"Measuring the inboard side scrape-off layer of DIII-D plasmas using Swing-Probes, Accounting for Sheath Expansion in Langmuir Probe Analyses without a 4th Parameter, and the DIII-D Inner-Wall-Limiter Heat Flux Experiment"
Event details
| Date | 10.11.2014 |
| Hour | 10:30 › 11:30 |
| Speaker | Dr. Cedric Tsui - EPFL-CRPP, visiting from UCSD, San Diego, USA |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
This seminar serves as a general introduction for my work and myself to the CRPP. I will be focusing on topics that members of the CRPP should find interesting.
To measure the inboard side SOL of DIII-D plasmas, a pair of in-vessel swinging Langmuir probes were installed on the DIII-D centerpost. These probes make active measurements in a region that previously had nearly no diagnostic access, making it impossible to fully constrain plasma solutions. Designing these probes for this harsh environment presented a real challenge to DIII-D engineers.
Langmuir probe analyses relies upon a fitting of a theoretical I(V) function to thousands of sets of data for each probe and each shot. The automatic fitting routine therefore needs to be highly reliable. This can be difficult in conditions where plasma fluctuations introduce noise and where sheath-expansion effects are non-negligible. Sheath expansion can be accommodated for using an additional freely fitted parameter, but this method is strongly influenced when the data is noisy. We will demonstrate some of the drawbacks of this method and present a simple way to account for sheath expansion using the Child-Langmuir Law. This new method improves the reliability of the automatic fitting routine, and is simple enough to be applied to a wide range of probes and plasma conditions.
In an inner-wall limiter experiment in DIII-D requested by ITER, the Swing-Probes made the first Langmuir probe measurements of a narrow region of enhanced heat flux just outside the LCFS. Currently, these are the only published data that show the narrow feature that is not taken with an IR Camera. Good agreement is shown between the Swing-Probe and IR camera, confirming that the narrow feature is not just an artefact of the IR camera analyses.
To measure the inboard side SOL of DIII-D plasmas, a pair of in-vessel swinging Langmuir probes were installed on the DIII-D centerpost. These probes make active measurements in a region that previously had nearly no diagnostic access, making it impossible to fully constrain plasma solutions. Designing these probes for this harsh environment presented a real challenge to DIII-D engineers.
Langmuir probe analyses relies upon a fitting of a theoretical I(V) function to thousands of sets of data for each probe and each shot. The automatic fitting routine therefore needs to be highly reliable. This can be difficult in conditions where plasma fluctuations introduce noise and where sheath-expansion effects are non-negligible. Sheath expansion can be accommodated for using an additional freely fitted parameter, but this method is strongly influenced when the data is noisy. We will demonstrate some of the drawbacks of this method and present a simple way to account for sheath expansion using the Child-Langmuir Law. This new method improves the reliability of the automatic fitting routine, and is simple enough to be applied to a wide range of probes and plasma conditions.
In an inner-wall limiter experiment in DIII-D requested by ITER, the Swing-Probes made the first Langmuir probe measurements of a narrow region of enhanced heat flux just outside the LCFS. Currently, these are the only published data that show the narrow feature that is not taken with an IR Camera. Good agreement is shown between the Swing-Probe and IR camera, confirming that the narrow feature is not just an artefact of the IR camera analyses.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci, CRPP
Contact
- Prof. P. Ricci, CRPP