[Polhe3] Convection Cell Items

[William A. Tobias]

Zhiwen:

I believe so.

 - AL


On Wed, 25 May 2011, Zhiwen Zhao wrote:

> Hi, AL
> 
> Thanks a lot for the detailed explanation.
> I think we are ready to make a purchase order as your drawing, aren't we?
> 
> Zhiwen
> 
> On 05/25/2011 05:10 PM, William A. Tobias wrote:
> >
> > Hello Zhiwen:
> >
> > Quick answers to your questions:
> >
> > Scott used 1-inch spherical cells in his research.
> >
> > As for the bulb, some of the motivations:
> >   a) to provide for more volume than the transfer tube alone: keep in mind
> > that a TT cylinder with 6mm I.D. is much less volume then a sphere with
> > 22mm I.D.
> >   b) allow for doing "Spin Echo" measurements: for various reasons, a spin
> > echo may allow one to more consistently measure the NMR amplitude for
> > polarization. For example, in cases where the FID signal is too short
> > (decays too quickly due to field inhomogeneities ie. short T2*) it becomes
> > difficult to fit the FID back to time zero to extract an amplitude. This
> > is especially true when there is much RF "ring down" from the initial
> > pulse that contaminates the beginning of the FID. The solution is to do a
> > spin echo in which case one just measures the peak of the echo. To do a
> > spin echo successfully, you want most of your gas in a region of good
> > RF (H1) field homogeneity since the pulses used in a spin echo are
> > important to flip the 3He spins properly. Gordon's idea is to use a
> > solenoid twice the length of the bulb so most of the gas lies well inside
> > a homogeneous RF field during pnmr measurements, with minimal gas within
> > the TT and other edges of the solenoid where the field is less
> > homogeneous.
> >
> > In a typical spin echo, one first applies a pulse that tips the spins as
> > much as 90-deg, just enough to get a large signal. During this time, the
> > spins dephase. After a time t, one applies a 180-deg (pi) pulse causing
> > the spins to rephase an additional time t later to give the spin echo. We
> > simply measure the amplitude of the echo.
> >
> > As for tube tolerance, I can specify an outer diameter on the drawing if
> > you prefer. I spoke to Mike and asked him what he thinks the OD of the
> > tube would be if I ask him to make an ID of 5 to 6mm. He said the OD would
> > be about 8 to 9mm (ie. 1.5mm wall thickness).
> >
> > Hope this information helps ...
> >
> >   - AL
> >
> >
> > _________________________________________________________________________
> >
> > Al Tobias                            Office: (434) 924-7681
> > Department of Physics                  Home: (434) 984-5025
> > University of Virginia                  Lab: (434) 982-2233
> > P.O. Box 400714                         FAX: (434) 924-7909
> > Charlottesville, VA 22904-4714       E-mail: wat4y at virginia.edu
> > _________________________________________________________________________
> >
> >
> > On Tue, 24 May 2011, Zhiwen Zhao wrote:
> >
> >> Hi, AL
> >>
> >> I briefly went through Scott thesis, but I couldn't find the cell shape
> >> he used.
> >> Is the transfer tube with bulb a total new design?
> >> Does the past experience from Gordon show that pulse NMR performs on the
> >> transfer tube not good enough due to limited volume?
> >> As the bulb is not much wider than the transfer tube, I do know the
> >> volume is well defined?
> >> I am a little worried that a bulb will actually bring more complexity here.
> >>
> >> Another thing is we want to find out what is the tolerance when Mike
> >> makes the tube. That information is crucial for the design of the new
> >> bottom oven piece. Do you know about that?
> >>
> >> thanks
> >>
> >> Zhiwen