Is it possible to obtain a MS in a physics field and say a MS in say computation?
How common is it?
It really depends on the school and its admission policies, but in prinicple, I'm sure it's possible. I know people with PhDs in other branches of physics who have then gone into a medical physics MSc program.
Concurrently or sequentially likely won't make too much of a difference. It will take just as long to get both degrees.
Concurrently might not be possible 'cause of administrative regulations. My school won't even let you apply for two different degree programs at the same time. Other schools give the degrees from two separate schools, and they may not allow concurrent enrollment. This is one of those bureaucratic minefields you want to wade through before you apply if your serious about it, and get everything in writing.
Separate names with a comma.