Talk:Spherical tokamak

How close to ignition

How do current STs compare to conventional tokamaks in density, temperature and confinement time re Lawson criterion and fusion triple product? - Rod57 (talk) 11:50, 9 December 2015 (UTC)

Sorry for the rather tardy reply. ST experiments to date are roughly the same level of development as tokamaks in the 1980s. The best results so far are from MAST, which reached 10^20/m3, compared to 10^22/m3 for JET at the end of its runs. MAST is currently being rebuilt as MAST Upgrade and should reach JET-level density and confinement times on the order of 5 seconds. Time will tell, it won't start early operations until 2017. Maury Markowitz (talk) 02:55, 23 January 2016 (UTC)

What is the confinement area

Since it says the magnets are inside it, it sounds like the vacuum chamber (rather than the plasma surface). Is this the normal meaning of confinement area ? - Rod57 (talk) 11:49, 9 December 2015 (UTC)

@Rod57: Sorry, I'm having trouble parsing this, but I'll take a stab at it. Aside from the geometry and magnet wiring, the cross-sectional layout of an ST is basically the same as a traditional tokamak. Both have the magnets outside some sort of first wall. In fact, MAST Upgrade's cross-section is not all that different than DEMO. Is this what you're asking? Perhaps there's a passage in the body you can point to that I could address? Maury Markowitz (talk) 02:59, 23 January 2016 (UTC)

@Maury Markowitz: Thanks for trying. The article uses 'confinement area' 9 times (sadly without references to follow up). I'm not sure the term has a clear meaning in relation to ST or tokamaks in general, or that it is being used consistently. The name 'area' makes it sound like it refers to a region on the cross-section but the way it is used makes it sound like a volume of space (which I guess given the symmetry is equivalent). Sometimes it sounds like they mean the region of the compressed plasma eg : "In the tokamak, stellarator and most pinch devices, the plasma is forced to follow helical magnetic lines. This alternately moves the plasma from the outside of the confinement area to the inside." but then it says "The later two of these designs place the magnets inside the confinement area, so the toroidal vacuum vessel can be replaced with a cylinder." and "Spheromaks are essentially "smoke rings" of plasma that are internally self-stable. They can, however, drift about within their confinement area." - Should some of these uses be corrected, &/or can someone provide a definition of CA (in the context of ST or tokamaks in general) ? - Rod57 (talk) 02:04, 24 January 2016 (UTC)

Excellent review.

"The name 'area' makes it sound like it refers to a region on the cross-section but the way it is used makes it sound like a volume of space (which I guess given the symmetry is equivalent)." Correct, the area in question is normally seen in cross sectional diagrams, but the actual geometry is that area pulled through the characteristic shape of the reactor - normally a torrid. So in the ST the area is roughly D shaped and the volume is roughly spherical.

"The later two of these designs place the magnets inside the confinement area" Yes, this passage is unclear because there is no first wall in these designs, but there is still a confinement area and this should be made more clear.

"They can, however, drift about within their confinement area" This is correct; in this case the confinement are is a rectangle and the volume normally a cylinder.

"someone provide a definition of CA" I'm not sure why one is needed? The term is not a specific one, and is not intended to be a defined term in the context you seem to be suggesting. Googling the term you will find many variations - "confinement area", "reaction area", "central region", "cylindrical region where it is confined", "confined areas", "confinement: holding the nuclei within a limited space". All of these are referring to the same concept, the specific terminology is not important and I simply selected a single variation, by far the most common combination, to refer to it every time. Maury Markowitz (talk) 02:48, 24 January 2016 (UTC)

Ok I've made a bunch of edits along these lines, let me know what you think. Maury Markowitz (talk) 14:58, 24 January 2016 (UTC)

Thanks - I like your edits, but it still seems we have inconsistent use of 'confinement area'. The whole tokamak article does not use the phrase once. It's in the lead of this article so it should be clear. Its very hard to read an article with apparently contradictory uses of the same undefined term.

Unless this is a well defined term in the tokamak literature Could we change each occurrence to which ever of 'plasma volume' 'initial/final plasma volume' 'region plasma is allowed to traverse' 'vacuum vessel' etc is appropriate ? - Rod57 (talk) 21:43, 24 January 2016 (UTC)

Sorry, is there a remaining inconsistent use of the term? I thought I had edited them all. Maury Markowitz (talk) 19:36, 26 January 2016 (UTC)

Helicity injection and non-inductive startup

Helicity injection (local or coaxial) and non-inductive startup seem to be relevant to most/all spherical tokamaks - so could describe here rather than grow it in Pegasus/URANIA ? - Rod57 (talk) 15:04, 4 May 2019 (UTC)

Start a list of STs

We have a section of external links to operational STs. Could we extend it to a list or table of past and present STs ? Ideally a table with some dates, and maybe major design & operational parameters ? - Rod57 (talk) 09:16, 25 October 2019 (UTC)