punctuation - Use of a hyphen when using a noun as an adjective

In my academic work (physics), I often use a noun as an adjective, and this seems to be a common practise to avoid long sentences. For instance sphere packing stands for packing made of spheres.

1. Is that correct? Is there a reason to avoid doing that?


2. What if I am given information about the spheres: they are soft spheres? I should talk about a soft-sphere packing, right?


3. Is the hyphen between soft and sphere mandatory, optional, or wrong? Is that always the case when an adjective-noun group becomes an adjective? References are appreciated!

Here are a few examples taken from my work. Some come from a plural, others from a singular. Please correct them if they are wrong.

• Soft-sphere packings (packings made of soft spheres)


• Infinite-dimensional limit (limit in which the dimension tends to infinity)


• Low-connectivity particles (particles having a low connectivity)


• Sparse-matrix methods (methods used with sparse matrices)


• Non-zero energy (energy not being zero)


• Non-zero-energy mode (mode having an energy that is not zero)