Red, ³⁸ 26 bytes

Thanks to @9214 for telling me about the loop command for -12 bytes.

x: a loop b - 1[x: a ** x] 

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Red, ^{38 26} 37 bytes

Thanks to @9214 for telling me about the loop command for -12 bytes.

+11 bytes to fix invalidities brought out by @Bubbler.

func[a b][x: a loop b - 1[x: a ** x]] 

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Red, 38 bytes

x: a while[b > 1][x: a ** x b: b - 1]x 

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Red, ³⁸ 26 bytes

Thanks to @9214 for telling me about the loop command for -12 bytes.

x: a loop b - 1[x: a ** x] 

Try it online!