The invention relates to a trough-shaped collector for radiation, in particular for solar radiation, comprising a trough-shaped mirror which extends in longitudinal direction and reflects the radiation into a focus region and an absorber line which extends in longitudinal direction through the focus region of the trough-shaped mirror and has a guide tube for the heat transport medium and an absorber pipe surrounding the guide tube such that an annular chamber is formed between guide tube and absorber pipe. 
Trough-shaped collectors of this type are known from the state of the art. 
In a known trough-shaped collector, the absorber line is preferably formed by a pipe which is arranged in the focus region of the trough-shaped mirror.  As a result of its construction, the trough-shaped mirror does not have an ideal focal line but rather a focus region which can have an extension of approximately 1% of the mirror diameter.  Since the aim is to have a large mirror aperture and thus a large mirror diameter for the trough-shaped mirror, it is necessary for the pipe to have a large diameter in order to cover the entire focus region as absorber.  In this respect, absorber pipes, the diameter of which can be in the order of magnitude of 10 cm, are required for a trough-shaped mirror which has, for example, a diameter of 10 m.
As a result of the radiation reflected from the trough-shaped mirror into the focus region, the pipe is heated unevenly in circumferential direction.  Due to the thermal load, mechanical problems result with respect to pressure resistance and rigidity of the pipe, in particular, when the pipe has a large diameter. 
Furthermore, the pipe bends out of its optimum position in the focus region and so an optimum irradiation of the absorber line is no longer ensured and the degree of efficiency of the trough-shaped collector deteriorates. 
In the case of the trough-shaped collector according to DE 43 31 784, the heat transport medium is guided in a guide tube within the absorber line on account of these problems, a thermal coupling element similar to a heat pipe taking care of the transfer of heat to the heat transport medium which takes place by way of vaporization of the heat transfer medium located in the annular chamber at the hot locations and subsequent diffusion of the vapor due to condensation at the colder locations of the gas chamber.  Trough-shaped collectors of this type place great demands on the physical properties of the heat transfer medium and the production possibilities. 
Proceeding on the basis of DE 43 31 784, the object underlying the invention is therefore to provide a trough-shaped collector of the generic type which has as simple a conception as possible and in which the problems existing as a result of the uneven irradiation of the absorber line are also reduced or eliminated.