JPS62295400A - Ion beam apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ion beam devices, and more particularly to such devices in which the generated ion beam is in a series of energy groups or packets. A common method is to generate a continuous stream of ions and direct these ions to the point where they need to be utilized. Because ion applications often rely on ions having sufficiently high energies, some applications require passing the ion beam through an accelerator that greatly increases the velocity of the ion beam. Ions are accelerated by passing them through a strong electric field, but since the voltages required to impart extremely high energies to the ions can be extremely high, the ions are accelerated in a series of accelerations along the length of the accelerator. It has previously been proposed that ions be subjected to a high-frequency alternating current voltage to provide them with a "propulsive force." During half-cycles of the alternating voltage, the ions are accelerated, but during half-cycles of unfavorable polarity they are shielded by the drift tube so that the true effect of always being accelerated in the same direction is achieved. An example of this type of linear accelerator is given in Physical Review 3
8 2021 (1931) by D. H., Sloan and E. O., Lawrence. However, there are other methods of accelerating ions using multiple low voltage acceleration stages. The effect of the high frequency alternating voltage is to convert the steady stream of ions into separate groups, but since many of the ions are shifted out of phase by the accelerating voltage,
This conversion is extremely inefficient. Naturally, this results in non-accelerating forces that result in partial loss of the ion beam.

The present invention seeks to provide an improved ion beam device that converts a relatively steady state ion beam into a swarm beam in an efficient manner.

Such swarm beams may be used directly if desired, or they may be made highly effective and efficient by providing a radio frequency accelerator within the ion beam device that accelerates the swarm beam to the required energy level. It may be accelerated.

According to the present invention, the ion beam device receives a steady ion beam having a predetermined average velocity and accelerates and decelerates the ions by a velocity smaller than the average velocity of the ions to generate a velocity-modulated ion beam. means for applying a high frequency alternating electric field to the beam, and arranged to receive the velocity modulated beam, wherein the transit time of the beam through the drift region exceeds a plurality of cycles of said high frequency, so that at the output of the drift region; and an elongated drift structure dimensioned such that the velocity modulated ion beam generates discrete groups of ions. Preferably, means are provided adjacent to the output end of the drift structure for applying a high frequency alternating electric field to the ion groups so as to receive the separate ion groups and accelerate the ion groups in the same direction; The electric field applied to the ion population is substantially greater than the electric field applied to modulate the ion beam.

The drift structure is preferably in the form of a conductive tube extending the entire length of the drift region, within which the true accelerating electric field acting on the ions is substantially zero. However, the drift structure can consist only of an initial euclastic collar following an open region, which is shielded from electric field fluctuations so as to constitute a substantially equipotential drift region. Preferably, the drift tube includes means for electrostatically focusing the ion beam so as to focus the ion beam onto a predetermined path and prevent the ion beam from spreading outwardly into the walls of the drift tube. Preferably, this focusing means consists of a plurality of separate stages to which different focusing means can be applied. However, these focusing voltages do not affect the longitudinal potential and therefore the velocity of the ions along the drift tube.

The magnitude of the alternating electric field applied to the incident steady-state ion beam is such that the change in velocity of the ions within the beam is relatively small so that the entire beam is in a substantially uniform energy state. Because the velocity modulation is small, the drift tube must be quite long to give the ions enough time to separate into separate groups. The point at which the ions form the most distinct group is quite critical, beyond which the group tends to coalesce again. A relatively large high frequency electric field is applied to accelerate each group as a whole at the point where the group is most distinct and to give a high average velocity with respect to velocity modulation. In this way, a group of ions can be considered as a single energy state.

In a preferred embodiment of the invention, the ion beam device includes an ion puncher combined with a linear accelerator, which utilizes a series of radio frequency stages, each to which an alternating current high voltage is applied, to drive a group of ions to extremely high velocities. To accelerate. Each stage imparts approximately eV of energy to the ions. If N stages are provided in sequence, the final energy will be approximately eV,N. By ensuring that the ions are in separate groups before applying a high acceleration voltage and ensuring that the ions within the group are in a nearly uniform energy state, it is possible to Storing groups allows for extremely efficient ion beam conversion within ion beam devices.

Naturally, this group of ions can be used for purposes other than supplying the linear accelerator. Once the stationary ion beam is split into streams of separate ion pulses, each pulse can be separately deflected and/or utilized as desired. The invention will be further explained by way of example with reference to the accompanying drawings, in which: FIG.

Referring to FIG. 1, an ion source (not shown) produces only a steady beam of ions whose charge density is substantially constant and whose average density of ions varies only slightly from a nominal value. Such a steady ion beam can be generated according to known techniques. To convert the steady ion beam into a continuous group of ions, the beam is passed through an ion puncher. This buncher consists of a first short earthed tube l, a 1-IF electrode tube 2, and a relatively long earthed drift tube 3, and the inside of the drift tube is an equipotential drift region. . At the output end of the drift tube 3, the ion group is separated by another II! “Den i~
The I(F electrode tube 4 serves to accelerate the ion group).

