A novel electron accelerator, Cornell Brookhaven Cornell Energy Recovery LINAC Test Accelerator (CBETA) has been successfully designed, constructed, installed and commissioned by collaboration between CLASSE and Brookhaven National Laboratory.Many unique accelerator technologies are implemented in CBETA, including photo-cathode electron injector, 4-turn superconducting RF (SRF) Energy Recover LINAC (ERL), non-scaling Fixed-Field Alternating Gradient (NS-FFAG) optics with 4x energy acceptance.The CBETA layout consists of an existing photo-cathode injector with an SRF cryomodule (ICM) as well as a main LINAC cryomodule (MLC), a NS-FFA return loop (that transports electron beams at four energies, 42, 78, 114 and 150 MeV in a single bore beampipe), and two splitter sections where the four energy beams are separated and combined. The total circumference of the CBETA loop is about 80-m.The basic requirement of the CBETA vacuum system is to achieve an adequate level of vacuum and physical aperture for transporting electron beams at four different energies.Furthermore, by the nature of this test accelerator, the vacuum system engineering must accommodate a very high density of beam diagnostics tools, such as over 150 beam position monitors, and insertable beam profile viewers.Beam path length change of up to 20° RF-phase are achieved in the splitter sections via one set of three RF-shielded sliding joints mounted on a pair of motorized stages in each of the eight-splitter beam lines.Aluminum alloy was chosen as primary beampipe construction material because of its good electric conductivity (resistive-wall), no residual radioactivity (from beam losses), low magnetization (from cold work and welding etc.) as well as its low cost of fabrication (machining, extrusion, etc.).Compact non-evaporable getter (NEG) pumps are used due to the space constraints.To preserve the high performance of the superconducting RF cavities in the MLC, all vacuum beam line components were constructed and assembled in strict particulate-controlled condition, and installed using portable clean rooms.The CBETA vacuum system installation was completed in the summer of 2019 and the entire CBETA accelerator system was commissioned shortly after.All CBTA milestones were successfully achieved, including full beam energy recovery after 8 turns of beam circulations through the SRF cavities and the NS-FFA return loop.We present the CBETA vacuum component construction and installation, and the vacuum system operational experiences.

Successful operations of the Cornell High Energy Synchrotron Source Upgrade (CHESS-U) have proven the in-service reliability of the compact non-evaporable getter (NEG) pumps in a new experimental vacuum system predominantly pumped with distributed NEG-strips and modular high-capacity NEG pumps. The 80-meter section improvement in the Cornell Electron Storage Ring (CESR) is composed of 6 double-bend achromats operating with a single positron beam up to 200 mA. After a successful commissioning period, a vacuum level of 10^-9 Torr was achieved with minimal maintenance and NEG re-activations.

The CHESS-U vacuum system experienced a catastrophic failure when a beam steering error created a pinhole leak in an undulator vacuum chamber (0.6-mm wall). The installed NEG-dominated pumping system had demonstrated an adequate pumping performance, which allowed a quick recovery and reconditioning of the affected 20+ meter vacuum section. With the hard work of the technical staff, X-ray user operations were able to resume after 10 days of recovery efforts (chamber fabrication and replacement, vacuum conditioning). The accidental air-exposure to the NexTorr pumps (combination of ion pump and NEGs) resulted in minor Argon instability issues that required mitigation. Corrective actions were developed in areas such as thermal monitoring, chamber construction, and beam steering while also granting the opportunity to test the pumping integrity of the effected NEG pumps after the exposure.

The 3-year operational experiences of the NEG pumping system will be presented.

The ITER project has the goal to demonstrate the feasibility of fusion and to advance the scientific and engineering understanding of fusion for future commercial reactors. The vacuum systems that are under development for the tokamak and supporting systems are expected to be dominated by one-of-a-kind devices due to their scale and varying operating environments.One specific challenge for these devices is the ability to process and recycle tritium, a radioactive hydrogen isotope in the fuel that is necessary for the fusion reaction to occur but is rare on Earth. Additionally, several of the vacuum systems are sensitive to water vapor which has the capability to inhibit pump performance if not removed from the gas stream. A custom designed water trap can enable both requirements to be met, and four of them are planned for the ITER vacuum system.

Due to vacuum operating pressures (as low as 1 Pa), a desiccant such as Zeolite cannot be efficiently used to adsorb and retain water vapor, so an alternative approach was chosen to utilize a cryogenically cooled water trap to desublimate water vapor from the process gas. The temperature must be lowered enough to remove the water vapor from the stream, but not so low as to remove the helium and gaseous hydrogen isotopes. With helium at a temperature of 80K available in ITER’s vacuum pumping room, this cooling load was selected as source for the water trap cooling.

To comply with the nuclear requirements, the tritium content inside the trap must be continuously monitored and removed to exhaust processing. The water trap must also be a double contained vacuum vessel with safety switches to mitigate the risk of tritium exposure to the vacuum pumping room. The tritiated water stored within must be removed batchwise to exhaust processing using heaters and inert purge gas. The capacity of the trap must be large (up to 5 kg of water) to account for the unlikely event of gross system water leaks, but in practice will accumulate water vapor at a low and steady rate of 1 Pa.m³/s. Each trap must fit within a 1 meter diameter by 1 meter tall space reservation and include embedded tubes that enable heat transfer between the cryogenic helium and the process gas.

In summary, a cryogenically cooled water trap has been designed to meet the unique requirements of ITER and its vacuum systems. Four of these traps will protect sensitive vacuum equipment from water vapor as well as enable the recycling of tritium back into the fuel.

Understanding the expected gas desorption of an accelerator is critical in the proper design of accelerator vacuum systems and can have a major impact on the machine design and cost. From some of the earliest work on the subject for the Cambridge Electron Accelerator up through and including LHC, desorption measurements have played an important role in predicting vacuum behavior of large accelerators susceptible to synchrotron radiation. Much of this early work served well the machines they applied to and other machines with similar parameters and material choices. But as machines continue to be developed with higher energy, beam current, stability and susceptibility to e-cloud, novel materials need to be investigated to improve vacuum, and in some cases reduce SEY (Secondary Electron Yield). Part of these investigations require careful study of their desorption yields. This would benefit future upgrades to the existing NSLS-II facility as well as other synchrotrons facilities with stringent design specifications. Additionally, such a beamline could have a major impact on the selection and validation of proposed materials and components for EIC, including possible coatings for the electron storage ring, IRs (Interaction Regions) and the beam screen of the Hadron/Ion ring. Desorption rates of these newly proposed materials would be used as inputs to advanced modeling tools such as Molflow and SynRad for accurate predictions of vacuum behavior. A beamline at NSLS-II, dedicated to the PSD/ESD study of novel and proposed vacuum materials has been constructed and commissioned to advance further research into desorption behavior. The PSD of stainless steel and OFHC copper to be used for the Rapid Cycling Synchrotron of EIC have been measured and compared to prior work to baseline the system, with plans to evaluate the NEG coated chambers for the EIC electron storage ring. The layout of the experimental line and the commissioning measurements will be presented.