DIONISOS: Upgrading to the high temperature regime G.M. Wright, K. Woller, R. Sullivan, H. Barnard, P. Stahle, D.G. Whyte Plasma Science & Fusion Center, MIT, Cambridge USA
Outline • DIONISOS • Advantages and capabilities • The high temperature regime • Importance • Details on upgrades • He concentrations and depth profiles in W fuzz layers • Heavy ion ERD analysis
DIONISOS has similar capabilities to other linear plasma devices in the US
What makes DIONISOS unique? • Simultaneous plasma and ion beam exposure of targets • Active target heating and cooling (Ttarget = 300-750 K) • In-situ, time-resolved ion beam analysis • In-situ target irradiation by high-energy (~MeV) ions for irradiated materials studies.
Why are we interested in the high temperature regime for DIONISOS? • Commercial fusion reactors will run with “hot walls” (e.g. 900-1000 K) • New physics and surface effects at high temperature. W nanostructure Bubbles Baldwin et al, JNM 390-391 Ueda, DIV-SOL ITPA, Amsterdam, May 2009 • Also allows for in-situ target thermal desorption spectroscopy and annealing.
A new target holder is required to reach these temperatures in DIONISOS • Heatwave Labs UHV substrate heater with DC power supply • Max operating temperature of 1473 K • Electrically isolated from target • Mo heat shielding on the sides and back • Active PID temperature control (K-type thermocouple) Substrate heater Isolated sample clips for target biassing Heat shielding Power leads
Some key differences between the current target holder and the high-T target holder • Operating range RT-750 K • Active cooling and heating • Large targets (> plasma column) Current target holder High-T target holder • Operating range 200-750 K • Active heating feedback • Small targets (< plasma column)
Other components must also be protected from the additional radiative heating from the target • Hot target leads to radiative heating of sensitive components. • Solid-state detectors used for IBA are cooled through thermal contact with a water-cooled plate. Cooling line Heat sink Detector Detector housing Support rod
Ion beam analysis on W nano-filament formation has yielded useful new data • Fuzz grown in Pilot-PSI with peaked flux and temperature profile. • ERD performed with 7 MeV O4+ ions for He detection. • Beam spot is 2.0 x 3.5 mm (oval) • Fuzz layer is only 5-10 % density of bulk tungsten. • Penetration depth of 7 MeV O4+ ions is ~950 nm Center 2mm 4mm 6mm 8mm 10mm
W Fuzz has been grown under a variety of conditions Grown in Pilot-PSI with peaked flux and temperature profile. G. De Temmerman, FOM Rijnhuizen, The Netherlands NOT exposure conditions for fuzz growth, just an example of possible gradients in Pilot-PSI exposures. PISCES targets have uniform conditions across the surface.
Radial scan on W13 demonstrates transition from fuzz to non-fuzz conditions • He is distributed uniformly throughout the fuzz layer. • Before fuzz formation, He is peaked at the surface. • All other targets had flat He profiles similar to the center of W13 He concentration (at. %)
Comparison of He concentrations from all other targets • He concentration in the W fuzz falls within 0.5-1.0 at.% for all conditions investigated here. • No clear dependence of He concentration on He fluence or surface temperature. • More data needed. Controlled parameter scans could reveal hidden dependences.
Future goals • Further investigations into the dynamics of PSI and PSI for irradiated materials • In-situ fuzz growth in Pilot-PSI • Time-resolved ERD measurements of W fuzz growth • Retention in high-temperature walls under irradiation conditions • Characterization of carbon deposition on high-temperature tungsten substrate