ECR Plasma Thruster development at Onera

ECR Plasma Thruster development at
Onera
Denis Packan
ONERA, Physics and Instrumentation Department, Palaiseau
EPIC Workshop, 25-28 November 20114, Brussel
Two Neutralizer-free gridded ion thrusters
developed at the LPP, Ecole Polytechnique, France
(Dr A. Aanesland)
1. PEGASES
Plasma Propulsion with Electronegative Gases
Accelerates positive and negative ions to generate thrust
T. Lafleur, D. Rafalskyi and A. Aanesland, PSST 24 015005 (2014)
State-of-the-art:
Principle:
A+
A2
A+
e-
RF
power
Advantages:
•
•
•
•
A+
A-
High density ion-ion plasma
Alternate ± ion
beams
A-
A-
Electronegative
plasma
A proof-of-concept combining experiments,
simulations and analytical models
Magnetic Ion-ion Alternate Recombination
barrier plasma acceleration
v
External e-neutralizer redundant
Interesting plume properties (no electrons
and low density of charged particles)
Control of the emitted net charge
Solid propellant (Iodine)
v
Generalized CL law for
alternate acceleration
Full space charge
compensation in the beam
Two Neutralizer-free gridded ion thrusters
developed at the LPP, Ecole Polytechnique, France
Technology transfer from the semiconductor industry
Accelerates continuously positive ions with burst of electrons
D. Rafalskyi and A. Aanesland, J.Phys.D: 47 495203 (2014)
2. Neptune
State-of-the-art:
Principle:
Laboratory proof-of-concept
RF rectification to a DC bias
RF to DC bias linear
dependency
RF source
(ICP)
RF biased
grid
A+
e
RF
Blocking
capacitor
Advantages:
•
•
•
•
•
•
mean ion
energy
v
No Cathode
Capacitive system ensure extracted Idc=0
Anisotropic EEDF = low plume divergence
No DC amplification needed
Any gas can be used also solid iodine
Technology heritage from ion engines
v
electron
extraction
Efficient RF extraction
High ion energies
Low anisotrop electron energies
ECR Thruster Principle
•
•
Electron heating in an electron cyclotron
resonance (ECR) source + Plasma acceleration
in a magnetic nozzle
ECR effect: application of an EM field at electron
cyclotron frequency
eB
ce 
at 2.45 GHz, B=875 Gauss
me
Efficient ionization of the propellant gas (Ar, Xe)
•
Magnetic nozzle: divergent magnetic field
electron acceleration: conversion of electron
gyrokinetic energy to longitudinal energy
formation of a space charge at the thruster exit
acceleration of ions by ambipolar electric field
ECRA Thruster : Advantages and challenges
Intrinsic advantages of ECRA thruster over existing electric propulsion technologies:
•
Plasma and plume electrically neutral
 no need for a neutralizer
 high thrust density (no space charge limit)
•
No DC electric field needed
 no grid or electrodes, no erosion (natural magnetic shiedling)
 no need for an additional power supply (only microwave)
→Simplicity: reduced cost, increased reliability
Potentially (observed): variable Isp (mission flexibility), magnetic beam steering
Challenges for studies (with respect to other thrusters):
-
Plasma physics more complex than other thrusters
(wave/ionisation/acceleration coupling): difficult to model.
No direct experimental knowledge of the total current and of the ion energy:
need for very refined experimental characterization
Previous studies
•
ECR thruster studied in the 60s, and at Caltech in the 80s.
•
Experimental limitations:
•
•
•
•
•
high power studies: cost of design iterations
limited pumping rates
mircowave technology not mature
no rare earth magnets
limited numerical simulations
→ new study with lower power, new approach, more mature
technologies. Results obtained already better.
