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Brazilian Journal of Physics, Volume: 32, Número: 1, Publicado: 2002
  • Foreword

  • Neutron anisotropy and X-ray production of the FN-II dense plasma focus device

    Castillo, F.; Herrera, J.J.E.; Rangel, J.; Alfaro, A.; Maza, M.A.; Sakaguchi, V.; Espinosa, G.; Golzarri, J.I.

    Resumo em Inglês:

    The FN-II Dense Plasma Focus is a small (< 5kJ ) Mather type device, where the dependence of neutron yield and its anisotropy, in terms of deuterium filling pressure, and the neutron emission angular distribution have been studied. Two diferent electrode configurations have been tested, showing that their geometry plays an important role both on neutron yield and anisotropy. Time integrated anisotropy has been measured with silver activation counters, on a shot to shot basis. CR-39 nuclear track detectors are used to determine the angular distribution of neutrons, averaged over tens of shots, showing that an isotropic pedestal accounts for 70% of the emission, while the anisotropy component accounts for the remaining 30%. The neutron yield shows a tendency to increase with anisotropy, as well as with the emission of hard X-rays observed on-axis. Scintillator- photomultiplier detectors show a slight Doppler shift in the neutron energy at backward angles, supporting the beam-target mechanism. Additional information has been obtained from time inte- grated X-ray diagnostics, which include filtered multi-pin-hole cameras.
  • Neoclassical ion transport in the edge of axially-symmetric arbitrary cross-section tokamak with plasma subsonic toroidal flows

    Severo, J.H.F.; Tsypin, V.S.; Nascimento, I.C.; Galvão, R.M.O.; Tendler, M.; Fagundes, A. N.

    Resumo em Inglês:

    General metrics of large aspect ratio tokamaks is used in the paper. General expressions for the neoclassical poloidal plasma rotation <img src="http:/img/fbpe/bjp/v32n1/03eq01.gif"> and radial ion heat flux gammaTi are obtained. Their dependence on the squared Mach number alpha = <img src="http:/img/fbpe/bjp/v32n1/03eq02.gif" align="absMiddle"> is analyzed (here Uzetai is the ion toroidal velocity and c s is the sound velocity, respectively). Some interesting peculiarities of this dependence are emphasized.
  • Industrial applications of plasma focus radiation

    Moreno, C.; Vénere, M.; Barbuzza, R.; Del Fresno, M.; Ramos, R.; Bruzzone, H.; González, Florido P. J.; Clausse, A.

    Resumo em Inglês:

    Applications of a small-chamber Plasma Focus used as portable radiation generator is presented. The device was designed to maximize the fluence. The mean neutron yield was 3 x 10(8) neutrons of 2.45 MeV per shot, corresponding to a 10(6) neutrons/cm² fluence on the external surface of the chamber. A technique to detect the presence of water in the neighborhood of a compact Plasma Focus is presented. The measuring system is composed by two neutron detectors operated simultaneously on every shot. The first detector is used to register the PF neutron yield in each shot; whereas the other one was designed for detecting neutrons scattered by the blanket. The results indicate that the system is able to detect water contents of few percents in volume. The correlation of the counts recorded by thedetectors located at different positions was mapped with the water distribution around the neutron source. The complete detecting system is very simple and inexpensive. Among many other potential applications, the technique is specially suited for soil humidity prospection. X rays radiation emitted by the compact Plasma Focus operated in Deuterium has been used for introspective radiographic imaging of metallic objects. The samples were located about 1 m away from the PF chamber wall. High-sensitivity, fast-response commercial radiographic film was used as x-ray detector. A set of experimental images is presented demonstrating a very high penetration power of the x-ray beam. Among many other applications, the presented technique is specially suited for introspective visualization of pieces manufactured on metal. Radiographic projections of a stainless steel BNC elbow taken at 8 different angles were processed to reconstruct transversal cuts of the piece. A computer technique for 3D reconstructions was combined with radiographic images of objects X-rayed with a compact plasma focus. The technique is able to automatically determine the position of the rotation axis, reconstruct the 3D-attenuation map, and display inner cuts. The system was demonstrated in introspective tomographic imaging of a stainless steel BNC elbow.
  • Tokamak NOVA-UNICAMP recent results

    Daltrini, A.M.; Machida, M.; Monteiro, M.J.R.; Kaminishikawahara, C. O.

