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Acta Physica Sinica  
  Acta Physica Sinica--1986, 35 (10)   Published: 15 October 1986
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BRIEF REPORT

FEEDBACK STABILIZATION OF AXISYMMETRIC MODES IN NON-CIRCULAR TOKAMAKS

Zhang Zuo-yang, Huo Yu-ping
Acta Physica Sinica. 1986, 35 (10): 1364 doi: 10.7498/aps.35.1364
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The feedback stability of axisymmetric MHD mode in tokamaks with unclosed shell has been studied analytically through solving directly the boundary problem of the perturbed magnetic surface in the vacuum region. For plasma torus with elliptical cross-section, a feedback system with conducting shell and active control coils has been suggested. The result shows that two unclosed shells arranged above and below the plasma have a very strong stabilizing effect. The re istive shell can suppress the modes with faster growth rate and the active coils can be used to stabilize the slower modes.

SPUTTERED ALUMINIUM-CARBON-OXYGEN SOLAR SELECTIVE ABSORBING SURFACES

Yin Zhi-qiang
Acta Physica Sinica. 1986, 35 (10): 1369 doi: 10.7498/aps.35.1369
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The calculations about A1-C-O/A1 solar selective absorbing surfaces have been carried out. Reasonable agreement is obtained between computed and experimentally measured reflectances and absorptances for multilayer Al-C-O thin films on aluminium base layer, which are prepared using magnetron sputtering with single aluminium cathode. Solar absorptance of A1-C-O/A1 selective surface is about 0.92 and emittance (room temperature) around 0.04. The sputtering systme is simplified and more efficient for the use of aluminium cathode.

ON APPLICATIONS OF PARAMETRIC ACOUSTIC SOURCES TO SHALLOW WATER

Qian Zu-wen, Shao Dao-yuan
Acta Physica Sinica. 1986, 35 (10): 1374 doi: 10.7498/aps.35.1374
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As is shown by westervelt, the difference-frequency sound pressure of the parametric array in the far field is proportional to the second power of f/f0, the downshift ratio of the frequency. However, a different result may occure in the near field, especially, when the distence to the field point is much less than the length of the parametric array, but larger than R0, the Rayleigh length of the transducer. In this paper, our previous theory is applied to the case of shallow water and an expression for the parametric array design has been given. It is shown that the parametric pressure is proportional to Ro, instead of proportional to the length of the parametric array or to the second power of f/f0. Futhermore, an analysis for Moffett and Mellen's theory is also made in this paper and on identical expression has been obtained. Finally, an experiment is carried out in a pool and the results obtained support the theory.

LOW FREQUENCY INTERNAL FRICTION OF MOVING MAGNETIC DOMAIN WALLS IN PURE IRON

Zhen Wen-guang, Zhang Jin-xiu, Lin Hao-qing, He Zhen-hui, Yao Yi-fa
Acta Physica Sinica. 1986, 35 (10): 1378 doi: 10.7498/aps.35.1378
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The low frequency internal friction (Q-1) of pure iron wires in a d.c. magnetic field increasing with a constant rate (H = const) was studied by a torsion pendulum a room temperature. It was found that Q-1 is composed of a static part Q0-1 (at H=0) and a dynamic part Qm-1 (at H≠0) which is viscoelastic type. The values of Qm-1 are independent of the strain amplitude Aε (in the range of 10-6 to 10-5), increase with the increase of H/ω and drop almost down to the ualues of Q0-1 when H changes suddenly from some ualue to zero. The behaviour of the static part is analogous to that of the resonance damped model of dislocation. The Qm-1-H curves of prestrained specimens are lower than those of annealed Ones and their peaks shift to higher magnetic field.

A NEW CRITERION OF CONSTRUCTING THE STRUCTURAL MODEL OF BINARY AMORPHOUS ALLOYS

Wang Jing-han, Cheng Xian-an, Wang Xu-wei, Chen Bing-yu, Li De-xiu, Chen Jing-chang
Acta Physica Sinica. 1986, 35 (10): 1383 doi: 10.7498/aps.35.1383
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The relative distribution of the metalloid atoms is one of the most important characteristic of the chemical short-range order in the structure of the amorphous alloys consist of metal-metalloid. Basing on this idea, a new criterion of constructing the structural model of this kind of alloys is proposed, and several models are made by a computer with this new criterion, which simulate the structures of amorphous alloy Ni64B36,Fe80B20,Ni81B19 and Co81P19 respectively. All of the partial distribution functions of these models are in agreement with the experiments. These results are also compared with other author's works and discussed.

