C-AD Accelerator R&D Division
Superconducting RF Group
Chemical Processing Facilities
In order to prepare the SRF cavities for testing at cryogenic
temperatures the cavities must first be cleaned. This process begins with removal of any dirt or grease in an ultrasonic bath with
a mild detergent, followed by ultrasonic cleaning with high quality DI water. This is followed by buffer chemical polishing (BCP) which is a chemical etching of the inside of the cavity to provide a
clean RF surface free of any foreign materials. This is followed by a high pressure water
(HPR) rinse of the inside of the cavity to remove any trace chemical or niobium salts that remain following the chemical etching. After this HPR process the cavity is dried
in a class 10 cleanroom to ensure the cavity is particulate free prior to
attachment of the vacuum hardware and RF test probes.
In addition, following a particularly aggressive chemical etching commonly
referred to as a heavy BCP, where 100-150 um of material is removed, the cavity is baked at 600 - 800°C
in a vacuum oven to remove hydrogen gas from the bulk niobium, and partially
anneal the material, thus increasing the size of the niobium crystal while
also reducing the stress in the material. The overall effect is a cavity
that performs better at cryogenic temperatures and exhibits less losses in
operation, resulting in a lower cryogenic load.
As the SRF group began to grow it became clear that a chemical processing
facility for BNL was necessary. As a result of several years of hard work a state of the art facility has been put in place at
Advanced Energy Systems in Medford NY. The choice of location was based on logistics and manpower necessary for its operation, and has resulted in a facility that will benefit both BNL as well as other
Academic and National Laboratories involved in SRF cavity work. The details of the various components mentioned above are given below.
The BCP Cabinet, manufactured by SPEC, is designed to accommodate
the 56 MHz RHIC Storage Cavity. This is currently our largest cavity in all respects, length, diameter and weight.
The BCP cabinet, shown below, can accommodate a cavity that is 80" long, 48" in diameter with a weight up to ~800 lbs. The chemical sump can hold 140 gallons of acid and is equipped with a
heat exchanger mated to a 7.5 Ton chiller designed to handle 17.5 kW of
heat. The fresh acid storage drums as well as the spent acid recovery drums are adjacent to the BCP cabinet thus simplifying the acid exchange process. The entire process is
PLC controlled and can be programmed with a variety of recipes depending on the cavity being processed.
The High Pressure Rinse (HPR) cabinet was also designed and built by SPEC and is again designed to
accommodate the 56 MHz RHIC Storage Cavity.
The HPR can provide up to 5 gallon per minute water flow at 1500 psi to rinse the inside of the SRF cavities. This HPR has two special provisions compared to many others currently in use at other
laboratories. First, the HPR wand comes down from the top, thus making it much easier to load and unload SRF cavities by keeping the center of gravity low. Second, the HPR
is equipped with a hot nitrogen drying feature that will provide two
benefits. First, it will reduce the amount of time a cavity needs to
drip dry in the class 10 area, allowing a cavity to be prepared
for testing much faster. Secondly, by drying the cavity before removing it from the HPR cabinet, the inner surface of the cavity will be less likely to attract any particulate matter that is
stirred up while transferring the cavity to the class 10 area for drying, thus helping improve cavity performance.
The HPR and BCP system are both tied into the 18 Mohm DI water system, manufactured by Millipore. This system is designed to provide 18 Mohm DI water at a make-up rate of ~5 gpm and is
equipped with a 1500 gallon storage tank to allow for HPR and BCP processes to be carried out without worrying about the DI water system running low
This system is also used to fill the ultrasonic cleaning tanks, which in
this case are three separate baths to cut down on the amount of DI water
that is normally drained between the washing and rinsing cycles.
The ultrasonic tanks are each 34" W x 34" D x 72" H and the cleaning
tank is equipped with 10 kW of RF power for cavity cleaning. The
other two tanks are heated rinse tanks that do not have RF transducers.
When necessary the cavities will be baked in a UHV oven
in order to de-gas the niobium as well as help partially anneal the
cavity and remove some of the stress introduced during the manufacturing
process. The oven is currently under construction, but when
complete will comfortably fit the 56 MHz RHIC Storage Cavity.
The oven provides a 72" long by 32" diameter hot zone to ensure uniform
heating of the cavity. The system is equipped with a large cryo-pump
to ensure the < 10-7 Torr vacuum is maintained at high temperature.
The system is also equipped with a residual gas analyzer and PLC control
system so that different cavity recipes can be programmed and monitored
in real time as a function of time and temperature. In addition to the
oven there is a large lift designed for loading
and unloading cavities from the oven. Once installed the entire
package will reside in a clean work space to minimize contamination of
the oven and subsequently the SRF cavities.
Chemical Processing Facility
Vertical Testing Facility
Last Modified: November 1, 2011