Horizontal Test Stand
Fermilab now has a completed cryostat for the Horizontal Test Stand, located in a shielding block cave in the Meson Detector Building. Designed to test both 3.9 Ghz and 1.3 Ghz 9-cell niobium cavities, the Horizontal Test Stand will play an important role in the growing ILC R&D program at Fermilab.
In order to qualify for the Horizontal Test Stand, the cavity must first get tested in the Vertical Test Stand, located in Fermilab’s Industrial Building 1. After a cavity passes the vertical test, it gets welded inside a helium vessel and dressed with a power coupler and tuner – a process that can be time consuming and reserved only for cavities that are more likely to meet performance goals. When a nine-cell bare cavity becomes a fully dressed cavity, you suddenly have something quite different that requires another test to see how it will now perform.
 |
| Fermilab is now commissioning the horizontal test stand |
 |
|
|
This time, however, the cavity gets tested horizontally with high power RF inside a cooled cryostat, in order to mimic the conditions inside the accelerator, only without the beam.
In the Horizontal Test Stand, approximately 300 kW (kilowatts) of RF power will get switched on for about 1.5 ms (milliseconds) at a time and repeat five times per second, the same way that the ILC will operate. As opposed to the vertical tests, which use lower power CW (continuous wave) RF, the horizontal test applies a much larger pulsed RF power to the cavity. This is the first time that the cavity will experience the pulsed RF power that will be similar to the conditions inside the ILC.
When testing, the cavity first undergoes RF processing, a procedure where physicists apply high power RF to blast away any lingering impurities. Similar to a stress test, physicists then apply as much power to the cavity as possible before it quenches, or fails, to see just how much it can tolerate. For the ILC cavities, the target is to reach an accelerating gradient of 35 mv/m (megavolts per meter) and a Q (quality) factor of 1010. A lower Q factor will indicate that the cavity is losing power and thus not fully efficient. The tuner motor and other components also get tested while inside the Horizontal Test Stand, giving the cavity a thorough exam before it can graduate and become part of a cryomodule.
Fermilab is now commissioning the Horizontal Test Stand and will start testing ILC cavities soon. During 2006 and 2007, Fermilab scientists built the cryogenic transfer lines to service the test stand cave and successfully cooled down the cryostat to 1.8 kelvin. A high-power, 1.3 GHz, RF system consisting of a modulator, charging supply, and 300 kW klystron was also installed and commissioned in the Meson Detector Building. This system has already been used to power Capture Cavity 2, another cavity/cryostat in the Meson Detector Building, to a peak gradient of 31.3 MV/m. The goal is for each horizontal test to take approximately ten days.
HTS- Update (ppt, 677KB)
|
