Mazzocchi, Francesco

Meier, A.

Scherer, T. A.

Torge, M.

Yamada, H.

English

KITopen

KIT – University of the State of Baden-Wuerttemberg and  National Research Center of the Helmholtz Association Francesco Mazzocchi - Institut für Angewandte Materialien - Angewandte Werkstoffphysik Hideaki Yamada – National Institute for Advanced Industrial Science and Technology www.kit.edu Loss Tangent Measurement on synthetic crystalline diamond (SCD) samples Karlsruhe Institute of Technology - IAM AWP 2 Outline • Introduction        ECRH&CD system       CVD Diamond Windows        SCD samples  • Experimental Setup      Vertical resonator       Double spherical resonator       Hemispherical XY mapping resonator  • Results        • Conclusions Karlsruhe Institute of Technology - IAM AWP 3 Electron Cyclotron Resonance Heating and Current Drive System Gyrotron Waveguide CVD  window Upper Launcher Vacuum Vessel ECRH&CD systems are meant to heat the plasma, destroy instabilities and drive current inside the vacuum vessel of a nucleare fusion reactor Karlsruhe Institute of Technology - IAM AWP 4 CVD Diamond Windows Diamond windows are fixed installations of a nuclear reactor primary confinement system, containing a potentially flammable mixture if exposed to air.  Requirement for the windows assembly include:  • Ultra low loss microwave transmission  • No dead volumes to minimize the stagnation of tritium and the pumping time.  • Full range of monitoring diagnostics (Tritium detection, microwave leakage, pressure, arc detection, temperature)  Source: Iter Tritium handbook, Iter vacuum handbook Karlsruhe Institute of Technology - IAM AWP 5 Single Crystalline Diamond Why single crystalline diamonds ?   Policrystalline CVD diamods  bulk sp2 boundaries  electrically conductive  microwave absorption hotspots Single crystal diamonds (SCD)  sp3 bindings only  improved transmissivity Karlsruhe Institute of Technology - IAM AWP 6 AIST SCD samples Commercially available SCD samples are too small for fusion applications, being in the 2-3 millimeter range, while polycristalline ones are available in up to 5 inches wafers.  Dr. Yamada at AIST (Osaka, JPN) proposed a technique to compose relatively small samples of SCD into a larger size area, with sufficient quality to fabricate freestanding wafers from it.  “Tiled SCD clones” technique samples  in the cm range (20 mm2) are possible.  Images courtesy of Dr. Hideaki Yamada – National Institute for Advanced Industrial Sciences and Technology (Osaka, JPN) Karlsruhe Institute of Technology - IAM AWP 7 Experimental Setup Vertical Cavity Resonator  Double Spherical Resonator (DSR) Hemispherical XY mapping resonator Setup consisted in three different kind of resonators, with sources at 90 – 100, 145 and 170 GHz. Beam profile is gaussian. The double spherical resonator has a resolution in the order of 10-6, while the other two attain 10-5.  • The DSR is capable of shifting the sample in the Z direction  estimation of bulk and surface losses.   • Change in the inverse cavity Q-factor (with and without sample)  Loss tangent values Iterative solution of the resonator equation  Relative permittivity εr   Karlsruhe Institute of Technology - IAM AWP 8 Results: Loss Tangent -10 -5 0 5 10-10-50510tan, 10-5   >  108 - 106 - 84  - 62  - 4<  24-fold  SCD reached the resolution limit of the XY mapping machine. Higher values towards the borders suggest diffraction as a cause of Q-factor degradation. Four different AIST SCD samples where tested (thicknesses between 0.9 and 1.35 mm) and compared with a commercial policrystalline disc (PCD) The commercial sample shows analogous results. It is worth to be noted that while the PCD disc is polished, the AIST 4-fold samples were polished only on the growing surface  Thickness:  1.3 mm  er: 5.67 Frequency: 145.07 GHz Karlsruhe Institute of Technology - IAM AWP 9 -10 0 10 20-20-1001020tan, 10-5   >  108 - 106 - 84  - 62  - 4<  2 Thickness:  1.25 / 1.35 mm  er: 5.67 Frequency: 145.14 GHz 8-fold SCD unpolished  higher losses in the central region  boundary between different tiles lowers the quality  Results: Loss Tangent „Monodimensional“ higher losses  angular offset of the growing direction, (~ 3°)  boundary perpendicular to the growth direction = good optical quality.  (cfr. S. Ohmagari et al. / Diamond & Related Materials 48 (2014) 19–23)  Karlsruhe Institute of Technology - IAM AWP 10 Results: Topography Unpolished SCD sample topography • ~ 200 μm wedge  low quality surface = bigger surface losses   • ~ 200 μm wedge  double spherical high resolution resonator measurements not good  Polished PCD sample central profile ~ 2μm max discrepancy  low surface losses (less 10-6 as measured with DSR)  Karlsruhe Institute of Technology - IAM AWP 11 Summary • SCD should be able to overcome the limitations imposed by PCD bulk losses (10-7)  • Tiled SCD clones technique seems to be a good way to obtain cm size samples  • Performances of the SCD samples seems to be heavily influenced by growing characteristics and surface quality Karlsruhe Institute of Technology - IAM AWP 12 THANK YOU francesco.mazzocchi@kit.edu Karlsruhe Institute of Technology - IAM AWP 13 Backup Slide: Bulk & Surface Loss Tangent Calculation • FF = filling factor (effective portion of the dielectric in the resonator)  • FL = loading factor (rescaling of stored and dissipated energy)  • Q1 = cavity quality factor (with sample)  • Q0 = cavity quality factor (without sample)  • Nλ = number of half wavelenghts in the sample  Resonant condition = Nλ integer   Node condition at the second surface  minimum surface losses  Antiresonant condition = Nλ half integer  antinode condition at the second surface  maximum surface loss R. Heidinger et al., IEEE transactions on plasma science, vol. 30, no. 3, June 2002 Karlsruhe Institute of Technology - IAM AWP 14 CVD Cloned Samples preparation 1. HPHT SCD seed crystal  PECVD growt of the tiles (source gas: 90% H2 10% CH4)   2. Grown diamond layers are separated from the seed through lift-off process involving high speed ion beam injection. Repeating this process generates several „cloned wafers“  3. Finally, cloned tiles are put side by side in the CVD reactor. An SCD layer that connects the tiles is grown ant lifted-off, obtaining a large SCD sample.    

Loss tangent measurement on synthetic single diamond (SCD) samples

https://publikationen.bibliothek.kit.edu/240097106/150406288

Loss tangent measurement on synthetic single diamond (SCD) samples

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