    Resumo em Inglês:

    Tokamak NOVA-UNICAMP is a small tokamak with iron core and conducting shell stabilization built to study plasma-wall interaction and optical diagnostic development. Characteristic plasma behavior was the appearance of 2-3 kHz spike oscillation during entire discharge with very high X-ray activity which prevent our optical diagnostic development. By modifying capacitance and charging voltage on OH and vertical field banks, in order to obtain similar discharge current shape, most of 2-3 kHz spikes has been taken out, although some activities still remains to be analyzed. Nevertheless, the high X-ray activity which jeopardize our optical measurements is completely eliminated and time varying parameter as ion temperature is now possible to be followed during whole discharge.
  • Magnetic coil system for the TCABR tokamak

    Saettone, E.A.; Vannucci, A.; Degasperi, F.T.; Galvão, R.M.O.; Kuznetsov, Y.; Sanada, E.K.; Nascimento, I.C.

    Resumo em Inglês:

    In this work, we discuss the preliminary analysis of some disruptive plasma discharges in the TCABR tokamak, operating in the high density limit. The Fourier analysis of the MHD activity was greatly facilitated because the magnetic coils inside the TCABR were installed as to take into consideration the toroidal geometry of the system, in a straight forward manner. What we have observed is that the m = 3, 4 and 7 MHD components dominate during almost the whole discharge duration, whereas the m = 2 MHD mode increased substantially just before the occurrence of a major disruption. Also, we could estimate the angular velocity of the magnetic islands, which was observed to increase up to three times just before the major disruption.
  • Calculations of alfvén wave heating in TCABR tokamak

    Elfimov, A.G.; Galvão, R.M.O.; Galkin, S.A.; Ivanov, A.A.; Medvedev, S.Yu.

    Resumo em Inglês:

    A two dimensional code ALTOK, which is designed for calculating plasma heating due to radio frequency fields in the Alfvén and in Ion Cyclotron Ranges of Frequencies in axisymmetric tokamaks, is used to analyze Alfvén wave absorption in multi species plasmas in TCABR (Tokamak Chauffage Alfvén Brasilien) [Nucl.Fusion 30, 503 (1996)]. A good agreement between the results obtained with ALTOK code calculations and with a two dimensional kinetic code [Phys. Plas., 6 (1999) 2437] is shown for Alfvén wave dissipation in hydrogen plasmas. The global Alfvén wave resonance of the m = 0 mode is found to be the best candidate to explain some heating regimes in TCABR.
  • Ergodic magnetic limiter for the TCABR

    Silva, Elton C. da; Caldas, Iberê L.; Viana, Ricardo L.

    Resumo em Inglês:

    In this work it is considered the effect of an ergodic magnetic limiter on the plasma confined in the TCABR tokamak. The poloidal distribution of the limiter currents is determined taking into account the toroidal geometry of this tokamak. The plasma equilibrium field is analytically obtained by solving the Grad-Schlüter-Shafranov equation in polar toroidal coordinates. The perturbing limiter field is obtained as a vacuum field by solving the Laplace equation. Supposing the limiter action as a sequence of delta-function pulses, a symplectic map is derived by using a Hamiltonian formulation for the perturbed field line. Examples are given to illustrate the influence of this design on the topology of the perturbed field line structure.
  • Digital control of plasma position in damavand tokamak

    Emami, M.; Babazadeh, A. R.; Roshan, M. V.; Memarzadeh, M.; Habibi, H.

    Resumo em Inglês:

    Plasma position control is one of the important issues in the design and operation of tokamak fusion research device. Since a tokamak is basically an electrical system consisting of power supplies, coils, plasma and eddy currents, a model in which these components are treated as an electrical circuits is used in designing Damavand plasma position control system. This model is used for the simulation of the digital control system and its parameters have been verified experimentally. In this paper, the performance of a high-speed digital controller as well as a simulation study and its application to the Damavand tokamak is discussed.
  • TCABR data acquisition system update

    Fagundes, A.N.; Sá, W.P. de; Dantas, A.L.

