A NEW METHOD FOR MEASURING THE MAGNETIC-FIELD IN A MICROWIGGLER BASEDON MAGNETIC-TAPE RECORDING

The new generation of FELs should be more compact than present designs . One important way to achieve this size reduction is to use microwigg lers. Measurement and mapping of the magnetic field inside electromagn etic microwigglers is at present a difficult task because of the small dimensions of the microwiggler, the requirement for high spatial reso lution in the measurement of the magnetic field, and the need to obtai n a fast response since the field-producing pulse may be of short dura tion. We present a new method for quick measurement and mapping of the microwiggler field. Like the pulsed wire method [1,2], it gives in on e measurement the magnetic field variation along the entire length of the electromagnetic wiggler. In addition it is possible to also measur e, instantaneously, the distribution of the magnetic field across the lateral dimension of the wiggler. Our method is based on the use of a magnetic recording tape which is inserted into the gap of the electrom agnetic microwiggler. The maximum local magnetic field produced during the driving-current pulse is recorded on the tape at all axial and la teral positions. The tape containing the recorded magnetic field can t hen be read (and ''heard'') by an ordinary tape recorder.