This message is a on the subject of the discussion
that we are having about mft making something other
than 2-3 transition. I did some calculations.
With the frequency we are running at, 60 MHz the magnetic
fields for 2-3 and 1-2 transitions are 40 Gauss and 44 Gauss
respectively. The gradient field was measured at 5 Amps to
be 2 Gauss/cm. We are running at -3 Amps. Thus, assuming
linear dependence, which is ok at this low field (well below
the saturation) our gradient is -1.2 Gauss/cm. The size of the
RF coil is about 5 cm. I'm neglecting the gradient due to the
BLAST field, since the effect of the absolute size of the BLAST
field is pretty low. If in fact this is true than
what we have is 1 <-> 2 transition first and then 2 <-> 3.
And this is probably what Hauke meant by saying
"I have already tuned the MFT 12-23 transition" in his
departing e-mail. This means that at the end (after
the last 6-pole magnet) we have (n2,0,0,0) which is fully polarized.
One could try to run a 2 <-> 3 transition by reversing the
gradient field and making it smaller (to make sure we don't run into
the 1 <-> 2 transition at larger field). This is risky though since we can
not tell if we run into the 1 <-> 2 transition.
According to the scheme we are running right now there should be no state-2
in the target. It would be purely speculative on my part but if we have bad
focusing in the to 6-pole (low flux into the target) then maybe we don't reject
all states-3 and by doing 2 <-> 3 in the MFT we actualy still have some state-2
at the end. But this is just speculation, in case we see better asymmetry
(or any) with lower target field value.
Cheers, Vitaliy
=====================================================================
Vitaliy Ziskin Tel: (617)253-9209
MIT 26-547 http://www.lns.mit.edu/people/vziskin/
77 Massachusetts Ave
Cambridge, Ma
02139
======================================================================
"For long you live and high you fly
And smiles you'll give and tears you'll cry
And all you touch and all you see
Is all your life will ever be"--Pink Floyd
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