摘要:

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is a high power, radio frequency-driven magnetoplasma rocket, capable of exhaust modulation at constant power. While the plasma is produced by a helicon discharge, the bulk of the energy is added in a separate downstream stage by ion cyclotron resonance heating (ICRH). Axial momentum is obtained by the adiabatic expansion of the plasma in a magnetic nozzle. Exhaust variation in the VASIMR is primarily achieved by the selective partitioning of the RF power to the helicon and ICRH systems, with the proper adjustment of the propellant flow. However, other complementary techniques are also being studied. Operational and performance considerations favor the light gases. The physics and engineering of this device have been under study since the late 1970s. A NASA-led, research effort, involving several terms in the United States, continues to explore the scientific and technological foundations of this concept. The research involves theory, experiment, engineering design, mission analysis, and technology development. Experimentally, high density, stable plasma discharges have been generated in Helium, Hydrogen and Deuterium, as well as mixtures of these gases. Key issues involve the optimization of the helicon discharge for high-density operation and the efficient coupling of ICRH to the plasma, prior to acceleration by the magnetic nozzle. Theoretically, the dynamics of the magnetized plasma are being studied from kinetic and fluid perspectives. Plasma acceleration by the magnetic nozzle and subsequent detachment has been demonstrated in numerical simulations. These results are presently undergoing experimental verification. A brisk technology development effort for space-qualified, compact, solid-state RF equipment, and high temperature superconducting magnets is under way in support of this project. A conceptual point design for an early space demonstrator on the International Space Station has been defined. Also, a parametric study of a fast (115 day,) VASIMR-driven human Mars mission has been completed. This paper reviews the progress obtained in all these areas and outlines plans and strategies for continued research. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424142

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We review the problems to be solved to interface wave and Fokker-Planck (FP) codes in view of selfconsistent simulations of heating and current drive in tokamak plasmas in the ion cyclotron range of frequencies. We stress, in particular, that agreement between the power deposition profiles predicted by the wave solver and the quasilinear heating rate predicted by the FP solver should be required as a test of consistency, rather than forced by renormalizing the quasilinear diffusion coefficients. Two examples of successful coupling between the full wave code TORIC and a FP solver are presented, one to investigate electron heating and current drive, the other to quantify the effects of suprathermal ion tails in minority heating experiments. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424143

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The solar corona is the hot, ionized outer atmosphere of the Sun. Coronal plasma expands into interplanetary space as a supersonic bulk outflow known as the solar wind. This tenuous and unbounded medium is a unique laboratory for the study of kinetic theory in a nearly collisionless plasma, as well as magnetohydrodynamic waves, shocks, and jets. Particle velocity distributions in the solar wind have been probed directly by spacecraft (outside the orbit of Mercury), and indirectly by ultraviolet spectroscopy (close to the Sun). Fluctuations in the plasma properties and in electromagnetic fields have been measured on time scales ranging from seconds to years. Despite more than a half-century of study, though, the basic physical processes responsible for heating the million-degree corona and accelerating the solar wind past the Sun’s escape velocity are still not known with certainty. Understanding the basic physics of the solar wind is necessary to predict the Sun’s impact on the Earth’s climate and local space environment. This presentation will review the kinetic origins of several physical processes that are currently believed to be important in depositing energy and momentum in coronal particle velocity distributions. Because ions in the solar wind are heated and accelerated more than would be expected in either thermodynamic equilibrium or via a mass-proportional process, an ion cyclotron resonance has been suggested as a likely mechanism. Other evidence for gyroresonant wave dissipation in the corona will be presented, and possible generation mechanisms for the (as yet unobserved) high-frequency cyclotron waves will be reviewed. The mean state of the coronal and heliospheric plasma is intimately coupled with kinetic fluctuations about that mean, and theories of turbulence, wave dissipation, and instabilities must continue to be developed along with steady state descriptions of the solar wind. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424144

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Neoclassical tearing modes (NTMs) may limit performance in Next Step tokamaks, degrading confinement and possibly leading to disruption. In recent years, excellent experimental and theoretical progress has been made in understanding NTMs and their control. The properties of NTMs and various stabilization schemes are described. Recent experimental results on the stabilization of NTMs using radio frequency waves are reviewed and outstanding issues discussed. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424145

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Internal transport barrier (ITB) modes have been observed with intense, off-axis ICRF heating in Alcator C-Mod. This barrier mode is routinely produced in enhancedD&agr;H-mode, 4.5 T, 0.8 MA discharges (H cyclotron position isr/a∼0.5to the high field side). From TRANSP analysis, the&khgr;effis significantly reduced insider/a∼0.4where the density peaking is observed. With the barrier formation, the toroidal plasma rotation near the axis reversed from co-current (+50 km/sec) to counter current direction (−20 km/sec). In an effort to maintain the barrier, experiments utilizing a third antenna, operated at 70 MHz, allowed central ICRF heating of the ITB mode. Initial experiments with up to 1.2 MW confirmed the energy transport barrier and allowed significant increase in the ion temperatures. With the central heating, the ITB was sustained and the density and impurity peaking were arrested. Furthermore, the central rotation was observed to rotate in the co-current direction with the central heating. We have also had success in detecting electron density fluctuations at the RF frequency with a heterodyned phase contrast imaging diagnostic. The fast wave was observed with peaked density profiles and the measured wave number was in reasonable agreement with the cold plasma dispersion relationship. The mode-converted ion Bernstein wave (IBW) has also been observed in H(3He,D)plasmas The measured wave number is in good agreement with the hot plasma dispersion relationship and indicates the wave is a backward wave as expected from the dispersion relationship, Simulations, utilizing the full wave code TORIC have been critical to this analysis. TORIC has recently been upgraded to allow for higher poloidal mode number resolution. The predicted electron absorbed power more accurately reflects the measured values. Recent success in commissioning a 4-strap (J-port) antenna has allowed the maximum injected power to reach 2.5 MW from this antenna. To obtain this power, some modifications were required: improved protection tile grounding; installed protective shields for Faraday screen ceramic isolators; and modified the transmission line configuration to optimize antenna spectrum. From analysis of the antenna performance, we have further modified the antenna to reduce the RF-plasma interaction, rotated the strip line feeders to make E perpendicular to the ambient B-field and increased the strip line spacing to reduce maximum electric fields. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424146

