NSTAR at half the specific mass (from 2.6 to
1.2 kg/kW)
DAWN
Nuclear Electric Propulsion NASAs NuclearSpace Initiative [10-15 yr. deployment time]
Electric Propulsion Proposals in NASAs 2002 In-
Space Propulsion Technologies NASA ResearchAnnouncement (NRA) for ultra-high-performance
engines (Isp > 6,000 s)
JIMO
HiPEP
90 cm x 40 cm
NEXIS
60 cm
Modern Ion Thrusters
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Ion Thruster Basics
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Slow
CEX Ion
Fast
CEX Neutral
CEX ions
that hit side
Lower j
High j
High PERVEANCE MARGIN - Low Ne but High
Ion Thruster Basics
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Ion Thruster Basics
Accel Grid
-300 V
Screen Grid~1170 V
Anode ~1200 V
Ion Birth Potential
Potential
Neutralization Plane
~ 0 V
Xa 2Xa
Equipotentials (simulation)
Lower j
High j
over-focus
under-focus
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Typical Ion Engine Parameters
! Within a few cm of grid, typical ion thruster& plasma parameters are:
nXe+~ 1012-1010 cm-3, ne~ 10
12-1010 cm-3>> nXe>> nXe++
! V+~ 1075 V at screen grid
! V-~ -150 V at accelerator grid
! Grid separation ~ 1 mm
! Screen grid opening diameter ~ 2 mm
! Accelerator grid opening diameter ~ 1 mm
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Assumptions of Applicability of LB
! Note local Kn:Crawford (2002)
! Kn~ O(0.1) around optics
! Ion veloc. distrib. Laser-
induced FluorescenceVelocimetry of Xe II in the
30-cm NSTAR-type Ion
Engine Plume, Smith and
Gallimore (AIAA-2004-3963)
! Maxwellian radialf(v)
Kn =!
L=
RT
2"d2NApL
L =#
d#/ dx
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBMEP Model
! The model assumes coupling of the velocitydistribution function w/the electrostatics
! Assume linear collision if close to thecontinuum limit so that Q= -"r(f-f
(eq))
! Adequate for near equilibrium plasma, simple
charge exchange (CEX) collisions or evenassume Q=0 for collisionless, electrically-driven plasma
!f
!t+ c "
rf#
q
m"
r$"
cf =Q(f,f)
%0"r
2
$=
e fd
3c
&
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Collision:
Sources:
Computational Procedure
Streaming:
t=t+dt
Calculate physical variables
%f!
(t)= f
!
(t) "1
#
f!
(t) " f!
(t,eq)$% &' +g!
f!
(t+"t)x i +ei"t,t+ "t( ) = f!
(t)x i,t( )
!(t+"t) = f#(t+"t)
#=0
N
$
!(t+"t)u( t+"t) = e#f#(t+"t)
#=0
N
$
f! = f
!
(eq)= "w
! 1+ 3
c2e!# u + 9
2c4(e
!# u)2- 32c
2u #u$
%&'()
Initialization:Assignf(eq)
Electrostatics:
!0"r2#=e f$
(t+%t)
$=0
N
&
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Axi-symmetric Cylindrical Coordinates
! In accordance w/thruster geometry! Use work of Yu, Girimaji & Yu (2004)
where cyl. coord. effects are incorporated
via source terms in LBE to satisfy macro-level cyl. coord. eqs. (NS)
g! = w!s +3
c2w!e!"a
where,
s =#u
r
r,az =
v
r
$uz$r
+q
m
$%$z
$f$vz
,ar =v
r
$ur$r
#u
r
r
&'(
)*+ +
q
m
$%$r
$f$vr
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Results
! Compare general trends: non-
dimensional
! Compare specific cases
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Dr. Jacques C. Richard
LBM Ion Thruster Exhaust Stream
Unitless ion #density contours; matches Crawford (2001)
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Ion Thruster Exhaust Stream
Ion velocity field
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Ion Thruster Exhaust Stream
Electrostatic potential
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Models of Ion Thruster Optics
! To look at grid erosion,we want to zoom in ona grid segment with2D/axi-symmetric
models as belowElectrostatic potential contours
from modeling a slit btwn grids
Electrostatic potential contours
from Duchemin (2001)
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Ion Thruster Optics
Electrostatic potential
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Models of Ion Thruster Optics
! Zoom in on a opticssegment with 2D/axi-symmetric models asbelow
Electrostatic potential contours
from modeling a slit btwn grids
Electrostatic potential contours
from Duchemin (2001)
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Electrostatic potential btwn grids
Electrostatic potential contours
from Gallimore (2004)
Electrostatic potential contours
from Duchemin (2001)
LBM Models of Ion Thruster Optics
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Department of Aerospace Engineering
Dr. Jacques C. Richard
(2D )? 2 1Jul 2004?
10 20 30 40 50 60 70
x
10
20
30
40
50
60
y
(2D )? 2 1Jul 2004?
LBM Ion Thruster Optics
vion: Vscreen=10V, Vaccel=-10V
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Models of Ion Thruster OpticsIon # density; screen grid 10V, accelerator grid -10
Crawford (2001)
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Models of Ion Thruster OpticsIon # density; screen grid 1075V, accelerator grid -180
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Department of Aerospace Engineering
Dr. Jacques C. Richard
LBM Models of Ion Thruster OpticsIon velocity field; screen grid 1075V, accelerator grid -180
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Conclusions & Future Work
! LBM does well w/modeling EP
! Next is to try
other species variations in collision operator,
e.g.,pseudo-random collision
frequency as used in DSMC
Other variations of BE form
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Computational Domain
Screen
grid
Accelerator
grid
Computational
Domain
S4
S3
S2
S1
S5
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Extrapolation Boundary
" Extrapolation boundary condition has beenapplied at S1 and S4 in computational domain.
"At S1, f(1,j,9) =f(2,j,9)
f(1,j,2) =f(2,j,2)
f(1,j,6) =f(2,j,6)
"At S4, f(NX,j,8) =f(NX-1,j,8)
f(NX,j,4) =f(NX-1,j,4)
f(NX,j,7) =f(NX-1,j,7)
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Free stream boundary
" Free stream boundary condition has been applied at S2 andS3 in the computational domain.
" At S2, f(1,j,9) = 0.0
f(1,j,2) = 0.0 f(1,j,6) = 0.0
" At S3,
f(NX,j,8) = 0.0
f(NX,j,4) = 0.0
f(NX,j,7) = 0.0
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Department of Aerospace Engineering
Dr. Jacques C. Richard
Symmetric Boundary
"Symmetric boundary condition has been
applied at S5 on the computational
domain.
"At S5,
f(i,1,7) =f(i,2,8)
f(i,1,3) =f(i,2,5)
f(i,1,6) =f(i,2,9)
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