A collaboration opportunity for next step tokamaks: ITER and DEMO (specifically a next generation diagnostic: the pulsed polarimetry technique)

Area: Diagnostics for future burning tokamak devices and stellarators. Benefit: An opportunity to develop compelling technology in the area of plasma diagnostics allowing internal field, n e and T e measurements on next step tokamaks and stellarators. Questions: 1) What can the US do in regards to ITER and DEMO to allow us to be an integral player, to play a bigger role? 2) Our importance within international MFE science is only as strong as our domestic MFE expertise and, as argued below, by any special techniques we can bring to the table. Can we continue our pre-eminence in plasma diagnostics as MFE matures to reactors? The US has not assumed a key role in the design and operation of ITER or DEMO, for those responsibilities, Europe has taken the lead. The US is playing an important role in implementing key diagnostics on ITER such as the mid-plane tangential interferometer/polarimeter and MSE diagnostics, to name two, diagnostics that the US was instrumental in developing. Our presence on ITER will be mainly through the territory staked out by our diagnostics and DEMO, perhaps the same. It has often been expressed that progress in magnetic confinement goes hand-in-hand with diagnostic development. The purpose of this white paper is to bring forth a new and developing diagnostic technique and propose it to the FESAC International Collaboration Panel as a topic for collaborative international research. The diagnostic is a remote sensing technique with potential for measuring internal magnetic field distributions, i.e. the local magnetic field on ITER plasmas and improves in this regard on DEMO. Its measurement capabilities encompass those of Lidar Thomson scattering (local n e and T e) and polarimetry and the MSE technique so that the development is of international interest and import. The diagnostic improves with device performance (higher parameters) and provides an important new field measurement capability in a context where other diagnostics are failing. Existing diagnostics within the magnetic fusion community are struggling to find purchase on ITER let alone DEMO. The International ITER diagnostic program should have a two fold purpose, 1) most importantly, to achieve a successful ITER program through device protection, operation/performance and physics discovery but also 2) to lay the foundation for diagnosing future fusion reactors. Most assuredly, DEMO and all future engineering reactors will require diagnostics to operate successfully. In this light, one might ask which diagnostics are merely bridging a gap to …