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

High-Harmonic Fast-Wave (HHFW), a radio-frequency technique scenario applicable to high-beta plasmas, has been selected as one of the main auxiliary heating systems on NSTX. The HHFW antenna assembly comprises 12 toroidally adjacent current elements, extending poloidally and centered on the equatorial plane. This paper reviews experimental results obtained with a symmetrical (vacuum) launching spectrum withk∥=14 m−1at a frequency of 30 MHz. We describe results obtained when HHFW power is applied to helium and deuterium plasmas, during the plasma-current flattop period of the discharge. Application of 1.8-MW HHFW pulse to MHD quiescent plasmas resulted in strong electron heating, during which the central electron temperature,Teomore than doubled from ≈0.05 keV to 1.15 keV. In deuterium plasmas, HHFW heating was found less efficient, with aTeoincrease of the order of 40&percent; during a 1.8-MW HHFW pulse, from ≈400 eV to ≈550 eV. (At HHFW power of 2.4 MW,Teoincreased by 60&percent;, reaching 0.625 keV.) HHFW heating in presence of MHD activity is also discussed. A short neutral beam pulse was applied to permit charge-exchange recombination spectroscopy (CHERS) measurement of the impurity ion temperatureTi.Preliminary CHERS analysis show thatTi≈Teduring HHFW heating. Of special interest are deuterium discharges, where the application of HHFW power was done during the current ramp-up. We observe the creation of large density gradients in the edge region. In the latter case, the density rose spontaneously toneo⩽8×1013 cm−3.©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424147

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

In the initial phase of ITER operation,4Heplasmas could be used in order to avoid activating the machine. The main ICRH scenarios foreseen for ITER4Heplasmas are(3He)4Heand(H)4He.ICRH experiments have been carried out on JET using4Heplasmas to validate these scenarios. At the same time, conditions for access to H-mode in plasmas of various isotope compositions from dominantly4Heto dominantly D have been studied. Experiments have also been carried out for the first time in4Heplasmas with the ICRF power added to4Heneutral beam injection at the third harmonic of4Hein order to produce a4Hetail for alpha particle studies. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424148

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Heating experiment using high-power ion cyclotron range of frequency (ICRF) waves has been carried out and remarkable results as an ICRF heating in helical system were obtained in LHD. The maximum ICRF power was 2.7 MW. Good he0ating condition was obtained when the ion cyclotron resonance layer was located near the saddle point of the magnetic field. In this condition, the wave frequency is 38.47 MHz and strength of magnetic field is 2.75 T. Most of ICRF power was absorbed by ions and behavior of high-energy ions was investigated in the various heating conditions. The stored energy more than 1 MJ was achieved by combination of the ICRF heating with NBI heating. Fundamental cyclotron heating was observed in the high stored energy experiment. Second harmonic heating regime was shown to be useful heating scheme in LHD. The length of the ICRF pulse was extended to more than two minutes in the low power operation. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424149

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The current results on the large UCLA Electric Tokamak (ET,R=5 m,a=1 m) indicate that its potential for ICRF heating and current drive is sufficiently robust to explore plasma stability beyond the Troyon limit up to the unity beta regime. The achievement of unity beta plasmas requires virtually steady state, non-inductive plasmas with an energy confinement time of about 1 second. Due to the large volume of ET (150 m3), the Ohmic plasma confinement is excellent (a central energy confinement time of 350 msec has been achieved) and we estimate that the anomalous electronic heat conduction will not be a limiting factor for high beta exploration. In this paper we will present the current status of the ICRF experiments and the realization of excellent antenna loading using water-loaded couplers in the range of 1 to 10 MHz. The goal is to achieve unity beta plasmas by ICRF heating and current drive, relying on a large bootstrap current fraction. The reactor related aspects of this research are very exciting, provided a deep second stable plasma core can be produced by ICRF-based techniques. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424150

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Direct observation of the generation of sheared ExB flows via Ion Bernstein Waves (IBW) at the fourth ion cyclotron harmonic is reported in the toroidal magnetized plasma Thorello. The measured ExB shearing rate from IBW induced Reynolds stress increases with increasing RF power. The experimental results show a decrease of the radial correlation length in the region of the shear layer. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1424151

出版商:AIP    

年代:1901

数据来源: AIP