Ion accelerator

Details Ion accelerator Ion accelerator

2002-05-01

2004-06-01

Wells, Nikita (Department: 2881)

Electric lamp and discharge devices: systems

High energy particle accelerator tube

Magnetic field acceleration means

C315S507000, C315S111210, C315S111610, C315S111810, C313S363100, C250S493100, C250S42300F, C250S482100

Reexamination Certificate

active

06744225

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion accelerator for efficiently injecting ions generated in plasma to an ion linac, and a high-intensity direct ion injection method using this ion accelerator and an ion accelerator which is improved and injects still more efficiently ions, generated in a plasma-generating target by radiating a plasma-generating laser, into an ion linac by using the diffusion velocity of this plasma.
2. Description of the Related Art
Ion accelerators which inject ions generated in plasma to an ion linac such as an RFQ linac or a drift tube linac and accelerate the ions have been developed.
It is possible to use such an ion accelerator as a first-stage ion accelerator in an accelerator for cancer treatment, in an ion implantation accelerator for semiconductor production, and in a large-scale accelerator complex for physical experiments.
This ion accelerator will be described with reference to FIG.
11
.
FIG. 11
is a plan for schematically showing the construction of a conventional ion accelerator
200
.
As shown in
FIG. 11
, the conventional ion accelerator
200
mainly consists of an ion source
210
, a beam line
220
, and an ion linac
230
.
Hereinafter, each major component of the conventional ion accelerator
200
will be described below.
As the ion linac
230
, a well-known ion linac such as an RFQ linac described later, or a drift tube linac is used.
In
FIG. 11
, reference numeral
60
denotes a laser generator for generating a plasma-generating laser L, and reference numerals
62
A and
62
B denote mirrors guiding the plasma-generating laser L to an ion source
210
.
In addition, reference numeral
70
denotes an analysis electromagnet for providing ions accelerated by the ion accelerator
200
, for other applications such as the accelerator for cancer treatment, ion implantation accelerator for semiconductor production, or large-scale accelerator complex for physical experiments, which are described above.
Generally, an ion source is an apparatus wherein plasma with ions and electrons coexisting with each other is generated in a vacuum chamber by high-frequency power, laser heating, etc., and a high voltage is applied to the vacuum chamber to take out only ions from its inside, producing an ion beam.
The ion source
210
that is used for the conventional ion accelerator
200
shown in
FIG. 11
comprises a plasma-generating target
212
which is subject to radiation of a plasma-generating laser L to generate the plasma, a focusing lens
214
which condenses the plasma-generating laser L at the plasma-generating target
212
, a vacuum chamber
216
which contains the generated plasma, and an ion extraction electrode
218
.
As shown in
FIG. 11
, the plasma-generating laser L generated by the laser generator
60
is radiated at the plasma-generating target
212
through the two mirrors
62
A and
62
B, and focusing lens
214
in the vacuum chamber
216
of the ion source
210
to generate the plasma by laser ablation.
Since the plasma generated in the vacuum chamber
216
is in the status in which ions and electrons coexist as described above, an ion beam is led to an adjoining beam line
220
by applying a negative voltage of several kV to several tens kV to the ion extraction electrode
218
.
The beam line
220
comprises one or more ion beam focusing lenses
222
(two in FIG.
11
), such as a solenoid type magnet or an Einzel electrostatic lens.
In addition, in order to control the status of an ion beam, a beam shape diagnostic tool
224
is often provided between the focusing lenses
222
.
In the above construction, the basic operation of the conventional ion accelerator
200
will be described by using FIG.
11
.
In the conventional ion accelerator
200
, the plasma generation laser L is radiated at the plasma-generating target
212
to generate the plasma, ions extracted by the extraction electrode
218
from this generated plasma are injected into the ion linac
230
through the beam line
220
.
At this time, it is possible to obtain the maximum values of the magnitude and gradient of an ion beam that suit the beam line
220
after the ion source
210
by adjusting the geometry and the applied potential gradient of the extraction electrode
218
which is an electrode for applying a high voltage.
In addition, the ion beam radius is expanded to large radius after the extraction by using a solenoid type magnet or the focusing lens
222
such as an Einzel electrostatic lens, travels with relatively low influence of Coulomb repulsion, is converged by means of the focusing lens
222
to the beam size of suitable injecting conditions for the ion linac
230
, and is injected.
Next, as an example of the ion linac
230
, as disclosed in Japanese Patent Laid-Open No. 7-111198, the well-known RFQ linac
230
will be supplementarily described by using
FIGS. 12 and 13
.
FIG. 12
is a cross sectional front view showing the construction of the RFQ linac
230
.
FIG. 13
is a longitudinal sectional side view showing the construction of the RFQ linac
230
.
The RFQ (Radio Frequency Quadrupole) linac
230
is mainly constituted by installing four vane electrodes
234
(or four rod electrodes), made to be perpendicular to each other, inside a conductive cylindrical container
232
whose inside is in vacuum.
A resonator comprises a cylindrical container
232
and vane electrodes
234
, as shown in
FIG. 13
, high-frequency power is supplied through the high-frequency waveguide
238
, and the vane electrodes
234
with end portions
234
a
in a wave form converge the ions and accelerates the ions in a direction of the central axis with a desired energy.
However, in the conventional ion accelerator with the above-described combination of the ion source, the beam line for transporting a low-energy ion beam, and the ion linac, the divergence of the beam by the Coulomb repulsion in the ion beam is large especially when a large-current ion source is used, and thus, only a part of the extracted ion beam can meet injection conditions of the ion linac, resulting a problem that only a small amount of ions to be accelerated.
In addition, since the amount of an ion beam current and the number of charges of generated ions, etc. largely change within a beam generating pulse of a duration of several &mgr;s when a pulsed ion source with laser heating etc. is used as an ion source, it is very difficult to appropriately design a beam line while considering the Coulomb repulsion.
Furthermore, the conventional ion accelerator has a problem that it requires a complicated beam line including apparatuses such as a focusing lens.
An object of the present invention is to provide an ion accelerator where an amount of accelerable ions significantly increases by solving the above-described conventional problems, dramatically simplifying the combination of an ion source, a beam line, and an ion linac, and furthermore, further reducing the influence of Coulomb repulsion, and a direct ion injection method for efficiently injecting ions by using this ion accelerator and an ion accelerator which is improved and injects still more efficiently ions, generated in a plasma-generating target by radiating a plasma-generating laser, into an ion linac by using the diffusion velocity of this plasma.
SUMMARY OF THE INVENTION
In order to solve the problems, a first aspect the present invention is an ion accelerator comprising: a plasma-generating source; a vacuum chamber for extracting ions from plasma generated from the plasma-generating source; an ion linac, the plasma-generating source, vacuum chamber, and ion linac being connected in series, the vacuum chamber being installed near an ion entrance of the ion linac; and a high voltage power supply for boosting the vacuum chamber to a desired voltage, wherein ions are directly injected from the vacuum chamber to the ion linac.
Owing to such construction, since Coulomb repulsion is not generated because electrons with negative charges and ions with positive charges coexist in plasma, its influence is

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