Vol. 33, No. 4 (1984)
In this article, the restraint of the spontanueous tearing modes caused by RHF is analyzed and calculated by solving the resistive MHD equations. We prove that the growth rate of the tearing modes of m=2 can be reduced about two times by the helical fields. The restraint of the tearing modes by the boundary controlled field is also discussed and calculated numerically.
1984, 33 (4): 457-464. doi: 10.7498/aps.33.457
The effect of confinement on the efficiency of ion stochastic heating with LH waves has been discussed. Increasing plasma current or making the current distribution concentrate close to the center can improve the confinement of fast ions and raise heating efficiency.
1984, 33 (4): 465-471. doi: 10.7498/aps.33.465
Soft X-ray diagnosis is a important method in the research of tokamak plasma instability. In this paper, we give the result of soft X-ray measurment in CT-6B tokamak by using Au(Si) surface barrier detector array, and present the spatial distributions of sofr X-ray emission for various plasma instability in our device.
1984, 33 (4): 472-476. doi: 10.7498/aps.33.472
We report here for the first time a two stage nonmagnetic high pressure equipment foi studying various transport phenomena. The structure and the principle of the design are described. the experimental results are presented. A completely hydrostatic pressure of 28 kbar is obtained. With this equipment, the resistivity and Hall coeffecient for Ge, InSb and HgCdTe have been measured under pressure up to 25 kbar. The energy gaps and the carrier mobilities as functions of pressure for these materials have been determined, the results are in good agreement with those of other experiments.
1984, 33 (4): 477-485. doi: 10.7498/aps.33.477
The interaction between hydrogen and defects in neutron irradiated n-type FZ silicon has been studied with deep level transient spectroscopy, transient capacitance at constant temperature and infrared absorption spectroscopy. It has been observed that the absorption peaks of infrared spectroscopy corresponding to the interstitial hydrogen reduce after neutron irradiation. In the unannealed neutron irradiated n-type FZ silicon grown in hydrogen, a new defect-Z center has been observed for the first time. Because the energy level of the Z center (Ec-0.20 eV) is very close to the energy level of the A center (Ec-0.16 eV) and the concentration of the former is much lower than that of the latter. In order to detect the Z center, neutron dose has been selected so that the Fermi level locates at several kT below the energy level of A center. In all probability the Z center is a hydrogen-vacancy complex. The possible electron structure of this center is discussed.
A METHOD FOR MEASURING CARRIER CAPTURE CROSS SECTIONS OF DEEP CENTERS WITH ELIMINATING THE INFLUENCE OF INHOMOGENEOUS CARRIER DISTRIBUTION
1984, 33 (4): 486-495. doi: 10.7498/aps.33.486
Zylbersztejn had pointed out that the in homogeneous distribution of carriers in the edge region of the space charge region exerts a disadvantageous influence on the measurement of carrier capture cross sections of deep centers and suggested a method to eliminate this effect. However, his method can only be used to measure carrier capture cross sections at low temperature for quite deep levels. We suggest a new method to remove the harmful impact of inhomogeneous distribution of carriers (including both the inhomogeneous distribution of the carriers in. the edge region and that due to nonuniform shallow donors and acceptors) on the basis of an analysis of the dynamic process of capacitance transient. This method is not subjeer to the serious restriction of the temperature range of measurement and the situation of the levels under measuring. This is important for the study of the temperature dependence of carrier capture cross sections and the tudy of the carrier capture dynamices. As an example. the method has been used to measure the electron capture cross section of gold acceptor in silicon. The results show that the accuracy of measurement is improved.
1984, 33 (4): 496-507. doi: 10.7498/aps.33.496
By using Lamb's theory, the concrete calculations for the amplitude and frequency-deter mining equations of laser field with arbitrary J values (total angular momentum of energy level) in the transverse magnetic field are made, the analytical expressions of the first- and third-order coefficients with arbitrary J values and J=1→2 are obtained. As a concrete applicable example, the beat frequency tuning curve of 6328? He-Ne20 transverse Zeeman laser is successfully explained.
