Ion Energy Distributions from a Permanent-Magnet Helicon Thruster. Francis F. Chen, UCLA. Low Temperature Plasma Physics Webinar, January 17, 2014. The “New Stubby” helicon source. Note “skirt”. Antenna: 1 turn at 27 MHz, 3 turns at 13 MHz. Aluminum top plate.
Francis F. Chen, UCLA
Low Temperature Plasma Physics Webinar, January 17, 2014
The “New Stubby” helicon source Thruster
Antenna: 1 turn at 27 MHz, 3 turns at 13 MHz.
Aluminum top plate
The magnet is 5” OD, 3” ID, and 1” thick. We use the almost uniform field below the stagnation point.
D. Arnush, Role of Trivelpiece-Gould Waves in Antenna Helicon Wave Coupling, Phys. Plasmas 7, 3042 (2000).
Sample loading curves from HELIC Thruster
R should be > 1W at operating density
Operating point on “Low-field peak” Thruster
Setting the antenna at 60 G Thruster
Discharge with the original magnet Thruster
Downstream density vs B and P Thruster rf
This shows that only 30 - 60 G is necessary.
The magnet is 4” OD,
2” ID, and 1/2” thick
The plasma potential is set by grounding the top plate.
The experimental chamber Thruster
The SEMion ion energy analyzer Thruster
by Impedans, Ltd., Ireland
4” diam x 1 cm thick
When the sensor is too close to the discharge, it forms an endplate, and the discharge is double-ended.
We know that the discharge is affected because the tuning is changed.
Gridded and Hall ion thrusters Thruster
A helicon thruster Thruster
Double-layer thrusters Thruster
A review of recent laboratory double layer experiments
Christine Charles, Plasma Sources Sci. Technol. 16 (2007) R1–R25
F.F. Chen, Phys. Plasmas 13, 034502 (2006)
Bohm sheath criterion
A sheath must form here
Single layer forms where r has increased 28%
Expect about 5 the KTe of 1.5-2 eV
IEDFs vs distance from source Thruster
close to tube
There is no sign of a double layer jump.
This is probably because the sensor changes the effective length of the discharge.
IEDFs vs RF power Thruster
Evidence of ion beam Thruster
IEDFs vs. pressure Thruster
Can we increase the ion drift speed? Thruster
Yes! Applying +24V to top plate
increases vi by ~16eV, while
applying -24V reduces vi by ~6eV.
The voltage is applied with a Pb-acid battery from an electric scooter.
Effect of top plate bias Thruster
A small helicon discharge was developed
using a permanent magnet for the B-field.
Ions are ejected with a drift velocity of
about 5KTe, measured with a retarding-
field energy analyzer.
The ion drift can be increased by biasing
the top plate of the discharge relative to
nearby grounded surfaces.
This device could be developed into a