KR20020022870A - Magnetic probe with screening tube for eddy current reduction - Google Patents

Abstract

PURPOSE: A magnetic probe having a screening tube for minimizing eddy current is provided to reduce efficiently the amount of eddy current by intercepting a path of the eddy current. CONSTITUTION: A multitude of slot(4) is formed parallel to an axis direction of a screening tube(3). The slots(4) are formed continuously from a surface of the screening tube(3) to a surface of an end portion. A multitude of pickup coil is arrayed in an inside of the screening tube(3). Eddy current is generated on a surface of the screening tube(3) when a magnetic field is passed. When the magnetic electric field flows on a probe, the eddy current is reduced by forming the slots(4) on the screening tube(3). Accordingly, the eddy current is reduced by intercepting a generation path of the eddy current generated from an arbitrary closed circuit. The slots(4) is used for intercepting and reducing the arbitrary closed circuit.

Description

Magnetic probe with protective tube with minimal eddy currents {MAGNETIC PROBE WITH SCREENING TUBE FOR EDDY CURRENT REDUCTION}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic probe that minimizes the eddy current of a screening tube. In particular, the present invention protects a magnetic field probe, which is a type of plasma diagnostic equipment, from a plasma at high temperature, This is to attenuate the eddy current generated in the protective tube.

Magnetic field probes are widely used as a very basic diagnostic equipment in scientific and industrial research using plasma in the radio frequency (RF) region. Especially, the protection of the probe is essential when the plasma is hot.

However, in the selection of the material for protecting the probe, in the case of using an insulator, a capacitance component is measured in addition to the inductance component to be measured by the magnetic field probe, thereby causing an error in the measurement value analysis.

On the other hand, when the conductor is used as a material for protecting the probe, the capacitance component is almost eliminated, but the eddy current generated on the surface of the conductor causes errors in the measured value.

Therefore, the development of a method and screening tube to protect the probe and measurement data together is essential.

The present invention relates to a method of minimizing eddy currents generated on the surface of a screening tube when a conductor having a relatively low error effect is selected as a protective material.

In the existing domestic and international experiments using magnetic field probes, when using a non-conductor such as glass as the protective material to protect the probe or using a conductor such as SUS, a simple slot is generated on the surface of the conductor tube to generate a eddy current. Attempts have been made to minimize, but this is not adequate as a way to fundamentally attenuate eddy currents formed along any closed loop.

The present invention has been invented to solve the conventional problems as described above, by effectively reducing the eddy current by blocking the path of the eddy current constituting any closed circuit on the surface of the protective tube of the magnetic field probe, to properly protect the magnetic field probe The purpose is to improve the sensitivity of the measurements.

It is also an object of the present invention to provide a magnetic field probe having a protective tube configured to minimize eddy currents.

1 is a conceptual diagram illustrating a method of blocking eddy currents by forming a closed path and a slot of eddy currents when a magnetic field passes through the conductor plate.

Figure 2a and 2b is a block diagram of the protective tube blocking the closed path of the eddy current by making a slot in the protective tube according to the present invention.

Figure 3 is a comparison of the conventional protective tube with a eddy current and the protective tube blocking the eddy current in accordance with the present invention.

Figure 4 is an embodiment of a mobile magnetic field probe having a protective tube minimized eddy current in accordance with the present invention.

5 is a measurement system of the magnetic field probe.

6 is a graph showing the results of a sensitivity comparison experiment of a probe without a protective tube, a probe with a conventional protective tube and a probe with a protective tube according to the present invention.

In order to achieve the above object, the present invention provides a magnetic field probe comprising a probe rod, a pickup coil formed at the tip of the probe rod, and a protection tube 3 covering the pickup coil to protect the probe from plasma, wherein the protection tube is composed of a conductor and a shaft. It is characterized in that the eddy current is minimized by forming a plurality of slots continuously from the surface to the end surface in the direction.

Hereinafter, the configuration and operation of the present invention with reference to the accompanying drawings in detail as follows.

1 is a conceptual diagram illustrating slotting in a conductor plate to reduce eddy currents generated when a magnetic field passes through the conductor.

When a magnetic field passes through a conductor, a eddy current is generated in a direction perpendicular to the direction of the magnetic field. In other words, the magnetic field generates eddy currents that constitute an arbitrary closed circuit in the conductor. Forming a slot in the conductor plate reduces the eddy current by blocking the eddy current constituting the closed circuit.

Figure 2a and 2b is a block diagram of a probe forming a slot in the protective tube according to the invention blocking the menopause. As shown in FIG. 2, a plurality of slots 4 are formed continuously from the surface to the distal end side by side in the axial direction of the protective tube 3. A plurality of pick up coils 2 are arranged inside the slot of the protective tube. When the magnetic field changes to the probe rod, a eddy current is generated on the surface of the protective tube 3 (FIG. 2B). If the slot is formed in the protective tube 3 as shown in FIG. 2A, this can be reduced. That is, it cuts off the generation path of the eddy current which arises in arbitrary closed circuits. The slots block any closed circuit where eddy currents are generated, and the spacing between slots should be smaller than the size of the probe.

