I recently asked a question conserning a planet I am designing: Can my planet maintain a magnetic field after being tidally locked?. Based on these answers I determined that my planet may be capable of having a magnetic field thanks to the decay of radioactive elements in its core creating magma currents, but it may not be strong enough to protect my planet's atmosphere from my star's solar activity, Especially considering that my star as a k7v orange dwarf will probably be proned to more frequent solar flares (for the sake of the argument let's just say the planet's magnetosphere is 1/3 of what we have on Earth). A lot of people have mentioned Venus to me as a possible solution since it doesn't have a magnetic field yet still retains a dense atmosphere to this day. The problem with using Venus as an example though is that it's not habitable. If I just make my planet's atmosphere incresingly more dense to make up for its weaker magnetosphere, the thickness may prevent sufficient sunlight from reaching plant life at the surface. On the other hand, since my plabet is tidally locked with one face always facing the star, the atmosphere on the day side is bound to be somewgat thinner than on the night side (Note: Somebody have mentioned to me that super rotating winds could carry effectivelly heat across the planet, so I don't really know how greatly will atmmospheric pressure differ between night and day. If someone can fill me in that would be wonderful)
For those who haven't read my earlier question: the planet I have in mind has a mass of 1.9 that of Earth's, a surface gravity of 1.44 g, its molten core makes up 49% of the planet's mass, it's distance from the star is 0.47 AU and its orbital and revolving period is about 0.39 Earth years or approximately 142 Earth days.
Now my question is, how thick should my atmosphere be in order to protect the surface from radiation but still be habitable.
Note: someone told me that in theory humans could survive atmospheric pressures far greater that what we have now, so I assume an alien organism should evolve far better methods to deal with pressure)