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<td><font face="Arial, Helvetica, sans-serif" size=2>June '01 Issue</font></td>
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<div align="right"><font face="Arial, Helvetica, sans-serif" size=2>LBNL-PUB-844-00-12</font></div>
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mbronte<BR>08/01/2001
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<td rowspan="0" width="536" height="516" align="left" valign="top" nowrap scope="col">
<Font face=helvetica size=3 color="#0033FF"><B>Flibe vapor pressure 30% lower than previous estimates</B></font><BR>
The pressure of the vapor species in equilibrium with the molten salt flibe
(Li2BeF4), in the range of 600° C, target chamber operating temperatures,
were determined using activity coefficients obtained from three independent
measurement methods. This work,<a href="fig1.jpg" onMouseOut="MM_swapImgRestore()" onMouseOver="MM_swapImage('Image7','','buttonovr.gif',1)">
<img name="Image7" border="0" src="fig1.gif" width="108" height="105" align=right></a>
performed by doctoral student Grant Fukuda
and Prof. Donald Olander, found that the vapor pressure of flibe
is approximately
30% lower than values estimated by extrapolation from high-temperature vapor
pressure measurements that have been used previously for IFE chamber design,
as shown in the figure. The lower vapor pressure will result in heavy ions
being stripped to lower charge states than previously thought, and therefore
the ions can be more easily focused on the target. The vapor phase is composed
of over 90% BeF2, with the remaining vapor being primarily the mixed dimer
LiBeF3. The methods developed in this work also predict the partial pressures
of these species. Beam ions will miss the target if they strip within the
final focus magnet region. For temperatures near the 460ƒC melting temperature
of flibe, the new results reduce the vapor pressure here, and the consequent
beam strippin
by a factor of approximately 50%. Despite this large improvement, even lower
flibe temperatures may be required to keep beam loss here sufficiently small.<Font color="#0033FF"><I>-
Per Peterson and Grant Fukuda</I></Font><BR><BR>
<BR>
<Font face=helvetica size=3 color=0033FF><B>First beam in Moscow accelerator</B></font><BR>
<DIV align=justify>
The TeraWatt Accumulator (TWAC) project at Moscows' Institute for Theoretical and Experimental Physics (ITEP)
has successfully passed its proof-of-principle test. TWAC is designed for studies in 3 areas: High-energy density
in matter, which is related to inertial fusion energy and stellar interiors; relativistic nuclear physics;
and cancer therapy using carbon ions. The design parameters are a beam energy of 105 Joules, delivered in
20-100 ns, for a power of „1012 W (1 Terawatt), and a power density that can be expressed as 120 TW/cm2, or
10 TW/g. In the TWAC proof-of-principle test, Carbon 4<sup>+</sup> ions from the laser ion source were pre-accelerated
in the accelerator/ accumulator facility's new U-3 pre-injector, injected and accelerated in the UK booster
ring to 300 MeV per nucleon, stripped to 6<sup>+</sup> and stacked into the U-10 storage ring. This marks the completion
and commissioning of the new facility's main systems of the new facility's main systems - ion source, ion
pre-injector, radio-frequency and power supply for the booster ring, beam transport lines and pulsed magnetic
elements. Later this year, the system to extract and transport the beam to the beam-target interaction area
will be constructed. Other upgrades over the next three years will bring the heavy-ion beam to its target
values. An emphasis will be placed on developing diagnostics to measure plasma parameters
in the unique parameter range of up to Te ~10 eV, ne ~ 1023 cm<sup>-3</sup>, and P = 10-100 Mbar. <Font color=0033FF><I>- Boris Sharkov</I></font></DIV><BR><BR>
<Font face=helvetica size=3 color=0033FF><B>Simulation of aiming and rotation errors in HCX</B></font><BR>
The HCX experiment will investigate the mechanisms that determine the fraction
of the open aperture that can be filled by beam, using a driver-scale beam
of ~700 mA at 1.7 Mev. By understanding <a href="fig2.jpg" onMouseOut="MM_swapImgRestore()" onMouseOver="MM_swapImage('Image8','','buttonover2.gif',1)">
<img name="Image8" align=right border="0" src="fig2.gif" width="122" height="117"></a>
how to optimize the transport system
aperture, we can maximize beam brightness and minimize fusion driver costs.
Near the electrostatic quadrupole surfaces, increasingly nonlinear forces
may degrade the beam quality and cause particle loss. A single-slice model
is used to explore these mechanisms. The transverse space charge forces
are treated self-consistently, but the three dimensional external forces
are represented by a moment expansion of the fully three-dimensional applied
fields, numerically obtained for the electrostatic quadrupole focusing elements.
The simulations exploit the flexibility designed
into HCX to study the sensitivity to varying the aiming of the beam from
the injector and to rotating the first electrostatic quadrupole. HCX can
be operated in a mode where simulations predict a circular cross section
beam with no measurable degradation. (All measurements here are at the end
of HCX after propagation through the 20 periods of electrostatic quadrupoles.)
However, simulating an aiming error of 0.006 radians into the transport
system, shows plainly observable effects in slit scan and witness plate
measurements of the beam. Similarly, a 4
f quadrupole rotation results inthe tilted and squared beam cross section shown in the figure.<Font color=0033FF><I>
- Irv Haber</I></font> </td>
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