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Ph.D. Thesis - Physics

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2. Check that 422 and 1092 are roughly coaligned (by eye with the IR card).<br />

3. Make sure the 405 is unblocked!!! This has caused the author to waste some time in<br />

the past.<br />

4. If it’s been a few days since someone trapped, check our wavemeter against Shannon’s<br />

or against the 674 laser.<br />

5. Look for neutrals.<br />

6. If there are neutrals but no ions, you’ll have to do some searching. Try to be sys-<br />

tematic: map out every point on a grid with the 422/1092 lasers. If you don’t find<br />

anything, you may vary the PI position as well, but at each point try to re-counteralign<br />

the 422/1092 with it.<br />

7. Check 422/1092 coalignment on the beam profiler.<br />

8. Lower (or raise) the rf amplitude and repeat the search pattern.<br />

9. If that fails, adjust the dc voltages. Don’t do so blindly, because that will take too<br />

long. Try another set of voltages from the group laboratory notebook blog that have<br />

worked in the past, or go to zero on all channels if you’re using different values.<br />

10. Give up. Usually if the trap is going to trap well, you find ions in a couple hours or<br />

less. There have been cases in which the author trapped nothing, then warmed up<br />

and baked the system for a day, then cooled down and realigned, and then found ions<br />

easily. Excessive charge getting trapped on the dielectric around the trap at 4K is a<br />

reasonable explanation for this.<br />

11. Good luck!<br />

C.6 Shutdown<br />

In this section, we focus on the procedure for shutting down the cryostat, which is really<br />

quite simple. First flip the green switch on the compressor, shutting it down. Then, fairly<br />

soon after, close off the chilled water supply to and from the compressor. You will see the<br />

pressure reading on the ion pump begin to rise rapidly. Close off the main valve on the<br />

UHP helium cylinder. Then, for a few moments, observe the bellows. Sometimes pressure<br />

within the bellows builds up to the extent that one wishes to relieve some of the pressure<br />

manually, using the safety valve. However, this is probably not necessary.<br />

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