A CTAspectStack is a CTAspect combined with an amount that shows how many aspect points the stack will be made of.

It might be required for you to import the package if you encounter any issues, so better be safe than sorry and add the import.
import thaumcraft.aspect.CTAspectStack;

You can retrieve a CTAspectStack object from the CTAspectStack Bracket Handler object:

ZenScript
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val aspect = <aspect:ignis>;

Name	Type
Name amount	Type int
Name internal	Type CTAspect

ZenScript
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//They do the same, both return a new CTAspectStack
val aspect = <aspect:ignis> * 10;

val aspect1 = <aspect:ignis>.setAmount(10);