ends so as to be closer to the rest of the enclosure 302 as shown in fig8 b to achieve this effect an attenuating material 360 may be placed near the antenna 338 in the region which is to be attenuated fig8 c shows an attenuating material 360 placed over antenna 338 at the ends of the enclosure 302 note that like fig7 c the attenuating material 360 covers the antenna 338 in the y dimension but covers only a portion of each coiled segment 371 in the x dimension a similar mechanism may be used for helical antennas such as that of fig6 for example if the enclosure of fig6 had a plasma density profile such as that shown in fig7 a the attenuating material 360 may be placed over the center of the enclosure 302 near top surface 339 and bottom surface 341 as shown in fig9 a this figure shows that the attenuating material 360 extends over a portion of the x dimension but across the entire z dimension similarly if the enclosure 302 of fig6 had a plasma density profile such as that shown in fig8 a the attenuating material 360 may be placed over the sidewalls 338 340 as shown in fig9 b this figure shows that the attenuating material 360 extends over a portion of the y dimension but across the entire z dimension while fig7 c 8 c and 9 a b show the attenuating material 360 extending beyond the relevant dimension of the enclosure 302 the disclosure is not limited to this embodiment in certain embodiments the attenuating material 360 may extend across only a portion.