The impurity concentration, the ion temperature, and the toroidal rotation velocity are key parameters which have to be monitored at a high level of accuracy for all the operating phases and for different operating scenarios of the ITER-oriented JET research programme. Therefore, a high resolution KX1 Bragg spectrometer operated in so-called Johann geometry will be equipped with new detectors. Both, Ni (7.8keV) and W (2.4keV) characteristic X-ray lines will be measured by a new generation energy-resolved micropattern gas detectors providing 1-D position reconstruction capability. Here we would like to address main characteristics and the first laboratory tests of the prototype Triple Gas Electron Multiplier (T-GEM) detectors designed for the KX1 diagnostic at JET.