Figure 3 shows a comparison between the conventional protective tube with a eddy current and the protective tube formed with a slot to block the eddy current in accordance with the present invention.

Conventional protective tubes are formed with a plurality of slots in the axial direction on the surface, one slot is formed separately from the end surface. On the other hand, the protective tube according to the present invention has a plurality of slots formed continuously from the surface to the end surface in the axial direction is configured differently from the conventional invention.

Figure 4 illustrates an embodiment of a mobile magnetic field probe according to the present invention.

In the present embodiment, the movable magnetic field probe 10 is composed of two small pickup coils B _z and B _θ 2, a protective tube 3 made of SUS 304 and a probe rod 1 having a diameter of 10 mm. The coil 2 is made of enamel wire having a diameter of 0.254 mm and wound five times on a ceramic tube having a diameter of 3.2 mm. The tube 3 is used for electrostatic shielding of the coil from the plasma. The tube 3 also reduces the frequency response of the probe due to the eddy currents induced over the tube. If the surface resistance of the pipe 3 is high, the influence is small. Several slots 4 are formed side by side on the axis of the tube so that the surface has higher resistance. 4 shows a conventional sheath and a sheath according to the invention. The slotted sheath is located near the pickup coil inside the sheath.

Conventional protective tube is formed with eight slots on the surface and one slot on the end surface. The sheath thickness is 1 mm and is used in the probe array.

On the other hand, the protective tube according to the present invention has six slots 4 formed in succession on the surface 31 and the end face 32 of the protective tube in order to reduce the eddy current. The thickness of the protective tube here is 0.3 mm. The protective tube according to the invention is used as a cover of a mobile magnetic field probe.

The sensitivity of the magnetic field probe is measured using a Helmholtz coil in the frequency range 1-10 MHz. 5 shows a measuring system of a magnetic field probe. The sensitivity of the probe using a network analyzer can be obtained by the following equation from the S parameter using a 2-port method.

Where S ₂₁ , S ₂₂ , and S ₁₁ are parameters measured by the network analyzer, I _HC is the current flowing through the Helmholtz coil, k is a constant, and Z is the input impedance. In particular, vacuum variable capacitors (VVCs) are used because they have low magnetic induction and high precision capacitance.

Figure 6 is a graph of the results of a comparison experiment of the frequency band sensitivity of the protective tube used in the prior art and the protective tube according to the present invention.

The graph of FIG. 6 is a graph showing the average of repeated experiments with different protection tubes only under the same conditions and places, and the frequency range used is 2 MHz to 10 MHz.

The straight line in the graph represents the thermodynamic theory. The thermodynamic theoretical value is calculated by the following formula.

Equation 2 shows an equivalent circuit for the magnetic field probe. In Equation 2, a probe measurement value of resistance (R _p = 0.6 to 1.1 mA) and inductance (L _p = 0.28 to 0.3 mA) is used. The discrepancy between measured and theoretical values increases with increasing RF frequency. The higher the frequency, the greater the discrepancy, because it excludes the probe's signal induction and calculates the sensitivity. A square line in the graph is used without the sheath, and the sheath according to the invention is smaller than the sensitivity of the probe without the sheath. Have a mismatch. When sheaths are used, the smaller the difference from this line, the better the results.

In addition, it can be seen that the line consisting of a triangle that is a result of the protective tube blocking the eddy current according to the present invention shows a much better result than the line consisting of a circle to which the protective tube used in the prior art. That is, the measurement sensitivity of the probe with the protective tube according to the present invention is higher than the conventional probe.

The sensitivity of the probe with a protective tube according to the invention is obtained at 0.05 to 0.55 V / Gauss at a frequency of 1 to 10 MHz.

Therefore, the magnetic field probe according to the present invention improves the sensitivity of the measurement of the RF region by using a retaining tube which minimizes the eddy current.

As described above, the magnetic field probe according to the present invention uses a protective tube with a minimum eddy current, thereby providing a method for simultaneously solving the probe protection problem and the electromagnetic reaction which may occur in the technical study of the RF plasma region. It works.

In addition, this method may be effectively applied in other areas where the conductor can be used safely from eddy currents.

As such, the present invention relates to a method of blocking a eddy current by forming a slot in a protective tube of a magnetic field probe, and may be sufficiently changed, converted, substituted, and replaced in consideration of the present invention, and is not limited to the above.

Claims (1)

A magnetic field probe comprising a probe rod, a pickup coil formed at an end of the probe rod, and a protective tube covering the pickup coil to protect the probe from plasma. The protective tube is made of a conductor and magnetic field probe, characterized in that to form a plurality of slots continuously from the surface to the end surface in the axial direction to minimize the eddy current.