public ActionResult GeneratorDetails(GeneratorDetailsModel model)
{
	// отображение странички генерации			
	return PartialView("GeneratorDetailsContent", model);
			
}

public FileStreamResult GeneratorFiles(GeneratorDetailsModel model)
{
       // запрос файла
	return File(model.File, "text/plain", "file.txt");
}

<form>
...
<input type="submit" value="Generate"  />
@{
	if (this.Model.FilesReady)
	{
		@Html.ActionLink("Download", "GeneratorFiles", "GeneratorDetails", new { filename = "file.txt" })
	}
}

</form>

<a href="/GeneratorDetails/GeneratorFiles" download>
	<button type="submit">Generate</button>
</a>

<form id="mainForm"...>
...
<input type="submit" value="Generate"  />

@Html.ActionLink("Download", "GeneratorFiles", "GeneratorDetails", new { filename = "file.zip", id = "FileLink", @class = "hidden" })

</form>

<script ...>
var form = $("#mainForm");
var link = form.find('#FileLink');
link[0].click();
</script>