    Resumo em Inglês:

    We describe recent proposed updates for TCAqs[1], the TCABR data acquisition system. Stable and in regular use, it shall be enriched in new future for better performance. Recent acquisitions widen the TCAqs capabilities in hardware and software, including new VME stations and special GPIB cards that will allow for the creation of local instrumentation network.
  • Multichannel photomultiplier for multipass thomson scattering diagnostics

    Monteiro, M. J. R.; Machida, M.; Daltrini, A. M.; Berni, L. A.

    Resumo em Inglês:

    The application of a new multichannel 64 parallel amplification 10 stage photomultiplier arranged in 8 x 8 matrix of 20.32 mm x 20.32 mm, detector XP1752 from Philips, for laser light scattering diagnostics is now under development. Signal intensity calibration curve for eight parallel and individual channels, as well as cross talk between channels was measured. Also, Rayleigh scattering on nitrogen gas, normally used as optical calibration method for electron density measurements in Thomson scattering was realized, and the intensity of both detectors was compared making measurements with a tungsten lamp.
  • The analysis of alfvén wave current drive and plasma heating in TCABR tokamak

    Ruchko, L.F.; Lerche, E.A.; Galvão, R.M.O.; Elfimov, A.G.; Nascimento, I.C.; Sá, W.P. de; Sanada, E.; Elizondo, J.I.; Ferreira, A.A.; Saettone, E.A.; Severo, J.H.F.; Bellintani, V.; Usuriaga, O.N.

    Resumo em Inglês:

    The results of experiments on Alfvén wave current drive and plasma heating in the TCABR tokamak are analyzed with the help of a numerical code for simulation of the diffusion of the toroidal electric field. It permits to find radial distributions of plasma current density and conductivity, which match the experimentally measured total plasma current and loop voltage changes, and thus to study the performance of the RF system during Alfvén wave plasma heating and current drive experiments. Regimes with efficient RF power input in TCABR have been analyzed and revealed the possibility of noninductive current generation with magnitudes up to ~8 kA. The increase of plasma energy content due to RF power input is consistent with the diamagnetic measurements.
  • Theoretical studies of non inductive current drive in compact toroids

    Farengo, R.; Lifschitz, A.F.; Caputi, K.I.; Arista, N.R.; Clemente, R.A.

    Resumo em Inglês:

    Three non inductive current drive methods that can be applied to compact toroids are studied. The use of neutral beams to drive current in field reversed configurations and spheromaks is studied using a Monte Carlo code that includes a complete ionization package and follows the exact particle orbits in a self-consistent equilibrium calculated including the beam and plasma currents. Rotating magnetic fields are investigated as a current drive method for spherical tokamaks by employing a two dimensional model with fixed ions and massless electrons. The time evolution of the axial components of the magnetic field and vector potential is obtained by combining an Ohm's law that includes the Hall term with Maxwell's equations. The use of helicity injection to sustain a flux core spheromak is studied using the principle of minimum rate of energy dissipation. The Euler-Lagrange equations obtained using helicity balance as a constraint are solved to determine the current and magnetic field profiles of the relaxed states.
  • Fast neutral lithium beam for density and its fluctuation measurements at the boundary regions of ETE tokamak

    Oliveira, R.M.; Ueda, M.; Vilela, W.A.

    Resumo em Inglês:

    A Fast Neutral Lithium Beam Probe (FNLBP) is being developed, in order, to perform measurement of the boundary plasma density in discharges of the Spherical Tokamak ETE, recently built at LAP/INPE. This plasma diagnostic method is adequate for use in fusion devices because it does not perturb the plasma and it provides data with high space and time resolution for the entire discharge lifetime. To obtain reliable measurements, however, FNLB probing depends on high signal-to-noise ratio (S/N) during beam emission spectroscopy of the Li beam injected into the plasma, specially if density uctuation measurements are sought. Hence, our effort is been focused in the achievement of high intensity Li0 output. Recently, probing of a low temperature (T ~ 5eV) and low density target plasma (n ~ 10(10) cm-3) produced in a plasma immersion ion implantation experiment (PIIIE) was performed by a2-5keV FNLBP. The method used for the density determination of this glow discharge plasma was based on the comparison of the fluxes of 6708 Å photons emitted from Li0 beam injected into nitrogen gas that filled the PIIIE chamber and from the same beam injected into the plasma discharge. For this case, the attenuation of the beam was neglected. The plasma density measured was n e = 8.5 × 10(10) cm-3 for pressure of operation of p = 7.0 × 10-4 mbar and n e = 7.2 × 10(10) cm-3 for p = 4.6 × 10-4 mbar. These results are in good agreement with Langmuir probe data. The success of this measurement was only possible after a tenfold increase in the Li+ output and the increase of the lifetime of Li source by vitrification of the beta-eucryptite source, besides the optimization of the optical detection system and the neutralization of the beam. Presently, a new 10keV FNLBP is been developed to probe ETE plasma. For this case, where the Li beam will be strongly attenuated by the high density plasma (n e ~ 10(13) cm-3), the method of density reconstruction from the whole photon flux profile will be used. All the improvements performed during the operation of the old FNLBP device, will be implemented on this new FNLBP.
  • Plasma recombination in runaway discharges in tokamak TCABR

