JPH01115035A - Ecr ion source - Google Patents

Abstract

PURPOSE:To reduce the fracture of a window for introducing a high frequency and enhance vacuum exhaust efficiency by providing the window at a position perpendicular to the axis of a magnetic field and off a resonance point by length corresponding to or over a unit wave length. CONSTITUTION:A high frequency introduction part 1 comprises a coaxial waveguide 2 and an internal lead body 3 extended into a vacuum vessel 8 via a window 4. The installation position of the high frequency introduction part 1 is off a resonance point 7 by a distance corresponding to or over a unit wave length in the basic mode of a high frequency within the vacuum vessel 8, and perpendicular to the axis of a magnetic field. According to the aforesaid construction, the window 4 does not view a plasma directly and, therefore, a thermal load or particle flux from the plasma 6 is alleviated and the possibility of window fracture is lowered. Also, as vacuum exhaust can be effectuated from a direction parallel to the axis of the magnetic field, the area of an exhaust port can be enlarged, thereby raising the efficiency of vacuum exhaust.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an ECR ion source (electron cyclotron resonance ion source) used in nuclear fusion devices, accelerators, semiconductor manufacturing equipment, etc.

(Prior Art) In an ECR ion source, a discharge is generated using the swirling motion of electrons in a magnetic field, and ions generated by the discharge are extracted by an electrostatic field and used as an ion beam. The ECR ion source will be described below with reference to the drawings. 5 and 6 are cross-sectional views showing a conventional ECR ion source. The ion source includes a magnet 9 that creates an ECR resonance magnetic field. A vacuum vessel 8 that generates plasma 6 (ions), a gas introduction pipe 10 that introduces gas into the vacuum vessel, an introduction section 1 and window 4 that introduce high frequency waves, and an ion extractor that extracts ions and transports them to the target location. It consists of an electrode, a vacuum container for transportation (not shown), a cooling path (not shown) for cooling the vacuum container, and a vacuum pump (not shown).

When a magnetic field exists, electrons experience a force perpendicular to the magnetic field,
The angular frequency of this rotating motion is ω (7 radians), and the strength of the magnetic field (magnetic flux density) is B (Tesla).
, the mass of the electron is m (kg), and the charge of the electron is e (coulomb), then a linear equation holds true.

= Appearance ω m On the other hand, from the outside, the frequency f (Hz
), the electrons resonantly absorb the high-frequency energy and the discharge is multiplied. The high-energy electrons thus generated collide with gas atoms, and plasma 6 is generated.

To introduce high frequency into the vacuum container 8, apply a vacuum.

It is passed through a window 4 which is sealed and has low high frequency loss.

For the reason mentioned above, the window 4 is manufactured by sealing ceramics such as alumina, boron nitride, or quartz glass inside the waveguide by brazing, diffusion bonding, or the like. A cooling path may also be provided. And in a conventional ECR ion source, window 4 is
Is it installed near the R resonance point 7 so as to be perpendicular to the axis of the magnetic field (No. 511)?

Alternatively, it was installed on the axis of the magnetic field so as to be parallel to the magnetic field (Figure 6).

(Problems to be Solved by the Invention) In such an ECR ion source, since the window 4 directly looks into the plasma 6, there is a problem in that the window 4 is damaged by particle flux and heat load from the plasma.

In addition, if the window 4 is installed parallel to the axis of the magnetic field, the load can be alleviated to some extent, but since the diameter of the evacuation pipe 11 cannot be increased, the evacuation efficiency decreases and the ultimate pressure cannot be lowered. there were.

It is an object of the present invention to overcome the above-mentioned problems and provide an ECR ion source that has a long life due to less damage to the window and has a low ultimate pressure due to high evacuation efficiency.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, the window is installed at a position perpendicular to the axis of the magnetic field and at least one wavelength away from the resonance point.

(Function) In an ECR ion source equipped with a window as described above, since the window does not directly look into the plasma, the particle flux and heat load from the plasma are significantly reduced, and the evacuation opening can be made larger, making it more efficient. can be made larger. In addition, by separating one wavelength or more from the resonance point, the direction of the magnetic field and the propagation vector of high-frequency electromagnetic waves become parallel at the resonance point, so the plasma density is greater than the plasma density shown by the following equation, which is generally known as the plasma cut-off frequency condition. Value plasma can be obtained.

