The interaction of low-temperature plasmas with solid surfaces is at the core of numerous applications such as thin film deposition or materials processing. On the other hand, the interaction of the confined plasma with the plasma-facing materials in a nuclear fusion device can have a serious impact on the operations of a fusion device. This is especially true during plasma instabilities where surfaces are exposed to high transient heat and particle fluxes (several MJ.m-2 for 0.2-1ms). A pulsed cascaded arc source has been developed [1] to produce fusion-relevant plasmas and study the surface modifications induced by simultaneous continuous and pulsed plasma exposure.

 

The cascaded arc source, extensively used for thin film deposition by PECVD is used, in the Pilot-PSI linear plasma device to reproduce the plasma conditions expected in a fusion reactor with particle and heat fluxes of 1024.m-2s-1 ~10 MW.m-2 respectively. Magnetic field of up to 1.6T is used to confine the plasma. The plasma source has been modified to allow for combined pulsed/continuous operations [1]. Parallel to the DC power supply, the plasma source is connected to a capacitor bank (5kV, 8.4mF, 100kJ), which is discharged in the source to transiently increase the input power. Peak surface heat fluxes in excess of 1 GW.m-2 have been generated with pulse duration of about 1 ms (up to 1MJ.m-2). To provide more flexibility, the shape and the duration of the pulse can be adapted to the needs. The plasma conditions during the continuous and pulsed phases can be varied independently. The source can be operated in a variety of gases (Ar, H, He, N) as well as with mixed gases. Plasma properties are studied using Thomson scattering, fast visible and infrared imaging.

 

We will describe how synergistic effects arising from the simultaneous exposure to continuous and pulsed plasma affect the surface of a polycrystalline tungsten surface. The field of applications of the pulsed cascaded source is however not restricted to fusion-related research. Using a slightly altered configuration, the pulsed plasma source system has also opened a new route for the efficient deposition of metallic nano-particles and nano-structured thin films. Complete coverage of the surface by 10-15nm diameter nano-particles can be obtained with only a few pulses (5-10). Under different conditions, deposition rates as high as 50nm per pulse (1ms duration) have been achieved for copper and aluminium films. With a possible repetition rate of 10Hz, the system combines unprecedented deposition rates and the possibility of in-situ surface processing in between pulses.

 

[1] G. De Temmerman et al., Appl. Phys. Lett. 97 (2010) 081502