Closed Drift Thruster Magnetic Circuit Design
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Solution Overview
Problem
High-power plasma thrusters with closed electron drift face thermal disadvantages due to significant wire dissipation and high winding mass, and non-uniform radial magnetic fields lead to inefficient plasma confinement and reduced engine life.
Innovation Solution
A thruster design with a magnetic circuit featuring a concave inner and convex outer pole piece profile, creating a variable air gap to maintain a uniform radial magnetic field, and using multiple external coils instead of a single large annular coil to minimize winding length and mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an external annular coil is used to magnetize the outer pole piece, then a radial magnetic field is created in the main annular channel, but significant wire length results in high thermal dissipation and high winding mass
Solution Approach 1:
The patent divides the single external annular coil into multiple smaller external coils distributed around the periphery of the thruster. This segmentation reduces the wire length of each individual coil and allows for more efficient magnetic field distribution, thereby reducing overall winding mass while maintaining the required magnetic field strength for high-power operation.
Solution Approach 2:
The patent employs pole pieces with non-circular cylindrical fitted profiles (concave inner peripheral surface and convex outer peripheral surface) that create a variable air gap. This local geometric modification optimizes the magnetic field distribution in specific regions, ensuring uniform radial magnetic field across the main annular channel while minimizing the total wire length required.
2Power
If an external annular coil is used, then magnetic field is generated, but thermal dissipation increases and cooling of the ceramic channel becomes difficult
Solution Approach 1:
By segmenting the external coil system into multiple smaller coils, the patent reduces the concentration of thermal load in any single location. This distributed coil arrangement improves heat dissipation efficiency and allows for better thermal management of the ceramic channel, particularly in the thermally critical downstream region.
Solution Approach 2:
The patent converts the previously harmful thermal dissipation issue into a beneficial cooling opportunity by removing the large external annular coil that blocked heat dissipation. The segmented coil arrangement allows thermal energy to be efficiently dissipated, and the reduced winding mass improves the thermal conductivity and cooling efficiency of the ceramic channel.
3Weight of stationary object
If multiple external coils are used instead of a single annular coil, then winding mass is reduced, but radial magnetic field uniformity deteriorates
Solution Approach 1:
The patent employs pole pieces with specifically designed non-circular cylindrical fitted profiles (concave inner peripheral surface and convex outer peripheral surface) that create a variable air gap. This local geometric modification compensates for the non-uniform magnetic field distribution caused by multiple external coils, ensuring uniform radial magnetic field across the main annular channel while maintaining reduced winding mass.
Solution Approach 2:
The patent modifies the geometric parameters of the pole pieces by introducing fitted profiles with concave and convex surfaces. This parameter change in the pole piece geometry optimizes the magnetic circuit, distributing the magnetic flux more uniformly across the air gap and compensating for the non-uniformity introduced by the segmented coil arrangement.
4Stability of the object's composition
If pole pieces with fitted profiles are used to create uniform magnetic field, then radial magnetic field uniformity is improved, but device complexity increases
Solution Approach 1:
The fitted profiles on the pole pieces are designed to create uniform magnetic field in the critical region (main annular channel) while keeping the overall structure relatively simple. The concave inner peripheral surface and convex outer peripheral surface are strategically shaped to optimize magnetic flux distribution, achieving uniform field with moderate manufacturing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design allows for effective cooling of the main annular channel, reduces winding mass, and ensures a uniform radial magnetic field, enhancing plasma confinement and thruster efficiency while maintaining high power capabilities.
Implementation Method 1
a magnetic circuit for creating a magnetic field in the main annular channel, the magnetic circuit comprising at least one axial magnetic core surrounded by a first coil and a pole piece of internal upstream revolution and a plurality of external magnetic cores surrounded by external coils
Implementation Method 2
The hollow cathode 40 provides a plasma 29 substantially at the reference potential from which the electrons are extracted heading towards the anode 25 under the effect of the electrostatic field E due to the potential difference between the anode 25 and the cathode 40
Implementation Method 3
Closed electron drift thrusters with an annular outer coil, such as the known thruster shown in the figure 8, guarantee a constant radial magnetic field in the air gap defined between the outer 34 and inner 35 pole pieces
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
In a closed-tail electron thruster, a magnetic circuit for generating a magnetic field in a main annular channel comprises at least one axial magnetic core surrounded by a first coil and an internal upstream pole piece of revolution, and a plurality of external magnetic cores (137) surrounded by external coils. The magnetic circuit further comprises a first essentially radial external pole piece (134) defining a concave internal peripheral surface (134) and a second essentially radial internal pole piece (135) defining a convex external peripheral surface (135a).The concave inner peripheral surface (134a) and the convex outer peripheral surface (135a) each have a distinct fitted profile of a circular cylindrical surface so as to form between them an air gap of variable width having zones (232) of maximum value at the external coils and zones (231) of minimum value between the external coils so as to create a uniform radial magnetic field.