Sketch of the ALESPI experiment as it is currently configured.
A Linear Experiment for Space Plasma Investigations (ALESPI), as the name implies, is located at Auburn University. ALESPI is used to study plasma physics phenomena in the laboratory important to space and astrophysics. Because you can't simulate space in the lab, experiments in ALESPI look at individual processes thought to contribute to the complex interactions in space. One of the most important processes is Alfvén waves, and work on ALESPI continues to investigate Alfvén wave propagation in helicon plasmas. Originally, ALESPI was used to do preliminary helicon studies for the Alpha and HelCat facility.
ALESPI is a 2.5 meter long, 20 cm diameter cylindrical chamber surrounded by seven magnets which create an axial background magnetic field. Power supply limitations dictate a maximum field strength on axis of about 1.3 kGauss, with an axial field ripple of ±12%. This field ripple, though usually annoying, may actually be helpful in studying Alfvén wave mode conversion.
The chamber is outfitted with several view ports and diagnostic ports. Diagnostics include Langmuir probes for measuring electron density and temperature, an axial probe carriage, magnetic fluctuation coils and a microwave interferometer. The chamber is pumped with a 450 L/s turbo pump, and the vacuum is monitored with ion and thermocouple gauges.
Sketch of the ALESPI experiment as it is currently configured.
The plasma is generated with a single helicon wave
source consisting of an m=1 (helical twist) style antenna 22 cm long
surrounding
a 10 cm diameter pyrex tube. The radio frequency (RF) power is supplied by
a standard ham radio amplifier (Henry) operating at 10 MHz and a power of
500-1000
W. ALESPI operates both in argon and helium with a typical fill pressures
of 3-10 mTorr, The background magnetic field is around 0.1 T.
At the right is shown the helicon discharge in argon. The antenna is the copper twist around the quartz cylinder to the left. The pink you see is a glow discharge as the plasma breaks down, while to the right, through the window, the characteristic "blue core" of the helicon discharge in argon is visible. The discharge extends twice that distance (1.8 m) to the right before the chamber ends. The large tan disk in the middle of the picture is one of the magnets. The white tube is for cooling the antenna.
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