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RSS1992 Vol. 04, No. 03
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1992,
04: 325-335.
Abstract:
A 3.3 -MeV linear induction accelerator (LIA) has been designed and constructed at the China Academy of Engineering Physics. The parameters of 3.4MeV、 2kA、 80ns and l×104A/ (rad·cm)2 have been achieved.It has been used for SG - 1 FEL experiments. The accelerator is mounted on a movable frame so that, after movign 3m transversely, it can be assembled with more modules into a 10-MeV LIA. This paper will summarize the physics and engineering aspects of the LIA facility and will describe the measuring means of characters for the beam.
A 3.3 -MeV linear induction accelerator (LIA) has been designed and constructed at the China Academy of Engineering Physics. The parameters of 3.4MeV、 2kA、 80ns and l×104A/ (rad·cm)2 have been achieved.It has been used for SG - 1 FEL experiments. The accelerator is mounted on a movable frame so that, after movign 3m transversely, it can be assembled with more modules into a 10-MeV LIA. This paper will summarize the physics and engineering aspects of the LIA facility and will describe the measuring means of characters for the beam.
1992,
04: 336-342.
Abstract:
Based on SG-1 LIA FEL amplifier parameters, the ASE output power and gain, as well as their relationship with electron beam quantity including beam energy spread, emittance, and beam intensity etc.are simulated and analysed by using 3-D WAGFEL code. The related scaling law has been given. Mearwhile the influence of the wiggler magnetic field's random errors on ASE output and the experimental results are also analysed.
Based on SG-1 LIA FEL amplifier parameters, the ASE output power and gain, as well as their relationship with electron beam quantity including beam energy spread, emittance, and beam intensity etc.are simulated and analysed by using 3-D WAGFEL code. The related scaling law has been given. Mearwhile the influence of the wiggler magnetic field's random errors on ASE output and the experimental results are also analysed.
1992,
04: 343-348.
Abstract:
A WP-2250 controller based programmable digitizer system is used on line to record and analyze the signals of the REB accleralar diode. The date acquisition and processing is introduced.
A WP-2250 controller based programmable digitizer system is used on line to record and analyze the signals of the REB accleralar diode. The date acquisition and processing is introduced.
1992,
04: 349-356.
Abstract:
A 2D-FEL code with geometry infinitely extended in direction of electron wiggling motion is established. Using this code, the evolution of optical field is calculated under the conditions of nonideal incidence of e-beam, which results in exponential degradation in output power and the excitation of transverse higher modes, as well as in displacement of the centroid of optical beam. In this paper, it is pointed out that, beside the emittance of e-beam, the geometry of transverse phase space is also an important parameter having influence on FEL performance.
A 2D-FEL code with geometry infinitely extended in direction of electron wiggling motion is established. Using this code, the evolution of optical field is calculated under the conditions of nonideal incidence of e-beam, which results in exponential degradation in output power and the excitation of transverse higher modes, as well as in displacement of the centroid of optical beam. In this paper, it is pointed out that, beside the emittance of e-beam, the geometry of transverse phase space is also an important parameter having influence on FEL performance.
1992,
04: 357-361.
Abstract:
This paper calculates the space-charge field of single charged sheath in cylindrical cavity with Green function method, and analyses the behaviour of the virtual cathode phenomenon relevant to time in cylindrical drifting space. Furthermore, we obtain the expression of limit charge in the nonrelativistic condition, and give numerical calculation and analysis for the position and velocity of charged sheath versus time. Results show intuitive physical picture of the virtual cathode formation.
This paper calculates the space-charge field of single charged sheath in cylindrical cavity with Green function method, and analyses the behaviour of the virtual cathode phenomenon relevant to time in cylindrical drifting space. Furthermore, we obtain the expression of limit charge in the nonrelativistic condition, and give numerical calculation and analysis for the position and velocity of charged sheath versus time. Results show intuitive physical picture of the virtual cathode formation.
1992,
04: 362-372.
Abstract:
In the paper, a $2 \frac{1}{2}$ dimensional, fully electromagnetic, relativistic CIC particle simulation code has been developed. The code is used to simulate the virtual cathode formation and the emission of high power microwave with a cold electron beam of cylindrical symmetry. A virtual cathode will be formed when the injected current exceeds the vaccum limited current of the beam. The current transmitted from the virtual cathode varies with time and its average is larger than the static vaccum limited current. A guide field is applied to confine efficiently the radial motion of the electrons. The virtual cathode oscillates well with a definite cycle. The oscillating axial current causes the microwave radiation and the power concentrates on TM modes. The guide field is in favour of microwave generation.
