Speakers
Mr
Chris Gowers
(Retired from JET, CCFE, Culham, Oxon, UK)Dr
Hans Salzmann
(Retired from MPI f. Plasmaphysik)Dr
Per Nielsen
(Retired: Consorzio RFX, Padova Italy)
Description
We have shown recently, and in more detail at this conference (Salzmann et al) that the LIDAR approach to ITER core TS measurements requires only two mirrors in the inaccessible port plug area of the machine. This leads to simplified and robust alignment, lower risk of mirror damage by plasma contamination and a much simpler calibration procedure, compared with the awkward and vulnerable optical geometry of the conventional imaging TS approach, currently being adopted by ITER.
In the present work we have extended the simulation code used previously to include the case of launching two laser pulses, of different wavelengths, simultaneously in LIDAR geometry. The aim of this approach is to broaden the choice of lasers available for the diagnostic. In the simulation code it is assumed that two short duration (300 ps) laser pulses of different wavelengths, from an Nd:YAG laser are launched together through the plasma. From the resulting combined scattered signals in the different spectral channels of the single spectrometer, the temperature and density profiles are deduced in the usual way. The spectral response and quantum efficiencies of the detectors used in the simulation are taken from catalogue data for commercially available Hamamatsu MCP-PMTs (types R3809U-61/-63/-64). The response times and gating properties of this type of photomultiplier have already been demonstrated in the JET LIDAR system. Here we present the new simulation results from the code. These results demonstrate that when the detectors are combined with the two laser wavelength approach, the full range of the specified ITER core plasma Te and ne can be measured with sufficient accuracy and spatial resolution. They also demonstrate that a suitable LIDAR system can be made with commercially available detectors combined with fundamental and 2$^{nd}$ harmonic outputs of the well developed Nd:YAG laser. In fact, with the addition of SBS compression, the laser could be very similar to that currently being used in the conventional ITER TS designs.
The design of the conventional core TS system that ITER is currently pursuing is well suited to somewhat smaller plasma machines with good regular access. The LIDAR TS system on the other hand, was originally developed for JET, the largest and by comparison a rather inaccessible fusion machine. The JET system has been working successfully for 30 years and has also coped well with the increased neutron fluxes encountered in the Deuterium-Tritium campaigns. LIDAR is much better suited to the large machine environments to be encountered on ITER and DEMO. The versatility of the LIDAR system is further demonstrated in the paper by Nielsen et al at this conference.
Primary author
Mr
Chris Gowers
(Retired from JET, CCFE, Culham, Oxon, UK)
Co-authors
Dr
Hans Salzmann
(Retired from MPI f. Plasmaphysik)
Dr
Per Nielsen
(Retired: Consorzio RFX, Padova Italy)
