Global magnetic fluctuations in spheromak plasmas and relaxation toward a minimum-energy state

Janos, A.; Hart, G. W.; Nam, Chang Hee; Yamada, Michio

doi:10.1063/1.865321

Cited by 29 publications

(8 citation statements)

References 20 publications

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“…This shows the evolution of the poloidal and toroidal fluxes, and of on the magnetic axis, during a plasma discharge in the S-1 spheromak (Janos et al. 1985 a , b ). Figure 34( c ) shows that rises rapidly from a small initial value and becomes close to that predicted for the relaxed state.…”

Section: Spherical Systems I: Spheromakmentioning

confidence: 99%

Special topics in plasma confinement

Taylor

Newton

2015

J. Plasma Phys.

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These notes are based on lectures given by one of us (J.B.T.) at the University of Texas in Austin in 1991. Part I concerns some basic features of plasma confinement by magnetic fields as an introduction to an account of plasma relaxation in Part II. Part III discusses confinement by magnetic mirrors, especially minimum-B systems. It also includes a general discussion of adiabatic invariants and of the principle of maximal ordering in perturbation theory. Part IV is devoted to the analysis of perturbations in toroidal plasmas and the stability of ballooning modes. PREFACEThe theory of plasma confinement is complicated and incomplete. Because current textbooks do not include material at the frontier of research, it is hard for students and researchers to become familiar with the state of the art. Bryan Taylor's notes are presented here to start filling that gap. Although based on lectures from over twenty years ago, they provide much needed clarity in selected areas of current plasma confinement research. Of course much of the original work on which these notes are based is by Bryan Taylor and collaborators; but here, he and Sarah Newton draw the many threads together. Indeed, while some may find the results familiar, the insight is fresh and enlightening. The research frontier is just beyond these notes. Some of the outstanding questions are posed and some are left to the reader to discern. For example, we still need to know: how fast plasmas relax; how three-dimensional reconnection works; how ballooning modes saturate and; how minimum B ideas can improve toroidal devices. The insights here will help anyone wanting to answer those and other questions.

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Section: Spherical Systems I: Spheromakmentioning

confidence: 99%

Special topics in plasma confinement

Taylor

Newton

2015

J. Plasma Phys.

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“…Spheromak confinement properties, as given in terms of q-value or magnetic shear will, therefore, also evolve in time [14]. On the other hand, the spheromak plasma is expected to have the ability to self-adjust its field configuration [15,16], i.e. to relax to a lower energy state when its energy state deviates from the minimum state.…”

Section: Introductionmentioning

confidence: 99%

Temporal evolution of the decaying spheromak in the CTCC-I experiment

et al. 1987

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In the CTCC-I spheromak experiment, after low-Z impurities have been suppressed by titanium coating on the inner surface of the flux conserver, MHD activity increases to the point that instabilities are present in every discharge at some time during the decay process. Most of the instabilities occur intermittently, as evidenced by the O V line radiation intensity which rises gradually and then drops abruptly. In some experiments, a conducting pole is inserted along the symmetry axis to increase the magnetic shear of the configuration. This conducting pole effectively suppresses a destructive instability, but other MHD instabilities are still present. Magnetic field measurements indicate that the occurrence of the instability is correlated with a relaxation process during which the peaked current profile at the magnetic axis is flattened by the MHD instability. An estimate of the energy loss during the subsequent relaxation process is given.

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“…Spheromaks 4 formed with a single pulse followed by free decay in a flux conserver with a magnetized gun initially relax to a stable, minimum energy Taylor-State 2 with a well defined ratio of poloidal to toroidal current, but then suffer from internal kink (or resistive tearing) mode instability 5,6,7,8 [Janos, Knox, Sgro, Ono] as the colder, more resistive edge causes the poloidal current to decay faster than the toroidal current causing a loss of toroidal magnetic field. This instability is often disruptive enough to rapidly terminate the plasma discharge and is consistent UCRL-JCVersion 0.3…”

Section: Introductionmentioning

confidence: 99%

Transport and fluctuations in high temperature spheromak plasmas

et al. 2006

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Globally coherent magnetic fluctuations often observed during the driven phase after spheromak formation in the Sustained Spheromak Physics Experiment 1 (SSPX) can be reduced to small amplitude by programming the magnetic flux=ψ gun and the discharge current=I gun in the formation gun. Scanning the edge normalized current=λ edge =λ gun =µ 0 I gun /ψ gun above and below the minimum energy eigenvalue 2 =λ FC of the flux conserver provides a variation in the internal q=safety factor profile producing the expected q=m/n=poloidal/toroidal mode spectrum. By driving the edge with the proper λ gun , the system can be operated with the poloidal/toroidal mode spectrum between the m/n=1/2 and 2/3 modes producing low magnetic fluctuation amplitudes and high electron temperature=T e > 350 eV. Transport and confinement parameters calculated using Thomson scattering-measured T e and n e profiles coupled with the equilibrium code internal current profiles show a reduction in electron thermal diffusivity as T e increases. This scaling behavior is more classical-like than Bohm or open field line transport models 3 where thermal diffusivity increases with T e . Electron diffusivity is calculated to be less than 10 m 2 /s, approaching levels seen in tokamaks.

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Global magnetic fluctuations in spheromak plasmas and relaxation toward a minimum-energy state

Cited by 29 publications

References 20 publications

Special topics in plasma confinement

Special topics in plasma confinement

Temporal evolution of the decaying spheromak in the CTCC-I experiment

Transport and fluctuations in high temperature spheromak plasmas

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