JP2545320B2 - How to generate high brightness light - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high intensity light.

[0002]

2. Description of the Related Art High-brightness light sources such as lasers, synchrotron radiation, and free electron lasers are currently used in an extremely wide range of industrial fields. An example of a free electron laser will be described. The free electron laser is, as shown in FIG. 1, an electron source (high-frequency linear accelerator) 1, a device that makes the electron orbit meander (hereinafter referred to as an undulator) 2, an optical resonator (mirror).
It consists of 3. The undulator 2 is a permanent magnet (S
_m C ₀₅ ) 5 and the like are arranged to form a periodic magnetic field (sinusoidal wave) in the y direction, and the direction of magnetization of the magnets is as indicated by a → mark, and one cycle is formed by four magnets. The wavelength of this period is λ _u
And

A relativistic electron beam is incident along the Z-axis and interacts with a periodic magnetic field to meander in a portion 6 surrounded by a dotted line in the xz plane in the figure. At this time, the electron beam emits undulator radiation. If an optical resonator can be used to further interact the emitted light with a subsequent electron beam, the light is amplified and becomes stimulated emission, producing a powerful light beam. If the energy of the electron beam is E and E = γmc ² (m is the rest mass of the electron, c is the speed of light), the wavelength λ of the undulator light is
Can be written as

[0004]

[Equation 1]

Here, n is the order of harmonics, θ is the direction of the emitted light with the Z axis, and K is a parameter that characterizes the emitted light.

[0006]

[Equation 2]

[0007] _{B o} is the maximum value of the undulator magnetic field. Here, considering the case of K <1, on the Z axis,

[0008]

(Equation 3)

The fundamental wave of is the main, and the number of periods of the magnet is N
At this time, due to the interference effect of the radiated light, the spectrum intensity becomes N ² times and the bandwidth is Δλ / λ 1 / N. Now, in order to obtain light with a short wavelength, it is necessary to shorten λ _u , that is, the period length of the undulator, or increase the energy of the electron beam.

Since the conventional undulator is made of an array of permanent magnets, it is difficult to shorten the cycle length. This is because, in order to make a space through which the electron beam passes, if the g (magnetic pole gap) in FIG. 1 is sufficient and a sufficient magnetic field strength is made on the Z axis, the size of the magnet must be increased. Because I don't get it. In practice, a cycle length of 3 cm to 5 cm is often used. Further, an attempt to make the magnet smaller and g also shorter has not been put to practical use.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems and to provide a method of generating high brightness light.

[0012]

The inventor of the present invention has conducted extensive studies to achieve this object, and as a result, a large number of filamentous plasmas are formed on a plane by parallel or antiparallel currents, and the periodic magnetic field distribution and We have invented a method of generating high intensity light which consists of meandering an electron beam by means of a periodic electric field distribution.

The present invention will be specifically described below.
In the present invention, the period length λ _u of the undulator is set to about 1 mm or less, and a large number of filamentous plasmas are arranged in place of the permanent magnets, and the current or density in the plasma is modulated to obtain Z A periodic magnetic field or electric field is created on the axis, and a force is applied in a direction orthogonal to the traveling direction to cause the electron beam to meander.

By introducing plasma, the following effects can be obtained. (1) Since the plasma is generated by the distant electrode, the electrode gap can be made larger than in the case of the magnet. (2) Since the generated magnetic field or electric field is created on the electron beam orbit, sufficient strength can be created. (3) An extremely short pitch can be realized by using thin electrodes and thin insulation.

(4) Since the effect of converging the electron beam by the ions in the plasma (plasma lens function) is expected, the broadening effect becomes maximum on the axis. (5) In plasma, since the refractive index for electromagnetic waves (light) changes, there is a function of converging electromagnetic waves on the optical axis (optical guide function). Therefore, a high efficiency free electron laser can be obtained by utilizing this phenomenon. To be

(6) Plasma density (≦ 10 ¹⁶⁾
/ Cc), the collisional scattering between the relativistic electron beam and the particles (ions and electrons) that compose the plasma, whether Rutherford scattering, Mueller scattering, or bremsstrahlung,
The impact on the electron beam trajectory from the linear accelerator is small. (The linear accelerator was used in contrast to a ring accelerator that uses the same beam for a long time. Even a ring accelerator can be used if the density distribution is localized by using differential evacuation, the puff method, and evaporation of the electrode material.) (7) The undulator action (action of causing the electron beam to meander) can be created in a pulsed manner.