In the paper, a $2 \frac{1}{2}$ dimensional, fully electromagnetic, relativistic CIC particle simulation code has been developed. The code is used to simulate the virtual cathode formation and the emission of high power microwave with a cold electron beam of cylindrical symmetry. A virtual cathode will be formed when the injected current exceeds the vaccum limited current of the beam. The current transmitted from the virtual cathode varies with time and its average is larger than the static vaccum limited current. A guide field is applied to confine efficiently the radial motion of the electrons. The virtual cathode oscillates well with a definite cycle. The oscillating axial current causes the microwave radiation and the power concentrates on TM modes. The guide field is in favour of microwave generation.
1992,
04: 373-380.
Abstract:
The acceleration and transport of electron beams in the $3.3-\mathrm{MeV}$ LIA are simalated using the Electron Trajectory code SLAC-226, and the obtained results are compared with the solutions of envelope equations derived from the nonlinear theory of the electron beam transport. Both the code and the envelope equations take account of the self-electromagnetic field and applied electromagnetic field of the beam current.
The acceleration and transport of electron beams in the $3.3-\mathrm{MeV}$ LIA are simalated using the Electron Trajectory code SLAC-226, and the obtained results are compared with the solutions of envelope equations derived from the nonlinear theory of the electron beam transport. Both the code and the envelope equations take account of the self-electromagnetic field and applied electromagnetic field of the beam current.
1992,
04: 381-386.
Abstract:
Experiments on a Raman FEL with a tapered field have been done. A maximum radiution output of 31MW at 8 ~ 10.4mm has been obtained with an energy efficiency of 9.68%. The tapering technique is effective in increasing the efficiency in the Raman FEL for large current and low energy electron beam.
Experiments on a Raman FEL with a tapered field have been done. A maximum radiution output of 31MW at 8 ~ 10.4mm has been obtained with an energy efficiency of 9.68%. The tapering technique is effective in increasing the efficiency in the Raman FEL for large current and low energy electron beam.
1992,
04: 387-391.
Abstract:
From the projection of 6 -dimensional phase space on its 2 -dimensional subspaces, the relationships between the 2 -dimensional beam phase space ellipse and the measured beam emittance are deduced.
From the projection of 6 -dimensional phase space on its 2 -dimensional subspaces, the relationships between the 2 -dimensional beam phase space ellipse and the measured beam emittance are deduced.
1992,
04: 392-396.
Abstract:
This paper describes a new method for aligning a positive-branch co -focal unstable resonator without any precise alignment instrument. It also eliminates a small hole in centre of the concave mirror. By utlizing the reflectivity of the backside of the outcoupling mirror and a converging beam with definite focal length and aperture, we can successfully align an unstable resonator. Meanwhile, a bright coaxis reference beam is provided which can be used to adjust outside optical elements. The alignment accuracy is estimated to be about 10μrad. Furthermore, the experiment demonstrated that the zero-grade reflected beam can be filtered successfully when the method presented in this paper was used. Therefore, He -Ne reference beam can show the sitiuation of the alignment and parameter variation of the resonator more clearly. After a concave mirror with a small hole is replaced by a concave mirror with no small hole on it, the output performance of a DF laser is improved.
This paper describes a new method for aligning a positive-branch co -focal unstable resonator without any precise alignment instrument. It also eliminates a small hole in centre of the concave mirror. By utlizing the reflectivity of the backside of the outcoupling mirror and a converging beam with definite focal length and aperture, we can successfully align an unstable resonator. Meanwhile, a bright coaxis reference beam is provided which can be used to adjust outside optical elements. The alignment accuracy is estimated to be about 10μrad. Furthermore, the experiment demonstrated that the zero-grade reflected beam can be filtered successfully when the method presented in this paper was used. Therefore, He -Ne reference beam can show the sitiuation of the alignment and parameter variation of the resonator more clearly. After a concave mirror with a small hole is replaced by a concave mirror with no small hole on it, the output performance of a DF laser is improved.
1992,
04: 397-404.
Abstract:
The Potential curves of non - neutral rare -gas halide ionic excimers are presented based on the amended Rittner potential and calculated with a ab initio code (Gaussian 80). The corresponding spectroscopic constants of the energy - levels for XUV transitions are discussed.
The Potential curves of non - neutral rare -gas halide ionic excimers are presented based on the amended Rittner potential and calculated with a ab initio code (Gaussian 80). The corresponding spectroscopic constants of the energy - levels for XUV transitions are discussed.
1992,
04: 405-410.
