Field electron emission enhancement of amorphous carbon through a niobium carbide buffer layer

Xu, Ling; Wang, C.; Hu, Chaoquan; Zhao, Zhongyi; Yu, Wenjie; Zheng, Weitao

doi:10.1063/1.3032686

Cited by 2 publications

(1 citation statement)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The exact chemical form, bonding strength and effect on the work function for carbon and hydrocarbon compounds on transition metals is a very rich and complex topic [23][24][25][26][27]. To estimate how hydrocarbon contaminants can affect field emission for SRF cavities, the work function of niobium samples with hydrocarbons at the top surface was measured and compared to work function of the niobium oxide.…”

Section: Insert Figure 3 (Height~3" Width~38")mentioning

confidence: 99%

In-situ plasma processing to increase the accelerating gradients of superconducting radio-frequency cavities

Doléans

Tyagi

Afanador

et al. 2016

Nuclear Instruments and Methods in Physics Research Section A:

View full text Add to dashboard Cite

A new in-situ plasma processing technique is being developed at the Spallation Neutron Source (SNS) to improve the performance of the cavities in operation. The technique utilizes a low-density reactive oxygen plasma at room-temperature to remove top-surface hydrocarbons. The plasma processing technique increases the work function of the cavity surface and reduces the overall amount of vacuum and electron activity during cavity operation; in particular it increases the field-emission onset, which enables cavity operation at higher accelerating gradients. Experimental evidence also suggests that the SEY of the Nb surface decreases after plasma processing which helps mitigating multipacting issues. In this article, the main developments and results from the plasma processing R&D are presented and experimental results for in-situ plasma processing of dressed cavities in the SNS horizontal test apparatus are discussed. 2. FIELD EMISSION AND END-GROUP THERMAL INSTABILITY LIMITING THE ACCELERATING GRADIENTS IN THE SNS LINAC Field emission in superconducting radio-frequency (SRF) cavities is a well-known limiting factor for operation at high accelerating gradients [1-3]. Beyond certain electric field thresholds, the electrons from the metal surface of the cavity have a non-negligible probability of tunneling out. The field emitted electrons are accelerated by the stored electromagnetic fields in the cavity and subsequently deposit their energy by collision with the cavity radio-frequency (RF) surface leading to vacuum activity, increase of the surface temperature and Bremsstrahlung radiation. If the deposited energy-density is larger than the cooling capacity it can also lead to thermal breakdown of the superconductivity.

show abstract