JPS6052389B2 - Atomic beam detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an atomic beam detection device for an atomic beam tube used in a frequency standard device.

A cesium atomic beam tube is known as a typical atomic beam tube used in small, lightweight, portable frequency standard equipment. This cesium atomic beam tube is in high vacuum,
”, Enno TJ7! , has a configuration that utilizes the resonance phenomenon between the energy levels of the n-i-beam and the microwave incident from the outside. The cesium atomic beam tube has a structure as shown in FIG.

In the figure, a cesium atomic beam 3 emitted from an atomic beam source 2 installed in a vacuum sealed tube 1 is spatially separated by an A-deflecting magnet 4 according to energy units based on the ultrafine structure of atoms. The light is then incident on a microwave cavity resonator 6 which is magnetically shielded by a shield case 5 . Inside the microwave cavity resonator 6, cesium atoms resonate at a microwave frequency corresponding to the frequency between energy levels due to the hyperfine structure, and transition between energy levels. After the transitioned cesium atoms are deflected by a B-deflecting magnet, this atomic beam is extracted as an electrical output signal by a detection device 8 consisting of an ionized ribbon. A small, lightweight, portable frequency standard device controls the microwave frequency incident on the microwave cavity resonator to maximize this electrical output, thereby obtaining an ultra-high and stable frequency.

As such a frequency standard device, the Japanese Patent Publication No. 42-275
The configuration shown in FIGS. 1 and 2 of Publication No. 17 is known.
As shown in the same publication, the detection device 7 (Fig. 1)
An error is detected in the output of the control circuit 1 (FIG. 2), and a stable frequency is obtained by controlling the oscillator 12 based on this error. There are two types of conventional atomic beam detection devices:

One is a device that ionizes an atomic beam by the surface ionization effect of a red-hot ionization ribbon, collects these ions with a metal collector, and extracts them as an ion current.
The first method is to accelerate an ionized atomic beam using a parallel plate, pass it through a mass spectrometer magnet, and then input it into an electron multiplier tube.The secondary electrons generated in the electron multiplier tube are converted into electric signals. It is a device for taking out. However, the former device has the following drawbacks. That is, what is utilized in the frequency standard device in the output signal of the cesium atomic beam tube is an AC component generated by a phase modulated signal of a microwave that is phase modulated for making the cesium atoms resonate. However, in the former device, the lead wire extending from the metal collector to the outside of the vacuum sealed tube has a stray capacitance, which causes a drop in the output signal, that is, the upper C component. That is, in the characteristic of output signal level versus frequency, which is usually called a frequency characteristic, the value of the frequency at which the output signal level decreases by 3 decibels (cutoff frequency FO) can be expressed as follows. Therefore, if the stray capacitance of the lead wire increases more than the cesium atoms attached to the 2πRC lead wire, the cutoff frequency Fc will gradually decrease, and the output signal (AC component) will decrease.

The latter device has the disadvantage that the output of the atomic beam tube is reduced due to dissipation of the ionized atomic beam as it passes through the mass spectrometer magnet and enters the electron multiplier tube.
Also, in the latter device, B
This method directly measures the amount of the cesium atomic beam that passes through the deflecting magnet 7 and enters the detection device, and has the disadvantage that it is difficult to optimally control the amount of radiation from the atomic beam source. SUMMARY OF THE INVENTION An object of the present invention is to provide an atomic beam detection device that eliminates the above-mentioned drawbacks.

The atomic beam detection device of the present invention is composed of an ionization ribbon, a metal collector plate, a mass spectrometry magnet, and an electron multiplier, and simultaneously extracts the ionization current from the metal collector plate to the outside of the atomic beam tube as an electrical output signal. It is characterized in that the output signal from the secondary electrons of the electron multiplier tube is taken out of the tube as an electrical output signal of the atomic beam tube.

That is, the electron multiplier tube output with a stable AC component is taken out for frequency control of the frequency standard device, and the output from the metal collector plate with little DC level fluctuation is taken out to the outside for atomic beam source control. There is.

