a virtuous circle

「好循環」。

反対のvicious circle、「悪循環」はよく使いますが、こちらも併せて使えるようにしておきたいですね。

例文は、前回、そして前々回と同様、CNNの記事、 'Free and easy? One man's experiment in living without money By Matt Ford' から。

’With this in mind he put the money from the sale of his houseboat towards setting up justfortheloveofit.org, a social networking Web site that aims to help reconnect people in their local communities through the simple act of sharing.

Essentially users sign up and offer skills, spaces and tools they have to others for free. When you need something, you just ask. It's a virtuous circle’.