Wednesday, 31 August 2016

Ta da!

My apologies for the delay in updating the blog - with the refurbishment works now underway in our NMR  Facility and our 600 Cryoplatform deciding to commit seppuku (presumably in solidarity with her fallen comrade) I haven't had an opportunity to post the final images until now.

I am going through old Oxford patents trying to piece together a better understanding of what has been revealed (and would welcome any input from readers!) but can at least identify the cryoshim windings that are visible (picture left) beneath the layers of black tape.   
The man responsible for carrying out all of this hard work with such care and attention to detail has suspended the original front piece from the rear of the magnet - a beautiful finishing touch, thank you Sam!  :)

Friday, 26 August 2016

And we're through!

But we've decided to open up the window a little more so that the internals are more comfortably observed from standing height, so just a sneak preview for now... 


Almost there...

After a day of respite, the magnet was back under the angle grinder this morning and quick work was made of the 20K radiation shield (aluminium) and liquid helium vessel casing (stainless steel again). 
What lies behind door number 5?


Having cut through the liquid helium vessel, we can now see the aluminium baffle surrounding the magnet itself.  This baffle protects the magnet from fluctuations during helium fills (as well as serving as an additional radiation shield).  In the image above we can also see the quench resistors that protect the windings from the huge currents that reside therein in the event of quench.  These resistors are arranged in a double row on top of the baffle and run behind the bore tube and around the other side.

In the images to the right, we can see the transfer lines that direct the flow of liquid helium during a fill (front line) and measure the helium level when required (back line).

The aluminium baffle should be the last significant barrier to the windings - once that's down, we'll be down to a Stanley knife!

Wednesday, 24 August 2016

Smooth (Density) Operator

After more hard yakka and some smoothing and cleaning up, things are shaping up better than imagined!
Behold - the 20K radiation shield!
(or the outside of it, at least)
Spec Trek: Into Darkness (ugh don't get me started)
(the liquid nitrogen is fed into this void)

As can now be seen, this particular super-conducting magnet features an annular liquid nitrogen vessel which is separated from the 20K radiation shield (this shield is another 4-5mm layer of aluminium)  by an additional vacuum layer.  The single layer of aluminium foil also acts as a radiation shield. 


This is quite different to what was exposed in the dissection of a 270 MHz Oxford magnet by JEOL USA Inc. in around 1999 (see right).  The design change may be down to the relative ages of the magnets, or may be associated with the higher field strength of our magnet.  For field strengths below 300 MHz, it is in fact not necessary for the entire solenoid to be submerged in liquid helium (the vapour is sufficiently cold to maintain the superconducting state).  For (lots) more information, see the full story of JEOL's dissection here.

Tuesday, 23 August 2016

And we're through!

In life, the magnet required regular offerings of nitrogen and helium.  In death she requires sacrifice in other forms, including cutting blades and drill bits.  
She will not go gentle into that good night, it seems.

Grinder: 1  Magnet: 0

However where there's a will (and a strong, careful pair of hands) there's a way.  The cut-out section from the top of the liquid nitrogen tank (pictured right) is aluminium so it is actually surprisingly light, but it's extremely tough when you try to cut through it!


With the upper cap now out of the way, we can see the liquid helium stacks and the bore tube. 



The inner void that's also visible (see right) would have been under high vacuum before the magnet was decomissioned.

Up next: the 20K radiation shield!

Hello Spinlanders. Do you want to play a game?

Turns out a jigsaw and a thick aluminium can are a nightmarish combination (although not as nightmarish as the title might suggest).

The void that is now visible was the liquid
nitrogen reservoir

The aperture visible directly below the liquid nitrogen
port allowed nitrogen gas to vent during weekly fills. 
Liquid nitrogen was fed into the reservoir through a
similar aperture on the other side.

After our quick progress yesterday through the outer stainless steel layer, it was a real struggle to cut a window into the liquid nitrogen vessel.  This vessel is constructed from a sheet of aluminium ca. 4-5mm thick, and getting through it with the jigsaw was hard going!

We have now arrived at a point that differs somewhat from the records we have available and it's not entirely clear how best to proceed.  But fortune favours the bold, so forward we go...

Monday, 22 August 2016

Hull breach! Shields at 0%!

One layer down, five to go.

Well much to my delight and contrary to expectation, the excellent fellow charged with the exciting task of peeling this particular onion has managed to cleanly extract a segment of the outer casing in only 3 hours!  Huzzah!  

All of that tin foil (aluminised Mylar, actually) is only serving to solidify this very Chrismassy feeling.  

BoPET (Biaxially-oriented polyethylene terephthalate)
by Rohieb - own work, CC BY-SA 3.0,

Mylar is also used in emergency blankets to treat shock.
Mylar, or biaxially-oriented polyethylene terephthalate, is a polyester film that when metallised by vapor deposition of aluminium reflects infrared radiation from the inside of the outer can (remember only ca. 3mm of stainless steel separates this space from the magnet's room-temperature environment, and the next layer in is the liquid nitrogen reservoir). 
Prior to the quench, the space that this super-insulation fills was under vacuum.

Cheeky selfie!

Next up on the cutting agenda: 
the liquid nitrogen vessel.