A DISCRETE SAMPLING METHOD IN OPTICAL TRANSFORMATION

Chen Yan-song, Zheng Shi-hai, Wang Yu-tang, Dong Bi-zhen
Acta Physica Sinica. 1986, 35 (10): 1390 doi: 10.7498/aps.35.1390
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A discrete sampling method in optical transformation has been suggested in this article. Based on the consideration of unitary transformation, that is important for opcical transformation, conditions of sampling an optical system are obtained. The expression of propagation matrix including the effect caused by the width of sampling window is derived. As an example, the distributions of holographic amplitude and phase calculated by designing a given Walsh transformation are given.

THE KINETIC STUDIES OF KrF* AND Kr2F* IN He/Ar/Kr/F2 MIXTURES

Gu Zhi-yu, Wang Shao-ying, Fei Rui-an, Yuan Da-chang, Xei Fong-qing, Wang Yong
Acta Physica Sinica. 1986, 35 (10): 1395 doi: 10.7498/aps.35.1395
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By investigating the time integrated spectra, the kinetics of Kr2F* in fast discharge excited He/Ar/Kr/F2 mixtures have been studied, the paths feature of the formation of Kr2F* have been probed. According to the theoretical analysis and the experimental results, it was shown that under the fast discharge excitation, the three-body collision reactions KrF* + Kr + M→Kr2F* + M are the main paths to the formation of Kr2F* and KrF* can be formed efficiently via displacement reaction ArF* + Kr→KrF* + Ar. The corresponding formation rate constants of Kr2F* have been measured by the experiments.
CONTENT

MACROSCOPICAL BEAM-PLASMA KINK INSTABILITY RESEARCH IN TOKAMAK

Xu Xue-qiao, Huo Yu-ping
Acta Physica Sinica. 1986, 35 (10): 1259 doi: 10.7498/aps.35.1259
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In this paper, the kink modes of the plasma in a tokamak with parallel NB injection have been studied. The fast ion component of the plasma has been modelled by a mono-energetic ion beam. Negleiting the dissipative process, an energy principle could be derived from the Vlasov equation in low frequency and small Lamar-radius limit. It is found that none of the entemal kink modes (m≥2) are influenced by the ion beam in the thintorus approximation. But the existance of the fast ion component has changed the kink modes (m = l). Obviausly, by proper choice of the velocity profile of ion beam m = l, n=2 modes can be stabilized absolute. The behaviour of the m/n =1/1 kink mode is very complicated. It could be stabilized or destabilized depending on the beam energy βb, axial safety factor q(0) and radial velocity profile of the beam. A numerical culculation shows that when q(0)<0.924 and the beam velocity profile is properly chosen, the m/n = 1/1 mode can also be totaly stabilized.

ELECTRON CYCLOTRON RESONANCE HEATING METHOD FOR CREATING ENERGETIC ELECTRONS IN HIGH β TOKAMAK

Chen Yan-ping, Ke Fu-jiu, Cai Shi-dong
Acta Physica Sinica. 1986, 35 (10): 1271 doi: 10.7498/aps.35.1271
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Rosenbluth et al. have suggested that energetic particles trapped at unfavorable curvature region of a tokamak can provide an access to the second stability region. The ECRH processes for achieving this novel state in reactor tokamak is proposed. The RF within the proper ranges of frequency and wave vector are injected from the outside of tokamak of a chosen magnetic surface. Only a few percent of electrons is heated by the high electron cyclotron harmonic resonance successively. The numerical results show that heating is efficient for both ordinary and extraordinary modes.

MONTE-CARLO SIMULATION OF PARTICLE CONFINEMENT IN MIRRORS WITH SPACE-VARING MAGNETIC FIELD

Wang Long
Acta Physica Sinica. 1986, 35 (10): 1281 doi: 10.7498/aps.35.1281
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The particle confinement has been studied by Monte-Carlo simulation in the intermediate regime between the collisional and collisionless regimes for the mirrors with space-varing magnetic fields, for example, LAMEX and parabolic magnetic field profiles. The particle confinement time in the intermediate regime is longer than the extrapolation values based on the formulas in other two regimes, and proportional to the mirror ratio. The density profiles have been obtained as self-consistent solutions from the simulation. The dependence of the density profile on the plasma parameters are discussed.

