Abstract
A fast-ion deuterium-alpha (FIDA) diagnostic, first commissioned on DIII-D in 2005, relies on Doppler-shifted light from charge-exchange between beam neutrals and energetic ions. The second generation (2G) system was installed on DIII-D in 2009. Its most obvious improvement is the spatial coverage with 11 active in-beam and three passive off-beam views; the latter allows for simultaneous monitoring of the background signal. Providing extended coverage in fast-ion velocity space, the new views possess a more tangential component with respect to the toroidal field compared to their first generation counterparts. Each viewing chord consists of a bundle of three 1.5 mm core fibers to maximize light gathering. For greater throughput, fast f/1.8 optical components are used throughout. The signal is transmitted via fiber optics to a patch panel, so the user is able to choose the detector. FIDA was originally installed with a spectrometer and charge-coupled device (CCD) camera to monitor the full D(α) spectrum for two spatial views. 2G adds another spectrometer and CCD that monitor the blue-shifted wing for six spatial views at 1 kHz. In addition, a photomultiplier tube and fast digitizer provide wavelength-integrated signals at 1 MHz for eight spatial views.
Highlights
To achieve burning plasmas in future tokamak reactors, substantial heating power will be required
The heating efficiency is strongly dependent on how well the energetic ion population deposits its energy to the core bulk plasma
Plasma instabilities can lead to a redistribution or complete loss of fast ions, thereby impairing heating efficiency in the core
Summary
To achieve burning plasmas in future tokamak reactors, substantial heating power will be required. One such diagnostic method is the fast-ion deuteriumalphaFIDAtechnique.[1,2] It relies on charge-exchange between injected neutral beam particles and the energetic deuterium ions of interest. A single FIDA installation provides a measurement of essentially one component of the fast-ion velocity. A FIDA diagnostic relies on charge-exchange between injected neutral atoms and energetic deuterium ions.
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