The plasma undulator is formed by the following method. (1) Magnetic field type (orthogonal type: reverse current) plasma undulator. As shown in FIG. 2, a large number of roasted electrode wires (copper, carbon, tungsten, etc.) are arranged on an insulating pipe (Teflon, etc.), and they are arranged facing each other. A voltage is applied between the opposing electrode lines 9 and 10 to flow a current. Currents in opposite directions are made to flow between the electrodes adjacent to each other. The → mark indicates the direction of the plasma current 11. The plasma contracts finely due to the pinch effect, and becomes a filamentous plasma. Plasma
It is created by moderate gas pressure or discharge of gas by evaporation of electrode material and insulating material.

A magnetic field is generated by the current in the plasma so as to surround the plasma, and a magnetic field distribution By (Z) in the y direction which is periodic in the Z direction on the electron beam orbit is created. Lorentz force, where v is the electron beam velocity

[0019]

[Equation 4]

The force of is received in the x direction, and undulator radiation light is generated. As is clear from the graph of FIG. 3 showing the magnetic force lines and the magnetic field strength distribution, the pitch of the undulator has one cycle with two electrode lines, and if the electrode line interval is d, then λ _u = 2d.

As a circuit for discharging, as shown in FIG. 4, there are (a) a serial system in which the same current flows and (b) a parallel system in which a capacitor is attached to each electrode pair.

(2) Magnetic field type (orthogonal type: current in the same direction) plasma undulator. As shown in FIG. 5, this is a method in which the currents in the plasma are directed in the same direction. Similar to the case of FIG. 4, 9 and 10 indicate electrode lines, and the → mark indicates the direction of the plasma current 11. In this case, λ _u = d. Also, unlike the previous item, By = 0 at the central portion and the peripheral portion of the plasma. As a discharge circuit for generating plasma, there is a method in which a capacitor and a switch are connected in parallel with each electrode and discharge is performed simultaneously with the electrodes. The capacitor can be a pulse-form network (PFN) to make the discharge waveform rectangular. Instead of connecting the semiconductor elements, the switch can trigger the discharge with an electron beam or X-rays generated at the same time, or laser light (or laser light when a photocathode is used). In this case, make the electrode wire and the low impedance delay cable as one,
It can be an alternative to PFN. (Fig. 4 (b))

(3) Electric field type (oblique type) plasma undulator. As shown in FIG. 6, the relativistic electron beam 12 is obliquely passed through the filamentous plasma 11. The relativistic electron beam is
Because the mass is heavy, push away the plasma electrons,
As a result, you will feel the ion ripple electric field. In other words, the electric field is felt periodically. By diagonally intersecting, it has an electric field component in the orthogonal direction, and becomes meandering. In this case, it is effective when the effect of the electric field is larger than the effect of the current (the density is large). Λ _u is 2 ^1/2 times the electrode line spacing (when tilted at 45 °). The meander is the ZX plane.

The theoretical calculation of an ion ripple laser utilizing the electric field by the method of generating an ion acoustic wave in the plasma or the method of ultrasonic wave + laser is published in the following document ^* .

K. R. Chen and J. M. Da
wson: Physical Review Lett
er, 68 29 (1992)

The kink instability, sausage instability and the like are well known in the filamentous plasma, and as a countermeasure for stabilizing the filamentous plasma, magnetic lines of force are extended in parallel (reverse) to the current direction so that the core is inserted into the plasma. The magnetic field strength required for stabilization is Bx
Then, in the case of FIG.

[0027]

(Equation 5)

Where B _o is the magnetic field on the surface of the plasma current.
The influence of the magnetic field due to the adjacent current is neglected. _Io is the current in the plasma.

[0029]

(Equation 6) And

[0030]

(Equation 7) Becomes

As a method of creating this magnetic field, a pair of magnetic fields in the opposite direction are created so that the orbit of the electron beam is not greatly bent by this B _x . As shown in FIG.
The electrodes 9 and 10 are sandwiched from above and below by the ones sandwiched by, and arranged so as to face each other so that a magnetic field enters the plasma.

