Alpha particle physics experiments in the Tokamak Fusion Test Reactor

Zweben, S. J.; Budny, R.; Darrow, D. S.; Medley, S. S.; Nazikian, R.; Stratton, B.; Synakowski, E. J.

doi:10.1088/0029-5515/40/1/307

Cited by 106 publications

(113 citation statements)

References 181 publications

(444 reference statements)

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“…The concentration of the latter is proportional to the thermonuclear birth rate, while above a modest concentration the radial density profile of the ashes is proportional to the density profile of all other ions. For energies larger than a few times the temperature of the plasma, moreover, the distribution function of the suprathermal population is predicted to be proportional to (v 3 +v 3 crit ) −1 up to the birth energy [14,15]. Adapting the model proposed by Stix to describe the slowing-down of thermonuclear alpha particles [16], the Fokker-Planck equation can be integrated analytically [17] …”

Section: The Distribution Function Of Thermonuclear α-Particlesmentioning

confidence: 99%

On radio frequency current drive in the ion cyclotron range of frequencies in DEMO and large ignited plasmas

Brambilla

Bilato

2015

Nucl. Fusion

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Abstract. To explore the possibility of efficient Fast Wave current drive in an ignited plasma in the Ion Cyclotron (IC) range of frequency in spite of competition from absorption by ions, we have added to the full-wave toroidal code TORIC a set of subroutines which evaluate absorption by these particles at Ion Cyclotron harmonic resonances, using a realistic "slowing-down" distribution function, and taking into account that their Larmor radius is comparable or even larger than the Fast Wave wavelength. The thermalized population of α-particles is not a serious competitor for power absorption as long as their number density is compatible with maintenance of ignition. By contrast, the energetic slowing down fraction, in spite of its even greater dilution, can absorb from the waves a substantial amount of power at the cyclotron resonance and its harmonics. An extensive exploration both in frequency and in toroidal wavenumbers using the parameters of one of the European versions of DEMO shows that three frequency windows exist in which damping is nevertheless predominantly on the electrons. Designing an antenna capable of shaping the launched spectrum to optimize current drive, however, will not be straightforward. Only in a narrow range when the first IC harmonic of Tritium is deep inside the plasma on the highfield side of the magnetic axis, and that of Deuterium and Helium is still outside on the low-field side, it appears possible to achieve a satisfactory current drive efficiency with a conventional multi-strap antenna, preferentially located in the upper part of the vessel. Exploiting the other two windows at quite low and quite high frequencies is either impossible on first principles, or will demand novel ideas in antenna design.PACS numbers: 52.25 Fi, 52.25 Ya, 52.55 Fa

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Section: The Distribution Function Of Thermonuclear α-Particlesmentioning

confidence: 99%

On radio frequency current drive in the ion cyclotron range of frequencies in DEMO and large ignited plasmas

Brambilla

Bilato

2015

Nucl. Fusion

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“…The results from 30 years of study are summarized in review papers by Heidbrink and Sadler 1 and the International Thermonuclear Experimental Reactor ͑ITER͒ Energetic Particle Expert Group. 2 Other noteworthy review papers include a summary of alpha-particle experiments on the Tokamak Fusion Test Reactor ͑TFTR͒ by Zweben et al 3 and a summary of experimental observations of the toroidicityinduced Alfvén eigenmode ͑TAE͒ by Wong. 4 The goal of this paper is to use this extensive knowledge base to identify key alpha-particle physics issues that require a ''burning'' plasma experiment for clarification.…”

