# Presentation: 469563

## Vacuum Vessel and Shell Time Constant Issuesfor C82

- NCSX PAC Meeting
- June 3-4, 1999
- Art Brooks, Wayne Reiersen,
- David Williamson, Mike Zarnstorff

- AWB 060399

## Guidance from last PAC Meeting

- “Examine the error fields produced by eddy currents in support structures such as the thick aluminum shell...
- Response
- Aluminum shell has been replaced by segmented shell of a higher electrical resistivity bronze
- Striving to reduce longest time constant of structures to ~10 ms
- Plan has been created to assess impact of error fields from eddy currents in structures on magnetic islands and kink stability

- AWB 060399

## Plan Designed to meet Physic Objectives

- Equilibrium evolution, for candidate engineering designs:
- Spark calculation of eddy currents, assuming linear evolution between reference plasma configurations
- calculate resonant perturbed fields => islands due to eddy currents
- ensure induced islands small enough
- Effect on Kink stability & disruptions
- NCSX strategy
- can we have a credible kink & disruption experiment with a thick conducting wall (wall) ~ (pulse)
- brainstorm with MHD group
- set requirement on (wall) for kink eigenfunction
- requirements for testing disruptivity at high beta
-  calculate kink B eigenfunction for phyics configurations
- need to examine range of profiles
-  for each candidate engineering design strategy:
- Spark calculation of penetration of kink eigenfunction

- AWB 060399

## Eddy Current Study Statusfor Vacuum Vessel and Coil Winding Structure ( Shell )

- Models generated of the individual structures to determine structure time constants for eddy current decay using the SPARK Code
- Eigenvalue analysis performed and the longest time constant is reported
- Vessel assumed to be 1 cm thick Inconel, with resistivity = 130.e-8 ohm-m
- Longest time constant =  6.0 ms
- Agrees with analytic calculation of torus of comparable size
- Shell assumed to be 4 cm thick Bronze, with resistivity = 18.e-8 ohm-m.  Number of segments is a parameter
- Presence of Outboard Ports ( not modeled initially ) lowers time constant value.

- AWB 060399

## Time Constants for Segmented Shell

- Without Ports
- Shell Modeled Separately
- No Thick Wall Effects
- Rotational Symmetry Assumed

- Present Design
- 8 Bronze Segments

- AWB 060399

## Eigenmodes of longest time constantsVacuum Vessel                       Shell Structure

- Eigenmodes of longest time constantsVacuum Vessel                       Shell Structure

- Longest Mode may not be significant
- since it is probably difficult to excite

- AWB 060399

## Vacuum Vessel and Shell StructureComposite full 360 deg Spark Model with Ports

- Vacuum Vessel and Shell StructureComposite full 360 deg Spark Model with Ports

- , max = 17.6 ms
-       with 8 segments/period
- Modes of concern will be less

- AWB 060399

## Summary

- Work still in progress to support shell design with 8 toroidal segmentations
- Eigenvalue analysis give longest time constants which appear promising
- Initial Transient results with real excitations show much faster eddy current decays ( with corresponding error field decay)
- ie decay from fast TF ramp show induced saddle currents decay with a time constant = 10.9 ms

- AWB 060399