insert 36 is covered by a respective frame 46 which holds its associated insert 36 and seals 40 42 in place in recess 32 with the aid of a plurality of screws not shown that extend through screw holes 48 between the two seals 40 and 40 u2032 there is provided at least one passage to atmosphere shown at 52 in fig4 this passage is fabricated to extend to a location outside of enclosure 4 for access when the system is totally assembled passage 52 allows for leak checking both seals 40 and 40 u2032 thus both sealing with respect to the coolant fluid 54 between chamber 2 and wall 4 and sealing with respect to the vacuum in region 10 can be checked with one port rf energy can flow from coil 8 into region 10 through inserts 36 and slots 34 fig5 shows another form of construction of the embodiment of fig1 in the form of construction shown in fig5 housing 2 is provided with vertically elongated slots 60 that extend through the entire wall thickness of housing 2 in the illustrated embodiment each slot 60 has an outwardly diverging or flaring portion adjacent the exterior surface of housing 2 and a portion 64 having a surface that is perpendicular to the.