1984, 33 (4): 508-514. doi: 10.7498/aps.33.508
The highly ionized Argon spectrum in the vacuum ultraviolet region from 2000? to 194? is reported. A lot of new spectral lines are observed. Among them, 64 new spectral lines are identified, the new energy levels are found as follows: ArIV 3s23p2(3P)3d2F5/2,7/2, ArIV 3s23p2(1D)3d2S1/2, ArV3s23p3d1D2 and ArVI3p32)P1/2,3/2. Nine energy level values of ArIV3s23p2(3P)3d2P1/2,3/2,ArIV3s23p2(1D)3d2P1/2,3/2,ArIV 3s23p2(1D)3d2D3/2,5/2,ArIV 3s23p2(1D)4s2D3/2,5/2 and ArV 3s23p3d1P1 are revised.
1984, 33 (4): 515-522. doi: 10.7498/aps.33.515
This paper reports the spectra and the excited energy transfer in phosphate glass doped with Nd3+ and Yb3+. The transfer rates are determined experimentally, at different tempcralures. We confirme that the mechanism of energy transfer is a process in which the energy is transferred from 4F3/2(Nd3+) to 2F5/2(Yb3+) and at the same time a single phonon is emitted. The energy back transfer process from Yb3+ to Nd3+ may occur in two possible ways, one is the process 2F5/2(Yb3+)→4F3/2(Nd3+) which is accompanied by the absorption of a single phonon, and the other is the process 2F5/2(Yb3+)→4I15/2(Nd3+), being accompanied by emission of 4 phonons. Therefore Yb3+→Nd3+ transfer rate depends strongly upon the temperature. At room temperature, the transfer time from Nd3+ to Yb3+ and from Yb to Nd are 197μs and 13ms respectively. The efficiency of energy transfer is 47% for Nd3+→Yb3+ and 8% for Yb3+→ Nd3+.
1984, 33 (4): 523-529. doi: 10.7498/aps.33.523
In this paper, the structure of glasses in Li2O(LiCl)2B2O3-Al2O3 system, particularly the influence of Al2O3, is investigated by Raman spectra. For Li2O-B2O3 glasses, with increasing Li2O content, triangular BO3 units change into BO4 tetrahedra and borate groups containing more BO4 are formed. When Li2O content is greater than 35 mol% the metaborate groups begin to form. By replacing B2O3 with Al2O3, the Al3+ ions introduced in glasses take the four-coordination, and AlO4 tetrahedra replace BO4 tetrahedra under the condition of existing sufficient Li2O. However, when Al2O3/Li2O ratio is close to or even greater than unity, part of Al3+ ions are no more in the four-coordination. The experiment also indicates that Raman spectra only depends upon the O/B/Al ratio, showing that the LiCI molecules introduced into the glass are dissociated by glass network. These results can be used to interprete the variations of ionic conductivity with composition.
In this paper, we present experimental results of acoustic emission in bare Nb-Ti single core superconductor and multifilamentary superconducting composite, which have undergone different excitation procedure in Si-rubber potted and dry modes.We have found that AE signals are chiefly generated by conductor motion or flux-ju-inping, but not by flux motion. The starting driving force for motion in Si-rubber potted sample is an order of magnitude higher than that in dry sample.Acoustic emission technique is a possible means for monitoring magnet quench as conductor goes through a series of microslip (or incomplete flux jump) before macromotion.
1984, 33 (4): 538-546. doi: 10.7498/aps.33.538
This paper examines the recognition of underwater targets by the method of the poles and presents the experimental results. The underwater targets used in experiment are hollow cylinders made from different materials, and with different lengths and thicknesses.The features of the underwater target are extracted in the following three steps. First, the impulse response function of the target is identified in the frequency domain by using the short pulse as the incident signal. Second, the method of the so-called "convolution-modified recursive least-squares" is employed to estimate the parameters of the ARMA model of the target. Third, the poles are calculated in the frequency domain. The poles are adopted as the features of the target and considered to be a constant quantity. The computer simulation shows that the anti-noise ability of the method of the pole is 12dB improved compared with the AR model.In the experiment, the matched- filtering classifier is applied to classify the underwater target. The experimental results has demonstrated that 100% correct recognition rate can be achieved for signal-only cases. With white noise added to the echoes, 100% correct recognition rate is still achieved when signal-to-noise ratio is as low as 8dB, and 87.5% correct recognition rate is achieved for S/N = 5dB.
