The group "Experimental Physics II - Reactive Plasmas" at the faculty of physics and astronomy at Ruhr University Bochum.

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Electron density, temperature and the potential structure of spokes in HiPIMS

In high power impulse magnetron sputtering (HiPIMS) bright plasma spots are observed during the discharge pulses that rotate with velocities in the order of 10 km s −1 in front of the target surface. It has proven very difficult to perform any quantitative measurements on these so-called spokes, which emerge stochastically during the build-up of each plasma pulse. In this paper, we propose a new time shift averaging method to perform measurements integrating over many discharge pulses, but without phase averaging of the spoke location, thus preserving the information of the spoke structure. This method is then applied to perform Langmuir probe measurements, employing magnetized probe theory to determine the plasma parameters inside the magnetic trap region of the discharge. Spokes are found to have a higher plasma density, electron temperature and plasma potential than the surrounding plasma. The electron density slowly rises at the leading edge of the spoke to a maximum value of about 1e20 m −3 and then drops sharply at the trailing edge to 4e19 m −3 . The electron temperature rises from 2.1 eV outside the spoke to 3.4 eV at the trailing end of the spoke. A reversal of the plasma potential from about −7 V outside the spoke to values just above 0 V in a spoke is observed, as has been proposed in the literature.

Release Date
Permanent Identifier (URI)
Is supplementing
Plasma Source Name
Plasma Source Application
Plasma Source Specification
Plasma Source Properties
magnetron: Thin Film Consulting IX2U power supply: TRUMPF Hüttinger TruPlasma Highpulse 4002, voltage: 670 V applied, 570 V after breakdown, peak current: 40 A or 2 A/cm², pulse length: 100 µs, repetition frequency: 30 Hz, 2 inch target
Plasma Medium Name
Plasma Medium Properties
40 sccm, 0.5 Pa
Plasma Medium Procedure
Chamber base pressure of 4e-6 Pa, argon is continuously flowing and pumped during discharge operation. Gas tubes are pumped and flushed prior to the experiment.
Plasma Target Name
Plasma Target Properties
50 mm diameter, 3 mm thickness
Plasma Diagnostic Properties
Probe diameter: 125 µm Probe length: 3.5 mm Probe position: above the middle of the racetrack, in 6.3 mm, 8.7 mm and 10 mm distance to the target surface A small part of the plasma is monitored with a photomultiplier, which will detect spokes moving past the probe position. In post-processing, the probe data is shifted in time to provide synchronization between the probe current and the spoke movement. A detailed explanation can be found in the supplemented publication.
Plasma Diagnostic Name
English (United States)
Public Access Level
Funding Agency
Contact Name
Held, Julian
Contact Email

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