CN110859019A

CN110859019A - Undulator and laser plasma X-ray source comprising same

Info

Publication number: CN110859019A
Application number: CN201810979375.5A
Authority: CN
Inventors: 谭军豪; 李毅飞; 朱常青; 陈黎明
Original assignee: Institute of Physics of CAS
Current assignee: Institute of Physics of CAS
Priority date: 2018-08-22
Filing date: 2018-08-22
Publication date: 2020-03-03
Anticipated expiration: 2038-08-22
Also published as: CN110859019B

Abstract

The invention provides an undulator and a laser plasma X-ray source comprising the same, wherein the undulator comprises: the capacitor coil target comprises a first electrode plate and a second electrode plate which are oppositely arranged, and the second electrode plate is provided with a through hole; the double-winding spiral coil comprises a first spiral coil and a second spiral coil which are mutually staggered and have the same winding direction, the two ends of the first spiral coil are electrically connected with the first electrode plate and the second electrode plate, the two ends of the second spiral coil are electrically connected with the first electrode plate and the second electrode plate, and the current directions in the first spiral coil and the second spiral coil are opposite. The laser plasma X-ray source has compact structure, and the generated X-ray has high brightness, short wavelength and tunable wavelength and energy.

Description

Undulator and laser plasma X-ray source comprising same

Technical Field

The invention relates to the field of X rays, in particular to an undulator and a laser plasma X-ray source comprising the same.

Background

Laser plasma acceleration refers to the generation of high-energy charged particles by the interaction of ultra-strong and ultra-short pulse laser and plasma. The laser plasma acceleration has ultrahigh acceleration electric field gradient, and the electron beam generated by the laser plasma acceleration has the characteristics of femtosecond time scale, Kiloampere (KA) strong beam, small emittance and the like, has wide application prospect in the fields of novel accelerators, radiation sources, national defense, industry, particularly ultrafast X/gamma rays and the like, and is widely concerned by domestic and foreign scientists.

The period length of the undulator and the peak magnetic field strength in a laser plasma X-ray source are related to the wavelength and brightness of the radiated light. The shorter the period of the undulator is, the more favorable the generation of the radiation light with shorter wavelength is; the stronger the peak magnetic field strength, the more favorable it is to generate high-brightness radiation light. However, the magnetic field strength generated by the existing undulator based on the permanent magnet is generally about 1 tesla (T), and the magnetic field strength is small; in addition, the cycle length is about 10 cm, the length dimension is about 1-2 m, and the volume is large. And the existing laser plasma X-ray source lacks stability and tunability.

Disclosure of Invention

In view of the above technical problems in the prior art, the present invention provides an undulator, comprising:

the capacitor coil target comprises a first electrode plate and a second electrode plate which are oppositely arranged, and the second electrode plate is provided with a through hole;

the double-winding spiral coil comprises a first spiral coil and a second spiral coil which are mutually staggered and have the same winding direction, the two ends of the first spiral coil are electrically connected with the first electrode plate and the second electrode plate, the two ends of the second spiral coil are electrically connected with the first electrode plate and the second electrode plate, and the current directions in the first spiral coil and the second spiral coil are opposite.

Preferably, the first and second solenoids have the same pitch and number of turns, the axial directions of the first and second solenoids coincide, and the distance between any one turn of the first solenoid and an adjacent one turn of the second solenoid in the axial direction thereof is half of the pitch.

Preferably, two terminals of the first and second coils on the same side are respectively connected to the first and second electrode plates.

Preferably, the first spiral coil and the second spiral coil have the same pitch and are 1-2 mm.

Preferably, the length of the double-winding solenoid coil along the axial direction is 1-2 cm.

Preferably, the first electrode plate and the second electrode plate are circular plates made of copper.

Preferably, the aperture of the through hole of the second electrode plate is half of the diameter of the second electrode plate.

The invention also provides a laser plasma X-ray source, comprising:

the undulator as described above;

a laser plasma device, wherein the emitted electron beam is incident along the axial direction of the double-wound spiral coil of the undulator; and

and the pulse laser emits pulse laser which is focused on the capacitance coil target of the undulator.

