CN103745760A - All-optical laser plasma accelerator-based Gamma ray source - Google Patents

Abstract

The invention provides an all-optical laser plasma accelerator-based small-sized Gamma ray source. The ray source comprises a synchronous dual-output high-power laser system (200), a double-compression-delay system (12), a laser plasma accelerator (18), a particle beam focusing system (24), a scattered light focusing mirror (27) and a particle beam separation system. A bunch of initial laser pulse is separated and amplified through the laser system (200) to generate two bunches of synchronous high-energy laser pulses (10 and 11); the two amplified laser pulses are compressed in a time domain through the double-compression-delay system (12), and proper delay is performed to form a drive pulse (13)-scattering pulse (14) pair; a drive pulse (13) passes through the laser plasma accelerator (18) to generate a relativistic electron beam (21); the particle beam focusing system (24) is used for transmitting the electron beam (21); the scattered light focusing mirror (27) is used for focusing a scattering pulse (14) to the electron beam (21) so as to generate a gamma ray 31); the separation system is used for separating the electron beam (21) from the gamma ray (31).

Description

Based on the gamma ray projector of full ray laser plasma accelerator

Technical field

The present invention relates to a kind of novel gamma ray projector implementation.The present invention relates to the application of this gamma ray projector in the novel manufacture of detection, nuclear battery, gamma ray laser and the medical-isotope of nuclear physics research, nuclear astrophysics research, nuclear material or radioactive waste simultaneously.

Background technology

Current people produce gamma-ray mode and mainly contain following several.

Radioactive isotope gamma ray projector: tellurian natural Gamma ray source is from radioisotopic decay process, such as ⁴⁰k(launches the gamma-rays of 1.46MeV by trapped electrons) and ⁶⁰co(by β decay launch 1.17 and the gamma-rays of 1.33MeV).These gamma ray projectors are widely used in medical treatment (such as γ cutter operation), non-contact type industry detection, container safety inspection facility etc.But due to the restriction of radioactive isotope kind, gamma-rays photon energy and intensity all can not effectively be controlled.

Bremsstrahlung gamma ray projector: because high energy electron is called bremsstrahlung by another charged particle (such as atomic nucleus) radiation of sending of slowing down.This radiation has continuous spectrum, and spectrum peak energy is along with electron energy increases and increases.The electron beam of hundreds of MeV acts on the gamma-rays photon that can produce tens of MeV mutually with solid target (as tantalum target).This radiographic source has been applied to inner structure and has surveyed, and shows very high spatial resolution (tens of micron dimension).But wider power spectrum has limited the brightness in this source, if will there be application widely, also need to improve this source.

Inverse Compton scattering gamma ray projector: just as the X ray that high energy electron in oscillator or rocker can be launched, do mutually the used time can produce gamma-rays when high energy electron and laser oscillator, this process is called contrary Compton process.This gamma ray projector, according to the difference of electron beam energy spectrum width, can be that monoenergetic can be also wide power spectrum.The brightness of this gamma ray projector can the high several magnitudes of specific activity isotope gamma ray projector.The electronics of current this gamma ray projector derives from conditional electronic accelerator.Involving great expense of conditional electronic accelerator, bulky, limited the range of application of this gamma ray projector.The electron accelerator of use based on laser tail field can become a revolution of inverse Compton scattering gamma ray projector.

Electronic induction radiation gamma ray projector: this is another kind of synchrotron radiation source.In the accelerator of laser tail field, electronics when longitudinally being accelerated also by swaying.When electron energy approaches GeV magnitude, the electronics swaying that the transverse focusing field of laser tail field causes can produce gamma-rays.Because longitudinally accelerated during electron synchrotron, this source generally has wider power spectrum.In nearest laser tail field accelerator experiment, can produce 10 ⁷individual energy is 1 to 7MeV photon.This provenance can have been widely used after improving.

Invention target

Target of the present invention is the limitation that overcomes prior art.

More specifically, a target of the present invention is to provide a kind of new embodiment of gamma ray projector, and this embodiment is compacter, effective with respect to the gamma ray projector of prior art, and cost is lower, operates easier and has a better performance.

Another target of the present invention is to provide a kind of desktop yardstick of excellent performance, gamma ray projector easily, for carrying out basis, medical treatment and commercial Application and research in small-scale experiment chamber.

Summary of the invention

In order to achieve the above object, gamma ray projector provided by the invention comprises:

There is the high power laser system of two cascade amplifiers, this laser system can synchronously be exported the laser pulse that two beam energies are exaggerated, after laser system, connect two optical pulse compressor reducers, for generation of thering is the pulsewidth of optimization and the electron beam driving pulse of energy and gamma ray scattering pulse;

Laser plasma accelerator, driving pulse can produce relativistic electron beam in this laser plasma accelerator;

Particle beams focusing system, this particle beams focusing system is for the electron beam transmitting and laser focusing plasma accelerator produces;

Scattered light focus lamp, this scattered light focus lamp is for focusing on scattering pulse the electron beam of backpropagation, and scattering pulse and electron beam interact and due to inverse Compton scattering effect, produce the gamma-rays of collimation;

Particle beams piece-rate system, electron beam is deflected in this particle beams piece-rate system, thereby is separated with the gamma-rays producing.Gamma ray projector according to the present invention is compacter, efficient than gamma ray projector of the prior art, and cost is lower, operates easylier, and performance is better.

Preferably, above-mentioned high power laser system comprises:

Fore device, this fore device comprises the oscillator for generation of femto-second laser pulse, with in time domain, extend primary laser pulse according to the pulse stretcher of chirped pulse Optical Amplification Technology (CPA), after fore device, connect beam splitter the pulse after broadening be divided into two bundles;

Two parallel for amplifying the cascade amplifier of energy of two pulses after beam splitting;

Two according to chirped pulse Optical Amplification Technology (CPA) by the pulse shortener of pulse compression after amplifying.

Utilize chirped pulse Optical Amplification Technology (CPA), laser instrument can produce the pulse of very high energies.

Preferably, this laser plasma accelerator comprises:

Be filled with the first air chamber of mixed gas;

Be filled with the second air chamber of pure helium;

Gas feed channel; And

Gas regulating system.