PRESSURE DEPENDENCE OF THE ABSORPTION EDGE OF SEMIMAGNETIC SEMICONDUCTORS Cd1-xMnxTe

Shan Wei, Shen Xue-chu, Zhao Min-guang, Zhu Hao-rong
Acta Physica Sinica. 1986, 35 (10): 1290 doi: 10.7498/aps.35.1290
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The effect of pressure on the optical absorption edge for mixed crystals Cd1-xMnxTe with different manganese concentrations in the range of lbar to 40 kbar and at room temperature is reported. The observed absorption edge shifts to higher energy with increasing pressure at a rate of a = 6-8 ×10-3 eV/kbar and a second order coefficient with the order of magnitude 10-5 eV/kbar2 for the samples with x<0.5; to lower energy with increasing pressure at a rate of a=-5.0×10-3 eV/kbar for the samples with x≥0.5. A phase transition from zinc blende to NaCl-type structure occurs for all the samples studied. The transition pressures depend on the Mn contents in the samples in the region of 25—40 kbar. The physical origins of different pressure coefficients are discussed in the light of the deformation potentials of energy band slates and the hybridization of the Mn2+ 3d levels with the p-like states in the valence band.

LOW FREQUENCY ABSORPTION BAND IN Hg1-xCdxTe

Fu Rou-li
Acta Physica Sinica. 1986, 35 (10): 1299 doi: 10.7498/aps.35.1299
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A new interpretation on the low frequency absorption band in Hg1-xCdxTe is presented.By the calculation of the vibrational spectra of CdTe (or HgTe) diatomic chain with one substitutional impurity Hg (or Cd), and the discussion of the characteristic of vibrational modes in the mixed crystal Hg1-xCdxTe, ive show that there exist acoustic phonons, the frequency of which doesn't approach zero at k→0. These acoustic phonons can absorb the photons in far infra red range and cause the low frequency absorption band. The characteristics of low frequency absorption band reported so far can thus be interpreted. We also predict that there may exist similar low frequency absorption band in the other mixed crystals, the optical phonons of which have "two-mode" behaviour.

INVESTIGATION ON CRYSTALLIZATION PROCESS OF AMORPHOUS LITHIUM IONIC CONDUCTOR B2O3-0.7Li2 O-0.7LiCl-xAl2O3 WITH ONE DIMENSION ANGULAR CORRELATED POSITRON ANNIHILATION RADIATION

Su Fang, Jiang Hui-lin
Acta Physica Sinica. 1986, 35 (10): 1306 doi: 10.7498/aps.35.1306
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One dimension angular correlated positron annihilation radiation curves of amorphous lithium ionic conductor B2O3-0.7Li2O-0.7LiCl-xAl2O3 (x = 0.15, 0.10, 0.05) during the crystallization process have been measured, and the linear parameters S in normalized dispersion of electron momentum have been calculated. From the parameters S we can also disclose the variations in defect-density during the crystallization process.Experimental results show that the parameters S at room temperature are not Largely affected by the content of Al2O3, each and all greatly decrease after full crystallization process, each and all slighly increase at the beginning of crystallization, but then increase anomalously at about 400-450℃ only when x= 0.15. These results verify and complement the results obtained from measuring average positron lifetime. From them we are convinced of the physical picture that the boundary layer contains a lot of defects.

ENERGY BAND CALCULATION FOR GaAs, GaP AND GaAsxP1-x

Xue Fang-shi
Acta Physica Sinica. 1986, 35 (10): 1315 doi: 10.7498/aps.35.1315
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The energy bands of GaAs, GaP and GaAsxP1-x are calculated using the zone-variational method. Since there are different atoms in a cell, different radii are selected for various atomic spheres according to the actual size for corresponding atoms. The crystal potential is calculated by superposing various atomic potentials. Since the atomic potentials are distorted in the bonding sphere under the interaction with other atoms in crystal, a few adjusting parameters are selected to adjust the corresponding atomic potential and an analytical expression is used to approach the resulted potential. The potential adjusting parameters are selected to make the calculated energy band close to experimental results. The band structures which agree with experimental results are obtained for GaAs and GaP. Furthermore, these poteatials are used to calculate the energy band of GaAsxP1-x.

