Congratulations on having the seedlings sprout! I don’t have much experience with the ‘Tavor’ variety, but I did grow a few artichoke plants last year, purchased as established plants. Yes, they were slow growing, but seemed to like the warm south bed and lots of water. They would wilt if the soil was getting dry. My plants took up lots of room. Here what mine looked like in mid August:

And here it is again in mid September, looks like a more decorative variety:

I noticed the year before there were artichokes planted the in flower beds around town, the plants themselves were also quite large.

I would assume for your seedlings is the main thing your seedlings need is adequate light and temperatures to prevent stretching and lots of time, https://www.gardenweb.com/discussions/1392420/3rd-try-with-artichokes-in-z5-any-pointers?n=17

These both mention how a cooling period later on can help bud formation:

https://www.gardenweb.com/discussions/2050914/just-have-to-share-my-unusual-successartichokes?n=4

http://www.damseeds.ca/productcart/pc/viewCategories.asp?idCategory=838

Great picture, it is a beautiful plant but why did you not harvest and eat? I classify this plant of mine an educational endeavour.

The first time last year we started the seeds in Aril or May...guess too late and didn't have large enough heads, cocked it up anyway but wasn't worth the trouble.. ..not sure which one's these are