    Soboleva, T.K.; Galvão, R.M.O.; Krasheninnikov, S.I.; Kuznetsov, Yu.K.; Nascimento, I.C.

    Resumo em Inglês:

    A new regime of runaway discharges has been observed in the TCABR tokamak. One of the most distinctive features of this regime is the effect of plasma detachment from the limiter. This experimental fact can only be explained by the volume recombination, which requires a low-temperature plasma. The analysis of the energy and particle balance in the system plasma-relativistic runaway beam in TCABR, which takes into account only the collisional mechanism of the heat transfer from runaways to thermal electrons, predicts electron temperatures Te = 0.1 - 2 eV; the temperature decreases with the neutral density increase. The recombination process with the rate constant around 10-16 m³/s is required for the explanation of plasma density behavior in the experiment. At present, it is difficult to conclude about the mechanism of recombination. More reliable and detailed experimental data, mainly about the plasma temperature, are necessary.
  • Statistics of turbulence induced by magnetic field

    Ferreira, A.A.; Heller, M.V.A.P.; Baptista, M.S.; Caldas, I.L.

    Resumo em Inglês:

    Using the TCABR tokamak facility, we analyze turbulent electrostatic fluctuations in a stationary toroidal magnetoplasma, created by radio-frequency waves and confined by two different toroidal magnetic fields. The increase of toroidal magnetic field leads to gradients in the mean plasma radial profiles and the onset of electrostatic turbulence. For the turbulent fluctuations, we show that the statistics of data collected using fixed sampling time is the same than the statistics of the time in which measurements of the data return to a specified reference interval of values. With these statistical analyses we find special invariant probability distributions, power-scaling laws for some average quantities, and long-range correlation for their oscillations. These observations suggest that turbulence has recurrent properties, as those observed in recurrent fully chaotic low-dimensional systems. Therefore, evolution of measurements of low-dimensional dynamical systems can be used to describe the recurrence observed in the tokamak edge turbulence.
  • X-ray and neutron emission studies in a new Filippov type plasma focus

    Babazadeh, A.R.; Roshan, M.V.; Habibi, H.; Nasiry, A.; Memarzadeh, M.; Banoushi, A.; Lamehi, M.; Sadat Kiai, S.M.

    Resumo em Inglês:

    We have performed experimental comparative studies of the x-ray and neutron emission generated by the new Filippov-type plasma focus "Dena", (90 kJ, 25 kV, 288muF) in the pressure range of 0.6-1 torr. Time-integrated and time-resolved detectors, together with an x-ray pin-hole camera, along with a Be filter of 10mum thickness have been used. For a working gas of neon and a at insert anode, the maximum soft and hard x-rays (SXR-HXR) yield obtained was 16 V and 1.5 V/shot over a 4pi solid angle, respectively, for a charging voltage range of 16-20 kV. As for the argon gas, the similar results such as 3.5 and 2 V/shot have been found, leading to a total conversion eAciency of x-ray emission of 0.09 % (for neon) and 0.03 % (for argon) of the stored energy. These efficiencies have been improved by the employment of a conic insert anode up to 0.4% and 0.1%. With deuterium puffing gas and a at insert anode, the maximum emission yield has been found to be 2.5 V for SXR and 1 V for HXR/shot which produce an ultimate emission profile width (FWHM) of 70-90 ns for x-rays and neutrons, giving rise to a maximum neutron yield of 1.2 × 10(9). Nevertheless, the maximum yield has been increased up to 5.5 times with the conic insert anode. In order to increase the neutron yield, we have introduced a krypton admixture to the deuterium filling gas and found that, for a krypton pressure of about 0.1 torr, the neutron yield increases by a factor of 3.5 for the flat insert and 1.5 for the conic insert anodes.
  • Statistics of plasma fluctuations in runaway discharges in TCABR tokamak

    Baptista, M.S.; Caldas, I.L.; Sá, W.P. de; Elizondo, J.I.