Preferably, the laser plasma apparatus includes:

a nozzle for ejecting gas at supersonic velocity; and

a femtosecond laser which emits femtosecond laser light focused on the gas to ionize the gas into plasma and accelerate the same.

Preferably, nanosecond laser light emitted by the pulse laser passes through the through hole of the second electrode plate and is incident on the first electrode plate, so as to generate current in the first and second spiral coils.

The magnetic field generated by the undulator has the advantages of short period, large magnetic field intensity and the like, and the laser plasma X-ray source based on the undulator can generate X-rays with shorter wavelength (hard X-rays), quasi-unienergy, high brightness and tunable energy, and improves the photon energy and the photon yield of the X-rays.

Drawings

Embodiments of the invention are further described below with reference to the accompanying drawings, in which:

FIG. 1 is a schematic plan view of a laser plasma X-ray source according to a preferred embodiment of the invention.

Fig. 2 is a perspective view of the undulator shown in fig. 1.

Fig. 3 shows the distribution of the strength of the magnetic field vectors in the x, y and z directions generated in the bifilar solenoid by different currents.

Fig. 4 shows a schematic representation of the displacement of an electron in a double-wound solenoid.

Fig. 5 is a graph of the energy spectrum of X-rays radiated by high-energy electrons at different currents.

Fig. 6 is a spectral power diagram of X-rays of a single electron radiation of different energies.

FIG. 7 is a graph of the energy spectrum of X-rays of electron beam radiation at different energies.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail by embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic plan view of a laser plasma X-ray source according to a preferred embodiment of the invention. As shown in fig. 1, the laser plasma X-ray source 1 includes a laser plasma device 11, an undulator 12, and a long pulse laser 13.

The laser plasma device 11 includes a femtosecond laser 111 and a nozzle 112, the nozzle 112 is used for ejecting supersonic high-density gas 113, the femtosecond laser emitted by the femtosecond laser 111 is focused on the high-density gas 113, ionizes the high-density gas 113 into plasma and accelerates, so that high-energy electron beams 114 are emitted from the high-density gas 113 and enter the undulator 12.

The undulator 12 includes a double-wound solenoid 121 and a capacitive coil target 122. Double-wound solenoid 121 includes

identical solenoids

1211 and 1212, with only three of

solenoids

1211, 1212 being shown in fig. 1 to simplify double-wound solenoid 121.

Fig. 2 is a perspective view of the undulator shown in fig. 1. As shown in fig. 2, the

helical coils

1211, 1212 each have a pitch (i.e., a distance between each adjacent two turns in the axial direction) of 1 mm. The axial directions of the spiral 1211 and the spiral 1212 coincide with each other, and coincide with the incident direction of the high-energy electron beam 114. The

spiral coils

1211 and 1212 are wound in the same direction, and are staggered with each other by half a pitch, that is, a distance between any one turn of the spiral coil 1211 and an adjacent one of the spiral coils 1212 in the axial direction thereof is 0.5 mm.

The capacitor coil target 122 includes an electrode plate 1221 and an electrode plate 1222 disposed in parallel and opposite to each other, whereby the electrode plate 1221 and the electrode plate 1222 form a capacitor. The electrode plate 1221 and the electrode plate 1222 are circular plates made of a metal material (e.g., copper), and the electrode plate 1222 has a circular hole 1223 at the center thereof through which laser light emitted from the long pulse laser 13 passes.

Both ends of coil 1211 are connected to electrode plate 1221 and electrode plate 1222, respectively, both ends of coil 1212 are also connected to electrode plate 1221 and electrode plate 1222, respectively, and both terminals on the same side of

coils

1211 and 1212 are connected to electrode plate 1221 and electrode plate 1222, respectively. When an electric field is present between electrode plate 1221 and electrode plate 1222, the direction of current flow in coil 1211 and coil 1212 will be reversed.

The nanosecond laser light emitted by the long pulse laser 13 is focused on a capacitive coil target 122.