Due to the high accelerating gradient of laser plasma accelerator, this laser plasma accelerator can produce high-quality relativistic electron beam very effectively.

Preferably, this laser plasma accelerator comprises that device for adjusting the second air chamber length is to adjust beam energy, thereby regulates electron beam and scattering pulse generation inverse Compton scattering and the gamma-ray photon energy that produces.

Preferably, particle beams piece-rate system comprises dipole magnets and the particle beams gatherer for deflection beam.

Advantageously, this gamma-rays is relatively can fall apart and be about 1% accurate monoenergetic gamma rays.

Gamma ray projector application of installation according to the present invention is in numerous areas, such as the nuclear physics in basic science and astrophysics, and medicine, and commercial Application etc.This radiographic source is compacter, efficient than gamma ray projector of the prior art, and cost is lower, operates easylier, and performance is better.

According to a preferred embodiment, described gamma-rays photon energy range can cover 1MeV to 20MeV interval.

Accompanying drawing explanation

Fig. 1 is according to the schematic diagram of the gamma ray projector of the embodiment of the present invention;

Fig. 2 is gamma ray projector device in Fig. 1 for synchronous right two compressions of driving pulse-scattering pulse-the postpone detail view of optical systems that produce;

Fig. 3 is the schematic diagram of the two-stage air chamber of the laser plasma accelerator of gamma ray projector device in Fig. 1;

Fig. 4 is the schematic diagram of the laser plasma accelerator of gamma ray projector device in Fig. 1, and this laser plasma accelerator comprises the two-stage air chamber in Fig. 3;

Fig. 5 is the schematic diagram that electronics is accelerated in laser tail field;

Fig. 6 is the schematic diagram of Miniature permanent magnet magnetic quadrapole (PMQ);

Fig. 7 is the schematic diagram that comprises the particle beams focusing system of four permanent magnetism magnetic quadrapoles as shown in Figure 6;

Fig. 8 is the schematic diagram of the scattered light focus lamp in the gamma ray projector device of Fig. 1;

Fig. 9 A, 9B and 9C show the particle beams piece-rate system of integration, and this particle beams piece-rate system comprises electron beam gatherer and the permanent magnet magnetic dipole for gamma-rays and electron beam are separated.

Figure 10 is the schematic diagram that produces gamma-rays part in Fig. 1 in gamma ray projector device, and the inverse Compton scattering of the relativistic electron beam of this part based on laser plasma accelerator gained according to the present invention produces gamma-rays.

Embodiment

According to embodiment of the present invention gamma ray projector, summarize

Fig. 1 is according to the schematic diagram of the gamma ray projector of the embodiment of the present invention.As shown in Figure 1, this gamma ray projector device comprises that high power laser system 200 is for generation of two synchronous bundle high energy laser pulses 13 and 14, this two pulses process compression chamber 15 is compressed and enter the laser plasma accelerator 18 and the scattered light focus lamp 27 that are arranged in reaction chamber 36, below will describe in further detail.

Because gamma ray projector device of the present invention has adopted the structure of optimizing, its size can significantly reduce with respect to prior art, thereby can in the laboratory of limited space, carry out basis, medical treatment and commercial Application and research.For example, according to of the present invention can produce power be that 1 to 20MeV gamma-ray gamma ray projector device can be made into overall dimensions and is about 3m × 6m, wherein the size of laser system 200 is about 3m × 5m, and the overall dimensions of removing all the other devices of laser system is about 3m × 1m.Should be understood that above-mentioned size is not intended to limit the scope of the invention, the size of gamma ray projector device also can be other suitable sizes.

The high power laser system of synchronous dual output:

In Fig. 1, the oscillator 1 in laser system 200 produces a branch of low-energy laser pulse 2.According to chirped pulse Optical Amplification Technology (CPA), this laser pulse 2 is by laser stretcher 3 broadening in time domain.Stretcher 3 is by a pair of diffraction grating to forming, and this can compensate the dispersion of low-energy laser pulse 2 in time domain to grating.Laser pulse 4 after broadened has wider pulsewidth and lower peak power compared with laser pulse 2.

Laser pulse 4 is pulse 6 and pulse 7 by beam splitter 5 beam splitting, and pulse 6 and pulse 7 enter respectively two parallel cascade amplifiers 8 and 9.Pulse 6 and 7 is exaggerated respectively device 8 and 9 amplifies, and becomes high energy pulse 10 and 11.Pulse 10 and 11 after two bundles amplify is compressed in time domain in two compressor reducers and delay system 12.Two compressor reducers and delay system 12 are arranged in compression chamber 15, and compression chamber 15 is found time to keep 10 by vacuum pump system 16 ^-3to 10 ^-4the internal pressure of handkerchief.

As shown in Figure 2, two compressor reducers 51 and 52 form to compensate the dispersion of laser pulse in time domain by diffraction grating to 53 and 54 respectively.Through the output pulse 13 and 14 after compressor reducer 51 and 52 have high energy and extremely short pulsewidth to such an extent as to they energy and pulsewidth can be optimized to respectively for accelerated electron beam 21 or for scattered electron bundle with generation gamma-rays 31.Delay system 55 and/or 56 is arranged on straight line regulating platform in order to the delay between regulating impulse 13 and 14, ultrafast photodiode 23 and 29 is in order to monitor the synchronism of two bundle laser, electronic current inductor 25 is in order to Measurement of Electron Beam, and gamma-ray probe 32 is in order to measure the gamma-rays producing.

The two-stage air chamber plasma accelerator that induced ionization is injected:

As shown in Figure 1, ultrashort, super strong laser pulse 13 is focused on the entrance of two-stage air chamber 18 by off axis paraboloidal mirror 17.First air chamber (be called and inject level) of two-stage air chamber has been filled mixed gas (for example helium and nitrogen), and the second air chamber (being called accelerating stage) has been filled clean gas (for example hydrogen or helium).Gas can be fed to respectively in two-stage air chamber 18 with different pressure by gas flow control system 19.