ωp = (-) εam Here, ωP: Plasma angular frequency (f=-": Cutoff frequency) (7 radians) nl,: Plasma density (m'"3) e: Elementary charge (coulombs) ε. : Dielectric constant m of vacuum : Mass of electron (kg) (Example) Examples of the present invention will be described below with reference to the drawings. In FIG. 1, a coaxial waveguide 2 is used to introduce high frequency waves into a vacuum vessel 8. In FIG. The high frequency introduction section 1 is composed of a coaxial waveguide 2 and an inner conductor 3 extending so as to be inserted into the vacuum container 8 through a window 4.

The inner conductor 3 does not need to be a single piece, but may be divided at any position and electrically and mechanically coupled.

Further, the shape of the high frequency introduction section 1 may be a structure in which the interior is hollow and heat generated by high frequency loss is cooled through a coolant.The shape of the high frequency introduction section 1 depends on the frequency of the high frequency to be used.

Determine by considering impedance consistency, etc. The window 4 is made by sealing ceramics such as alumina or boron nitride on the inside of the flange 5, and the portion through which the inner conductor 3 passes is also sealed. The high frequency introduction section 1 is installed at a distance from the resonance point 7 by at least a length corresponding to one wavelength in the fundamental mode of the high frequency within the vacuum vessel 8 .

Perpendicular to the axis of the magnetic field.

According to the ion source of this embodiment configured as described above, since the window 4 does not directly look into the plasma 6, the heat load and particle flux from the plasma 6 are reduced, and the possibility of breakage is reduced. Furthermore, since evacuation can be performed in a direction parallel to the axis of the magnetic field, the area of the evacuation hole can be increased, and the efficiency of evacuation can be increased. moreover,
Since the high frequency is introduced from a point at least one wavelength away from the resonance point, the direction of the magnetic field and the propagation vector of the high frequency become parallel at the resonance point, making it possible to obtain a plasma density that exceeds the cutoff condition.

(Other Embodiments) In FIG. 1, the part inserted into the vacuum vessel 8 is the inner conductor 3 of the coaxial waveguide 2, but as in the embodiment shown in FIG. The conductor 3a may also be used, which not only improves the matching but also reduces the heat load from the plasma. Further, the same effect can be obtained by using a wave (mountain) shaped groove body 3b as shown in FIG. 3, or a closed circuit type conductor 3c as shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the window used for introducing high frequency waves does not directly look into the plasma, so the heat load and particle flux from the plasma are reduced, and the possibility of the window being damaged is reduced. Therefore, the life of the ion source can be extended. Also.

Since the exhaust hole for evacuation can be made larger, the exhaust efficiency increases and the ultimate pressure can be easily lowered. Furthermore, since it is possible to obtain a plasma density that exceeds the cutoff condition, a large ion beam current can be obtained even at a low frequency.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main parts of an ECR ion source according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a high-frequency introduction part of an ECR ion source according to an embodiment of the present invention using a helical conductor. , FIG. 3 shows an ECR of an embodiment of the present invention using a wave (mountain) groove body.
4 is a sectional view showing the high frequency introduction part of the ECR ion source according to the embodiment of the present invention using a closed circuit type conductor, and FIGS. 5 and 6 are sectional views showing the high frequency introduction part of the ion source. E
FIG. 2 is a cross-sectional view showing the main parts of a CR ion source. 1... High frequency introduction part 2... Coaxial waveguide 3...
Inner conductor 3a... Spiral conductor 3b... Wave (
Mountain) type groove body 3c...Closed circuit type conductor 4...Window
5...Flange 6...Plasma
7...Resonance point 8...Vacuum vessel 9...Magnet 10...Gas introduction pipe 11...Vacuum exhaust pipe Agent Patent attorney Nori Chika Ken Yudo Daishimaru Kendai 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] At a point more than one wavelength away from the ECR resonance point in the high frequency tube,
An ECR ion source characterized in that a high frequency introduction section is installed perpendicular to the axis of the magnetic field for ECR resonance.