In a burning plasma, it is essential to be able to diagnose the alpha particles produced by the DT reactions. A novel technique is being investigated, which involves the use of XUV spectral line intensity ratios to measure the product 'alpha particle density x collisional excitation rate' (ca ne qa, where ca is the alpha particle concentration). In practice, several ratios from different elements and ionisation stages would be used to give information about both the alpha particle density and its energy distribution function.