At ANKA there is an ongoing R&D program for superconducting insertion devices (IDs). One of the key issues for the development of superconducting IDs is the understanding of the beam heat load to the cold vacuum chamber. Possible beam heat load sources are: synchrotron radiation, resistive wall heating, electron and/or ion bombardment, RF effects. The values of the beam heat load due to synchrotron radiation and resistive wall heating have been calculated and compared for the different cold vacuum chambers with the measured values. The difference between beam heat load measured and calculated is not understood. Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Low energy electrons (few eV) are accelerated by the electric field of the beam to the wall of the vacuum chamber, induce non-thermal outgassing from the cryogenic surface and heat the undulator.
A dedicated instrument for the measurement of beam heat load in a cold bore device installed in accelerators called COLDDIAG (COLD vacuum chamber for DIAGnostics) will be constructed. An experiment is envisaged at the third generation synchrotron facility Diamond light source. In this presentation I will concentrate on the description of the preliminary design of COLDDIAG which foresees the following diagnostics: i) retarding field analyzers to measure the electron energy and flux, ii) temperature sensors to measure the total heat load, iii) pressure gauges, iv) and a mass spectrometer to measure the gas content.