As mentioned below, in the injection level of air chamber 18, laser pulse 13 excites high-intensity Plasma Wake Wave, and because induced ionization is injected mechanism, the inner-shell electron of gas can be caught and accelerate to this coda wave.In air chamber 18, the Plasma wake field that driving laser pulse produces has the accelerating field of 1GV/cm magnitude, and a branch of electron beam 21 after the preaceleration of injection level is further accelerated to the energy with 1GeV magnitude at air chamber accelerating stage.The driving laser of transmission is led into recycling box 22 by the porose catoptron 20 in one side center, and this recycling box 22 comprises photodiode 23 and laser absorption device.

When this plasma accelerator is when combining according to the high power laser system of dual output of the present invention, particle beams focusing system, scattered light focus lamp and particle beams piece-rate system, excellent performance will be had.But thisly comprise that the plasma accelerator of the second air chamber that the first air chamber of mixed gas is housed and pure helium is housed also can combine for producing high energy electron beam with the laser instrument of other kinds.

Particle beams focusing system, scattered light focus lamp and particle beams separation vessel:

The electron beam 21 that plasma accelerator 18 is exported is transferred to scattered light focus lamp 27 places through particle beams focusing system 24, and these devices are all arranged in reaction chamber 36.As mentioned below, electron beam 21 clashes with being scattered the laser pulse 14 that light focus lamp 27 focuses on after being focused on by the magnetic quadrapole of particle beams focusing system 24, because inverse Compton scattering produces gamma-rays 31.

After passing through the central small hole of scattered light focus lamp 27, electron beam 21 is by deflection magnet 33 deflections that produce magnetic dipole and separation with gamma-rays 31 and collected by particle beams gatherer 34, and gamma-rays 31 penetrates from reaction chamber 36, become adaptable gamma-rays.

Laser plasma accelerator is described in detail:

Two-stage air chamber:

Fig. 3 is the schematic diagram of two-stage air chamber 18.This two-stage air chamber, for effectively electron capture and the acceleration of laser coda wave field, comprises and injects level 61 and accelerating stage 62.As shown in Figure 4, this two-stage air chamber is placed on the middle of reaction chamber 36.Laser beam 13 after compressed in pulse compression chamber 15 is focused on the porch of injecting level by off axis paraboloidal mirror 17.

Inject level and 61 be filled with mixed gas 65, for example 98% helium and 2% nitrogen, gas is fed to and injects level from gas flow control system 19 by gas feedthrough 63.Accelerating stage 62 is filled with clean gas 66, for example hydrogen or helium, and gas is fed to accelerating stage by gas feedthrough 64 from gas flow control system 19.The bellows structure 67 that length-adjustable accelerating stage is driven by electric machine structure 68 forms.It is 10 that reaction chamber 36 is evacuated to keep air pressure inside by vacuum pump system 37 ^-3to 10 ^-4handkerchief.

Physical process description:

Fig. 5 has described electron capture in coda wave field excitation and coda wave field and the physical process 100 of acceleration, and coda wave field is being injected the neutral gas transmission of level 61 and formed by high intensity laser beam.In Fig. 5,101 evolutions that show plasma electron density above, 102 vertical of coda waves that show laser excitation below.

As shown in the center section 100 in Fig. 5, the outer-shell electron of helium and nitrogen (ionization is to+5 valencys at most) is in the forward position of laser pulse (light intensity 1.5 × 10 ¹⁶w/cm ²) ionized completely, in the periphery of laser pulse, forming plasma electron, its border is represented by choice refreshments line 103.Due to two electronics of innermost layer (K shell) of nitrogen at laser intensity higher than 1 × 10 ¹⁹w/cm ²just can be ionized, inner-shell electron only has and can near the peak value of laser pulse 13, be ionized, for normalization laser field a ₀≈ 0.855 × 10 ^-9i ^1/2[W/cm ²] λ _l[μ m]=2, wherein I[W/cm ²] be light intensity, λ _l[μ m] is optical maser wavelength, and the intensity distributions of laser pulse is represented by thick dotted line 108.In Fig. 5, above 101 in, heavy line 109 represents the evolution of nitrogen degree of ionization (electron number of axial each nitrogen atomic ionization).The zone boundary of two electron ionizations of nitrogen hypostracum is represented by choice refreshments line 104.

The plasma electron comprising in border 103 is had relativity intensity a ₀the ball shape electric shell that one deck is thin is pushed and formed to the radiation pressure (ponderomotive force) of the laser pulse 13 of > > 1 open.This shell is wrapped in the laser pulse spherical ion region that is commonly called cavity 105 below.In electron density, be 10 ¹⁸cm ^-3plasma in, this charge separation field has formed the strong longitudinal electric field 110 of 100GV/m magnitude, this electric field is than large three orders of magnitude of the accelerating field in conventional radio frequency accelerator.In cavity 105, electronics also experiences extremely strong focousing field in accelerated.Therefore, once electronics 21 is caught by cavity, they just can be continued to accelerate to the energy with 1GeV magnitude efficiently, and accelerating length is by the control of dephasing length.

When above-mentioned nitrogen inner-shell electron is ionized, near cavity center, tail field potential is maximal value herein, and the laser ponderomotive force of repelling is minimum value.Different from the free electron of preionization, moving axially to cavity afterbody near cavity after inner electron ionization.Cavity afterbody has minimum tail field potential, and electronics can be hunted down herein, as shown in electronic orbit 106.And the electronics shown in electron beam trace 107 due to the time being ionized early, and off-axis to, so skidded off the gesture well of tail field.The mechanism that this electron capture injects is called as induced ionization and injects.Due to catch occur time electronics near cavity axis, the swaying of electronics a little less than.The theory of injecting according to induced ionization is calculated, and can at laser field peak value place, be ionized by injected electrons, and minimum laser intensity is by formula

