Penetration of Electro-Magnetic Fields through a Thin Resistive Layer

In 1999 and 2000 experiments were carried out in the EPA machine to investigate the shielding properties of a ceramic vacuum chamber with a thin Titanium coating on the inside. A single electron bunch was extracted and sent consecutively through two ceramic chambers. The upstream chamber was coated, the downstream was not and served as a reference. The magnetic field was measured in the horizontal plane close to the outer ceramic wall on both chambers. Four different configurations of the upstream chamber were measured. In the first configuration no second shield was installed. Then three different shields were installed at the outside of the ceramic. The penetration of the electro-magnetic fields through the thin Titanium layer was very small in the first case (reduction of nearly 40dB) but substantial in the three other cases.