Referring again to fig. 1, the nanosecond laser light emitted from the long pulse laser 13 is focused and then incident on the electrode plate 1221 through the through hole 1223 of the electrode plate 1222. The nanosecond laser ionizes and accelerates electrons in the electrode plate 1221 to a large thermal velocity (keV-MeV) and escapes to the oppositely disposed electrode plate 1222, thereby positively charging the electrode plate 1221 and negatively charging the electrode plate 1222, so that currents of the order of tens of kiloamperes are present in the spiral 1211 and the spiral 1212, thereby generating a magnetic field that applies a force to the high energy electron beam 114 passing through the spiral 1211 and the spiral 1212. The invention can adjust the current in the spiral coil 1211 and the spiral coil 1212 by changing the distance between the electrode plate 1221 and the electrode plate 1222, the aperture size of the circular hole 1223, and the wires of the

spiral coils

1211 and 1212. For example, the hole 1223 has an aperture half the diameter of the electrode plate 1222 to increase the current in the

coils

1211, 1212.

For convenience of describing the magnetic field generated by the bifilar solenoid 121, the axial direction of the bifilar solenoid 121 (i.e., the horizontal direction in fig. 1) is defined as the x direction in fig. 1, the direction perpendicular to the paper in fig. 1 is the y direction, and the vertical direction in fig. 1 is the z direction.

Fig. 3 shows the distribution of the strength of the magnetic field vectors in the x, y and z directions generated in the bifilar solenoid by different currents. Where the abscissa corresponds to the x-direction and the ordinate is the magnetic field strength (in T) expressed as magnetic field vectors Bx, By and Bz in the x, y and z directions, respectively. As shown in fig. 3, since the

coils

1211 and 1212 are arranged with a half pitch offset in the x direction, when the

coils

1211 and 1212 are energized with reverse currents having equal amplitudes, the magnetic fields generated by the

coils

1211 and 1212 have equal and opposite components in the x direction, and thus Bx is substantially zero; the magnetic fields generated by the

solenoids

1211, 1212 are substantially the same magnitude and direction in the y and z directions, and have a period length equal to the pitch of the solenoid. Based on the double-wound solenoid 121 of the present invention, the period of the magnetic field can be adjusted by adjusting the pitch of the

solenoids

1211 and 1212, so as to obtain a short-period magnetic field with a strong magnetic field intensity.

As can be seen from fig. 3, when the current intensity in the

spiral coils

1211, 1212 increases from 10KA to 20KA to 30KA, the peak value of the magnetic field strength By of the double-wound spiral coil 121 in the y direction also increases, and the peak value of the magnetic field strength Bz in the z direction also increases accordingly. The present invention can adjust the magnitude of the magnetic field in the bifilar solenoid 121 by adjusting the magnitude of the current in the

solenoids

1211, 1212.

The magnetic field intensity Bx in the x direction of the magnetic field generated by the double-wound solenoid 121 is small and negligible, and thus the present invention obtains a periodic helical magnetic field having the same period as that of the

solenoids

1211 and 1212. Since the wavelength of the X-ray is proportional to the period length of the helical magnetic field, the helical magnetic field with a period of 1 mm generated by the double-wound helical coil 121 of the present invention can reduce the wavelength of the X-ray, which is beneficial to radiating the X-ray with short wavelength, even hard X-ray.

Fig. 4 shows a schematic representation of the displacement of an electron in a double-wound solenoid, with the abscissa corresponding to the x-direction. The uppermost curve in fig. 4 is a graph of the drift amount Y0 of the energetic electrons in the Y direction, which is the distance from the axis of the bifilar solenoid 121 in the Y direction as the energetic electrons are injected along and move inside the axis of the bifilar solenoid 121, as a function of the position of the energetic electrons in the x direction. It can thus be seen that the energetic electrons have a linear offset in the y-direction, which is mainly due to the incomplete homogeneity of the magnetic field. Although the drift amount of the high-energy electrons in the y direction is 1.5 micrometers, the linear drift amount is only slightly less than one-tenth, which is negligible, of the length of the bifilar solenoid 121 in the axial direction (i.e., 20 mm).

The middle curve Y and the lowermost curve Z of fig. 4 are graphs of the variation of the high-energy electrons in the Y-direction and Z-direction with their positions in the x-direction, in which the drift amount of the high-energy electrons is removed. It can be seen that, when the high-energy electron beam 114 is incident along the axial direction of the bifilar solenoid 121, the movement of the high-energy electron beam 114 inside the bifilar solenoid 121 is a spiral movement and radiates X-rays, wherein the direction of the X-rays is along the tangential direction of the trajectory of the high-energy electron movement, i.e., mainly forward along the solenoid axis.