    Resumo em Inglês:

    In this work we analyze the spikes in the Halpha emission, and density turbulence in runaway discharges in the TCABR tokamak. For the plasma edge density fluctuations, we find a symmetric-recurrent-type turbulence, with the same statistics found in measures of low-dimensional recurrent chaotic systems. For the plasma core fluctuations, we note that the line density oscillations are synchronized to the Halpha oscillations. In addition, we suggest that both the onset of the Halpha spikes and the line density oscillations are triggered by a process similar to the bifurcation responsible for the firing of neurons.
  • Role of the tokamak ISTTOK on the EURATOM Fusion Programme

    Fernandes, H.; Varandas, C.A.F.; Cabral, J.A.C.

    Resumo em Inglês:

    This paper describes the role of the tokamak ISTTOK on the development of the portuguese fusion research team, in the frame of the EURATOM Fusion Programme. Main tasks on education and training, control and data acquisition, diagnostics and tokamak physics are summarized. Work carried out on ISTTOK in collaboration with foreign teams is also reported.
  • Plasma resistivity determination in runaway discharges from positive voltage spikes on TCABR tokamak

    Kuznetsov, Yu. K.; Nascimento, I. C.; Galvão, R. M. O.; Tsypin, V. S.

    Resumo em Inglês:

    Plasma resistivity is estimated in runaway discharges on TCABR tokamak from the decay of positive voltage spikes using method developed in I. El Chamaa Neto et al., Phys. Plasmas 7, 2894 (2000). In this regime, the plasma detachment from the limiter is observed experimentally indicating that plasma recombination is the main process of plasma particle losses. In order to investigate if this process is actually taking place, measurements of electron temperature in the plasma are necessary. The electron temperature deduced from the plasma resistivity is in the range 0.2 - 1.5 eV.
  • Effect of the vacuum vessel on the measurements of mirnov oscillation in TCABR

    Kucinski, M. Y.; Kuznetsov, Yu. K.

    Resumo em Inglês:

    Magnetic field due to instabilities in plasma is expected to be reflected in the conductive vessel wall. We evaluate the reflection effect in the Brazilian tokamak TCABR. The magnetic field due to the plasma is represented by a toroidal harmonic function in vacuum and the reflected field is written as a series of harmonic functions in vacuum, generated in the external region. The conclusion is that a signal originated in the plasma may be strongly deformed, close to the wall. Even far from the wall, around the plasma, the effect of the wall may still be considerable.
  • Effect of suprathermal electrons on central plasma relaxation oscillations during localized electron cyclotron heating on the HL-1M Tokamak

    Liu, Y.; Guo, G.C.; Ding, X.T.; Wong, K.L.

    Resumo em Inglês:

    In this paper we discuss the typical behavior of HL-1M tokamak plasmas during ECRH. A large variety ofsawtooth types have been observed at different ECH power deposition locations. The observed central MHD activities detected by the soft x-ray diode array include saturated sawtooth, partially saturated sawtooth, double sawtooth, and strong m=1 bursts superimposed on the ramp phase of sawtooth. Complete suppression of sawtooth is achieved during ECRH, when the heating power is applied on the high-field side of low-density plasmas, and exceeds a threshold value of power. The m=1 bursts riding on the ramp phase of sawtooth can only be excited when the ECRH location is near the q=1 surface at the high field side. The conditions under which the various relaxation activities are produced, or suppressed, are described. Experimental results imply that the energetic electrons, generated during ECRH, are responsible for the modification or stabilization or excitation of the instability. Near the q=1 surface, while the passing electrons play a roleto reduce the shear and tend to stabilize the sawtooth activity, the barely-trapped electrons play a role to enhance or drive aninternal kink instability.
  • TCABR interferometer

    Elizondo, J.I.; Korneev, D.; Nascimento, I.C.; Sá, W.P. de

    Resumo em Inglês:

    The microwave interferometer of the TCABR tokamak is presented in this paper, describing in some detail the phase detection procedure and other technical features. The system has three transceivers and seven waveguide channels coupled to horn antennas. The operating frequency, 140 GHz, allows measuring the electronic density of the TCABR plasmas avoiding cutoff and with relatively small refraction effects. The high intermediate frequency, 18 MHz, together with the large pass-band lter and heterodyne detection system allows measuring fast density changes without loss of signal. Some experimental results and calculations are presented.
  • Toroidal geometry and plasma column displacement corrections in the analysis of Mirnov oscillations

    Araújo, M.S.T.; Vannucci, A.; Oliveira, K.A.