Currents flowing in antiparallel repel each other,
Currents in the same direction pull each other. To control this, it is advisable to attach an anchor coil as shown in FIG. 8 to a vertical magnetic field at the end of the filamentous plasma array. At the same time, the orbit of the electron beam can be adjusted so as not to be bent by the strength of the vertical magnetic field.

[0033]

[Function] As a relativistic electron beam, 20 MeV (γ
40)

[0034]

(Equation 8)

Considering the case of (I = 1 KA, the magnetic field due to the adjacent current is doubled in consideration)

[0036]

[Equation 9]

With an electron beam of 20 MeV, 0.
Since it can emit light of 62 μm, the energy of the electron beam is 1 compared with the conventional case to obtain the same wavelength.
It can be a few orders of magnitude smaller. The total radiation power for the electron beam of I (A) is

[0038]

[Equation 10]

L is the length of the undulator, 0.4
m and N = 200.

[Equation 11] Becomes

Here, I = 100 A is set. Similarly, considering the case of using as a free electron laser, assuming that the electron beam and light have the same cross-sectional area, the peak amplification rate G is

[0041]

(Equation 12)

It is represented by I is the peak current value of the electron beam, and Σ _o is the cross-sectional area of the electron pulse.

[0043]

(Equation 13)

Then, a maximum value of 0.54 is taken at x = 1 / 5N.

[0045]

[Equation 14]

And J ₀ and J ₁ are Bessel functions.

[0047]

(Equation 15) given that,

[0048]

[Equation 16] Therefore, even if I = 1A, oscillation occurs even if the loss of the optical resonator is 1%.

[0049]

EFFECTS OF THE INVENTION Since quadrature wavelength light can be obtained by a simple method, it becomes possible to make a desk-top free electron laser, and not only in the field of nuclear power but also in physical physics, chemistry, biotechnology, semiconductor industry, medical research. Can be used as a light source.

The present invention is one method of an undulator used for synchrotron radiation or free electron laser, and since it is a simple method that can easily shorten the wavelength, it can be used in an extremely large number of industrial fields. It is used as a light source from millimeter waves to X-rays, and depending on its wavelength, it is expected to be used in basic science, physical property research, medical research, semiconductor manufacturing technology, and biotechnology, as well as in the field of nuclear research.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the outline of the configuration of a free electron laser.

FIG. 2 is an explanatory diagram of a magnetic field type (orthogonal type) plasma undulator.

FIG. 3 is a graph showing the relationship between magnetic field lines and magnetic field strength distribution in a magnetic field type (orthogonal type) plasma undulator.

FIG. 4 is a circuit diagram 1 of the plasma undulator.
Here is an example.

FIG. 5 is an explanatory diagram of a magnetic field type (same direction current type) plasma undulator.

FIG. 6 is an explanatory diagram of an electric field type (oblique type) plasma undulator.

FIG. 7 is an explanatory diagram of a plasma stabilization method (longitudinal magnetic field method).

FIG. 8 is an explanatory diagram of a plasma stabilization method (vertical magnetic field method).

[Explanation of symbols]

 1 electron source (high frequency linear accelerator) 2 undulator 3 optical resonator (semi-transparent mirror) 4 total reflection mirror 5 magnet 6 meandering surface of electron 7 laser output (pulse) 8 electron pulse 9 electrode 10 electrode 11 plasma electrode 12 relativistic Electron beam 13 Synchrotron radiation 15 Magnetic pole plate 16 Direction of magnetic pole plate 17 Direction of magnetic field lines 18 Anchor coil 19 Column of filamentous plasma 20 Vertical magnetic field 21 Inductance 22 Switch 23 Charging power source 24 Electrode gap 25 Cable

Claims (2)

(57) [Claims] 1. A high-brightness light is produced by making a number of filamentous plasmas on a plane by parallel or anti-parallel electric currents and causing an electron beam to meander by the periodic magnetic field distribution or periodic electric field distribution generated thereby. How to make. 2. The method for generating high-intensity light according to claim 1, wherein the meandering period length λ _u is 1 mm or less.