That&#x27;s not accurate, stars have several fuel cycles for pure hydrogen.  At 1.3 solar masses you sun mostly get: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;CNO_cycle" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;CNO_cycle</a><p>As to size, on galactic scales all our current fusion designs are tiny.  Scale it up to even just 20 miles on a side and proton proton fusion is doable.  For a type III civilization capable of destroying starts that&#x27;s also tiny.  Remember your suggesting dysons spheres as the &#x27;reasonable&#x27; option.<p>PS: The proton proton chain also produces deuterium as an intermediary.  <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Proton%E2%80%93proton_chain_reaction" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Proton%E2%80%93proton_chain_re...</a>