    Resumo em Inglês:

    The influence of the toroidal geometry, and the plasma column displacement, over the usual tokamak poloidal magnetic field configuration was investigated for circular plasmas through a series of simulations. The results obtained clearly showed the existence of a change in phase modulation of the Mirnov signals, which are not usually considered when the magnetic signals are Fourier analyzed in the frame of cylindrical approximation, that is, by neglecting any possible toroidal effect. Furthermore, if the occasional displacements of the plasma column in tokamaks are considered, some differences on the mode composition are also observed. These discrepancies, however, do not seem to affect the analysis of the magnetic signals as strongly as in the former case, when toroidal effects are neglected.
  • Dense plasmas research in the Chilean Nuclear Energy Commission: past, present and future

    Soto, Leopoldo; Silva, Patricio; Moreno, José; Zambra, Marcelo; Sylvester, Gustavo; Esaulov, Andrey; Altamirano, Luis

    Resumo em Inglês:

    A review of the dense transient plasmas researches, developed in the Chilean Nuclear Energy Commission, is presented. A brief summary of the researches done in collaboration with the Pontificia Universidad Católica de Chile, between 1993 to 1997, is shown. In addition, the program "Plasma Physics in Small Devices", developed at the Comisión Chilena de Energía Nuclear since 1999 is delineated. The diagnostics development and results obtained during three experiments using small pinch devices are shown: a capillary discharge; a Z pinch driven by a small generator; and a low energy plasma focus. The experiments were complemented by magnetohydrodynamics numerical calculations, in order to assist the design and physical interpretation of the experimental data. The diagnostics techniques used in these experiments include current and voltage monitors, multipinhole camera, plasma image using a ICCD camera gated from 3 to 20 ns, holographic interferometry, and vacuum ultraviolet spectroscopy. Recently, the pulse power generator SPEED 2, a medium energy and large current device (187kJ, 4MA, 300kV, 400ns, dI/dt ~ 10 13 A/s), has been transferred from the Düsseldorf University to the Comisión Chilena de Energía Nuclear. Future experiments, and the perspectives of using this device, are also discussed.
  • Design and testing of ECE radiometer for Sinp-Tokamak

    Ray, R.; Hugenholtz, C. A. J.; van de Pol, M. J.

    Resumo em Inglês:

    A multi channel ECE Radiometer, in the frequency range of 75 - 110 GHz, has been designed, constructed and tested for the SINP-Tokamak to diagnose second harmonic X-mode electron cyclotron emission (ECE). This frequency range covers approximately 80% of the plasma cross section in case of a magnetic eld of B = 1.5 T. For the maximum field of the SINP-Tokamak B = 2.0 T, about 50% is covered. The ECE radiation is received by a single horn antenna with a gain of approximately 30 dB. To increase the spatial resolution perpendicular to the line of sight, a focusing lens is employed. The incoming radiation power is split into two branches by a 3dB coupler. Before down conversion of the input spectrum, the upper and the lower side band are selected respectively by means of a high pass and a low pass filter. Behind the filters, identical components are employed. The local oscillator frequency is 92 GHz for both mixers. The IF frequency range after down conversion is 2 to 18 GHz. The IF spectrum is amplified by two amplifiers with a total gain of approximately 60 dB. The outputs of these amplifiers are split into 6 branches. The frequency selection is made by band pass filters and the received power is detected by Schottky diode detectors followed by video amplification and ltering. The data is recorded by an ADC with 1 MHz sampling rate. The radiometer has been tested and calibrated with a high temperature blackbody radiator. The effective input noise temperature for the radiometer channels is found to be in the order of 0.1 eV. The linear regime of operation extends up to an input power which corresponds to an electron temperature of approximately 200 eV. Above this temperature the 1 dB compression point of the Schottky diode detectors is exceeded and the IF gain should be reduced. This can be easily done by incorporating appropriate attenuator behind the IF amplifiers.
  • Studies of mode lock instability in the HL-1M tokamak

