Problems related to the development of diagnostics for steady state fusion plasma experiments are discussed. The paper concentrates on those necessities already appearing in current non-burning plasma fusion experiments when extending pulse lengths beyond 10 s, i.e. thermal load, erosion, deposition and long-time signal integration in magnetic diagnostics. Problems arising from high power ECRH under conditions of incomplete absorption are outlined. Individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation. Burning plasma experiments characterized by intense n- and γ-radiation are briefly reviewed for reasons of completeness, dealing with radiation induced processes in windows, fibres, cables and mirrors. Methods of data handling, real time monitoring and plasma control are outlined.

/pdf/diagnostics-for-steady-state-plasmas-3yh19dtxc0.pdf

Diagnostics for steady state plasmas

Diamond windows diagnostics for fusion reactors—Updates of the design

Fusion power holds the promise of electricity production with a high degree of safety and low environmental impact. Favourable characteristics of fusion as an energy source provide the potential for this very good safety and environmental performance. But to fully realize the potential, attention must be paid in the design of a demonstration fusion power plant (DEMO) or a commercial power plant to minimize the radiological hazards. These hazards arise principally from the inventory of tritium and from materials that become activated by neutrons from the plasma. The confinement of these radioactive substances, and prevention of radiation exposure, are the primary goals of the safety approach for fusion, in order to minimize the potential for harm to personnel, the public, and the environment. The safety functions that are implemented in the design to achieve these goals are dependent on the performance of a range of materials. Degradation of the properties of materials can lead to challenges to key safety functions such as confinement. In this paper the principal types of material that have some role in safety are recalled. These either represent a potential source of hazard or contribute to the amelioration of hazards; in each case the related issues are reviewed. The resolution of these issues lead, in some instances, to requirements on materials specifications or to limits on their performance.

http://iopscience.iop.org/article/10.1088/1741-4326/57/9/092003/pdf

Materials-related issues in the safety and licensing of nuclear fusion facilities

In accordance with the goals of this ITER Task experimental and theoretical investigations on 1 MW, 170 GHz, CVD-diamond gyrotron and torus windows for continuous wave (CW) operation have been continued. Two gyrotron window units were tested in collaboration with the Russian Hometeam. Unfortunately, both window disks cracked after operation at mm-wave power levels around 1 MW and pulse lengths up to 1.5 s. The reasons are only known for the second unit where a sag of the window disk (120-140 μm), introduced by its brazing, led to a static stress of approximately 0.7-0.8 MPa. A third CVD-diamond disk unit does not show any sag. The high power tests are scheduled for January 2002. A CVD-diamond window disk was irradiated with a neutron fluence of almost 10 2 1 n/m 2 and then brazed to two Inconel waveguide cuffs. The window unit has been mounted into a test housing in an evacuated corrugated HE 1 1 waveguide (I.D. = 63.5 mm) and successfully tested in collaboration with the Japanese Hometeam at mm-wave power levels of 0.58 MW (0.2 MW) and pulse length 15 s (132 s). The temperature rises of the disk at a diameter of 65 mm and at the disk water cooling rim were 27°C and 2°C, respectively. Simulation calculations show agreement with the measured temperature rise curves for tanδ = 4.8 10 - 5 and k = 1200 W/mK which reveals that the reduction of the thermal conductivity by a factor of 2 after neutron irradiation was partially removed during the brazing at temperatures above 600°C. A 118 GHz CVD-diamond torus window unit was successfully in collaboration with CES Cadarache at a mm-wave power level of 0.3 MW and pulse durations up to 111 s. Dielectric, thermal and mechanical properties of a series of CVD-diamond window disks manufactured by DeBeers (Charters, UK) and FhG-IAF (Freiburg, D) have been analyzed. The permittivity at room temperature always is e r = 5.67 ′ 0.01 and the loss tangent at the disk centers tanδ = 1- 2 10 - 5 . Only a small variation with temperature has been observed up to 700 K. Surface losses introduced by the brazing process are still being investigated. Irradiation by a neutron fluence of almost 10 2 1 n/m 2 increaded the loss tangent to 4 10 - 5 but did not change e r . Thermal conductivity was found to be strongly reduced (840 W/m K as compared to 1800-2000 W/m K for unirradiated CVD diamond). The mechanical strength (growth face under tension) is 400 (′ 30) MPa and has not been weakened by the neutron irradiation mentioned above.

ITER ECRF window development: CVD-Diamond Window

/pdf/iter-ecrf-window-development-cvd-diamond-window-final-report-4vexp1onkx.pdf

ITER ECRF window development - CVD-diamond window. Final report. ITER Task No.: G 55 TT 19 EU (TWO-ECRF/WIN)

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ITER ECRF window development: CVD-Diamond Window

ITER ECRF window development - CVD-diamond window. Final report. ITER Task No.: G 55 TT 19 EU (TWO-ECRF/WIN)