Player wants his wizard to R&D a spell

Hello, all. Apologies if this is the wrong place or flair!

A very good player (the sort that listens, takes notes and wants to miss nothing in the session) has been running a wizard for a bit, and he's level 7 now. For some background on the character, he's a bit of a prodigy (gasp).

The player approached me about creating a spell during his downtime activities, short and long rests and whatnot. He's sent me this text:

Raffghellian's Lightning Sling

(*Concentration)LEVEL: 2ndCASTING TIME:* 1 ActionRANGE/AREA: 60 ftCOMPONENTS: V, S, M *DURATION: Concentration / 1 MinuteSCHOOL: EvocationATTACK/SAVE: CON SaveDAMAGE/EFFECT: Lightning

Make a ranged spell attack at a creature that you can see within range. You sling three orbs made of lightning at the target creature. It makes a constitution saving throw or it takes 2d6 lightning damage and the target is stunned until the spell ends.

At Higher Levels. You can target an additional creature for each level above the 2nd, but you will have to chose one creature to concentrate the spell effects, the other creatures that have failed the test will only be stunned until the end of your next turn, but no damage is received.

– (3 ball bearings), a forked rod*

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So, what do you think? Maybe changing the damage to 3d4 instead of 2d6? Same total, slightly higher mininum value, goes with the Material component.

Thank you for your feedback.

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Edit: This is what I got after reading your opinions!

Raffghellian's Lightning Sling

LEVEL: 4th

CASTING TIME: 1 Action

RANGE/AREA: 60 ft

COMPONENTS: V, S, M *

DURATION: Until the end of your next turn.

SCHOOL: Evocation

ATTACK/SAVE: CON Save

DAMAGE/EFFECT: Lightning

Make a ranged spell attack at a creature that you can see within range, it takes 2d6 lightning damage on a hit, and it makes a constitution saving throw, on a failure the target is stunned until the end of your next turn.

At Higher Levels. You can target an additional creature for each level above the 2nd.

* – (3 ball bearings)