Fig. 5 is a spectrum diagram of X-rays emitted by high-energy electrons under different currents, wherein the energy of the high-energy electrons is 1Gev, and the energy spectrum from left to right corresponds to 50KA, 20KA and 10KA of current in a solenoid coil. In addition, the intensity of the generated spiral magnetic field is increased as the current in the spiral coil is increased, and the number of photons (i.e., photon yield) of the radiated X-ray is increased, which is advantageous for increasing the brightness of the X-ray.

Fig. 6 is an energy spectrum of X-rays of a single electron radiation of different energies, in which the current in the solenoid is 20KA, and the energies of high-energy electrons corresponding to the four radiation spectra in fig. 6 from left to right are 0.5Gev, 1Gev, 1.5Gev, 2.0Gev, and the electron energy dispersion is not considered. It can be seen from fig. 6 that the greater the energy of the high-energy electrons, the greater the energy of the radiated X-ray photons. By changing the energy of the high-energy electrons, the energy and the wavelength of the X-ray can be continuously adjusted in a large range. In addition, hard X-rays can be emitted even when the electron energy is 0.5 Gev.

FIG. 7 is an energy spectrum of X-rays radiated by electron beams of different energies, in which the currents in the solenoids are all 20 KA. As can be seen from fig. 7, the energies of the X-ray photons radiated at 0.6Gev, 2.0Gev and 4.2Gev are about 9kev, 30kev and 120kev, respectively. As the energy of the high-energy electron beam increases, the energy of the radiated X-ray photons also gradually increases, enabling tuning of the energy of the X-rays over a larger range. The laser plasma X-ray source based on the invention generates quasi-unienergy X-rays because the relative energy dispersion of the X-rays is about 30 percent. The brightness of the X-ray is up to 5.0X 10¹⁹Photon number/(sec. times.mrad)²X mm²X0.1% bandwidth) to produce high intensity X-rays. The invention generates a peak magnetic field of about 15T by obtaining dozens of KA current in the spiral coil, thereby being beneficial to generating high-brightness X rays.

The double-winding solenoid of the undulator of the invention generates a strong magnetic field (about 15T) with a short period (about 1 mm) and a spiral shape, and the length of the undulator along the axial direction of the undulator is about 1 cm, compared with a permanent magnet, the undulator has the advantages of small volume and low cost, thereby obtaining a laser plasma X-ray source with compact structure. And the wavelength and photon yield of the X-ray can be continuously adjusted in a larger range by adjusting the energy of the high-energy electron beam and the current in the solenoid.

In other embodiments of the invention, the pitch of the solenoid in the double-wound solenoid is 1-2 mm and the length in the axial direction thereof is 1-2 cm, and the number of turns of the solenoid is adjusted according to the required magnetic field intensity.

Although the present invention has been described by way of preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and modifications may be made without departing from the scope of the present invention.

Claims

1. An undulator, comprising:

2. The undulator of claim 1, wherein the first and second coils have the same pitch and number of turns, the axial directions of the first and second coils coincide, and a distance in an axial direction of any one turn of the first coil from an adjacent one of the second coils is half of the pitch.

3. The undulator of claim 1, characterized in that two terminals of the first and second solenoids on the same side are connected to the first and second electrode plates, respectively.

4. The undulator of claim 2, wherein the first and second solenoids have the same pitch of 1-2 mm.

5. The undulator of claim 1, wherein the length of the double-wound solenoid in the axial direction thereof is 1 to 2 cm.

6. The undulator of any of claims 1 to 5, characterized in that the first and second electrode plates are circular plates made of copper.

7. The undulator of claim 6, characterized in that the aperture of the through hole of the second electrode plate is half the diameter of the second electrode plate.

8. A laser plasma X-ray source, comprising:

the undulator of any one of claims 1 to 7;

9. The laser plasma X-ray source of claim 8, wherein the laser plasma device comprises:

a nozzle for ejecting gas at supersonic velocity; and

10. The laser plasma X-ray source of claim 8, wherein nanosecond laser light emitted by the pulsed laser is incident on the first electrode plate through the through hole of the second electrode plate to generate a current in the first and second solenoids.