8 research outputs found
The discrete energy method in numerical relativity: Towards long-term stability
The energy method can be used to identify well-posed initial boundary value
problems for quasi-linear, symmetric hyperbolic partial differential equations
with maximally dissipative boundary conditions. A similar analysis of the
discrete system can be used to construct stable finite difference equations for
these problems at the linear level. In this paper we apply these techniques to
some test problems commonly used in numerical relativity and observe that while
we obtain convergent schemes, fast growing modes, or ``artificial
instabilities,'' contaminate the solution. We find that these growing modes can
partially arise from the lack of a Leibnitz rule for discrete derivatives and
discuss ways to limit this spurious growth.Comment: 18 pages, 22 figure
Experience with the ALPI linac resonators
Abstract The medium β section of the linac accelerator ALPI [G. Fortuna et al., Nucl. Instr. and Meth. A 328 (1993) 236] is now in operation: beams of 32 S, 37 Cl, 58 Ni, 76 Ge, 81 Br were accelerated for nuclear physics experiments in the first half of 1995. The medium β section of ALPI includes 12 cryostats containing four accelerating quarter-wave resonators each ( β = 0.11, f = 160 MHz). Two similar resonators are installed in a buncher cryostat and two in a rebuncher unit. Accelerating fields around 2.5 MV/m are available. The experience in cavity preparation, installation, conditioning and operation is described