The purpose of the tube 1 is to shield the ion source and the front stage from the effects of the HF signal on the HF electrode 2. The effect of the HF signal applied to the ion beam by the electrode tube 2 is to generate an oscillating electric field that accelerates or decelerates the ions relative to their initial velocity depending on their position relative to the electrode. Therefore, the ions entering the long drift tube 3 have slightly different velocities and the HF
The magnitude of the electric field is selected such that the velocity distribution is relatively small. The HF signal applied to the electrodes ranges from 2M Hg to 30MHg. The length of the drift tube 3 is such that the passage time of ions passing through the drift ffI region is HF.
It is chosen to be significantly longer than the frequency repetition time. Thus, typically the length of the drift tube 3 is such that the time required for an ion to travel from one end of the drift tube to the other corresponds to approximately six cycles of the HF signal. The effect of the initial fluctuation of individual ions during this time is to separate them into distinct ion groups. These separately separated ion groups are arranged to reach the gap in the HF drift tube 4 such that the phase of the HF signal on the HF drift tube 4 is oriented to accelerate each ion group as a whole.

The increased energy increased by this electrode 4 is much larger than the energy distribution within one group of ions.

The circuit shown in FIG. 1 is used to provide some control over the relative phase of the HF signals applied to electrode tubes 2 and 4. This HF signal is generated by an HF drive source 5, a power sprocket 6, a respective phase adjuster 7.
8 and fl F amplification 2g9.10 to the respective electrode tubes 2 and 4. Amplifiers 9 and 1
The effect of 0 is to increase the level of the signal required to be applied to electrodes 2 and 4 and to provide the necessary degree of impedance matching. The output of the signal from each HF amplifier is compared with the input signal in a respective phase discriminator 11.12 and any phase difference is corrected by a phase adjuster 7.8.

This compensates for undesirable phase differences caused by the operation of amplifiers 9 and 10.

These two phase discriminators 11 and 12 are such that the phase discriminator performed by one discriminator is also applied to the other discriminator, so that the phase of the HF signal at electrode 4 is equal to the phase of the HF signal on electrode 2. are coupled together so that they are known to each other. Ideally, these two electrodes - HF
The signals are in phase, but some 3J1 node is required depending on the input energy of the steady ion beam and the length of the drift tube 3.

Referring to FIG. 2, a modified ion puncher is shown. In this puncher, the phase and voltage control for the beam group is performed using a method different from the method shown in FIG. For example, the AC voltage delivered to the electrode tube 2 is taken directly from the common HF drive source 14 via attenuation 815 . The necessary drive amplifiers are not shown. Initially, the ion beam is given an iR
! The height of the IF voltage must be substantially lower than the voltage applied to the electrode tube 4.

Typically, the AC voltage applied to the electrode tube 4 is 5
0 KV, but the voltage applied to the electrode tube 2 is only 2.5 KV in magnitude, and the actual value is that when the ion group reaches the electrode tube 4, the ion group is in good condition. The variable attenuator 15 separates the signals into 11 sections. In this case, the long drift tube 3 is provided with internal focusing elements 20, 21, 22, 23 which serve to focus the ion beam onto the central axis of the ion beam focusing electrode. These focusing elements are electrostatic in nature and operate in a known manner. Relatively high voltages may be applied to these electrodes to accelerate the ions transversely to the longitudinal axis of the drift tube 3;
These voltages do not substantially affect the longitudinal velocity of the ions.

The phase difference between HF tube 2 and lt can be compensated by applying a dc lightning voltage from source 32 to tube 3. When a positive voltage is applied, the positive ions in the gap between tubes 2 and 3 will not gain 5i more power/' + energy than when tube 3 is at ground potential. Drift tube 3 These same ions as they leave tube 3 gain more energy. The net result of this is that the energy gain by tube 3 is zero. However, the time it takes for a particular ion to pass through tube 3 is at ground potential.The negative voltage therefore shortens the time required for the ions to pass through the tube 3.

Therefore, when a DC voltage is applied to the tube 3, the attenuator 1
5 can compensate for the phase difference between the H F tubes 2 and 4. Therefore, the DC bias source is connected to the ion puncher at the output end of the drift tube 3 and the electrode tube 4.
The magnitude and polarity of that voltage can be adjusted to optimize its relationship with the HF signal above.

