Atrial fibrillation (AF) is the most common type of cardiac arrhythmia. An arrhythmia is a problem with the rate or rhythm of the heartbeat. The purpose of the study is to see whether an investigational medical device called the DiamondTemp Ablation Catheter (also called the DiamondTemp Ablation System) can restore the heart to a normal heart rhythm. Every participant will receive the same treatment, radiofrequency (RF) ablation, for atrial fibrillation with the DiamondTemp Ablation System. The results of this study may be used to help the Food and Drug Administration (FDA) determine if the device should be approved in the USA.