Section: Introductionmentioning

confidence: 99%

Alpha particle physics in a tokamak burning plasma experiment

Heidbrink

2002

Physics of Plasmas

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Much is known about the behavior of energetic ions in tokamak devices but much remains to be understood. Single-particle effects are well understood and provide a firm basis for extrapolation to a burning plasma. In contrast, collective effects involving fast ions are more poorly understood and extrapolations are unreliable. Collective modes of concern include toroidicity-induced and ellipticity-induced Alfvén eigenmodes, kinetic ballooning modes, and internal kink modes. In addition to these magnetohydrodynamic normal modes, there are also energetic particle modes characterized by strong dependence on the fast-ion distribution function. Although many issues are important areas of study in current experiments, five issues distinguish burning plasma experiments. First, the energetic alphas are not the dominant source of free energy for the instabilities unless the fusion power exceeds the heating power by a factor of 10. Second, the damping of the instabilities depends sensitively on mode coupling to other heavily-damped waves. The magnitude of this coupling is expected to depend on the normalized thermal gyroradius, which is much smaller in a reactor. Third, in a reactor, both the radial extent of the instabilities and the fast-ion orbit contract relative to current experiments, so the fast-ion transport will change. Fourth, when instability occurs, a larger number of modes are unstable, so the mechanism of nonlinear saturation could shift from fast-ion transport to mode coupling. Fifth, because of the extreme sensitivity of energetic particle modes to the distribution function, an isotropic alpha particle distribution function differs from anisotropic fast-ion populations.

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“…While the NTM impact on the global confinement is rather well established, less is known on how they influence energetic particles, like for example ICRH heated ions, or ions of NBI (Neutral Beam Injection) origin. Experiments on this subject have been performed in TFTR [5], [6] and DIII-D [7]. The study of the effect of NTMs on the fast ion confinement is important, for example, to fully asses the efficiency of NBI heating and current drive.…”

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confidence: 99%

NTM induced fast ion losses in ASDEX Upgrade

et al. 2007

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The loss of fast (i.e. suprathermal) ions from a magnetically confined fusion plasma due to the interaction with magnetohydrodynamic instabilities has been experimentally characterized and interpreted by means of a numerical model. It is found that for a special class of instabilities, the so-called Neoclassical Tearing Modes, fast ions losses are increased and modulated at the same frequency of the mode. This new experimental finding is explained as a result of the drift islands formed by energetic ions in particle phase space. An eventual overlapping of these drift islands leads to an orbit stochasticity and therefore to an enhancement of the fast ion losses. This explanation is confirmed by statistical analysis of simulations of fast ions trajectories performed with the ORBIT code. The mechanism is of general importance for understanding the interaction between MHD modes and fast particles in magnetic confinement experiments. A significant fraction of plasma pressure in a magnetized fusion experiment is carried by suprathermal (fast) ions, which are produced either by fusion reactions (like α particles), injected through energetic beams, or by RF heating. In general, these fast particles play an important role in the energy balance of a fusion plasma, either for the heating and/or for current drive processes [1], [2] and [3]. The confinement of fast particles is therefore an issue of great importance, since significant losses of these ions may drastically reduce the heating as well as the current drive efficiency. In addition, an intense and localized loss of fast ions may cause damage to plasma facing components. Due to their high energy, the dynamics of fast ions in a magnetized plasma is rather different than that of thermal ions and, in many aspects, still experimentally unexplored. Several issues are still open, for example, about the interplay between a population of fast particles and a key player of magnetized fusion plasmas, like the Magnetohydrodynamic (MHD) instabilities.In this Letter we present the first measurements of fast ion losses with simultaneous high time, energy and, pitch angle resolution due to Neoclassical Tearing Modes (NTMs). We explain the measurements on the basis of drift islands and their overlap, which leads to orbit stochasticity. The main experimental phenomenology is in fact reproduced by a model simulating the guiding center orbits of fast ions. The results reported here are important for next-step fusion devices like ITER where a significant population of α-particles and of NBI and ICRH generated fast ions will be present.NTMs are metastable modes driven by the missing bootstrap current within a preexisting seed magnetic is- * Electronic address: Manuel.Garcia-Munoz@ipp.mpg.de land, provided that the plasma poloidal beta, β pol , is larger than a threshold value [4]. When a NTM grows in the plasma, global confinement is severely affected. NTMs set the limit to the maximum β pol achievable in conventional scenarios. While the NTM impact on the global confinement is rather w...

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Alpha particle physics experiments in the Tokamak Fusion Test Reactor

Cited by 106 publications

References 181 publications

On radio frequency current drive in the ion cyclotron range of frequencies in DEMO and large ignited plasmas

On radio frequency current drive in the ion cyclotron range of frequencies in DEMO and large ignited plasmas

Alpha particle physics in a tokamak burning plasma experiment

NTM induced fast ion losses in ASDEX Upgrade

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