CATHODE LESS GRIDDED ION THRUSTERS SMALL … Propulsion with Electronegative Gases - Accelerates positive and negative ions to generate thrust Advantages: • No additional cathode

Laboratoire de Physique des Plasmas

CATHODE-LESS GRIDDED ION THRUSTERS FOR SMALL SATELLITES

Ane Aanesland and Dmytro Rafalskyi Laboratoire de Physique des Plasmas,

CNRS-Ecole Polytechnique, France

3 classes of Electric Propulsion systems

Gas

Heater Expansion

Electrothermal thrusters

Resistojet Arcjet Isp ~ 300 – 600 s

Electromagnetic thrusters

Cathode

Anode Arc current B

F=JxB

Anode

Gas

Plasma

Magneto Plasma Dynamic thrusters Pulsed Plasma thruster

Isp ~ 800 – 1200 s

Electrostatic thrusters Neutralizer

Plasma

e-

Xe+

Grids

B Gas

F=qE

Gridded Ion thrusters Hall thrusters

Isp ~ 1500 – 4000 s

Energy source (Sun)

Electrical energy

directed kinetic energy

Out of 1168 active satellites, 236 runs with EP systems

Data from Aerojet Rocketdyne (IEPC-2013-439)

0%

10%

20%

30%

40%

50%

60%

Resistojet Arcjet Hall Gridded ion

PPT

GPS station keeping Attitude control

De-orbiting

N-S Station keeping

Station keeping Attitude control Orbit insertion De-orbiting Deep space

E-W Station keeping

LEO GEO

Miniaturization possibilities


Plasma

e-

Xe+

Grids

B Gas

F=qE Gas

Heater Expansion

Electrothermal thrusters Electromagnetic thrusters

Cathode

Anode Arc current B

F=JxB

Anode

Gas

Plasma

Cold gas thrusters Never used in space and systems with

magnetic fields are difficult to downscale

Electrospray thrusters Gridded ion thrusters

Hall thrusters

Miniaturization of gridded ion thrusters


Plasma

e-

Xe+

Grids

B Gas

F=qE Flow Control Unit (XFU)

Power Unit (PPU)

Neutralizer

Gas discharge

Acceleration

Xe propellant storage

Solar arrays



Plasma

e-

Xe+

Grids

B Gas


Power Unit (PPU)

Neutralizer

Gas discharge

Acceleration


Solar arrays

Initiate the discharge is difficult

Efficiency decreases by more electron losses to the walls

λiz =1

ngσ iz



Plasma

e-

Xe+

Grids

B Gas


Power Unit (PPU)

Neutralizer

Gas discharge

Acceleration


Solar arrays



Grid separation scales inversely with applied acceleration voltage

λiz =1

ngσ iz



Plasma

e-

Xe+

Grids

B Gas


Power Unit (PPU)

Neutralizer

Gas discharge

Acceleration


Solar arrays



Grid separation scales inversely with applied acceleration voltage

Neutralizer cannot easily be downscaled

λiz =1

ngσ iz

v

D. Rafalskyi and A. Aanesland, J Phys D Appl Phys 47, 495203 (2014)

The NEPTUNE thruster A new promising thruster with strong technology heritage

One Radio-Frequency power source for plasma generation, ion acceleration and electron neutralization

Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid

v




Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid

RF CB

C1 C2

Plasma Sheath G1 Sheath G2

v




Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid

RF CB

C1 C2

Plasma Sheath G1 Sheath G2

C=ε0A/d such that C1>C2 and V1<<V2 Blocking capacitor CB charges up to ensure that Ie=Ii

v


Rectification of the applied RF voltage


Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid

RF bias rectification to a DC bias

v




Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid


VDC~0.80 VRF

v




RF

RF source (ICP)

A+

e

RF biased grid


VDC~0.80 VRF

The space charge limited current is:

JCL = ξ2eM!

"#

$

%&1/2 V 3/2

d 2

ξDC =49= 0.44 ξRF =

200243

= 0.82

v




Blocking capacitor

RF

RF source (ICP)

A+

e

RF biased grid


VDC~0.80 VRF

High ion energies and low anisotropic electron energies

The NEPTUNE thruster is promising for miniaturization

Advantages: •  No additional cathode •  PPU simplified – only one RF power supply •  Propellant flexibility •  Scaling flexibility •  Beam current can be x2 the one for a DC system •  Emitted net charge is always zero

Laboratoire de Physique des Plasmas

THANK YOU FOR YOUR ATTENTION

This work was supported by a Marie Curie International Incoming Fellowships within the 7th European Community Framework

The PEGASES thruster promising for miniaturization?

v

A+

e-

A+

A-A-RF

power

A2A+

A-

Magnetic barrier

Electronegative plasma

Ion-ion plasma

Alternate acceleration

Recombination

Plasma Propulsion with Electronegative Gases - Accelerates positive and negative ions to generate thrust

Advantages: •  No additional cathode •  Plume with almost no electrons •  Control of the emitted net charge •  Solid propellant (Iodine)

Disadvantages: •  Need magnetic fields •  Need square voltage waveforms •  Electronegative gases are

chemically reactive

A. Aanesland, A. Meige, and P. Chabert, J. Phys. D 162, 012009 (2009).

PEGASES state-of-the-art

v

Proof-of-concept combining experiments, simulations and analytical models

0 5 10 151013

1014

1015

1016

1017

1018

x [cm]

n [m

−3] ne (Ar)

n− (SF6)

ne (SF6)

High density ion-ion plasma

−200 0 2000

1

2

3

4

5

6x 10−7

Collector Voltage [V]

dI/d

V [A

]

a)

positive ions

negative ions

secondary electrons

Alternate ± ion beamsGeneralized CL law for alternate acceleration

Full space charge compensation in the beam

A+

e-

A+

A-A-RF

power

A2A+

A-

Magnetic barrier

Electronegative plasma

Ion-ion plasma

Alternate acceleration

Recombination

A. Aanesland, A. Meige, and P. Chabert, J. Phys. D 162, 012009 (2009).

T. Lafleur, D. Rafalskyi, and A. Aanesland, PSST. 24, 015005 (2015).

Documents

CATHODE LESS GRIDDED ION THRUSTERS SMALL … Propulsion with Electronegative Gases - Accelerates positive and negative ions to generate thrust Advantages: • No additional cathode