Add the artichoke hearts and 1/2 cup of the salted water. Cook, stirring constantly, until the rice starts to have a creamy consistency and is tender to the bite. Stir in the fennel fronds, lemon zest, Parmesan, chives, 1 tablespoon mascarpone cheese, and 1/8 teaspoon ground white pepper. Taste and season with kosher salt as needed. Cover and keep warm while you cook the scallops.