Double Penning Trap (image) Johannes Gutenberg Universitaet Mainz Caption Double Penning trap used to measure the magnetic moment of the proton. The double Penning trap is made of gold-plated cylindrical trap electrodes; the individual trap electrodes are isolated from one another using sapphire rings. During measurements the trap is in an ultra-high vacuum. To the right of the image is the outer housing of a detection instrument which allows for the observation of single protons. The entire structure is about 20 centimeters long. Credit photo/©: Andreas Moser, JGU Usage Restrictions Only to be used in connection with the press release Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.