A new radiation-hard endoscope for divertor spectroscopy on JET

Real-time protection of the JET ITER-like wall based on near infrared imaging diagnostic systems

“…Additionally, systems like KL11, shown in figure 8, include options for the in situ calibration of the endoscope transmittance during the experimental campaign, which allow the continuous tracking of possible degradation with time. The measured transmittance of the entire endoscope system for wavelengths λ > 500 nm does not show any detectable altering of the transmittance [26,27]. For λ < 500 nm we observe some degradation (≈40% at 400 nm).…”

“…A new endoscope [26,27] with an improved spatial resolution and thus delivering images of high quality, gives a unique opportunity for monitoring the surface temperature of the divertor tiles in the NIR spectral range. The endoscope covers the spectral range from 390 nm to 2500 nm with a high optical transmittance (⩾60% in the NIR wavelength range) as well as a high spatial resolution, that is less than 2 mm at the object plane.…”

“…The external telescope consists of a four-mirror aspherical off-axis arrangement and a beam splitter unit, the first optical element of which is the reflective 50/50 beam splitter (BS). Detailed information about this mirror based endoscope system as well as about the detection system can be found in [26,27]. Figure 9 shows an example of an ITER-like wide-angle system (KL14 camera system) on JET-ILW.…”

“…Examples of the divertor view and wide angle viewing system at JET-ILW The majority of the imaging systems are mirror-based and are installed inside the JET-ILW vacuum vessel. Figures 8 and 9 show examples of the divertor view and wide angle viewing system at JET-ILW.A new endoscope[26,27] with an improved spatial resolution and thus delivering images of high quality, gives a unique opportunity for monitoring the surface temperature of the divertor tiles in the NIR spectral range. The endoscope covers the spectral range from 390 nm to 2500nm with a high optical transmittance (≥60% in the NIR wavelength range) as well as a high spatial resolution, that is less than 2 mm at the object plane.…”

Impact of the JET ITER-like wall on H-mode plasma fueling

“…The recycling flux close to the divertor target plates was measured by Langmuir probes as well as spectroscopically by deuterium Balmer-α and molecular emission of the Fulcher band [15]. A spectroscopic camera was used to discriminate the D α and WI emission on the HFS top and bottom divertor during the ELM and in the inter-ELM period [29].…”