Using an atomic beam detector with such a configuration, it is not only possible to directly measure the amount of cesium atomic beam and control the atomic beam source, but also to prevent the output of the atomic beam tube from decreasing due to changes in the stray capacitance of the detector. can be prevented.

Next, the present invention will be explained in detail with reference to the drawings. FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, the cesium atomic beam detection device installed inside the vacuum sealed tube 9 is
It consists of an ionization ribbon 11 made of a metal ribbon, a metal collector plate 12 disposed in front of the ribbon, a mass spectrometry magnet 13, and an electron multiplier 14. A neutral cesium atomic beam 3 from an atomic beam source 2 is ionized by an ionization ribbon 11, and the ionized cesium atoms (cesium ions) are transferred to a collector plate 12 whose potential is lower than the bias voltage applied to the ionization ribbon.
I am drawn to it. A slit is provided in the center of the metal collector plate 12, and some of the cesium ions drawn to the metal collector plate 12 pass through this slit. Impurity ions other than cesium ions are removed from the cesium ions that have passed through the slit in a mass spectrometry magnet 13, and the cesium ions are supplied to an electron multiplier 14. On the other hand, the cesium ions collected on the metal collector plate 12 are led out of the atomic beam tube as a beam current via a lead wire 17, and are taken out from a terminal 20 as an electrical output signal (output 1). Used as a control signal. Note that the resistor 18 and the amplifier 19 are used to amplify the output from the collector plate, and these resistors 1
8 and the amplifier tube 19 can also be arranged inside the vacuum sealed tube 1. On the other hand, the cesium ions incident on the electron multiplier tube 14 collide with the electrodes of the electron multiplier tube to generate secondary electrons, and these secondary electrons are taken out of the tube from the terminal 21 via the lid wire 15. output (output).

This output H corresponds to the output of the detector 7 described in the above-mentioned patent publication, and is used as a control signal for the microwave incident on the cavity resonator. As the electron multiplier 14, a multistage dynode type secondary electron multiplier or a channel type secondary electron multiplier is used.

FIG. 3 shows an example of the dependence of the electric output signal 1 on the bias voltage of the ionized ribbon. The output 1 and the output change as shown in the figure by changing the bias voltage of the ribbon, respectively.

Normally, the bias voltage is set to a value such that the output is 1 and the output is maximum. As described above, in the present invention, two types of output signals are used as the atomic beam detection signal, namely, the output signal of the electron multiplier tube as the microwave control signal and the output signal of the collector plate as the atomic beam control signal. While controlling the atomic beam, it is also possible to control the microwaves that enter the cavity.

Although cesium was used as the atomic beam in this embodiment, it is also possible to use atomic beams other than cesium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a cesium atomic beam tube, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a characteristic diagram of the apparatus of the present invention shown in FIG. 1 and 2, 1, 9... vacuum sealed tube, 2... atomic beam source, 3, 10...
・Atomic beam, 4...A-bending magnet, 5...
・Shield case, 6・Microwave cavity resonator, 7・
...B-bending magnet, 8...detector, 11...
...Ionization ribbon, 12...Metal collector plate,
13... Mass spectrometry magnet, 14... Electron multiplier, 15, 17... Lead wire, 16, 18
・・・Resistance, 19 ・・・Amplifier.

Claims (1)

[Claims] 1. An atomic beam detection device used in an atomic beam tube for atomic beam detection includes an ionization ribbon that ionizes the atomic beam, a hole in the center that collects the ionized atomic beam, and a ribbon that collects the ionized atomic beam through the hole. a collector plate that allows a portion of the ionized atomic beam to pass through; a mass spectrometer magnet that removes impurity ions from the atomic beam that has passed through the collector plate; An atomic beam detection device comprising: an electron multiplier tube that generates an atomic beam; and an electric signal is extracted from the collector plate and the electron multiplier tube.