The transient containment of high magnetic energy densities in coils of various geometries is discussed. Inherent mechanical and thermal limitations are shown to apply to coils relying solely on the strength of materials. The usefulness of inertial effects is demonstrated. Instrumentation is described for producing 10 μsec range pulses of amplitude up to 1.6 megagauss in single-turn coils. Experimental observations document the appearance of ``saw effect'' and Kruskal-Schwarzschild instabilities at very high fields. The limitations characteristic of conventional coils can be overcome in force-free geometries. The appropriate mathematics is developed and illustrated with practical examples.
We report the first measurements of the polarization of x rays emitted from bound-bound transitions in a highly ionized He-like ion. Polarization was measured for the decay to the ground state, Is 2 'So, of the He-like Sc 19+ levels \slp l P\> \s2p 3 Pi, ls2p 3 Pi, and \s2s 3 S\. The measurements were made with the Electron Beam Ion Trap at two electron-beam energies: 4.36 and 5.62 keV. Polarization of two of the lines is strongly influenced by the hyperfine interaction with the Sc nucleus, demonstrating that polarization measurements can be used to investigate hyperfine interactions in highly ionized atoms.PACS numbers: 32.30. Rj, 34.80.Kw Evidence for the hyperfine interaction in He-like ions has been seen in beam-foil spectroscopy, where hyperfine effects were found 1 to explain the measured lifetime of the \s2p 3 P2 level in V 21+ . The hyperfine interaction can mix "pure" atomic levels, changing the level lifetimes and even allowing decay by an otherwise forbidden transition. The hyperfine interaction also effects the populations of magnetic sublevels, thus affecting the polarization of the radiation emitted when a state decays. Measurements of the polarization of line emission can be used to test the theory of the hyperfine interaction, as well as provide information relevant to the understanding of solar flares and tokamaks, 2 where nonthermal electron distributions can produce polarized radiation.We have measured, for the first time, the polarization of electric dipole (E\), magnetic dipole (Ml), and magnetic quadrupole (M2) emission lines emitted from a highly ionized He-like ion. The particular emission lines that were observed are the £1 resonance line 1J 21 SO\s2p ] P\, the M2 quadrupole line Is 2 l S 0 -ls2p 3 /> 2 , the E\ intercombination line Is 2 x S$-\s2p 3 P\, and the Ml line Is 2l So-ls2s 3 S\ in Sc 19+ . These transitions are known as w, x, j>, and z, respectively, 3 and are important for solar and tokamak plasma diagnostics. 4,5 The emission lines of Sc 19+ appear in the x-ray region near 2.9 A and were observed with a Bragg crystal spectrometer attached to the Lawrence Livermore National Laboratory Electron Beam Ion Trap (EBIT). Their energies 6 are shown on an energy-level diagram in Fig. 1.Sc 19+ was chosen because it was the He-like ion most suitable for polarization studies with our apparatus. The He-like Sc (Z=21) w = 2 to « = 1 lines fall at wavelengths 7 that correspond to Bragg angles of about 45° for the Ge(220) (2^=4.00 A) curved crystal installed in our Johann spectrometer. 8 Sc is monoisotopic with an / = y nuclear spin. The hyperfine interaction with the nuclear magnetic moment of Sc can influence the polarization of the atomic transitions.EBIT is described in detail elsewhere. 9,10 Briefly, ions are injected into a cylindrical electrostatic well approximately 2 cm long and 70 /zm in diameter. The ions are ionized to high charge states and collisionally excited by a tunable (in energy) electron beam. The electron beam is nearly monoenergetic with a width of 50 eV -1s2p 1 P, ...
The mechanism of evaporative cooling of highly charged ions in an electron-beam ion trap (EBIT) is discussed. Computer simulations of evaporative cooling in superEBIT indicate that with the use of neon, nitrogen, or helium coolants, significant amounts of bare and hydrogenlike dysprosium ions can be trapped indefinitely for the observation of bound-state P decay.
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