A large area multifilamentary plasma source

Abstract

This paper discusses a large area multifilamentary plasma source used in the large volume plasma device. This source, based on directly heated filaments, is simple in design and produces quiescent (δn/n ≈ 1%) plasmas of high density ( 10 18 m −3 ), low temperature (∼1-2 eV), over a large area (≈1.1 m 2 ) and a large volume (≈1.6 m 3 ). With the investment of ≈40 kW (1350 A, 30 V) power, the filaments are heated to ≈2000 K to yield emission current density ∼1 A cm −2 at the filament surface. Experiments demonstrate that this source is suitable for carrying out electromagnetic wave excitation studies in the electron magnetohydrodynamics regime. There are certain inherent difficulties associated with direct heating which sets a maximum limit to the filament length and with the requirement of field tailoring. As far as the present study is concerned, these difficulties are acceptable in comparison with the distinct advantages the source possesses, in terms of its low cost and technical features, making it user-friendly.

Role of return current in the excitation of electronmagnetohydrodynamic structures by biased electrodes

“…1. The plasma is produced by a multifilamentary electron emitter [9]. The plasma is immersed in and confined by a uniform background magnetic field of 5G.…”

Electron magneto-hydrodynamic waves bounded by magnetic bubble

“…1, is discussed in detail in earlier reports. 13,15,16 For experiments in the uniform field condition, a set of 10 external magnet coils have been appropriately charged to produce a uniform magnetic field in the range 4-20 G, in the z direction (device axis).…”

“…15 The main diagnostics constitute Langmuir probes, magnetic probes for measuring the diamagnetic response of plasma (diameter ¼ 12 cm, 4 turns), and miniature magnetic probes (diameter 2 mm; length, 5 mm; 30 turns) for diagnosing the wave field perturbations. Fig.…”

“…The wave excitation experiments are carried out at about 400 ls in the afterglow plasma, where the background plasma density $2:5 Â 10 11 cm À3 and the temperature $1 eV show nearly uniform spatial profiles over the experimental volume. 13,15 For experiments in the bubble configuration (right), the field compensation is carried out just prior to the switch off of the discharge (at 4.9 ms) so that the desired low field plateau (marked by a circle), obtained 500 ls later, is devoid of energetic electrons. A period of $10 ls is chosen within this 200 ls plateau, for EMHD excitation.…”

Oxide cathodes for reliable electron sources

“…The two main types of thermionic cathodes are oxide and dispenser cathodes [2]. Oxide cathodes, since they were first discovered by Wehnelt in 1904 [3], have played an important role in modern physics [4] and are still fascinating as economical electron sources for various applications [5][6][7][8][9][10][11][12].…”