SIO Paleomag Lab blog

The SI-4 AF Demagnetizer isn't working. The control unit seems to be fine, though it's unable to be tuned and the coil no longer builds a charge after it's triggered. The coil, control unit, cradle, and power supply are being sent back to M. Stupavsky for servicing.

Filled BUBBA with approximately 30 liters of liquid helium (8/3/05). This was the first smooth fill in a couple of months. Julie helped with fill and it took about 20 minutes to complete. An obvious change in the plume occured this time. BUBBA'a reservoir was then measured with the dip stick, measuring ~28 inches meaning it's 100% full.

Filled BUBBA with about 25 liters of liquid helium today. The fill went smooth and took about 15 minutes. Roi assisted with the fill.

The 2G magnetometer (FLO) is temporarily down. During annual maintenance of the adsorber, the brass hose line began to fail. A loose o-ring in the connector may have been the cause of this failure. Later during this maintenance the system was exposed to atmospheric pressure. The first instant the system reached atmospheric pressure there was a cracking/popping noise that came from the coldhead. The noise may have been ice forming instantly inside the coldhead sleeve. After this, the coldhead motor was kind of running but the piston didn't seem to be moving at all. 12 hrs later, the pressure in the liquid helium reservior had reached about ~8psi (safety valve pops at 10psi) and the vent valve was completely frozen over. The extreme buildup of pressure in the initial 12 hours may have been due to the coldhead was running, trying to pump helium in though unable to recycle any out. After turning the cold head off, defrosting the ice around the vent valve, and depressurrizing back to ~2.5psi the system began to boil off liquid helium at a safer rate. About 65 liters of liquid helium boiled off in 8 days. Best case scenario for the 2G is that only the coldhead will have to be replaced. Then we can make a new vacuum, use the cryocooler to precool the reservoir, and fill her up with liquid helium.

Normal operating pressure for the CTI 8200 Compresor is about 270-290 psig and static pressure should be around 245-255 psig. If the normal operating pressure increases above 295 the pressure needs to be lowered. In order to bleed the pressure down, follow these steps.

1.  Turn off the compressor
    
2.  If the static pressure is higher than 250 psig,  SLOWLY open the
    helium gas fitting and charge valve.  The pressure will begin to 
    slowly decrease.  Bleed the pressure down to 250.  

3.  Turn on the compressor nominal operting pressure should be about
    270-290 psig)

Filled BUBBA with about 33 liters of liquid helium. There were no problems and the fill took about 20 minutes. During the last fill a partial ice block was noted. This may have been caused from a humid day. To prevent ice blocks, pressurize the transfer line very slowly and insert the line into the magnetometer before it completely liquifies. :>

The sample tower for BUBBA consists of the main base, a custom fabricated sample holder, and a lowering system set up with fishing line. The fishing line is always streching and eventually fails. Well, today it snapped while Julie was using it and she restrung the tower with fresh fishing line. There is a new diagram on how to restring the tower just to the north of BUBBA. It usually takes a couple of attempts to have the fishing line tight enough so it doesn't slip along the wheel. Hopefully, this set up will last forever. :)

Today, Julie was going to show me how to use the curie balance. When we started going through the startup procedure, we discovered that water had been leaking from the cooling loop. We shutoff the cooling lines right behind the chiller, but if you use the AGFM, make sure that you check for water leaking from the lines right where they go into the furnace and the two magnets. Jason mentioned that the furnace had a bad weld the last time there was a leak, but this time it looks like a leak at both the furnace and the front magnet.

Here are some pictures from July 2004 that show the insides of Bubba the magnetometer along with many of the people in the SIO Paleomagetics Lab.

  Bubba's Guts and Fill

A liquid helium fill was performed on BUBBA today and it wasn't the smoothest fill. To begin with, the liquid helium supply dewar had 38 liters recorded on the tag, though we measured only 28 liters. Then, when we began to fill BUBBA the exhaust plume appeared weaker than normal and the supply dewar was ~5 psi (normal supply dewar psi ~3-4psi). So we pulled the transfer line from BUBBA. When we took the transfer line out, there was a partial ice block on the end of the transfer line. This caused the weak plume and the higher than normal supply dewar pressure. I cleared the ice from the end of the transfer line, and we began the fill again. The supply dewar remained steady around 3 psi and the exhaust plume appeared normal. After 25 minutes of filling with a normal pressure, we should have seen the plume change, but of course we didn't. So we pulled the transfer line and measured the amount of helium left in the supply dewar. The supply dewar was empty, which means that we must have added ~25 liters of liquid helium into BUBBA, almost filling it 100%