transformer high voltage spike

[Boschi]

hi, it's mi first post here in the EEVBlog forum 

i bought my first scope ever just a week ago, and since then i have worked on a tracking pre-regulator PSU.

i found this  circuit:

https://www.eevblog.com/forum/projects/very-low-noise-preregulator-for-benchtop-power-supply/

 after changing a bit the feedback using a optocupler,remove Q4 and change D3 to 5 volt i got a fully working tracking pre-regulator, but i also get some voltage spikes out of the transformer.
now im using a 60VA 12Vac transformer, but i want to upgrade the transformer to 24Vac, so the spike will become dangerous to the MOSFET.

is there something that i could do to minimize the spikes? Thanks!

in the attached photos the blue wave is the scr gate control, the purple wave is the scr trigger  and the light blue one is the rectified output of transformer