Ion Beam Lab

5:45 am - irradiation

The irradiation achieved 2.5 dpa (TiC alloys) before the cathode died.

4:43 pm - new cathode installed

The irradiation on ceramics will be resumed tomorrow morning.

12:27 am - update on ceramic 600C irradiation

1.7dpa over 3.0dpa has been obtained.

9:53 am - Irradiation

The 1dpa 500C irradiation on Andy Nelson's HT9 diffusion bonded samples was concluded last night at 7:30.

8:45 am - irradiation

The 600C 1dpa (Ti alloys) irradiation is complete. The cathode installed yesterday at 3pm lasted over 17 hours.

5:11 pm - stage · Attached File

On Tuesday Yong made up some thermocouples welded to dummy metal samples. With this configuration the thermocouples could be mounted similarly to the actual samples, and hopefully report more accurate temperatures. On Wednesday two TCs were installed with the dummy metal samples and one was left in the original configuration, being secured between the face plate and the stage with a set screw. The stage was heated to 330C with a heater power of 35%. With ~30uA of current on the stage, the two TCs mounted as samples read 585 and 605C, while the set screwed TC read 515C. The camera sample temperature readings were 580-610C. This new method of mounting the TCs proved to be a quite accurate way of monitoring the sample temperatures. Another note is that the air cooling has also been found to be useful. With the heater holding the stage temperature at 330C the air cooling was easily able to decrease the temperature by over 100C. Today all three TCs have been converted to the new style and the stage has been installed. The chamber is being pumped down and baked out and a 1 dpa 600C irradiation will start tomorrow morning. A picture of the stage set up is attached.

12:20 am - irradiation

When the stage was opened yesterday to examine the samples that appeared to be overheating, the samples in fact had cracked. The imaging of the edge of this crack by the camera is what, I think, cause the temperature readings to be higher. Yong and I decided that 94% of the irradiation is sufficient, and a new set of samples have been loaded. Tomorrow we will also try to regulate the temperature with either water or air cooling to achieve similar dose rates to previous 800C irradiations.

2:46 am - irradiation

The o.5 dpa (Ti alloys) irradiation is 94% complete. This morning the cathode lasted shorter than I had expected and it was changed around 1pm. Yong ran that cathode until 11pm when a third cathode was installed. Since the current on the stage was only ~21uA to maintain the irradiation temperature, it again seemed the second cathode could have lasted longer. As the third cathode was initially being run, I reduced the cathode potential from 8.5 kV to 6.5 kV and simply ran the ionizer slightly higher to achieve the same current. While this last cathode was not used to failure it will be interesting to see if this has any effect on its lifetime. The irradiation was stopped there were two samples, not ZrN which had been the problem before, that showed some localized heating. I'll pull out the stage, check the samples tomorrow, and finish the irradiation on Wed.

5:55 pm - irradiation

The 0.5 dpa 600C irradiation is 12% complete. Everything was running smoothly today, then I noticed the temperature of one of the samples had begun to rise over 900C while all the other sample temps were 600-630C. To avert a scenario similar to what happened during the 900C irradiation in which a single sample overheated, degraded and compromised all the other samples, I stopped the irradiation, let the stage cool to <100C, and opened the chamber. The sample in question, ZrN, was still quite secure on the stage, however the polished surface had fractured and the newly exposed surface had a quite different emissivity due to its roughness. While the camera caused the sample to appear to be overheating, I believe it remained at a suitable temperature throughout the run. This surface fracturing has been seen before with both ZrN and a currently unused batch of TiN. The damaged sample was removed and replaced with a fresh ZrN sample and the stage is in the process of being re installed.

5:03 pm - Irradiation

This morning the pressure in the experimental chamber had dropped into the mid 10^-7's, slightly higher than what is typical. So in preparation for the irradiation I began to heat the samples to ~500C to calibrate their emissivities. This caused a very sharp increase in the chamber pressure, one with which I was uncomfortable. It seemed that the stage and chamber needed to be baked out, so I let the stage sit at 300C for a couple hours while the accelerator was being conditioned. I still wanted to get a good calibration for the sample emissivities so I increased the temperature to slightly above 500C. Once the samples came to a stable 500C+ temperature and then cooled down it was already mid afternoon, and by that time I had already decided to test out the gas cathode more instead of waiting around while the samples cooled to a sufficiently low temperature. The good news is that everything is ready to go for tomorrow - the accelerator is conditioned, the samples are calibrated to a high temp, and the chamber vacuum is again reading in the low 10^-7's. This 0.5 dpa irradiation will be completed tomorrow, a new set of samples installed over the weekend, and a 1 dpa 600C irradiation will start on Monday.