    Qingwei, Yang; Yan, Longwen; Qian, Jun

    Resumo em Inglês:

    Locked mode instability in the HL-1M tokamak has been investigated in this paper. In the HL-1M tokamak the mode lock instability often appears in with low density discharges (<img src="http:/img/fbpe/bjp/v32n1/27eq01.gif" align="absMiddle"> < 1 × 10(19) m-3). The precursor perturbations on both soft-X rays and Mirnov signals simultaneously increase before mode locking. Their frequencies are the same and gradually decease, which indicate that the perturbation is global. Their existence time-scale is about 10ms. The plasma will suddenly stop rotating when the fluctuation amplitude or frequency reaches a threshold. Mode lock instability can often cause major disruptions. The rotation frequency is decreased to about 3kHz before mode locking in the HL-1M tokamak, which is consistent with the theoretical model.
  • Powerful quasi-steady-state plasma accelerator for fusion experiments

    Tereshin, V.I.; Chebotarev, V.V.; Solyakov, D.G.; Garkusha, I.E.; Makhlaj, V.A.; Trubchaninov, S.A.; Mitina, N.I.; Morozov, A.I.; Tsarenko, A.V.; Wuerz, H.

    Resumo em Inglês:

    The full-block quasi-steady-state plasma accelerator (QSPA) device and its operation as well as some possible applications of powerful plasma streams, generated by the QSPA, are described in this paper. The main attention was paid to plasma parameters measurements in the different regimes of operation. Analysis of efficiency of powerful plasma streams penetration into mirror magnetic field and plasma magnetization taking place under their propagation along the uniform magnetic field is carried out. Some results of thermal quench disruption simulations carried out with irradiation of solid targets by high energy plasma streams are presented in this paper.
  • Deuterium plasma focus measurements using solid state nuclear track detectors

    Springham, S.V.; Lee, S.; Moo, S.P.

    Resumo em Inglês:

    A camera obscura technique was used to investigate the spatial distribution of fusion protons emitted from a small deuterium plasma focus device operated in its neutron-optimized regime (14 kV, 3 kJ, and 400 Pa D2 gas). An indium-foil activation detector was employed simultaneously to measure the shot-to-shot neutron yield. The camera obscura was positioned on the forward axis of the plasma focus, 12 cm from the tip of the hollow copper anode, covering a conical field-of-view of half-angle slightly less than 20 degrees. The nuclear track detector material PM-355 was used in the camera focal plane to register protons from the ²H(d, p)³H reaction, hence imaging the spatial distribution of fusion occurring in the plasma focus. A kapton film covering the camera entrance pupil served to protect the detector from the hot plasma jet; it also stopped completely all energetic charged particles other than the (<img src="http:/img/fbpe/bjp/v32n1/sigual.gif" align="absMiddle"> 3 MeV) fusion protons. Following chemical etching of the detector plates, the track parameters - size, circularity, average-grey-value and (x-y) position - |were measured by an automated scanning system comprising an optical microscope equiped with a CCD camera, motorized stage and focus-adjust, and interfaced to a PC computer. From the accumulated track data, representing 119 plasma focus shots, the imaged fusion density profile was obtained. A detailed Monte Carlo simulation program was used to interpret this profile. The results indicate that the beam-target mechanism, in which energetic deuterons emitted in a forwardly directed cone from the plasma focus pinch interact with the cold deuterium gas, accounts for 90 to 96% of the fusion production for our device. There is however clear evidence for a non-zero (4 to 10%) contribution emitted directly from the pinch region.
  • Collisionless dissipation of radio-frequency waves in axisymmetric tokamak plasmas

    Grishanov, N.I.; Azevedo, C.A. de; Neto, J.P.