Abstract:
Based upon modulation transfer function, the Strehl ratio and compensation efficiency of an adaptive optical technique in the region of strong turbulence are discussed.The amplitude-fluctuation correlation is taken into account. Theoretical expreessions of Strehl ratio and compensation efficiency are derived. Calculations show that the theoretical predictions coincide with the experimental values very well. In the case of noncompelet compensation, the adaptive optical technique is useful even in the region of strong turbulence.
Based upon modulation transfer function, the Strehl ratio and compensation efficiency of an adaptive optical technique in the region of strong turbulence are discussed.The amplitude-fluctuation correlation is taken into account. Theoretical expreessions of Strehl ratio and compensation efficiency are derived. Calculations show that the theoretical predictions coincide with the experimental values very well. In the case of noncompelet compensation, the adaptive optical technique is useful even in the region of strong turbulence.
1992,
04: 411-416.
Abstract:
This paper presents a perturbation algorithm for constructing conjugat field using two deformable mirrors. The simulations demonstrated that the diffraction intensity pattern with this algorithm is in good agreement with the wanted intensity pattern. The requirement on the dynamic range of deformable mirrors and the error of the intensity is also estimated.
This paper presents a perturbation algorithm for constructing conjugat field using two deformable mirrors. The simulations demonstrated that the diffraction intensity pattern with this algorithm is in good agreement with the wanted intensity pattern. The requirement on the dynamic range of deformable mirrors and the error of the intensity is also estimated.
1992,
04: 417-423.
Abstract:
The Results of one -dimensional effective melting heat, laser melting threshold intensity and metallography microscope analysis for the LY12 aluminium alloy targets irradiated by long-duration （6ms） 1.06μm laser beams are given in this report. A new explanation of yielding material damage by laser ablation combined with laser thermal stress is also presented. When laser intensity ranges from 24kW/cm2 to 220kW/cm2, the effective melting heat Q = 3.5 57kJ/g, and the laser threshold intensity for melting is about 10kW/cm2.
The Results of one -dimensional effective melting heat, laser melting threshold intensity and metallography microscope analysis for the LY12 aluminium alloy targets irradiated by long-duration （6ms） 1.06μm laser beams are given in this report. A new explanation of yielding material damage by laser ablation combined with laser thermal stress is also presented. When laser intensity ranges from 24kW/cm2 to 220kW/cm2, the effective melting heat Q = 3.5 57kJ/g, and the laser threshold intensity for melting is about 10kW/cm2.
1992,
04: 424-430.
Abstract:
In this paper an expression of radiative transfer equation with reflective boundary condition is given for solving problems of laser target interaction. Numerical method and its approximation are discussed here. An example of numerical calculation is given in an simple case.
In this paper an expression of radiative transfer equation with reflective boundary condition is given for solving problems of laser target interaction. Numerical method and its approximation are discussed here. An example of numerical calculation is given in an simple case.
1992,
04: 431-437.
Abstract:
The principle and experiments of double exposure holographic interferometry for measuring plasma plume from an LY12 aluminum target (φ50 ×3mm) irradiated by a Q -Switched Nd: glass Laser beam (50ns , 5 ×109W/cm2) are described. The holographic interference photo was taken by double exposure holography for t = 70.4ns. Using the Abel inversion and Saha equation the holographic interferogram are treated to yield parameters for Laser interactions with materials.
The principle and experiments of double exposure holographic interferometry for measuring plasma plume from an LY12 aluminum target (φ50 ×3mm) irradiated by a Q -Switched Nd: glass Laser beam (50ns , 5 ×109W/cm2) are described. The holographic interference photo was taken by double exposure holography for t = 70.4ns. Using the Abel inversion and Saha equation the holographic interferogram are treated to yield parameters for Laser interactions with materials.
1992,
04: 438-444.
Abstract:
The stress histories of aluminum plates with different thicknesses induced by a Q -swiched Nd -glass laser beam of pulse duration 70ns and flux of 107 ~ 108W/cm2 measured with a piezoelectric transducer of x -cut quartzcrystul of 10mm in diamerer and 1.2mm or 2mm in thickness. The spot diameter on the samples front was 10mm. The experimental results show that the peak stress σmax is proportional approximately to the square of laser bear flux I2 for I=（3 7）J/cm2. The scaling of σmax vs the propagation distance x seems tobe σmax∝x-（1.02～1.29）. An analytical calculation identifies the hot -elastic mechanism of the laser induced stress wave in the aluminum targets herein.
