Background

• The Wien filter (AKA U-WIen) is based on the CEBAF Wien design. It was first built using brazed electrodes, spare from CEBAF V-Wien, and 20 kV SHV-style feedthroughs. New magnet coils were made for higher current (15 A) intended for beam operations at 200 keV. This higher beam energy required ~ 18 kV per electrode plate, compared to ~13 kV at 130 keV. The initial coil design did not fit in the magnet steel yoke, which had to be modified with a groove. The U-Wien was installed in the UITF beam line, it was powered up, but it was not tested with beam (need to verify this). The coil was later re-designed with a smaller profile, and now it fit int he original magnet yoke. This was implemented in the CEBAF Wiens, but the groove in the U-Wien magnet had to be 'filled back up'. The machine shop did this. The U-Wien magnet yoke and magnet coil are now the same profile and size as the CEBAF ones.

• Later on, it was removed and used as a testbed for upgrading the CEBAF Wiens for 200 keV operation. Gabriel Palacios did electrostatics simulations and re-designed the HV feedthroughs now rated for 40 kV. Other design details can be found here: [link to Gabriel's page, and to Gabriel's presentation on the Wien filter[.

• After the tests, which showed significant gas load with applied voltage, the U-Wien was disassembled and new electrode made from a single SS piece were manufactured. The thinking was that breed electrodes could trap gas, desorbing with applied voltage. This was clear from one of the breed electrodes, but was not present in the other electrode. We also thought outgassing might come from metal screws securing the major insulators that mechanically hold the electrode to the Inconel frames. All screws were replaced with ceramic ones. The last thing to try is the new single piece electrodes. This is the next test.

• All the Wien components are located in the Wien cabinet. The internal components are inside a Tupperware contained label as U-Wien. I still have to locate the pins that hold the HV spring to its cylindrical holder that attached to the feedthrough.

• A total of six, single piece SS electrode were manufactured by Xometry. Bubba is polishing two electrode, the best ones we could identify.

• The original Inconel frames that provide 15 mm gap spacing are in storage. Additional Inconel frames were made for 14 mm and 13 mm gap.

• Return to UITF Wien page