## 2 Experimental Arrangement
### 2.2.200 W-Class Hall Thruster  
A Hall thruster is an electrical propulsion device that uses a plasma discharge with magnetized electrons to ionize and accelerate a propellant gas [34; 35; 36; 37]. The principle relies upon a magnetic barrier and a low-pressure dc discharge generated between an external cathode and an anode. The latter is located at the upstream end of a coaxial annular dielectric channel that confines the discharge. A fraction of the electrons emitted by the thermionic cathode flows downstream to neutralize the ion beam. The remaining part travels toward the anode to maintain the plasma discharge. The propellant gas, typically xenon, is introduced at the back of the channel. Magnetizing coils or permanent magnets, incorporated into a magnetic circuit, provide a radially directed magnetic field of which the strength is maximum in the vicinity of the channel exhaust. The magnetic field is chosen to be strong enough to make the electron Larmor radius much smaller than the discharge chamber characteristic dimensions, but weak enough not to affect ion trajectories. The electric potential drop is mostly concentrated in the final section of the channel owing to the low axial mobility of electrons in this restricted area. The electric field governs the propellant atoms ionization and the ion acceleration. The combination of the radial magnetic field with the axial electric field generates an E \(\times\) B electron drift in the azimuthal direction, the so-called Hall current. The latter is responsible for the very efficient ionization of neutral atoms inside the channel. The ISCT200 Hall thruster is a 200 W-class HT with a classical magnetic field topology. Details about the ISCT200 series and thruster architecture can be found in [34; 38]. The annular channel walls of the ISCT200 are made of BN-SiO2 ceramic. The channel geometry is in the so-called 25\({}_{0}\) configurations, which means the channel cross-sectional area is twice the one of the well-known Russian SPT100 [39; 40]. The 25\({}_{0}\) configuration ensures a high ionization degree. The magnetic field is generated by way of small cylindrical samarium-cobalt magnets. The xenon propellant gas is injected homogeneously inside the channel using a high porosity nullite ring ceramic placed behind the channel back plate. The anode is a wide stainless steel ring placed at the back of the channel against the outer wall. During operation, the thruster body is floating. A heated 5 A-class hollow cathode with a disk-shaped LaB\({}_{6}\) emitter was used to generate the electron current [5; 41]. The cathode is located outside the channel with its orifice in the vertical plane that contains the channel outlet, tilted towards the thruster. The cathode, which is operated with a constant xenon mass flow rate (\(\Phi_{c}\)) of 0.3 mg/s, is electrically connected to the thruster anode and floating. The Faraday cup has been tested in the NExET chamber with the 200 W-class ISCT200 Hall thruster. Figure 2 shows the ISCT200 in operation with Xenon at 200 V during the campaign. One can notice the slight deviation of the inner beam to the positive side of the angular distribution (left in the picture). The deviation is visible in the measured ion current profiles display in next sections. The origin of the deviation is not completely known. However, we expect the phenomena to be caused by inhomogeneous or asymmetrical distribution of the magnetic field in the azimuthal direction because, for versatility \begin{table}
\begin{tabular}{c c c} \hline
**Step** & **Action** & **Duration** \\ \# & **\#** & **min** \\ \hline
1 & Cathode heating (16–18 A) & 20 \\
2 & Thruster ignition (200 V and 1 mg/s) & \\
3 & Hall thruster stabilization & 30 \\
4 & Setting of the operation point and stabilization & 5 \\
5 & Measurements & \\
6 & Next operation point and stabilization & 5 \\  & Repeat step 5 and 6 if needed & \\
7 & Thruster shutdown & \\
8 & Cathode shutdown & \\ \hline \end{tabular}
\end{table} 
Table 1: Heat-up, ignition, measurements and shut down procedure of the ISCT200.