The stress histories of aluminum plates with different thicknesses induced by a Q -swiched Nd -glass laser beam of pulse duration 70ns and flux of 107 ~ 108W/cm2 measured with a piezoelectric transducer of x -cut quartzcrystul of 10mm in diamerer and 1.2mm or 2mm in thickness. The spot diameter on the samples front was 10mm. The experimental results show that the peak stress σmax is proportional approximately to the square of laser bear flux I2 for I=（3 7）J/cm2. The scaling of σmax vs the propagation distance x seems tobe σmax∝x-（1.02～1.29）. An analytical calculation identifies the hot -elastic mechanism of the laser induced stress wave in the aluminum targets herein.
1992,
04: 445-450.
Abstract:
The termal degradation effects in the preloaded metal thin plate irradiated by CW laser beam are calculated with the finite element method. A two dimensional mode to calculate the degradation effects induced by CW laser beam is set up. The yielded degradation thresholds and time as well as the dependence of the degradation threshold and time on the laser power densities and the preloads are given.
The termal degradation effects in the preloaded metal thin plate irradiated by CW laser beam are calculated with the finite element method. A two dimensional mode to calculate the degradation effects induced by CW laser beam is set up. The yielded degradation thresholds and time as well as the dependence of the degradation threshold and time on the laser power densities and the preloads are given.
1992,
04: 451-454.
Abstract:
The development of chirped -pulse amplification (CPA) technique requires to optimize CPA for the production of high power ultrashort light pulses with low pedestal. In an ideal CPA system, compressed pulse will be determined solely by the power spectrum of the amplified pulse. The temporal pulse shape I (t) can be given by the power spectrum I (ω). It's shown that I (ω) of Gaussian spectral lineshape without modulation may produce clean, high contrast pulses.
The development of chirped -pulse amplification (CPA) technique requires to optimize CPA for the production of high power ultrashort light pulses with low pedestal. In an ideal CPA system, compressed pulse will be determined solely by the power spectrum of the amplified pulse. The temporal pulse shape I (t) can be given by the power spectrum I (ω). It's shown that I (ω) of Gaussian spectral lineshape without modulation may produce clean, high contrast pulses.
1992,
04: 455-460.
Abstract:
The characteristics of ions emission from laser -produced plasma in hohlraum is presented here. It differs obiviously from two - temperature electron velocity distribution observed in laser -planar target interaction, and presents a multi - temperature electron velocity distribution. This phenomenon reflects the evolution of plasma state in a hohlraum target. Furthermore, experimental results have shown that the DT fuel pellet placed in the hohlraum is probably bombarded by the fast ions in the explosion experiments.
The characteristics of ions emission from laser -produced plasma in hohlraum is presented here. It differs obiviously from two - temperature electron velocity distribution observed in laser -planar target interaction, and presents a multi - temperature electron velocity distribution. This phenomenon reflects the evolution of plasma state in a hohlraum target. Furthermore, experimental results have shown that the DT fuel pellet placed in the hohlraum is probably bombarded by the fast ions in the explosion experiments.
1992,
04: 461-466.
Abstract:
Based on the experimental data, the radiation temperature of hohlraum targets has been analysed for a number of cylindrical geometries and the scaling relation to the laser energy, pulse duration and hohlraum inner surface area has been derived.
Based on the experimental data, the radiation temperature of hohlraum targets has been analysed for a number of cylindrical geometries and the scaling relation to the laser energy, pulse duration and hohlraum inner surface area has been derived.
1992,
04: 467-472.
Abstract:
Using a simple theoretical model, in which we assume that laser energy is absorbed resonantly at critical surface, and the laser - produced plasma expands isothermly, we simulated the pinhole closure by a laser -produced plasma. It agrees with the experimental results.
Using a simple theoretical model, in which we assume that laser energy is absorbed resonantly at critical surface, and the laser - produced plasma expands isothermly, we simulated the pinhole closure by a laser -produced plasma. It agrees with the experimental results.
1992,
04: 473-476.
Abstract:
A method of a relative calibration of SWR film used for mearuring intensity of X rays from laser produced plasma was reported in this paper. Using X rays from the plasma as a source of calibration, we have measured characteristics of Kodak SWR film produced by U.S.A. The result was used to modify the gain coefficiet of X-ray laser measured in our laboratory.
A method of a relative calibration of SWR film used for mearuring intensity of X rays from laser produced plasma was reported in this paper. Using X rays from the plasma as a source of calibration, we have measured characteristics of Kodak SWR film produced by U.S.A. The result was used to modify the gain coefficiet of X-ray laser measured in our laboratory.
