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Neutron Crystallography Data Collection and Processing for Modelling Hydrogen Atoms in Protein Structures

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H- radio frequency source development at the Spallation Neutron Source.

R F Welton¹, V G Dudnikov, K R Gawne

¹Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37830-6471, USA. welton@ornl.gov

The Review of Scientific Instruments

|March 3, 2012

Summary

Antenna failures at the Spallation Neutron Source (SNS) limit operational uptime. This study investigates failure mechanisms and mitigation strategies, including developing a new external antenna source for improved reliability.

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Area of Science:

Particle accelerators
Plasma physics
Materials science

Background:

The Spallation Neutron Source (SNS) operates at high beam power (∼1 MW) and current (∼38 mA), requiring reliable ion source performance.
Internal RF antennas in the H(-) ion source are a leading cause of downtime due to failures.
Increased duty factor and RF power have exacerbated antenna failure rates, impacting overall accelerator availability.

Purpose of the Study:

To identify the physical mechanisms responsible for the failure of internal RF antennas in the SNS ion source.
To describe efforts to mitigate antenna failures through design modifications and improved operational criteria.
To report on the development and performance of an external antenna source as a long-term solution.

Main Methods:

Statistical analysis of approximately 75 failed antennas from the SNS.
Scanning electron microscopy (SEM) of antenna surfaces and cross-sectional analysis.
Calorimetric heating measurements to assess thermal load on antennas.

Main Results:

Identified failure mechanisms related to antenna geometry, material degradation, and thermal stress.
Implemented mitigation strategies including modified antenna design and stricter acceptance criteria.
The external antenna source demonstrates comparable beam currents and potential for higher performance (up to ∼100 mA demonstrated).

Conclusions:

Internal antenna failures are primarily driven by operational stresses and material limitations.
Mitigation efforts have improved the reliability of the current antenna design.
The external antenna source represents a promising long-term solution for enhanced ion source reliability and performance at the SNS.