Figure 1

Schematical drawing of the experimental arrangement of Pilot-PSI and its optical emission spectroscopy diagnostic.Reuse & Permissions

Figure 2

The cascaded arc plasma source. The working gas enters the plasma source via the gas inlet. It is ionized in the arc channel of the cascaded plates due to the discharge between the three cathodes and the anode. The nozzle is electrically connected to anode which is attached to the vessel wall. Plasma exits the source through the nozzle. Thomson scattering and OES measurements are performed at $40\mathrm{mm}$ from the nozzle.Reuse & Permissions

Figure 3

A potential distribution over cascaded plates in a hydrogen plasma. In a magnetic field the voltage over the arc is significantly higher. The extra voltage drops mainly between the anode and the first plate.Reuse & Permissions

Figure 4

The radial electron (a) density and (b) temperature profiles of the hydrogen plasma jet measured with Thomson scattering at $40\mathrm{mm}$ from the source in a magnetic field of 0.4, 0.8, 1.2, and $1.6\mathrm{T}$.Reuse & Permissions

Figure 5

(Color) A typical OES measurement at a magnetic field strength of $1.6\mathrm{T}$. (a) Part of a raw CCD-image of the spectrally as well as spatially resolved Balmer-$\beta$ light, indicating plasma rotation. The 17 bands of light correspond to individual optical fibers. The spectral line appears shifted to the red at the bottom of the plasma jet and to the blue at the top. At the jet edges it is unshifted. The spectral shift reveals rotation of the radiating species. The maximum Doppler shift from the central wavelength value is about $5\text{pixels}$. This corresponds to a velocity of $9.3\mathrm{km}∕\mathrm{s}\pm 10\%$ (b) The corrected lateral intensity profile displaying a flat top, pointing to a hollow emission profile. (c) Spectral profiles from, respectively, above, on, and under the jet axis. The off-center profiles are clearly asymmetric, with the direction of asymmetry depending on the lateral position. In the jet center, the profile is symmetric.Reuse & Permissions

Figure 6

Lateral intensity profiles at (a) $0.4\mathrm{T}$ and (b) $1.6\mathrm{T}$. Data is fit with the sum of two Gauss profiles, one of which is inverted.Reuse & Permissions

Figure 7

Radial emission profiles for the four magnetic field values, obtained by Abel inverting the fit of the intensity profiles. Emission profiles are clearly hollow in the center of the plasma beam. A schematic cross section of plasma beam is shown indicating positions of strongest emission by shading.Reuse & Permissions

Figure 8

A double Voigt fit of spectra taken at $1.6\mathrm{T}$ from (a) below the jet axis (b) on the jet axis. The two single Voigt components are shown, one corresponding to the hot, rotating population, the other to the cold and almost nonrotating population.Reuse & Permissions

Figure 9

An off-center asymmetric Balmer-$\beta$ line fitted with a single and a double Voigt profile $(B=1.2\mathrm{T})$. The residues for the double Voigt fit are significantly smaller and more stochastic.Reuse & Permissions

Figure 10

Lateral profiles of rotation velocity determined from a double Voigt fit of the Balmer-$\beta$ line shape at magnetic field strengths of $0.4\mathrm{T}$, $0.8\mathrm{T}$, $1.2\mathrm{T}$, and $1.6\mathrm{T}$.Reuse & Permissions

Figure 11

Lateral profiles of ion temperature determined from a double Voigt fit of the Balmer-$\beta$ line shape at magnetic field strengths of $0.4\mathrm{T}$, $0.8\mathrm{T}$, $1.2\mathrm{T}$, and $1.6\mathrm{T}$.Reuse & Permissions

Figure 12

The electrons cannot close the circuit within the source due to their limited mobility across the magnetic field. The radial electron current path spreads out in the axial direction until the resistance of the axial and radial current paths are equal.Reuse & Permissions

Figure 13

Lateral profiles of (a) electron density and (b) temperature of the cold neutral population determined from a double Voigt fit of the Balmer-$\beta$ line shape at magnetic field strengths of $0.4\mathrm{T}$, $0.8\mathrm{T}$, $1.2\mathrm{T}$, and $1.6\mathrm{T}$.Reuse & Permissions

Figure 14

Results from a double Voigt fit of the Balmer-$\beta$ line shape in which each Lorentz profile is replaced by a double Lorentz profile in order to simulate Stark splitting. The lateral profiles shown are of the (a) rotation velocity, (b) electron density, (c) ion temperature, and (d) cold neutral population.Reuse & Permissions

Figure 15

Schematic picture of expected plasma emission on the basis of radial electron density profile and molecular hydrogen profile. The molecular hydrogen density profile is hollow due to a high dissociation degree and short penetration depth due to charge exchange. The emission is proportional to both electron density and molecular hydrogen density for low electron densities, however above about $n_e>5\times {10}^{19}{\mathrm{m}}^{-3}$, the emission is solely proportional to $n_{{\mathrm{H}}_2}$. The result is that the measured emission originates mostly from a ring at a radius depending on the penetration depth of molecular hydrogen into the beam.Reuse & Permissions

Figure 16

Potential difference between the anode and the first cascaded plate plotted against the magnetic field for a nozzle diameter of 5, 6, 7, and $8\mathrm{mm}$. The voltage increases with both magnetic field and nozzle diameter.Reuse & Permissions

Figure 17

The electrons cannot close the circuit within the source due to their limited mobility across the magnetic field. The radial electron current path spreads out in the axial direction until the resistance of the axial and radial current paths are equal.Reuse & Permissions

Figure 18

Rotation velocities of the plasma jet (the maxima of the lateral profile) derived from the Doppler shift of the Balmer-$\beta$ line plotted against magnetic field. The measurements were performed for nozzle opening diameters of 5, 6, 7, and $8\mathrm{mm}$ for magnetic field settings, 0.4, 0.8, 1.2, and $1.6\mathrm{T}$. The velocity increases approximately linearly with magnetic field.Reuse & Permissions

Figure 19

The lateral rotation frequency profiles for each of the four magnetic field settings, 0.4, 0.8, 1.2, and $1.6\mathrm{T}$.Reuse & Permissions

Figure 20

A comparison between the electric fields available and those needed to drive the maximum rotation frequency. The available electric field is calculated from the potential drop between the anode and the first cascaded plate. The radial distance of this potential drop is taken to be the width of the rotation frequency profile. The maximum rotation frequency is taken to be the highest data point in the fit of the rotation frequency. The electric field required to drive it is calculated from $E=vB=r\omega B$.Reuse & Permissions