provide, wherein

relativity factor of coda wave field phase velocity, β _pit is plasma phase velocity of wave.For parameter γ _p=33, the laser intensity that produces electronic injection is necessary for a ₀>=1.7.The PIC simulation of one dimension shows, because beam loading effect and phase space are injected separatrix and initially injected electronics loss effect, when mixed gas length is L _mix≈ 1000 λ ₀, plasma density is n _e=0.001n _c(1.7 × 10 ¹⁸cm ^-3), nitrogen gas concn α _n=1%, laser intensity a ₀=2, pulsewidth c τ ₀≈ 15 λ ₀time maximum injection number of electrons when saturated (number of electrons) the chances are N _emax～5 × 10 ⁶μ m ^-2, wherein λ ₀optical maser wavelength, n _cthat plasma critical density (can be expressed as $n_c=m_e{\mathrm{\ω}}_L^2/4\mathrm{\π}{e}^2=\mathrm{\π}/\left(r_e{\mathrm{\λ}}_L^2\right)\≈1.115\×{10}^{21}\left[{\mathrm{cm}}^{-3}\right]/{\left({\mathrm{\λ}}_L\right[\mathrm{\μm}\left]\right)}^2$ ）。Work as α _nk _pl _mix≤ 2 o'clock, injection number of electrons was N _e[μ m ^-2]～8 × 10 ⁷α _nk _pl _mix(n _e/ n _c) ^1/2.Can loose with mixed gas length and nitrogen gas concn, all be directly proportional.According to a ₀=2 two-dimentional PIC simulation, injects electron beam and can fall apart for δ E/E=0.02[%] (L _mix/ λ _l) (n _e/ 10 ¹⁷cm ^-3) ^-1/2, laterally normalized emittance can be estimated as ${\mathrm{\ϵ}}_{n0}\≈0.5\left[\mathrm{\μm}\right]a_0^{1/2}{(n_e/{10}^{17}\left[{\mathrm{cm}}^{-3}\right])}^{-1/2}.$

For a ₀>=2 cavity (or claiming emptying) territory, the cavity shape being arranged completely due to electronics can be balanced each other and be decided by the ponderomotive force of the Lorentz force of ion ball and laser pulse, the radius R of cavity _bcan be roughly by

provide, wherein k _p=(4 π r _en _e) ^1/2plasma-wave number, k _pby the axial plasma density n without disturbance _edetermine r _e=e ²/ m _ec ²=2.818 × 10 ^-13cm is classical electron radius, and e is single electron electric weight, m _ebe single electron quality, c is the light velocity in vacuum.Accelerating field E _zby formula E _z/ E ₀=(1/2) α k _pr _bprovide, wherein E ₀=mc ω _p/ e ≈ 96[GV/m] (n _e/ 10 ¹⁸[cm ^-3]) ^1/2, α considers the gap of beam loading effect and simulation and theoretical calculation and the coefficient that adds.Due to dephasing effect, the obtainable ceiling capacity of electronics is by formula Δ γ _max=W _max/ m _ec ²≈ (2/3) α κ _selfa ₀(n _c/ n _e) provide, wherein ${\mathrm{\κ}}_{\mathrm{self}}=(a_0^2/8){\{{(1+a_0^2/2)}^{1/2}-1-\ln \left(\right[{(1+a_0^2/2)}^{1/2}+1]/2)\}}^{-1}$ It is the modifying factor of introducing due to relativistic laser pulse bootstrap group velocity.The group velocity β of laser nondimensionalization _g=v _grelativity factor of/c is ${\mathrm{\γ}}_g^2=1/(1-{\mathrm{\β}}_g^2)\≈{\mathrm{\κ}}_{\mathrm{self}}({\mathrm{\ω}}_L^2/{\mathrm{\ω}}_p^2)={\mathrm{\κ}}_{\mathrm{self}}(n_c/n_e)={\mathrm{\κ}}_{\mathrm{self}}{\mathrm{\γ}}_{g0}^2,$ Wherein γ _g0=ω _l/ ω _pto work as

time linear group speed relativity factor.The dephasing length L in bootstrap cavity territory _dpby

provide.If the electron energy of wanting laser plasma accelerator to accelerate will reach prescribed energy E _b, important parameter below must meet:

Plasma train operation density:

$n_e=\frac{2}{3}\mathrm{\α}{\mathrm{\κ}}_{\mathrm{self}}{a}_0\frac{n_c}{{\mathrm{\Δ\γ}}_{\max }}\≈1.9\×{10}^{18}\left[{\mathrm{cm}}^{-3}\right]{\mathrm{\κ}}_{\mathrm{self}}{a}_0{\left(\frac{1\mathrm{\μm}}{{\mathrm{\λ}}_L}\right)}^2\left(\frac{200\mathrm{MeV}}{E_b/\mathrm{\α}}\right)$

Accelerating length is consistent with dephasing length:

$L_{\mathrm{acc}}=L_{\mathrm{dp}}\≈\sqrt{\frac{3}{2}}\frac{{(\mathrm{\Δ}{\mathrm{\γ}}_{\max }/\mathrm{\α})}^{3/2}}{\mathrm{\π}{\mathrm{\κ}}_{\mathrm{self}}^{1/2}{a}_0}{\mathrm{\λ}}_L\≈\frac{3.1\left[\mathrm{mm}\right]}{{\mathrm{\κ}}_{\mathrm{self}}^{1/2}{a}_0}\left(\frac{{\mathrm{\λ}}_L}{1\mathrm{\μm}}\right){\left(\frac{E_b/\mathrm{\α}}{200\mathrm{MeV}}\right)}^{3/2}$

Because the pulse depletion length causing is corroded in laser pulse forward position:

$L_{\mathrm{pd}}\&ap;c{\mathrm{\&tau;}}_L\frac{n_c}{n_e}=\frac{3}{2}\frac{c{\mathrm{\&tau;}}_L{\mathrm{\&Delta;\&gamma;}}_{\max }/\mathrm{\&alpha;}}{{\mathrm{\&kappa;}}_{\mathrm{self}}{a}_0}\&ap;\frac{5\left[\mathrm{mm}\right]}{{\mathrm{\&kappa;}}_{\mathrm{self}}{a}_0}\left(\frac{{\mathrm{\&tau;}}_{\mathrm{<figure-callout\; id="30"\; label="L"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">L</figure-callout>}}}{30\mathrm{fs}}\right)\left(\frac{E_b/\mathrm{\&alpha;}}{200\mathrm{MeV}}\right)$

Laser pulse has the pulsewidth that makes dephasing length be greater than pulse depletion length:

${\mathrm{\&tau;}}_L\&GreaterEqual;18\left[\mathrm{fs}\right]{\mathrm{\&kappa;}}_{\mathrm{self}}^{1/2}\left(\frac{{\mathrm{\&lambda;}}_L}{1\mathrm{\&mu;m}}\right){\left(\frac{E_b/\mathrm{\&alpha;}}{200\mathrm{MeV}}\right)}^{1/2}$

The laser facula radius of coupling:

$r_m\&ap;3.9\left[\mathrm{\&mu;m}\right]\frac{R_m}{\sqrt{{\mathrm{\&kappa;}}_{\mathrm{self}}{a}_0}}\left(\frac{{\mathrm{\&lambda;}}_L}{1\mathrm{\&mu;m}}\right){\left(\frac{E_b/\mathrm{\&alpha;}}{200\mathrm{MeV}}\right)}^{1/2}$

Wherein

$R_m=k_p{r}_m={\left\{\frac{\ln (1+a_0^2/2)}{\sqrt{1+a_0^2/2}-1-2\ln [(\sqrt{1+a_0^2/2}+1)/2]}\right\}}^{1/2}$

Correspondingly, the laser power of coupling is:

$P_L=\frac{k_p^2{r}_L^2{a}_0^2}{32}{P}_c\&ap;0.312\left[\mathrm{TW}\right]\frac{a_0{\mathrm{<figure-callout\; id="2"\; label="R\; m"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">R</figure-callout>}}_m^{}}{{\mathrm{\&kappa;}}_{\mathrm{self}}}\left(\frac{E_b/\mathrm{\&alpha;}}{200\mathrm{MeV}}\right)$

Required pulsed laser energy is U _l=P _lτ _l.

Suppose that beam loading efficiency is

(being defined as plasma wave energy is σ by root mean square radius _bthe ratio that absorbs of electron beam), load the accelerating field of electron beam be

wherein E _mit is the accelerating field while there is no beam loading.Therefore load electric weight expression formula is

By plasma density n _eexpression formula is brought into, and load electric weight can be calculated as

$Q_b\&ap;55\left[\mathrm{pC}\right]\frac{{\mathrm{\&eta;}}_{\mathrm{<figure-callout\; id="2"\; label="b\; k\; p"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">b</figure-callout>}}{k}_p^{}{}_2^{}{\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{{\mathrm{\&kappa;}}_{\mathrm{self}}^{1/2}\sqrt{1-{\mathrm{\&eta;}}_b}}\left(\frac{{\mathrm{\&lambda;}}_L}{1\mathrm{\&mu;m}}\right){\left(\frac{E_b/\mathrm{\&alpha;}}{200\mathrm{MeV}}\right)}^{1/2}\&ap;55\left[\mathrm{pC}\right]\frac{1-{\mathrm{\&alpha;}}^2}{{\mathrm{\&alpha;}}^{3/2}}\frac{{\mathrm{<figure-callout\; id="2"\; label="k\; p"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">k</figure-callout>}}_p^{}{\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{{\mathrm{\&kappa;}}_{\mathrm{self}}^{1/2}}\left(\frac{{\mathrm{\&lambda;}}_L}{1\mathrm{\&mu;m}}\right){\left(\frac{{\mathrm{<figure-callout\; id="200"\; label="E\; b"\; filenames="HDA0000457955690000011.png"\; state="\{\{state\}\}">E</figure-callout>}}_b}{200\mathrm{MeV}}\right)}^{1/2}$

Acceleration electric weight is Q _belectron cloud to energy, be E _bfield discount factor α by formula α ²+ C α ^3/2-1=0 obtains, wherein $C\&equiv;(Q_b/55\mathrm{pC}){\mathrm{\&kappa;}}_{\mathrm{self}}^{1/2}{\left({\mathrm{<figure-callout\; id="2"\; label="k\; p"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">k</figure-callout>}}_p^{}{\mathrm{\&sigma;}}_b^2\right)}^{-1}{({\mathrm{\&lambda;}}_L/1\mathrm{\&mu;m})}^{-1}{(E_b/200\mathrm{MeV})}^{-1/2}.$

The detailed description of particle beams focusing system, reaction optical system and particle beams separation vessel

Particle beams focusing system:

The particle beams producing from laser plasma accelerator 18 need to transmit and focus in the focus of scattered light focus lamp 27, and the focusing of the particle beams is provided by the particle beams focusing system 24 of short focal length.The field gradient of two-dimentional Haier becker type (Halbach-type) the permanent magnetism magnetic quadrapole (PMQ) shown in Fig. 6, this field gradient can be expressed as wherein B _rdelamination tip-field intensity, r _iradius of bore, r ₀it is PMQ external radius.For r _i=2.5mm, the rare earth element magnet (Nd of the Nd-Fe-B type that permanent magnet rank is N50 ₂fe ₁₄b), B _r=1.45T, can obtain field gradient is B '=1160[T/m] (1-2.5[mm]/r _o).Fig. 6 has shown the magnetic quadrapole (PMQ) 76 being comprised of 12 Haier's becker types (Halbach-type) permanent magnet 71 and 72, and magnetic quadrapole comprises for the outer cover 73 of supporting and location and 74 and support 75.This magnetic quadrapole comprises that four wedge shape radial permanent magnet body 71(materials are Nd ₂fe ₁₄b or SmCO etc. have the material of high remanent magnetization), direction of magnetization is as shown by arrows in FIG..The connection of the peripheral magnetic line of force is completed by eight wedge shape permanent magnets 72.These four wedge-shaped magnets that play a major role 71 are by the central suction to quadrapole consumingly, and its mechanical precision and a degree of accuracy can realize by the non magnetic drum 73 at insertion permanent magnetism magnetic quadrapole (PMQ) center and the shell 74 of PMQ periphery.

As shown in Figure 7, particle beams focusing system 24 comprises two to four the permanent magnetism magnetic quadrapoles (PMQ) that are arranged in chamber shell 86, as a pair of (being called FD), and three (being called FDF), or four (FFDD) 76-79.Each permanent magnetism magnetic quadrapole (PMQ) regulates optimization along the lengthwise position of electron beam axis by computer-controlled mobile system 80-83, and this mobile system comprises vacuum linear motion executor driven by stepper motors.The collimation of magnetic quadrapole (PMQ) can accurately be guaranteed by guide track system 85.