1984, 33 (4): 547-553. doi: 10.7498/aps.33.547
The harmonic generation by resonant absorption in the laser-produced plasmas is analytically investigated by considering the steepened plasma density gradients in the vicinity of the critical density. The efficiency of the second-harmonic generation obtained is in agreement with experimental results. The calculation has also been extended to estimate the efficiency of the third harmonic generation.
1984, 33 (4): 554-560. doi: 10.7498/aps.33.554
Kink instabilities of a sharp boundary plasma with small aspect ratio are studied. The results of numerical calculations show that a conductive shell has a stabilizing effect to some extent and critical beta of toroidal mode number n=1 is the minimum whether there is a conductive shell or not, i.e. the perturbation with n=1 is the most dangerous one. With decrease of aspect ratio, the critical beta increases initially, when a/R = 0.7, it appears as a maximum, when a/R≥0.6, the critical beta values of high beta limit and low beta limit are nearly equal.
1984, 33 (4): 561-563. doi: 10.7498/aps.33.561
In a recent paper, the form factor of radiation scattering in a bi-maxwellian plasma had been calculated, distinguishing the case T⊥≥T∥ form the case T⊥≤T∥ . It had led to different analytic expressions for the form factor in these two cases respectively. The present note shows that it is not necessary to differentiate the cases T⊥≥T∥ and T⊥≤T∥, and the common analytic expression for the form factor can be obtained with better accuracy.
A STUDY OF THE PRETRANSITIONAL BEHAVIOR OF LIQUID CRYSTAL BY TIME-RESOLVED DEGENERATE FOUR-WAVE MIXING
1984, 33 (4): 564-567. doi: 10.7498/aps.33.564
Using time-resolved degenerate four-wave mixing, we have studied the pretransftional behavior of liquid crystal, MBBA, by measuring the temperature dependence of the molecular orientational relaxation time. The experimental result agrees fairly well with the theoretical prediction based on Landaude Gennes mode.
1984, 33 (4): 568-570. doi: 10.7498/aps.33.568
Degenerate four-wave mixing effect due to thermally induced index grating is studied in liquid crystal MBBA. By measuring the relaxation time of the thermal grating decay, we obtain the diffusion coefficient of MBBA in its isotropic phase, i.e., D=8.6×10-4cm·S-1 at T = 45.1℃.
1984, 33 (4): 571-574. doi: 10.7498/aps.33.571
We present a empirical relationship between the superconducting transition temperature, Tc, and the doses of implanted ions, φ, namely Tc=1.13θDexp[-1/(A/(Φ+1)+B)] In comparing with experimental results, the calculated values of Tc by this expression are found in good agreement with them. Finally, we discuss the physical base of this relationship. The analysis indicates that the existance of the impurity band near the fermi surface results in the change of Tc.
1984, 33 (4): 575-578. doi: 10.7498/aps.33.575
In this letter, some comments are presented on the problem proposed and discussed by Ho et al. and Chen in the papers -.
1984, 33 (4): 579-582. doi: 10.7498/aps.33.579
The preparetion of BaFe12O19 ferrite by two hydrothermal synthetic methods is described. The phase transition is studied by magnetic analysis, X-ray diffraction, M?ssbauer effect and electron microscope.
1984, 33 (4): 583-587. doi: 10.7498/aps.33.583
The photoluminescences of GaP (N, Te, Zn) at 77 K have been studied under high pressures. The pressure coefficients of donor Te and exciton levels bound to N, NN1, NN3, and neutral donor Te have been obtained. The pressure behaviors of these levels have been discussed. The zero-phonon line of free excitons in GaP is observed for the first time.
The photoluminescences of nitrogen implanted GaAs samples at 77 K have been studied under high pressures. The luminescence peaks of excitons Nx bound to N trap central cell potential and excitons NT bound to deformation potential were observed. The exprimen-tal value of pressure coefficient of Nx level is 2.8 meV/kbar. Under the atmospheric pressure, the N resonant state is at 179 meV above the conduction band edge. The pressure behaviors of electron-phonon coupling strength of N isoelectronic trap and effective radius of bound exciton are discussed.