In FIG. 2, the ion puncher is shown with two first stages 24 and 25. It is arranged to supply power to the linear accelerator. This linear accelerator consists of a number of separate HF stages, each of which has 5
An accelerating voltage of 0 KV is applied. In this way, the total accelerating voltage applied to the ions is doubled by the number of stages, so there is no need to generate an extremely large accelerating voltage in the second step. The principle of linear accelerators using II F signals is that only ions that are correctly positioned relative to the HF signal are accelerated. In the present invention, the ions are sent in separate groups to the first stage of the HF ion accelerator, so that it is possible to accelerate all the ions in the group in an efficient manner. The spacing between adjacent HF electrodes: e.g. the spacing between electrode 4 and electrode 26 and the spacing between electrode 26 and electrode 27 corresponds to the time it takes for an ion to travel during one cycle of the HF signal. selected to correspond. As with increasing the ion velocity so that the ions travel further during each period of the HF signal, increasing the electrode tube length causes the ions to travel further into the accelerator. The action of grounded drift tubes 28 and 29 is to provide a reference potential for the electric field and to shield the ions from the electric field reversal of the HF signal. Each grounded drift tube 28,29 includes a focusing element 30.

FIG. 3 shows a conventional ion source 39 that sends a steady beam of ions having an energy of 50 KeV(7) to an ion beam puncher 40 of the form shown in FIGS.
A system consisting of an ion beam 'A'II is shown. The output of this ion beam puncher 40 is a series of discrete groups or packlets of ions having a superimposed relatively small energy distribution of an average energy of about 50 KeV as described above. These ion groups are then accelerated by a linear accelerator 41. Assuming 50 stages are provided, approximately 2.4 million electron volts of output energy is available at output port 42.

The energy at this output port is actually quite large, but will be narrowly distributed. When it is important to accurately distribute the energy of the ion beam,
The ion beam is made to pass through an electrostatic separator 43 which gives individual ions a predetermined curve in a known manner depending on the ion energy. By selecting ions with a predetermined narrow hand energy at port 44, only the necessary ions can be directed to the point of utilization facility 45.

The transport efficiency of such ion beam devices can be increased very significantly with the ion puncher according to the invention. In conventional ion beam systems that apply a steady ion beam to a linear accelerator, the beam transport efficiency is only on the order of 16-17%. Using the ion beam puncher according to the invention, the transport efficiency can be increased up to 70%.

[Brief explanation of the drawing]

1 schematically shows an ion beam puncher, FIG. 2 shows a modified ion beam puncher, and FIG. 3 shows an ion beam device including a linear accelerator and an ion beam puncher. 1...Short grounded first tube 2...HF electrode tube 3...Drift tube 4...HF electrode tube 5...HF drive source 6...Power splitter 7.8... Phase adjuster 9.10... HF amplifier 11.12... Phase discriminator drawing drawing (no change in content) Figure 1 Procedure amendment (method)

Claims (11)

[Claims] (1) A high-frequency alternating current electric field is applied to the beam so as to receive a steady ion beam having a predetermined average velocity, accelerate and decelerate the ions by a velocity smaller than the average velocity of the ions, and generate a velocity-modulated ion beam. and means for applying the velocity modulated ion beam, the beam passing through the drift region exceeding a plurality of cycles of said radio frequency, the velocity modulated ion beam being arranged to receive the velocity modulated ion beam at the output end of the drift region. an elongated drift structure dimensioned to generate separated populations of ions. (2) means for applying a high frequency AC electric field to the ion groups so as to receive the separate ion groups and accelerate the ion groups in the same direction is provided adjacent to the output end of the drift structure; 2. The apparatus of claim 1, wherein the electric field applied to the ion population is substantially greater than the electric field applied to modulate the ion beam. (3) The device according to claim 1 or 2, wherein the drift structure is in the form of a conductive tube. (4) The applied high frequency AC electric field has a frequency relative to the average velocity of the ion beam passing through the electric field such that the ion transit time is at least approximately a plurality of periods of this high frequency. , the second term or the third term
Apparatus described in section. (5) A patent in which the drift structure includes means for electrostatically focusing the ion beam so as to focus the ion beam onto a predetermined path and prevent the ion beam from spreading outward into the drift structure itself. Claims 1 to 4
Apparatus according to any of paragraphs. (6) The device according to claim 5, wherein the focusing means comprises a plurality of separate stages arranged along the longitudinal direction of the drift structure and to which mutually different focusing voltages are applied. (7) Any one of claims 1 to 6, wherein a common frequency source is arranged to apply a high frequency electric field to a stationary ion beam and to apply a high frequency electric field to a group of ions generated by the drift tube. The device described. (8) The apparatus according to claim 7, wherein the magnitude of the high-frequency electric field applied to the stationary ion beam is substantially smaller than the magnitude of the electric field applied to the ion group. (9) Any one of claims 2 to 8, wherein the means for applying a DC bias voltage to the drift structure is provided to the means adjacent to the drift structure to which a high frequency signal is applied. The device described in Crab. (10) The device according to claim 9, wherein the DC bias voltage can vary in magnitude and polarity. (11) A multi-stage high frequency linear accelerator is positioned to receive the group of ions and accelerate the group of ions by the action of an applied high frequency electric field synchronized with the position of the individual group of ions. Apparatus according to any of paragraphs.