    Resumo em Inglês:

    Contributions of trapped and untrapped particles to the transverse and longitudinal dielectric permittivity elements are present for radio-frequency waves in a tokamak with circular cross-sections of the magnetic surfaces and arbitrary aspect ratio. Imaginary parts of the longitudinal permittivity elements are important to estimate the wave power absorbed by electron Landau damping (e.g., during the plasma heating and current drive generation) in the frequency range of Alfvén, fast magnetosonic, and lower hybrid waves. Whereas, imaginary parts of the transverse permittivity elements are necessary to estimate the cyclotron-resonant wave dissipation at the fundamental cy-clotron frequency of ions and/or electrons. The dissipated wave power is expressed by summation of terms including the separate contributions of trapped and untrapped particles to the imaginary parts of both the diagonal and non-diagonal elements of the dielectric permittivity. The concrete computations are carried out for a tokamak plasma with the main TCABR parameters.
  • Hot-spots in plasma-focus discharges as intense sources of different radiation pulses

    Jakubowski, L.; Sadowski, M.J.

    Resumo em Inglês:

    The paper concerns pulsed discharges of the Plasma-Focus (PF) type, and in particular the formation of micro-regions (so-called hot spots) with very high electron concentration and relatively high electron temperature. Particular attention is paid to the correlation between X-ray pulses emitted from the hot spots and the emission of pulsed electron beams, ion beams, and the pulsed neutron fluxes.
  • SST and ADITYA tokamak research in India

    Bora, Dhiraj

    Resumo em Inglês:

    Steady state operation of tokamaks plays an important role in high temperature magnetically confined plasma research. Steady state Superconducting Tokamak (SST) programme in India deals with the development of various technologies in this direction. SST-1 [1] machine has been engineered and is being fabricated at the Institute for Plasma Research. The objectives of the machine are to study physics of plasma processes under steady state condition and develop the technologies related to steadystate operation. Various sub-systems are being prototyped and developed. SST-1 is a large aspect ratio machine with a major radius of 1.1 m and a plasma minor radius of 0.2 m with elongation of 1.7 to 1.9 and triangularity of 0.5 to 0.7. It has been designed for 1000 sec operation at 3 T toroidal magnetic eld. Neutral beam Injection and Radio frequency heating systems are being developed to heat the plasma. Lower hybrid Current Drive system would sustain 200 kA of plasma current during 1000 sec operation. ADITYA tokamak [2] has been upgraded with new diagnostics and RF heating systems. Thomson Scattering and ECE diagnostics have been operated. 200 kW Ion Cyclotron Resonance Heating (ICRH) and 200 kW Electron Cyclotron Resonance Heating (ECRH) systems have been successfully commissioned. RF assisted initial breakdown experiments have been initiated with these systems.
  • The spacetime of a Dirac magnetic monopole Regular Articles

    Lima, Marcelo Costa de; Soares, Ivano Damião

    Resumo em Inglês:

    We construct a spacetime whose only source of curvature is a Dirac magnetic monopole, and whose geometry inherits the structure of lines of singularities of the monopole electromagnetic potentials. The spacetime has the topology S³ × R, is stationary and asymptotically at but not asymptotically Minkowskian, with its at null infinity having the topology of S³. These mild pathologies, as acausality and string structure, allow the spacetime configuration to have a gravitational magnetic mass, which results proportional to the charge mu of the monopole. This suggests that the Dirac monopole may be the source of magnetic mass in gravitational configurations, which has no Newtonian analogue. Alsomu has the role of a NUT parameter in the metric of the spacetime, suggesting that the charge of the monopole can provide a physical realization of the NUT parameter.
  • Compactification of gauge theories and the gauge invariance of massive modes Regular Articles

    Amorim, R.; Barcelos-Neto, J.

    Resumo em Inglês:

    We study the gauge invariance of the massive modes in the compactification of gauge theories from D = 5 to D = 4. We deal with Abelian gauge theories of rank one and two, and with non-Abelian ones of rank one. We show that Stückelberg fields naturally appear in the compactification mechanism, contrarily to what usually occurs in literature where they are introduced by hand, as a trick, to render gauge invariance for massive theories. We also show that in the non-Abelian case they appear in a very different way when compared with their usual implementation in the non-Abelian Proca model.
  • Sewing string tree vertices with ghosts Regular Articles

    Sandoval Junior, Leonidas

    Resumo em Inglês:

    It is shown how to sew string vertices with ghosts at tree level in order to produce new tree vertices using the Group Theoretic approach to String Theory. It is then verified the BRST invariance of the sewn vertex and shown that it has the correct ghost number.
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