SPACE-TIME STRUCTURE OF THE SUPERPOSITION OF TWO CO-LINEAR KERR BLACK HOLES'METRICS

Huang Chao-guang, Wang Yong-cheng
Acta Physica Sinica. 1986, 35 (10): 1322 doi: 10.7498/aps.35.1322
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The space-time structure of the superposition of two colinear kerr black holes is studied by the imaginary weyl coordinate method. The space-time region within the horizons in this case is described. Also, the variation of the shape of the inner infinite redshift surface and theposition change of singularities with z0 when 2z0>(M12-a12)1/2+(M22-a22)1/2 is obtained. Fromthis, we can conclude that when z0→(M2-a2)1/2, the space-time structure does not tend to one kerr space-time for parallel identical kerr solutions or one Schwarzschild-NUT metric for anti-parallel identical kerr solutions even though the structure of the space-time outside the outer horizons does, and that there exist the solutions of Einstein's equations without naked singulari-ties (but not without any singularity) when 2z0>(M12-a12)1/2+(M22-a22)1/2.

RESONANCE PERTURBATION OF A HAMILTONIAN BY COUPLING OF TWO DIBBERENT KINDS OF MODES

He Kai-fen
Acta Physica Sinica. 1986, 35 (10): 1330 doi: 10.7498/aps.35.1330
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A Hamiltonian system with coupled two dibberent kinds of modes is studied. When the coupling vanishes, one kind of modes is nonlinear oscillators, describing coherent three-wave interaction and consisting an integrable Hamiltonian. Another kind of modes is constants of motion. In the first order of approximation, resonance occurs due to the coupling between these two kinds of modes. The resonace condition is relevant to the existing linear brequencies and their mismatch as well as the harmonic frequencies of the nonlinear variations of the amplitudes of the oscillators.

THE TOPOLOGICAL ENTROPY OF ONE-DIMENSIONAL UNIMODAL MAPS

Chen Rui-xiong, Chen Shi-gang
Acta Physica Sinica. 1986, 35 (10): 1338 doi: 10.7498/aps.35.1338
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On the basis of computational calculation for the logistic map, we analyse the inverse orbital structure of one-dimensional unimodalmap and prove the different recurrence formulae which show that the total number of inverse orbit N(n) changes with inverting time n at different parameters. By this way, we analytically obtain h(f)=0 within the period-doubling region; h(f) = logamp on m = 3 + 21 period point of U -sequence RLR21, where amp is the largest real root of equation am-2am-2-1 = 0; hj(f) = (1/2)j log2 on the boundary between 2j-1 band and 2j band, from this result we find the scaling exponent of topological entropy near the accumulation point μ, t = 0.449806…. By means of above conclusion, we obtain the topological entropy within each "window" in chaotic region and on U-sequence RLaRb period points, we also get the relation of hR*Q(f)=(l/2)hQ(f). Because we carry out our proofs on the basis of M.S.S. rule and "*" composition law, the results in this paper are universal to all the one-dimensional unimodal maps.

ONE-WAY IMAGE TRANSMISSION THROUGH ONE LAYER AND MULTI-LAYER OF THIN DISTORTING MEDIUM USING FOUR-WAVE MIXING

Lin Hong, Zhang Hong-jun, Dai Jian-hua
Acta Physica Sinica. 1986, 35 (10): 1347 doi: 10.7498/aps.35.1347
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A method of transmitting image through one layer and multi-layer of thin distorting medium using four-wave mixing is presented in this paper. Experimental results of image transmission through one layer and two layers of thin distorter are given, which are in agreement with the theoretical analysis. This method provides a possible way for transmitting image through thick distorting medium.

INVESTIGATION ON ABSORPTION EDGE OF LiNbO3 CRYSTALS WITH DIFFERENT COMPOSITIONS

Liu Si-min, Zhang Guang-yin, Cuo Jian-bin
Acta Physica Sinica. 1986, 35 (10): 1357 doi: 10.7498/aps.35.1357
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In this paper, it is affirmed that the absorption edge below 3.8 eV is attributable to indirect transition, the rational ownerships of three straight-line parts of spectral line are obtained by studing the a1/2-hν curve of LiNbO3 crystals with different compositions. According to the relation between LiNbO3 lattice constant and compositions, we are sure that the energy band structure change with composition. Redfield's and ours expermental results of absorption edge are explained.
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