# Presentation: 396775

## Surface Analysis of Electrodes before and after 800 MHz MTA breakdown tests (selected results)

- surface measurements by
- Mahzad BastaniNejad

- Mike Neubauer, Muons, Inc.

## Recent results from MTA tests in high pressure H2

- Mike Neubauer, Muons, Inc.

## Copper with various atmospheres

- Katsuya MTA test data

- Mike Neubauer, Muons, Inc.

## Issue to Address

- If there is a linear relationship between the melting point (or some related characteristic) of the elemental material and breakdown gradient in high pressure gas, why did the Aluminum and Copper electrodes (this time around) have a higher gradient than one would expect?
- If the explanations are plausible for the increase in breakdown gradient, do they point to a process to increase surface breakdown gradients in high pressure gas?

- Mike Neubauer, Muons, Inc.

## 6061 Aluminum --- before

- Size of asperities not yet determined.
- 95.85% Aluminum Machined and electro-polished --- maybe electro-polishing increases the size of asperities around other elements?

- May be able to determine height and shape, by the shadow.  About 20 micron diameter

- Mike Neubauer, Muons, Inc.

## 6061-Aluminum --- after

- Melting without an arc?
- Or partial melting dependent on asperity geometry?  Or growth of asperity

- Mike Neubauer, Muons, Inc.

## Aluminum Summary

- Electro-polishing may have created asperities on the 6061 Aluminum
- Local “non-Al” constituents did not erode at the same rate
- Size of asperities may be estimated in size by further analysis
- Gives us some idea of what to model
- There may be partial melting and no arc for some asperities
- Need registration technique for improved “before and after” analysis
- A theory: 95.85% Aluminum alloy (6061) may have a higher breakdown gradient than pure aluminum because of some TBD “local surface chemistry conditions”

- Mike Neubauer, Muons, Inc.

## Copper Before

- Surface roughness seems to be smooth with less evidence of asperities, but lots of “holes”
- It was not electro-polished

- Mike Neubauer, Muons, Inc.

## Copper before

**Before pictures of copper**. The appearance of holes in regions of the grain boundaries indicate this is not OFHC copper, and it was confirmed as C110:
- C110 copper is 99.9% Cu .04% O
- C101 copper 99.99% Cu .0005% O
- But: C110 Copper may have a higher breakdown gradient than C101 copper explaining the 20% increase over the expected result

- Mike Neubauer, Muons, Inc.

## Copper After

- This may be the appearance of arcs on copper in two different atmospheres.

- Arc in H2 and C110 creates copper oxide

- Arc in H2 + SF6 creates copper sulfate

- Mike Neubauer, Muons, Inc.

## Copper after all tests

- SEM Carbon dot map shows the presence of carbon is concentrated in the regions of the arc, and sulfur and oxygen are ubiquitous.
- (The carbon may have come from machining oils and light cleaning)

- Mike Neubauer, Muons, Inc.

## Appearance of Copper Electrode after all tests

- Copper Oxide

- Copper Sulfate

- Mike Neubauer, Muons, Inc.

## Copper Summary

- The surface of the copper after MTA tests was littered with layers of discoloration and its difficult to review the results for direct cause and effect, but we try.
- Fundamentally, for high pressure gas operation, is it possible that contamination in any form increases the breakdown gradient of the pure metal?
- C110 (99.9%)   62 MV/m
- C101 (99.99%) 50 MV/m
- (In vacuum, it is known that contamination decreases breakdown gradients)

- Mike Neubauer, Muons, Inc.

## Overall Summary

- Copper and Aluminum Alloys had higher breakdown gradients than we would expect for the pure metals
- Is there some alloy, better than any other alloy, which can increase the breakdown gradient?
- Contamination in any form, seems to increase breakdown gradients in high pressure gas
- What happens if we coat an electrode with a thin dielectric which reduces the field gradient at the surface?

- Mike Neubauer, Muons, Inc.