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High-Speed Axial Reciprocating Probe
(HARP):
In plasmas with highly energetic charged
particles, probe material is generally sputtered and/or ablated on very small
time scales by the direct flux of these particles.
The local plasma temperature and density may then be modified through
emission of relatively cool probe material. These
perturbations may remain localized near the probe, or may propagate further into
the plasma affecting the macroscopic properties of the plasma being
interrogated. As time scales
increase, probe survival becomes an issue.
A high speed, reciprocating probe system can reduce the amount of ablated
material, allowing for more accurate measurements of local plasma parameters and
assuring probe survival.
The HARP is a linear motor assembly providing
direct linear motion at very high speed and acceleration.
The linear motor is an LM210 manufactured by Trilogy.
It has a three-phase brushless DC servomotor consisting of a linear,
“U”-shaped magnetic track and a “T”-shaped coil moving on a set of
linear tracks. The motor employs Sine commutation, using a linear encoder
built into the magnet track to provide position feedback for very smooth motion.
The linear encoder provides positioning resolution to 5 microns.
The table is covered by a stainless steel and graphite shroud to protect
the HARP from excessive heating and high-energy ions.
One side has a thin slit running the length of the table through which a
probe boom extends.
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-
Haas,
J. M., "Low-perturbation Interrogation of the Internal and Near-field
Plasma Structure of a Hall Thruster Using a High-Speed Probe Positioning
System," Ph.D.
Dissertation, University of Michigan, 2001.
- Haas,
J. M., Gallimore, A.D., McFall, K., and Spanjers, G., "Development of a
High-Speed, Reciprocating Electrostatic Probe System for Hall Thruster
Interrogation," Review
of Scientific Instruments, Vol. 71, No. 11, pp. 4131-4138, November
2000.
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