On the form invariant volume transformation in phase space by focusing neutron guides: An analytic treatment

• Form invariant volume transformation in phase space.
• Focusing modules for neutron beams.
• Analytical approach.
• Attenuation effects in linearly and nonlinearly tapered guides.

Tapered guides with supermirror coating are frequently used to focus neutron beams on specimens. The divergence distribution in the focused beam is of a great importance for the quality of neutron instrumentation. Using an analytic approach we derive the tapering which is needed to achieve a form invariant phase space transformation of a rectangular phase volume. In addition we consider the effect of beam attenuation by the finite reflectivity of supermirrors.