  TeV center of mass energy lepton-hadron collider is necessary both to clarify
fundamental aspects of strong interactions and for adequate interpretation of
the LHC data. Recently proposed QCD Explorer utilizes the energy advantage of
the LHC proton and ion beams, which allows the usage of relatively low energy
electron beam. Two options for the LHC based ep collider are posibble:
construction of a new electron ring in the LHC tunnel or construction of an
e-linac tangentially to the LHC. In the latter case, which seems more
acceptable for a number of reasons, two options are under consideration for
electron linac: the CLIC technology allows shorter linac length, whereas TESLA
technology gives higher luminosity.
