Magnetic dipole discharges. III. Instabilities

A simple discharge is described which uses a permanent magnet as a cold cathode and the metallic chamber wall as an anode. The magnet's equator is biased strongly negative, which produces secondary electrons due to the impact of energetic ions. The emitted electrons are highly confined by the strong dipolar magnetic field and the negative potential in the equatorial plane of the magnet. The emitted electrons ionize near the sheath and produce further electrons, which drift across field lines to the anode while the nearly unmagnetized ions are accelerated back to the magnet. A steady state discharge is maintained at neutral pressures above 10 À3 mbar. This is the principle of magnetron discharges, which commonly use cylindrical and planar cathodes rather than magnetic dipoles as cathodes. The discharge properties have been investigated in steady state and pulsed mode. Different magnets and geometries have been employed. The role of a background plasma has been investigated. Various types of instabilities have been observed such as sheath oscillations, current-driven turbulence, relaxation instabilities due to ionization, and high frequency oscillations created by sputtering impulses, which are described in more detail in companion papers. The discharge has also been operated in reactive gases and shown to be useful for sputtering applications. V

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“…This effect is used to produce high-current microsecond pulses requiring no fast switching circuits, as described in a companion paper. 17…”

Section: -3mentioning

confidence: 99%

“…Instabilities, pulsating discharges, and electromagnetic effects are treated in companion papers. 16,17 This paper is organized as follows: After describing the experimental setup in Sec. II, the observations of basic discharge properties will be presented in Sec.…”

Section: Introductionmentioning

confidence: 99%

Magnetic dipole discharges. I. Basic properties

et al. 2013

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“…Probe transient signals are important to understand because they are much larger than probe signals from waves and instabilities, which are addressed in the third companion paper. 10 This paper is organized as follows: After describing the experimental setup and diagnostics in Sec. II, the observations of instabilities will be presented in Sec.…”

Section: Introductionmentioning

confidence: 99%

Magnetic dipole discharges. II. Cathode and anode spot discharges and probe diagnostics

et al. 2013

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The high current regime of a magnetron-type discharge has been investigated. The discharge uses a permanent magnet as a cold cathode which emits secondary electrons while the chamber wall or a grounded electrode serves as the anode. As the discharge voltage is increased, the magnet develops cathode spots, which are short duration arcs that provide copious electrons to increase the discharge current dramatically. Short (1 ls), high current (200 A) and high voltage (750 V) discharge pulses are produced in a relaxation instability between the plasma and a charging capacitor. Spots are also observed on a negatively biased plane Langmuir probe. The probe current pulses are as large as those on the magnet, implying that the high discharge current does not depend on the cathode surface area but on the properties of the spots. The fast current pulses produce large inductive voltages, which can reverse the electrical polarity of the magnet and temporarily operate it as an anode. The discharge current may also oscillate at the frequency determined by the charging capacitor and the discharge circuit inductance. Each half cycle of highcurrent current pulses exhibits a fast (' 10 ns) current rise when a spot is formed. It induces high frequency (10-100 MHz) transients and ringing oscillations in probes and current circuits. Most probes behave like unmatched antennas for the electromagnetic pulses of spot discharges. Examples are shown to distinguish the source of oscillations and some rf characteristics of Langmuir probes. V

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The radiofrequency magnetic dipole discharge

et al. 2016

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This paper describes a novel and simple concept of plasma source, which is able to produce a radiofrequency magnetized discharge with minimal power requirements. The source is based on the magnetron concept and uses a permanent magnet as an active electrode. The dipolar field produced by the magnet confines the electrons, which cause further ionization, thus producing a toroidally shaped plasma in the equatorial region around the electrode. A plasma can be ignited with such scheme with power levels as low as 5 W. Paschen curves have been built for four different working gases, showing that in Helium or Neon, plasma breakdown is easily obtained also at atmospheric pressure. The plasma properties have been measured using a balanced Langmuir probe, showing that the electron temperature is around 3–4 eV and higher in the cathode proximity. Plasma densities of the order of 1016 m−3 have been obtained, with a good positive scaling with applied power. Overall, the electron pressure appears to be strongly correlated with the magnetic field magnitude in the measurement point.

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Magnetic dipole discharges. III. Instabilities

Cited by 5 publications

References 33 publications

Magnetic dipole discharges. I. Basic properties

Magnetic dipole discharges. I. Basic properties

Magnetic dipole discharges. II. Cathode and anode spot discharges and probe diagnostics

The radiofrequency magnetic dipole discharge

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