There are a few different ways to make swirls in Illustrator, using the Arc, Circle or Path tools, and even with the Blend tool. When it comes to making spiral gradients there are also different methods you can use to achieve the same effect. Today I will show you a quick and easy way to make spiral gradients in Illustrator starting with a single circle and using the powerful Transform Panel to make the gradient look exactly how you want.
Open Illustrator and make a new file at any size you want. In this case, I will make mine at 900 x 900 px.
In the toolbar, be sure to have the fill set to "none".
Select the Ellipse Tool (L) and click once over the artboard. Set the Width and Height values to 650 px and click OK.
Go to Window > Stroke and set the stroke Weight to 10 pt.
Go to Window > Gradient and be sure to have the Stroke selected.
Select the Linear Gradient and use any color combination that you want. In this case I will be using #11DAB3 and #9B1CCF for mine.
With the circle selected go to Effect > Distort & Transform > Transform.
Lastly, in the Transform Effect window apply the following values and click OK.
Now you know how to make spiral gradients in Illustrator, you can experiment with different values on the Transform window (scale, angle and copies). You can also use 3 or more colors for different gradient effects like in the following examples.