Magnetic field shield for high resolution nondestructive DC current monitors

点击翻译按钮获取中文摘要

A beam intensity monitor using a SQUID was designed at RCNP in order to measure the ion beam intensity in a non-destructive manner.1. Magnetic field shilding is an essential point to realize the high resolution. Shielding effects of superconductors were simulated following the London equation.2. Two types of small-sized models were tested ; a coaxial cavity and a folder type cavity with five ring type shield elements. Cavity walls were made of 1 mm thick lead.3. A double washer DC SQUID was used as the magnetic flux sensor.4. For the coaxial type cavity, the shielding efficiency of 10ィイD1-13ィエD1 was observed as expected from the numerical simulations. However, the caxial cavity cannot be used as an actual monitor, because it is generally difficult to accommodate the long cavity in the beam line.5. Shielding efficiency of the folder type cavity was measured to be 10ィイD1-8ィエD1 which was 10 times worse than numerical estimations.6. From these investigation, a current monitor was designed and fablicated. From preliminary tests, 10 nA current was detected with 1-2 nA resolution.