Single stage vs multistage plasma thruster electrostatic tests during Pulsotron Plasma Thruster test programme

                      Javier Luis López, Jorge Juan López, Judy Atkins. Pulsotron S.L.

The electric field potential inside two plasma thruster configurations was tested.
Index Terms – Pulstron, Plasma Technology, Plasma Thrusters, Nuclear fusion, Particle accelerators, Electrostatics, Electrostatics discharge.

Table of contents
I.    Introduction    
II.    The test setup    
III.    Test results    
IV.    Conclusions    
V.    References    

I.    Introduction

In order to design plasma thrusters to be used in nuclear fusion tests it has to be decided whether it is better to use multistage or only one stage voltage acceleration.  The present work consists of measuring and comparing both configurations.

In order to design plasma thrusters to be used in nuclear fusion tests, it is needed to test if it is better to use multistage or only one stage voltage acceleration. The present works consists on measuring and compare both configurations.

II.    The test setup
A scale model of a multistage Plasma Thruster was built consisting of a long, thin cylinder and another wide in accord with the accompanying figure.  The long cylinder is covered with 5 conductive films in grey.
Then it is attached to a wider and short one that simulates the electron source.

                                                                   Multistage configuration

The short cylinder that simulates the electron source and is also covered with a conductive tape.
It is connected to a power supply of different voltages as can be seen in the diagram.  The voltage difference between successive stages is the same.

In a second configuration the main body grey plates are connected to the same voltage:


Monostage configuration

The body length of the main tube was 350mm.  The hot wire distance to the body was 110mm diameter.

The main body dimensions were 350mm long and 110mm diameter and the short wide section that simulates the hot wire is 2cm in length and 210mm in diameter.

The electric field potential was measured along its axis (Y=0) and close to the inner surface of the body at Y=40mm from the axis.

III.    Test results
The measured voltage was:

Here is the resulting plot:

As can be seen in the monostage configuration measurements, there is a plateau between 80 and 300mm where ions cannot be accelerated.
Nevertheless in the 5 stage configuration the voltage field drops at a constant rate.

IV.    Conclusions
Multistage configuration allows a constant acceleration of ions along the tube, then a bigger difference of voltage between ion inlet and the electron source is allowed.
In the monostage configuration there is a lack of acceleration in about 2/3 of the tube.  This is a big disadvantage because the lack of acceleration generates less ion speed being less affected by the magnets outside the thruster, so such ions could erode the internal face of the ion thruster.  There is also a lot more abrupt difference of voltage between the inner tube extreme and the electron generator, so it will be necessary to apply less voltage to avoid direct electron discharge.

V.    References
    IEPC-2007-110 Status of the THALES High Efficiency Multi Stage Plasma Thruster development for HEMP-T 3050 and HEMP-T 30250 N. Koch*, H.-P. Harmann, G. Kornfeld


About jlopez2022

Experimental Physicist
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