Reaction optical system:

Fig. 8 shows second half structure of reaction chamber 36.The scattering laser pulse 14 passing out from above-mentioned compression-delay optics cavity 15 reflexes to for example spherical mirror of scattered light focus lamp 27(or the off axis paraboloidal mirror with central small hole by having the injection catoptron 26 of beam hole), be scattered again the focus place of light focus lamp 27 reflect focalizations to scattered light focus lamp, and bump against and inverse Compton scattering effect occur and produce gamma-rays at the electron beam 21 that this focus place and particle beams focusing system 24 are sent.After reacting with electron beam 21, scattering pulse 14 is had the catoptron 28 of central small hole to derive reaction chamber 36 by another, enters recycling box 30, and recycling box 30 comprises photodiode 29 and is used for the absorber of the laser pulse that absorbs transmission.

Particle beams separation vessel:

As shown in Fig. 9 A, 9B and 9C, the dipole field bending of the permanent magnet (particle beams separation vessel 33) that the path of scattering electron beam 21 is later made by material NdFeB, and the copper particle beams gatherer 34 with water-cooled element 94 is collected.Permanent magnetism magnetic dipole (PMD) 33, for example Haier's becker type (Halbach-type) permanent magnetism magnetic dipole, comprises the wedge-shaped magnets of 8 blocks of NdFeB materials, the direction of magnetization of wedge-shaped magnets is as shown in the arrow in Fig. 9 B.The dipole field B of Haier's becker type (Halbach-type) permanent magnetism magnetic dipole _dby B _d=B _rln (r _o/ r _i) provide wherein B _rmost advanced and sophisticated magnetic field intensity, r _ithe radius of bore of PMD, r ₀it is the external radius of PMD.For r _i=5mm, r _o=100mm, the NdFeB material that permanent magnet rank is N50, B _r=1.45T, can obtain dipole field is B _d=4.34T.The mechanical precision of permanent magnetism magnetic dipole 33 and degree of accuracy can be by being inserted in the non magnetic drum 91 at PMD center and the shell 92 of PMD periphery is realized.The path of electron beam 21 is collected by copper particle beams gatherer 34 after by 33 bendings of permanent magnetism dipole field, and gamma-rays 31 is penetrated by a narrow gamma-rays perforation hole 93.Gamma-rays perforation hole 93 is processed the edge of permanent magnetism magnetic dipole bore hole in particle beams gatherer 34.For B _d=4.34T(r _o/ r _i=20) magnetic dipole, making deflection distance is d ≈ 2r _ithe permanent magnetism magnetic dipole length of [mm] is by L _pMD[cm]=10[(r _i/ 3.26mm) (E _b/ 1GeV)] ^1/2provide.In copper particle beams gatherer, because electron beam is X at radiation length ₀=1.44cm place by the ratio of electromagnetism cascading off-energy is

energy is that the electronics of 1GeV is 10X in length ₀(being about 15cm), diameter is 7X ₀can the nearly all kinetic energy of loss in the copper billet of (being about 10cm).Permanent magnetism magnetic dipole and particle beams gatherer are cooling by water-cooled element 94.

Gamma-rays device:

As shown in figure 10, above-mentioned gamma-rays device comprises the laser plasma accelerator 18, particle beams focusing system 24 and the reaction optical devices that are installed in reaction chamber 36, and reaction chamber 36 is by vacuum pump system 37 vacuum pumpings, and keeping pressure in its chamber is 10 ^-4the magnitude of handkerchief.Particle beams separation vessel 33 and gatherer 34 are connected to the exit of electron beam 21 and the gamma-rays 31 of reaction chamber 36.According in the embodiment of gamma ray projector of the present invention, all parts of gamma-rays device are all assembled on track structure 35, track structure 35 comprises two ends disk 40 and 41, four supports 42 and four guide rails 43 for support component, and the horizontal and vertical collimation of parts can be adjusted easily and accurately be limited.As shown in Figure 4 and Figure 8, the disk 40 and 41 at guide rail structure 35 two ends is supported by lathe 38 by vacuum bar 39, can prevent like this guide rail structure 35, in the rarefied process of reaction chamber 36, deformation occurs.

The design of inverse Compton scattering gamma ray projector

Design based on inverse Compton scattering gamma ray projector realizes by the quantum electrodynamics result of photon-electron interaction, for example, and the Klein-Nishina equation of the photon providing in quantum electrodynamics and single electron lowest-order differential scattering.At an energy, be (for given laser wavelength lambda _l[μ m],

) laser photon and electron beam in the Compton scattering of an electronics in, maximum scattering photon energy by

provide, wherein γ _e=E _b/ m _ec ²that energy is E _brelativity factor of electron beam, m _ec ²≈ 0.511MeV is the static mass-energy of electronics, the factor

under the reference frame of laboratory, the differential scattering of Compton scattering is

$\frac{\mathrm{d\&sigma;}}{\mathrm{d\&kappa;}}=2\mathrm{\&pi;a}{r}_e^2\{1+\frac{{\mathrm{\&kappa;}}^2{(1-a)}^2}{1-\mathrm{\&kappa;}(1-a)}+{\left[\frac{1-\mathrm{\&kappa;}(1+a)}{1-\mathrm{\&kappa;}(1-a)}\right]}^2\}$

Wherein κ=E _γ/ E _{γ max}by the scattered photon energy after maximum photon energy normalized,

r _eit is classical electron radius.Under the reference frame of laboratory, the scatteringangleθ of photon by

provide.By differential scattering integration in the scope of 0≤κ≤1, the total scatter cross-section that obtains Compton scattering is

${\mathrm{\&sigma;}}_{\mathrm{total}}=\mathrm{\&pi;}{r}_e^{2}a[\frac{2a^2+12a+2}{{(1-a)}^2}+a-1+\frac{6a^2+12a-2}{{(1-a)}^3}\ln a].$

This total scatter cross-section is at beam energy limit E _bbe converted into Thomson cross section at → 0 o'clock

as Δ κ=Δ E _γ/ E _{γ max}during < < 1, photon energy range E _{γ max}-Δ E _γ≤ E _γ≤ E _{γ max}mark scattering cross-section be

