Benchmark and threshold analysis of longitudinal instability in the PSR
- Sarah M.
- Jeffery A.
- Robert J.
- Chris
A set of inductive inserts used to provide passive longitudinal space charge compensation in the Los Alamos Proton Storage Ring cause a strong longitudinal instability in the beam when the inductors are at room temperature. We use the ORBIT code to perform benchmarks of the instability dynamics, including the mode spectrum and the instability growth time. Additionally, we analyze the experimental instability intensity threshold and compare it with the simulated threshold. For all parameters benchmarked, results from simulations are in good agreement with the experimental data. The Proton Storage Ring (PSR) is the accumulator ring portion of the Los Alamos Neutron Science Center (LANSCE), a 100 kW proton driver used for neutron spallation. In order to satisfy low beam loss requirements during high intensity operations, the PSR must maintain a clean beam gap to accommodate extraction kicker rise and fall fields. In 1999 three inductive inserts were placed in the ring to provide passive longitudinal space charge compensation. Though the inductors were shown to be effective in reducing the beam in the gap, they also caused an unacceptably large longitudinal instability, and were thus removed from the ring. Later the same year, two of the inductors were reintroduced into the ring, this time heated to 125 degrees Celsius, which resolved the instability. The PSR machine now operates with two heated inductors and does not suffer from the instability during normal operation. The ORBIT code is a particle-in-cell tracking code developed for realistic modeling of beams in rings and transport lines. A primary use of ORBIT is in the design and optimization of future high intensity machines. It is therefore of particular importance to benchmark the code's algorithms which model collective effects with existing experimental data. In this work, we benchmark ORBIT's longitudinal space charge and impedance model against the PSR longitudinal instability. We compare the mode spectrum and the growth time of the instability, and additionally perform an analysis and benchmark of the intensity instability threshold. Two separate data sets are studied: One with three room temperature inductive inserts in the ring, and the other with two room temperature inductive inserts.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 977732
- Report Number(s):
- LA-UR-04-4426; TRN: US1003704
- Resource Relation:
- Conference: Submitted to 9th Euroopean Particle Accelerator Conference, July 5-9, 2004, Lucerne, Switzerland
- Country of Publication:
- United States
- Language:
- English
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