4th. Quarter 2021

The NACES cathode was successfully tested in the JUMBO vacuum chamber at JLU Gießen, which possesses a pumping speed of 9900 l/s plus cryo pumping possibility. This allows testing of the neutralizer in an almost space like environment. As expected, the ignition required higher gas flows, but could be achieved reliably. Performance mappings were taken.

Besides the initial operation with argon, the NACES cathode was be operated with the noble gases krypton and xenon. Performance mappings were taken in will be presented at the next international conference.

Performance tests of NACES cathode was also successfully tested at FOTEC premises, with the data mappings shown hereafter.

The JLU hollow cathode was successfully operated over more than three hours with an electride insert and xenon as propellant .

C12A7:e- synthetized by ATD were machined and integrated in an Exotrail cathode design, in order to be coupled with a 50W-class Hall thruster. Two miniature C12A7:e- cathodes with heater were characterized in diode mode, in an operating range from 0.07A to 0.45A, and compared to the LaB6 emitter. Heating power required to start the cathode were 35 W and 48 W for C12A7:e- and LaB6, respectively.

Miniature C12A7:e- cathode was characterized in diode mode at Exotrail, in an operating range from 0.07A to 0.45A, and compared to LaB6. Heating powers required to start were 35 W and 48 W heating power for C12A7:e- and LaB6, respectively.

Some new additional improvements have been undertaken in the NACES prototype at ATD, and have driven to the results in performance ratio Ianode/Pcathode (mA/W) shown in the attached figure for different gases and gas flows for 10 V anode voltage.

Leveraging on the know-how developed within the project, several new cathode designs and architectures are being developed. One of them is the hollow cathode developed at ATD whose prototype and performance results are attached hereafter.

3rd. Quarter 2021

NACES cathode is achieving very good result as heater-less neutralizer working at low temperatures, as can be seen in the performance rations shown in the following table.

Anode current is measured even in absence of anode power supply (Vanode=0), when the anode is grounded and the only external power supply is the one provided by the cathode power supply.

Another remarkable ratio is the Ianode/Icathode (%), which is reaching values above 60-70%, meaning that most of all the injected cathode current is delivered at anode, with minimal current losses at keeper.

With some additional design variants we have been able to further improve this ratios till reaching performance ratios above 6 mA/W for anode current vs cathode power, and keeper current below 2% of the cathode current. The prototype and its plume can be seen in the following pictures, and the characterization and performance curves are also shown hereafter.

After successful manufacturing of hollow cylinders from high quality electride material, they were tested in JLU Giessen hollow cathode design. The plume can be seen left of the black keeper.

First tests of the NACES cathode were performed at JLU. The easy ignition procedure from room temperature of the could be reproduced and current was extracted. Different argon gas flows in the range from 20 sccm to 50 sccm were tested.

2nd. Quarter 2021

The first tests of the improved cathode prototype have shown very promising results. The
performances of a 20 W cathode power are displayed in the figures.

Prototypes at ATD for delivery to UPM, JLU Giessen, and FOTEC.

The UPM team has set up
the vacuum equipment
and data acquisition
system for low pressure
discharge plasma cathode
endurance testing.

Several characterization tests have been performed on 8 different C12A7:e- production batches, each one with a different electron concentration, with 5
characterization techniques: Electron Spin Resonance, Raman, Hall Effect, Thermionic emission, and Kelvin Probe Force Microscopy.

Figure shows the operation of a cold plasma source rst tests performed
at UPM on the cold plasma source designed by the UPM for the
thermionic electron emission tests of NACES cathode.

1st. Quarter 2021

First prototype tests at ATD have shown an outstanding performance
of the C12A7:e- material when operating under ionized gases. Cathode
design improvements are being introduced and new prototype versions.

Testing the same cathode design to compare LaB6 material under Xe and Ar gas flows, showed a higher performance of C12A7:e- material.

JLU performed comparison tests of some C12A7:e- samples from
ATD that have been used at EXOTRAIL and at JLU, obtaining
comparable results in terms of Work Function.

The data acquisition and control software for UPM test activities has been checked and validated in a realistic electron emission experiment using a DC heated tungsten hairpin.

First tests performed with the EXOTRAIL 1A lab prototype comparing LaB6 and C12A7:e- materials.

4th. Quarter 2020

Preparation at JLU of the samples and the test environment for the first Hall measurements on conductivity.
Successful manufacturing at JLU workshop of a test hollow insert from a C12A7:e- cylinder, reducing external diameter and drilling the central hole.

Thermal camera measurements performed by Exotrail revealed thermal gradients of up to 50 ºC across the emitting surface of C12A7:e- .

Exotrail laboratory C12A7 cathode is now ready and tests have started for LaB6 and awaiting for C12A7:e- samples.

Finished the build up of the test chamber Dory at JLU Giessen, which is now fully operational for neutralizer testing, starting by the Hollow Cathode with LaB6 insert.

Heater containers have been finally manufactured at ATD based on the different tests performed on heater radiation confinement techniques and

Conductivity increase with
temperature verified in ATD lab tests.

September 2020
Completion of the vacuum chamber, test environment, and control and data adquisition SW at UPM.

Exotrail did perform 5 A cathode operation test both with LaB6 and with C12A7:e– for perfomance comparison purposes. Self-heating operation of C12A7:e– electride was got at 0,2 – 2,2 A.

FOTEC has documented the first thermionic emission got from a C12A7:e– thin film deposition via sputtering technique.

August 2020
Thermionic emission comparison tests performed at Exotrail for LaB6 and C12A7:e– emitting surfaces of 6 mm diameter disc.

Set-up improvements developped by Fotec.

Successful ignition and operation of neutralizer with LaB6, and thermal models of electride and LaB6 developed at JLU.

July 2020
New samples batches of C12A7:e- with high electron density produced at ATD