Hello. I have been reading up on quadrupole ion traps used in many mass spectrometers (I was trying to learn about mass spectrometry in relation to biological samples), and heard wind of "Penning traps" which also use electric quadrupoles for trapping, usually spoken of in conjunction with particle physics. The similarities are such that I am confused. What are the differences (are there any?) between Penning traps and the quadrupole traps used in mass spectrometers? Does the electric field for the dipoles oscillate between the end plates and the ring electrode on a Penning trap as it does for the quadrupole trap? (Does a Penning trap have ring electrodes and end plates?) I am confused.