Engineering topics
Ekdahl, Carl August Jr.
Publications and source records attributed to Ekdahl, Carl August Jr..
The Dual-Axis Radiographic Hydrodynamic Test Facility Capability eXpansion (DCX) Strategy
The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility is a vital and important part of the Nation’s nuclear security enterprise. The Department of Energy/National Nuclear Security Administration (DOE/ NNSA) Stockpile Stewardship Management Plan (SSMP) identifies DARHT as a weapons mission critical facility along with the need to modernize DARHT to support weapons modernization efforts. With more than two decades of operations, DARHT has a storied history. Conceived in the 1970s, constructed in the 1990s, and operational since 2000, DARHT has advanced from open-air hydrodynamic experiments (hydros) to foam-confined hydros, to vessel-confined hydros, and in 2022, the 75 th hydro was successfully completed. Radiography has advanced from a single-axis, single-pulse system to a dual-axis, multi-pulse capability to variable fields of view (VFV) on both accelerators. The culmination of these experiences, accomplishments, and advancements has brought us to a very important question: What do the next two decades at DARHT look like? The world is not the same place it was in the 1990s when construction at DARHT was in progress. Evolving threats, an expanding mission, and technology changes necessitate adaptation. The 2018 Nuclear Posture Review (NPR) states that the nuclear weapons infrastructure has suffered the effects of age and underfunding with no margin for further delay in recapitalizing the physical infrastructure. To adapt, the aging facility, accelerators, vessels, and detector systems require improvements to ensure DARHT remains the Nation’s hydrodynamic data foundation for stockpile certification, safety, surety, and global security threats.
Beam Envelope Stability in an Advanced Linear Induction Accelerator
A new linear induction accelerator (LIA) is under development for multipulse flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). It is, therefore, more susceptible to the parametric beam envelope instability (PEI), which has an instability threshold that has usually been typified by the vacuum phase advance per cell exceeding some large fraction of π . Here we derive a threshold criterion for PEI that depends not only on the magnetic field, but also on the beam space charge and emittance. A tune designed to suppress BBU in Scorpius is shown to be stable to the PEI according to this criterion, and also by the lack of emittance growth in particle-in-cell (PIC) code simulations.
A Diamagnetic-Loop-Based Beam Radius Monitor (BRM)
We describe a non-interceptive beam radius monitor that employs a diamagnetic loop. In order to increase the signal strength, the diamagnetic loop radius is considerably smaller than the outer wall radius, the device is placed inside a specially built solenoid magnet to allow independent adjustment of the guide magnetic field strength, and there are two counter-wound diamagnetic loops to double the signal strength and to eliminate common mode signals. This device is calibrated and the magnitude of the electron beam offset/tilt contribution to the measured radius estimated. This device is ready to be validated on an electron induction LINAC such a DARHT-I or DARHT-II.
Particle-In-Cell Computer Simulations of Beam Spill in the Scorpius Injector
Computer simulations of beam transport in the Scorpius injector were performed using the particle-in-cell computer code LSP. The simulations were used to predict spot size growth due to electron stimulated emission of ions from beam spill on the anode stalk and the entrance transport region.
Initial conditions for simulations of beam physics in linear induction accelerators
Flash radiography of hydrodynamic experiments driven by high explosives is a well-known diagnostic technique in use at many laboratories. At Los Alamos, the DualAxis Radiographic Hydrodynamic Test (DARHT) facility two linear induction electron accelerators (LIAs) make the bremsstrahlung radiographic source spots for point projection radiographs from orthogonal views. A new LIA, called Scorpius, is presently under development to advance this technology. To better understand electron-beam physics in these LIAs, numerical simulations are frequently performed with the objective of improving the radiography. At Los Alamos we frequently use the TRAK ray-trace and LSP particle-in-cell (PIC) codes to simulate the injector, and the XTR and LAMDA envelope/centroid codes along with LSP to simulate transport of the accelerated beam through the LIAs. The LIA simulations need the injected beam parameters as initial conditions for calculating beam transport and stability. The determination of these initial conditions is the topic of this note.