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Ballistic neutron guides are efficient for neutron transport over longdistances, and in particular elliptically shaped guides have received muchattention lately. However, elliptic neutron guides generally deliver aninhomogeneous divergence distribution when used with a small source, and do notallow kinks or curvature to avoid a direct view from source to sample. In thisarticle, a kinked double-elliptic solution is found for neutron transport to asmall sample from a small (virtual) source, as given e.g. for instruments usinga pinhole beam extraction with a focusing feeder. A guide consisting of twoelliptical parts connected by a linear kinked section is shown by VITESSsimulations to deliver a high brilliance transfer as well as a homogeneousdivergence distribution while avoiding direct line of sight to the source. Itperforms better than a recently proposed ellipse-parabola hybrid when used in aballistic context with a kinked or curved central part. Another recentlyproposed solution, an analytically determined non-linear focusing guide shape,is applied here for the first time in a kinked and curved ballistic context.The latter is shown to yield comparable results for long wavelength neutrons asthe guide design found here, with a larger inhomogeneity in the divergence buthigher transmission of thermal neutrons. It needs however a larger (virtual)source and might be more difficult to build in a real instrument.

An improved elliptic guide concept for a homogeneous neutron beam without direct line of sight