  We have set up a diagnostic magnet (D-Mag) laboratory for a wide range of
applications in plasma physics. It consists of a superconducting magnet for
field strengths of up to 5.9 T. The main purpose is to provide an experimental
environment for the development of plasma diagnostics for nuclear fusion
studies and the investigation of dusty plasmas in strong magnetic fields. We
describe in the article the setup and operation of the D-Mag. Some applications
are presented for the development of plasma diagnostics, such as neutral
pressure gauges and Langmuir probes that have to be operated in strong magnetic
fields. Among the examples is the test of the long-pulse capability and
stability of the diagnostic pressure gauge (DPG) for the ITER device.
