Major setbacks in RF and vacuum system - April 2008

In the beginning of 2008 we have had two major setbacks in the RF and vacuum system. Restoring these damages aquires a lot of time.

1. We broke our RF window during a vacuum backing test, when it was vacuum sealed to the RF flange on the RF input coupler using a gold O-ring.
   
   In the left picture you can see the RF input coupler (part with the copper rectangular waveguide). This part transforms the RF rectangular waveguide mode into a coaxial waveguide mode by a "door knob" mode transformer. At the end of the coaxial line the entrance iris of the cavity is positioned, so that the RF power is coupled into the cavity.
   
   Since, we use all-metal seals also the RF window was supposed to be sealed by a gold O-ring of 1 mm diameter cross section. Therefore, in the second half of 2007 the O-ring groove was adjusted. This was done at the time when the RF flange was being resoldered after the discovery of a vacuum leak in the soldering of this flange.
   
   Now, we continue using a Viton O-ring in stead of a gold one, to reduce the risk of breaking the our spare window as well. In the future, we will install a different type of RF window.
   
2. We cracked the soldering of the stainless steel flange connected to the cavity housing on the RF input coupler. This results in a big vacuum leakage.
   
   In the right picture you can the flange in which the soldering has been cracked. This flange is sealed by using a Helicoflex metal O-ring to achieve complete all-metal seals. Probably, during assembling the forces we so high on the fange that it was deforming and thereby cracking the joint between the stainless steel flange and copper part.
   
   At this moment, we are trying the repair the damage. When restored, we will use a Viton O-ring. In the future, we have to redesign the RF input coupler so that it is suitable for using metal seals.

Hopefully, we will get back on track next month by restaring the vacuum system. After a vacuum backing procedure we will start RF conditioning of the accelerator cavity.

RF input coupler installed in vacuum system. The RF window is connected to the upper RF flange of the RF input coupler.

The flange of the RF input coupler at which the inner joint was cracked when trying to assemble it to the stainless steel cavity housing using a metal O-ring.