JPS6141120B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an ion linear accelerator.

When a high-frequency voltage is applied to the plates of an ion linear accelerator, electrons in the residual gas between the plates are accelerated and hit one of the plates, which is the positive electrode, to generate secondary electrons. Furthermore, they are accelerated by a high-frequency electric field and hit the other plate, which is now the positive electrode, to generate more secondary electrons, and this process is repeated, causing an avalanche of electrons to increase in the ion accelerator (multipactoring phenomenon). . As a result, the high-frequency oscillator of the accelerator becomes overloaded and its operation is inhibited, making it difficult to start the ion accelerator. In order to start the ion accelerator and transition to a stable operating state while preventing the occurrence of multipactoring, the output tube of the high-frequency oscillator is excited with low power for a short period of time to remove foreign particles attached to the electrode surface with electrons. The foreign matter is removed by tapping and exhausting for a certain period of time. By repeating this, the excitation power is gradually increased after waiting for the adsorbed matter on the electrode surface to decrease. This method requires good judgment and patience on the part of the repeater. The work takes from several hours to several days. Another method is to increase the voltage between the electrodes so that the traveling speed of electrons is faster than the rate of change of the high-frequency voltage so that the multiplication condition does not hold. However, since applying a high voltage may cause discharge and destroy the power tube, the voltage must be lowered in a short period of time, and a high-speed control circuit is required for this purpose.

An object of the present invention is to provide a structure of an ion linear accelerator that eliminates the above-mentioned drawbacks of the prior art, suppresses the multipactoring phenomenon, and ensures and facilitates the start-up of the accelerator.

That is, the present invention has a configuration in which a DC voltage can be applied between the electrodes of the ion linear accelerator or between the electrodes and the outer cylinder, and thereby the speed of the reciprocating movement of electrons between the electrodes due to the high-frequency voltage is made different between the forward and return paths. This ensures that the multiplication condition does not hold true and ensures quick start-up and stable operation.

A first embodiment in which the present invention is applied to a dual channel ion accelerator will be described with reference to FIGS. 1 and 2.

A pair of parallel conductors 2 and 3 with drift tubes D ₁ to D ₅ extending therein extend inside the outer cylinder 1 . A support conductor 30 supports these parallel conductors 2 and 3 within the outer cylinder 1. A movable shorting plate 6 is attached so that the support conductor 30 can be moved up and down. These support conductors are insulated from the outer cylinder 1 by an insulator 4, and a DC bias voltage source 5 is connected between one of the supports and the outer cylinder 1 via a switch S. There is a gap between the shorting plate 6 and the inner surface of the outer cylinder, and they are insulated in terms of direct current, but the shorting plate 6 and the supporting conductor 30
It is in a state of direct current connection. For this purpose, the drift tubes D ₁ , D ₃ , D ₅ are implanted in the parallel conductor 3 via the stems 31 , 32 , 33, and the stems (one stem 22 is visible in Fig. 2) are installed in the parallel conductor 2. The potential is the same as that of the drift tube implanted therebetween, and in this embodiment, the potential is positive. Drift tubes d ₁ , d ₂ and the like arranged alternately with the aforementioned drift tubes in the outer cylinder 1 by the stems 11, 11', 12, etc. are at the same potential as the outer cylinder 1, and in this embodiment are at a negative potential. There is. Therefore, a DC electric field is established between adjacent drift tubes in each of the two acceleration channels, so that even if the remaining electrons at startup are accelerated by the high-frequency electric field, the forward and return velocities are different, resulting in avalanche multiplication of the electrons. is prevented. By closing the switch S even after starting, multipactoring phenomenon caused by starting following an accidental stop during operation is prevented, and stable operation is guaranteed.

A second embodiment in which the present invention is applied to a single channel ion accelerator will be described with reference to FIGS. 3 and 4.

In FIG. 3, a pair of parallel conductors 2 and 3 in which drift tubes D ₁ to D ₅ are implanted extend into the outer cylinder 1 . Support conductors 20 and 30 support the parallel conductors 2 and 3 within the outer cylinder, and a movable shorting plate 6 is provided on the support conductors. This movable plate 6 is separated from the inner surface of the outer cylinder with a gap, but the support 2
0.30 are in close contact. Support conductor 20, 30
is electrically insulated from the outer cylinder 1 by an insulator 4. A DC bias voltage source 5 is connected via a switch S between one support conductor 20 and the outer cylinder 1. The support conductors 20, 30 are kept at the same potential (positive potential in this embodiment) via the shorting plate 6, and all drift tubes _D1 to _D5 are kept at a positive potential.
The outer tube 1 is held at a negative potential, so that a DC electric field is established between the drift tube and the outer tube,
This DC electric field exerts a biasing force on the vibrations of the remaining electrons between adjacent drift tubes during startup, thereby suppressing the occurrence of the multipactoring phenomenon.

As is well known, in the startup operation of an ion accelerator, two movable shorting plates 6 are connected to supporting conductors 20 and 30.
, and fixed at a position at a distance n/2 times the wavelength λ fed from the loop antenna of the coaxial cable from the high frequency oscillator to establish safe waves on the Retzchel lines 2 and 3. Cation drift tube
Upon exiting D ₁ , it is accelerated by the accelerating electric field between it and the drift tube D ₂ . this drift tube
While passing through D ₂ , the phase of the high-frequency potential changes by π, and the electric field between it and the drift tube D ₃ also becomes an accelerating electric field and accelerates the positive ions. In this way, the cations are sequentially accelerated downstream.

Since both the first and second embodiments use the short circuit plate 6, the high frequency current flows along the upper surface of the short circuit plate 6, and therefore the inconvenience that the high frequency current flows through the insulator 4 and causes it to deteriorate due to heating is avoided. Does not occur.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line -' in FIG. FIG. 3 is a longitudinal cross-sectional view of a second embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along the line -' in FIG. In the figure, 1...outer cylinder, _D1 - _D5 ; _d1 , _d2 ...drift tube, 2; 3...parallel conductor, 20; 30
... Support conductor, 4 ... Insulator, 5 ... DC bias power supply, 6 ... Movable short circuit plate, S ... Switch.

Claims (1)

[Claims] 1. An outer cylinder, a pair of parallel conductors extending inside the outer cylinder and having a drift tube planted therein, a supporting conductor that supports these parallel conductors in the outer cylinder, and a movable shorting plate provided on these supporting conductors. , an insulator that insulates the supporting conductor from the outer cylinder, and an insulator connected to the support and the outer cylinder for generating a DC electric field between adjacent drift tubes or between the drift tube and the outer cylinder. An ion linear accelerator characterized by being equipped with a direct current bias voltage source.