ECRA Thruster ONERA : Principle
ωce 
7
eB
me
at 2.45 GHz
B=875 Gauss
Microwave chain
•
•
Measurement of forward power and reflected power
 power absorbed by the ECR source
Only coaxial cables are used (no waveguides)
compact thruster
Circulator
2.45 GHz
Bidirectional coupler
MW generator
50 Ω
Forward Reflected
power
power
DC block
ECR
source
ECR Source
•
•
•
•
•
Coaxial geometry: antenna-to-cylinder
Small dimensions (Diameter=13mm, source length=15 mm)
MW power provides a radial electric field
Antenna and cylinder are floating
Radial injection of the propellant gas (argon)
ECR Source
Magnetic field produced by permanent magnets: purely divergent in the source
and the magnetic nozzle
ECR source
1400
250
cylinder
1000
B
dBz/dz
150
800
resonance
at 2,45 GHz
100
600
50
400
0
200
-50
-100
0
0
magnet
10
20
30
40
Axial position z [mm]
50
60
dBz/dz [Gauss/m]
200
1200
|B| [Gauss]
•
View of ECR Thruster in Operation
ECRA design configuration
ECRA magnets version
13 mm diameter
ECRA Coil version
27 mm diameter
Influence of the Mass Flow on IEDF
•Ion energy peaks shifted to lower energy when increasing gas density
•Ion mean energy and thruster potential follow similar trends
(Hiden mass-energy spectrometer)
200
350
Qm(Xe):
150
250
200
100
150
100
50
50
0
0,0
0
100
200
Ion energy [eV]
300
400
0,1
0,2
Qm(Xe) (mg/s)
0,3
Thruster potential (V)
300
Ei (eV)
0.06 mg/s
0.1 mg/s
0.15 mg/s
0.2 mg/s
0.3 mg/s
Ion Mass Analysis
•
•
Mainly Xe+ ions
Small amounts of Xe2+, traces of Xe3+
Qm=0.1 mg/s, P=30 W
Xe+
Xe2+
0
20
40
60
80
m/z
100
120
140
Ion energy versus azimuthal angle.
Angular profile of energy spectrum
Qm(Ar)=0.2 mg/s
Magnetic nozzle: LIF and emissive probe measurements
240
0.1 mg/s
0.06 mg/s
220
200
Calculated from:
Doppler shift (LIF)
Emissive probe
110
100
180
Plasma potential [V]
Plasma potential [V]
0.1 mg/s
120
160
140
120
100
80
60
90
80
70
60
50
40
30
40
20
20
10
0
0
0
20
40
Axial position [mm]
60
80
0
20
40
60
80
100 120 140 160 180 200 220 240
Axial position [mm]
Good agreement between velocity measurements (LIF) and plasma
potential measurements (emissive probe)
Results and perspectives
Mass utilization Power Divergence Thruster Thrust to Power Mass flow rate Power ion energy Ion current Isp [s]
Thrust [mN]
efficiency [%] efficiency [%] efficiency [%] efficiency [%]
ratio [mN/kW]
[mg/s]
absorbed [W]
[eV]
[mA]
Gas
Xenon
0,1
30,0
248,5
45,5
0,98
33
1001
0,62
0,38
0,83
16,1%
Efficiency at the level of the state-of-the-art
•
Magnetic topology:
•
•
•
•
•
•
•
•
•
larger ECR zone (parallel B region)
magnetic mirror at the exit: control of energy, better ionization
magnetic mirror at the bottom: reduce losses to back wall
……
Microwave coupling: slit, waveguide, ….
n  e2
2
Frequency: try 5 GHz (potentially 4 times the density)
p 
m 0
Scale-up : 10 mN, then 100 mN
Advanced diagnostic: thrust balance (activity proposed under Neosat, with support of Astrium and TAS), 3D LIF
Modeling of the thruster
Roadmap:
Currently TRL 3. Promising performance, no show stopper at this time. Could be an emerging technology for
space propulsion.
Objective TRL 4: mastering all parameters and scale-up, get good averall efficiency
(objective 50% @ 1 kW): scientific study
~3 years for TRL 4 → Go / No Go in 2017. TRL 6/8 in 2022
Compatible with H2020.