$\mathrm{\&Delta;\&sigma;}=2\mathrm{\&pi;a}{\mathrm{<figure-callout\; id="2"\; label="r\; e"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">r</figure-callout>}}_e^{}\mathrm{\&Delta;\&kappa;}[{\left(\frac{1+a}{1-a}\right)}^2+\frac{4}{{(1-a)}^2}{(1+\frac{1-a}{a}\mathrm{\&Delta;\&kappa;})}^{-1}+(a-1)(1+\frac{\mathrm{\&Delta;\&kappa;}}{2})+\frac{1-6a-3a^2}{{(1-a)}^3\mathrm{\&Delta;\&kappa;}}\ln (1+\frac{1-a}{a}\mathrm{\&Delta;\&kappa;})].$

Photon in this energy area is all by forescatering to semi-cone angle

scope in.For being α with laser pulse in surface level (x plane) _intthe electron beam that angle acts on mutually, brightness (for the probability of electron beam in the representation unit scattering cross-section unit interval and laser beam collision) can be expressed as L[mb ^-1s ^-1]=N _en _lf _l/ 2 π Σ, wherein N _ethe number of electrons in electron beam, N _lthe photon number of single beam laser, f _lbe the repetition frequency of laser pulse, Σ (being the overlapping area of laser beam and electron beam) is provided by following formula

$\mathrm{\&Sigma;}={({\mathrm{\&sigma;}}_{\mathrm{ey}}^2+{\mathrm{\&sigma;}}_{\mathrm{Ly}}^2)}^{1/2}{[{\cos }^2({\mathrm{\&alpha;}}_{\mathrm{int}}/2)({\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="ex"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">ex</figure-callout>}}^2+{\mathrm{\&sigma;}}_{\mathrm{Lx}}^2)+{\sin }^2({\mathrm{\&alpha;}}_{\mathrm{int}}/2)({\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="ez"\; filenames="HDA0000457955690000011.png,HDA0000457955690000051.png"\; state="\{\{state\}\}">ez</figure-callout>}}^2+{\mathrm{\&sigma;}}_{\mathrm{Lz}}^2)]}^{1/2}$

Wherein σ _exand σ _eyrespectively root mean square (r.m.s.) size of electron beam level and vertical direction, σ _ezthe r.m.s. Shu Changdu of longitudinal electron beam, σ _lxand σ _lythe r.m.s. spot size of laser beam at level and vertical direction, σ _lzthat laser beam is in longitudinal r.m.s. pulse length.The efficient gamma-rays that produces adopts the mode clashing, so angle is elected α as between electron beam and laser beam _int=0.Adjust particle beams focusing system 24 and scattered light focus lamp 27 and make σ _ex≈ σ _ey≈ σ _lx≈ σ _ly, brightness expression formula turns to

wherein w _intit is the laser facula radius at reflecting point place.Get N _e=1.6022 × 10 ¹⁰(Q _e/ 1nC),

wherein Q _eelectron beam electric weight, U _lS=P _lSτ _lSthat peak power is P _lS, pulsewidth is τ _lSscattering pulse energy, brightness can be calculated as

Wherein I _intit is the scattering pulse light intensity at reflecting point place after focusing on.Therefore can fall apart for Δ κ=Δ E _γ/ E _{γ max}gamma-rays photon flux can be estimated as

ΔN _γ[s- ¹]＝LΔσ≈1×10 ^-14Δσ[mb]f _L[s ^-1]Q _e[nC]I _L[Wcm ^-2]τ[fs]λ _L[μm]。

The embodiment of the gamma ray projector accelerating based on full ray laser plasma

Described that to be 1MeV regulate electron energy to 20MeV(is 200MeV to 930MeV for the photon energy of nuclear physics research above) the gamma ray projector based on full ray laser plasma accelerator.In this gamma ray projector, driving pulse and scattering pulse (are all photon energy from running on 800nm wavelength

) high power laser system in obtain.All parameters of this gamma ray projector are to be all 2.5MeV(example A in order to obtain photon energy), 5MeV(example B), 10MeV(example C) and, 15MeV(example D) and 20MeV(example E) and design, wherein required beam energy is respectively E _b[MeV]=326,461,654,802,928.

It is Q that this laser plasma accelerator can provide electric weight _b=0.5nC, restraints long σ _ezit is the electron beam of 10 μ m magnitudes.A branch of driving pulse pulse 13 is focused on air chamber porch from compressor reducer 51 penetrates.Corresponding to laser intensity I=5.5 × 10 ¹⁸wcm ^-2, the normalized laser field intensity of driving pulse is a ₀=2.The bootstrap of this laser pulse in air chamber propagated and required group velocity modifying factor κ _self=1.19, and there is the spot radius R of coupling _m≡ k _pr _m=3.2.For electronic beam radius, be k _pσ _b=1 situation, load electric weight Q _bthe tail field discount factor α causing can be by formula α ²+ C α ^3/2-1=0 calculates.For example A, to E, parameter is respectively C=9.7,8.2,6.9,6.2,5.8, α=0.213,0.237,0.264,0.281,0.293.

Therefore laser plasma accelerator major parameter is as described below:

(1) beam energy E _b[MeV]=326,461,654,802,928

(2) operation plasma density n _e[10 ¹⁷cm ^-3]=9.2,7.3,5.7,4.9,4.5

(3) accelerating length L _acc[mm]=24,34,50,61,72

(4) required laser pulse pulsewidth τ _l[fs]=43,49,55,59,62

(5) the laser facula radius r of coupling _m[μ m]=18,20,23,24,26

(6) the laser peak power P of coupling _l[TW]=41,52,66,77,85

(7) driving pulse energy U _l[J]=1.78,2.56,3.68,4.55,5.31

Example A in E, for inverse Compton scattering, the factor

be respectively a=0.9923,0.9892,0.9847,0.9813,0.9784.Adjusting focusing system 24 makes horizontal root mean square (r.m.s.) size of electron beam arrival scattering laser 14 focal spot be set as σ _b=25 μ m.It is w that scattered light pulse is focused onto spot radius _int=25 μ m, thus with the electron beam of backpropagation with angle [alpha] _int=0 is overlapping.In order to suppress Relativistic Nonlinear (such as the video stretching and the higher hamonic wave that cause due to non-linear Compton scattering) when laser and electron beam interact, the scattering laser pulse intensity of focusing must be made as lower than I _int～10 ¹⁸wcm ^-2(controlling scattered light pulse peak power is P _lS≈ 10TW).Can, by adjusting another compressor reducer 52, thereby adjust scattered light pulse, control photon flux.Gamma-ray important parameter is as described below:

(1) total scatter cross-section σ _total[mb]=660,658,655,653,651

The mark scattering cross-section of (2) 1% power spectrum bandwidth

Δσ[mb]＝9.80,9.77,9.73,9.69,9.66

The scattering cone angle of (3) 1% power spectrum bandwidth

θ[μrad]＝313,222,157,128,111

(4) scattering pulse peak power P _l[TW]=10

(5 scattering pulse pulsewidth τ _lS[fs]=250

(6) scattering pulse energy U _lS[J]=2.5

(7) scattering pulse focuses on rear spot radius w _int[μ m] ≈ 25

(8) scattering pulse focuses on rear light intensity I _int[Wcm ^-2] ≈ 1 × 10 ¹⁸

(9) brightness L[mb ^-1s ^-1] ≈ 10 ⁶f _l

(10) maximum photon energy E _{γ max}[MeV]=2.5,5,10,15,20

(11) power spectrum bandwidth deltaf κ=Δ E _γ/ E _{γ max}=0.01

(12) total photon flux N _γ[10 ⁹f _l] ≈ 0.660,0.658,0.655,0.653,0.651

The mark photon flux Δ N of (13) 1% power spectrum bandwidth _γ[10 ⁷f _ls ^-1] ≈ 0.980,0.977,0.973,0.969,0.966

Generally speaking, under Desktop Dimensions (as, the reaction chamber that about 3m is long), the driving pulse that 5.3J is synchronously provided to laser plasma accelerator and scattering pulse that 2.5J is provided to react optical devices take carry out the dual output high power laser system of inverse Compton scattering provide can produce power as 1 to 20MeV, the flux of 1% bandwidth is as～10 ⁷f _ls ^-1the gamma ray projector of photon.Every 1% bandwidth of gamma-rays that is output as standard high power laser system that 100TW level, repetition frequency are 10Hz and provides has 10 ⁸s ^-1the flux of magnitude.More preferably, for example coherent optical-fiber laser system there is the output of several joules of levels and the high repetition frequency of 1kHz repetition frequency, every 1% bandwidth of gamma-rays that high power laser system provides have 10 ¹⁰s ^-1the flux of magnitude.

Table 1 has been summed up the laser plasma accelerator of example A to E and the major parameter of Compton scattering.

The gamma ray projector example of table 1 based on full ray laser plasma accelerator

Claims (10)

1. a gamma ray projector, comprising:

Dual output high power laser system (200), described laser system (200) comprises twin-stage connection laser amplifier (8,9), described laser system (200) is for separating primary laser pulse and amplifying synchronously to produce two bundle high energy laser pulses (10,11);

Two compression-delay systems (12), described two compression-delay system (12) comprises that diffraction grating is to (51,52) and postpone optical mirror slip group (55,56), wherein, described two restraint the laser pulse (10 being exaggerated, 11) by diffraction grating to (51,52) compressed in time domain and by postpone optical mirror slip group (55,56) carry out suitable delay to form respectively driving laser pulse (13) and the scattering pulse (14) with suitable peak power, pulsewidth and delay;

Laser plasma accelerator (18), described driving laser pulse (13) produces the relativistic electron beam (21) with suitable light beam parameters in described laser plasma accelerator (18);

Particle beams focusing system (24), the electron beam (21) that described particle beams focusing system (24) produces for transmitting described laser plasma accelerator (18), and focus on described electron beam (21) and make described electron beam (21) reach suitable bundle size;

Scattered light focus lamp (27), it is upper to produce gamma-rays (31) that described scattered light focus lamp (27) makes described scattering pulse (14) focus on described electron beam (21); And

Particle beams piece-rate system, described particle beams piece-rate system is for Fen Li with described gamma-rays (31) by described electron beam (21).

2. gamma ray projector according to claim 1, is characterized in that, described laser plasma accelerator (18) comprising:

Be filled with first air chamber (61) of mixed gas;

Be filled with second air chamber (62) of clean gas;

Gas feed channel; And

Gas regulating system.

3. gamma ray projector according to claim 2, is characterized in that, described laser plasma accelerator (18) comprises the device of the length for regulating described the second air chamber (62).

4. according to the gamma ray projector described in any one in claims 1 to 3, it is characterized in that, it is upper to form overall mini-system that described laser plasma accelerator (18), particle beams focusing system (24) and scattered light focus lamp (27) are assembled in track structure (35).

5. according to the gamma ray projector described in any one in claim 1 to 4, it is characterized in that, described particle beams piece-rate system comprises for the dipole magnets (33) of deflection beam (21) and particle beams gatherer (34).

6. according to the gamma ray projector described in any one in claim 1 to 5, it is characterized in that, described gamma-rays is that energy is the photon beam of 1MeV to 20MeV.

7. gamma ray projector according to claim 2, is characterized in that, the mixed gas of helium and nitrogen is housed in described the first air chamber (61), in described the second air chamber (62), pure helium is housed.

8. gamma ray projector according to claim 1, it is characterized in that, in described gamma ray projector, be provided with two recycling boxes (22,30), in described two recycling boxes, be respectively equipped with the laser absorption device for absorbing described driving laser pulse (13) and described scattering pulse (14).

9. gamma ray projector according to claim 8, is characterized in that, described two recycling boxes (22,30) in, be provided with photodiode (23,29), described photodiode (23,29) is for monitoring the synchronism of described driving laser pulse (13) and scattering pulse (14).

10. gamma ray projector according to claim 1, it is characterized in that, described particle beams focusing system (24) comprises 2～4 permanent magnetism magnetic quadrapoles (PMQ), described permanent magnetism magnetic quadrapole (PMQ) comprises wedge shape permanent magnet (71,72) and drum (73) and shell (74) for supporting and location.

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