Plotting Electric field gradient for studying the effect of DEP

I have an experimental FEM prepared for Electrophoresis and DEP study.
I am primarily using the Electrostatics module, Microfluidics module as of now.

I have explored the DEP module too, but i believe it requires me to mention about my particle's permittivity, conductivity etc. I am not really willing to see particle flow.

What i aim to analyse is the Surface velocity lines with DEP in place in the model. So far i have plotted the Surface velocity (m/s) for the setup and plotted the Electric field distribution using the following equation:
sqrt(Er*Er + Ephi+ Ephi+ Ez*Ez)

Specifically: sqrt(es2.Er*es2.Er+es2.Ephi*es2.Ephi+es2.Ez*es2.Ez)

Yes, my design is in r,phi,z coordinate system. My question:

I am not sure how do i plot the Electric field gradient next i.e ∇E^2. The quantity should have units of V^2/m^3.

Since DEP force is proportional to ∇E^2.

I believe something custom like the following should do the job:

(d(ec.normE^2,r), d(ec.normE^2,phi), d(ec.normE^2,z))

But COMSOL doesn't allow me to use commas separating those differentials.

Help will be appreciated!