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Layer- and tunnel-structured manganese oxide nanomaterials are important because of their potential applications in industrial catalysis. A novel soft chemistry method was developed for the synthesis of inorganic cryptomelane nanomaterials with high surface area. Bright field transmission electron microscopy (BF-TEM) and high-resolution transmission electron microscopy (HRTEM) techniques were employed to characterize this nanomaterial. A nanosized material with fibrous texture comprised of 140–160 nm striations was identified by BF-TEM imaging. HRTEM images show multiple atomic morphologies such as “helix-type,” “doughnut-like,” and tunnel structures lying on different crystallographic planes. The crystallographic parameters of this material were analyzed and measured by X-ray powder diffraction (XRD) showing that the synthesized nanomaterial is single phased and corresponds to cryptomelane with major diffraction peaks (for 10° < 2θ < 60°) at d-spacing values of 6.99, 4.94, 3.13, 2.40, 2.16, 1.84, 1.65, and 1.54 Å. A “doughnut-like” crystal structure was confirmed based on the crystallographic data. Structure and lattice parameters refinement was performed by XRD/Rietveld analysis. Simple simulation of HRTEM images and selected area diffraction patterns were applied to interpret the HRTEM images as observed.
The final beam transport in the reactor chamber for heavy ion
fusion in preformed plasma channels offers many attractive
advantages compared to other transport modes. In the past few
years, experiments at the Gesellschaft für
Schwerionenforschung (GSI) accelerator facility have addressed
the creation and investigation of discharge plasmas, designed
for the transport of intense ion beams. Stable, self-standing
channels of 50 cm length with currents up to 55 kA were initiated
in low-pressure ammonia gas by a CO2-laser pulse
along the channel axis before the discharge is triggered. The
channels were characterized by several plasma diagnostics including
interferometry and spectroscopy. We also present first experiments
on laser-guided intersecting discharges.
The aim of the presented experiments is to study the transport
of a heavy ion beam in a high-current plasma channel. The discharge
is initiated in NH3 gas at pressures between 2 and
20 mbar by a line-tuned CO2 laser. A stable discharge
over the entire electrode gap (0.5 m) was achieved for currents
up to 60 kA. Concerning the ion beam transport, the magnetic
field distribution inside the plasma channel has to be known.
The ion-optical properties of the plasma channel have been
investigated using different species of heavy ions (C, Ni, Au,
U) with 11.4 MeV/u during six runs at the Gesellschaft für
Schwerionenforschungs-UNILAC linear accelerator. The high magnetic
field allowed the accomplishment of one complete betatron
oscillation along the discharge channel. The results obtained
up to now are very promising and suggest that, by scaling the
discharge gap to longer distances, the beam transport over several
meters is possible with negligible losses.
Discharge plasma channels have been investigated in recent
years at Gesellschaft für Schwerionenforschung–Darmstadt
(GSI) and at the Lawrence Berkeley National Laboratory in Berkeley,
California, in a number of experiments. A short summary of the
experimental work at Berkeley and GSI is given. Different
initiation mechanisms for gas discharges of up to 60 kA were
studied and compared. In the Berkeley experiments, laser ionization
of organic vapors in a buffer gas was used to initiate and direct
the discharge while at GSI, laser gas heating and ion-beam-induced
gas ionization were tested as initiation mechanisms. These three
initiation techniques are compared and the stability of the
resulting discharge channels is discussed. A discharge current
of 50 kA, a channel diameter well below 1 cm, a pointing stability
better than 200 μm, and MHD stability of more than 10 μs
have been demonstrated simultaneously in the recent experiments.
These parameters are sufficient or close to the requirements
of a reactor application depending on the details of the target
design. The experimental results show that transport channels
work with sufficient stability, reproducibility, and ion optical
properties for a wide pressure range of discharge gases and
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