Transverse pumping chamber pickup coil adjustment

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User name Yi/Chiranjib/Jin

Log entry time 00:42:56 on January 10, 2009

Entry number 255276

keyword=Transverse pumping chamber pickup coil adjustment

During the final check of the target system before closing the target
chamber, we found out that the transerse pumping chamber pickup coil
inside the oven gave only 3 Ohm resistance with 230C oven temperature,
compared to 28 Ohm of the pairing coil outside the oven. Looks like
there's something going wrong of the coil, maybe short circuited.
However, as we tested this before with the room temperature, the coil was
normal. So we decided to shut down the heater. As the oven temperature
dropping, we clearly saw the resistance of the inside coil was increasing
and finally became 25 Ohm which is normal.

At room temperature we rotated the field to vertical and tried to do NMR
measurement with single pickup coil. The signal amplitude from only the
outside coil itself is very consistant with the polarization we measured
in the transverse direction using vertical pickup coils considering the
ratio of the calibration constants we previously got from the two pumping
directions. And the inside coil (even with 25 Ohm) gives a magnitude
smaller signal!! This implies one thing, the inside coil was not working
from the very beginning of the experiment!!!!! (Actually, the factor of
two difference in the calibration constants was alreadly trying to tell
us this, and unfortunately we just ignored that :S)

Then we turned on the longitudinal RF and checked the RF signal pickuped
by the two transverse coil. Inside coil gives 40 mV and outside coil
gives 120 mV. (The orginal ajustment was done with water cell) Again, we
turned on the heater, the signal from inside dropped to 5 mV and outside
stays the same, 120 mV.

Since the inside coil has a wierd problem and was not really used in the
experiment, we decided to disconnect it. And did some adjustment of the
outside coil to lower the RF background to 40 mV. After this, we clearly
saw some improvement in the NMR measurement in terms of signal to
background ratio.

As a conclusion, we were using single pickup coil for vertical pumping
all the time and may continue to use like this since replacing the inside
coil will involve a lot of work including taking the oven apart and most
importantly, the single coil worked already! Furthmore, we should have
better signal to background ratio from now on.

A copy of this log entry has been emailed to: jpchen