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1US PFC Meeting, UCLA, August 3-6, 2010
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
2US PFC Meeting, UCLA, August 3-6, 2010
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
3US PFC Meeting, UCLA, August 3-6, 2010
DIONISOS has similar capabilities to other linear plasma devices in the US
PISCES-B (UCSD) TPE (INL) DIONISOS (MIT)
Deuterium ion flux (m-2s-1) 1021–1023 1020 - 2x1022 1020-1022
Ion energy (eV) 20–300 (bias) 50–200 (bias) 20-350 (bias)
Te (eV) 4 – 40 5 – 20 5-10
Ti (eV) 2 – 5 2 - 5 2 - 5
ne (m–3) 1018–1019 1016 - 2x1018 1017-1019
Pmax (MW/m2) 5 0.5 0.6
Plasma diameter (mm) 75 50 50
Pulse length (s) Steady state Steady state Steady-state
Activated targets No Yes No
Tritium No Yes No
4US PFC Meeting, UCLA, August 3-6, 2010
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.
5US PFC Meeting, UCLA, August 3-6, 2010
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 nanostructureBubbles
• Also allows for in-situ target thermal desorption spectroscopy and annealing.
Ueda, DIV-SOL ITPA, Amsterdam, May 2009Baldwin et al, JNM 390-391
6US PFC Meeting, UCLA, August 3-6, 2010
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
7US PFC Meeting, UCLA, August 3-6, 2010
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)
• Operating range 200-750 K• Active heating feedback• Small targets (< plasma
column)
Current target holder High-T target holder
8US PFC Meeting, UCLA, August 3-6, 2010
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
9US PFC Meeting, UCLA, August 3-6, 2010
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
Center2mm4mm6mm8mm
10mm
10US PFC Meeting, UCLA, August 3-6, 2010
W Fuzz has been grown under a variety of conditions
W13 1200C 500s
W12 1500C 1000s
W11 1500C 500s
W10 1500C 200s
PISCES 850C 300s
PISCES 850C 1000s
PISCES targets have uniform conditions across the surface.
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.
11US PFC Meeting, UCLA, August 3-6, 2010
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
conc
entr
atio
n (a
t. %
)
12US PFC Meeting, UCLA, August 3-6, 2010
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.
13US PFC Meeting, UCLA, August 3-6, 2010
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