Development of robust machine-learning (ML) based surrogates for particle accelerators can significantly benefit the modeling, design, optimization, monitoring and control of such accelerators. It is desirable that the surrogate models embed fundamental physical constraints to the interaction and dynamics of the beams, for which an accelerator must be designed to operate upon. We implement and train a class of phase space structure-preserving neural networks - Henon Neural Networks (HenonNets) [1], for nonlinear beam dynamics problems. It is demonstrated that the trained HenonNet model predicts the beam transfer matrix to a reasonably good accuracy while strongly maintaining the symplecticity. To explore such model's applicability and flexibility for high brightness or intensity beams, we further test it with beam dynamics in the presence of electrostatic and radiative collective effects. Our results indicate that HenonNet may be used as a base ML model for the surrogate of complex beam dynamics, thus opening up a wide range of applications.

The Los Alamos Neutron Science Center (LANSCE) simultaneously provides both H and H beams to several user facilities. Opposite polarity beams are usually accelerated in the linac during the same macropulse when beam-loading limits are not exceeded. Presently, the Weapons Neutron Research (WNR) H and Isotope Production Facility (IPF) H beams are accelerated simultaneously during the same macropulse. The amplitude of the cavity field in the last 201-MHz buncher, located in the common transport just upstream of the DTL, is a compromise between the optimal values for each beam. Recent beam dynamics studies have shown that implementing a debuncher cavity in the H lowenergy beam transport would allow for more optimal operation of both beams. For this application where space is limited, a compact 201-MHz quarter-wave cavity will be used. This paper will report on the beam dynamics simulations performed and the quarter-wave cavity design being developed to address this issue.

A design for a negative ion source based on electron cyclotron resonance plasma heating and ionization by surface sputtering is presented. The plasma chamber of the source is an rf-cavity designed for TE111 eigenmode at 2.45 GHz. The desired mode is excited with a loop antenna. The ionization process takes place on a cesiated surface of a biased converter electrode (cathode). The ion beam is further “self-extracted” through the plasma region. The magnetic field of the source is optimized for both, plasma generation by electron cyclotron resonance heating, and beam extraction. The source can be used for a production of a variety of negative ions ranging from hydrogen to heavy ions. The potential users for the source concept range from large scale accelerator facilities, utilizing H ion beams, to dc tandem accelerators for heavy ions. The benefits of the source concept compared to widely used filamentand inductively coupled rf-driven sputter-type sources are the lack of consumable parts and low neutral pressure minimizing the stripping losses of negative ions. In this article we will focus on the H production scenarios with the novel source. The benefits and drawbacks of higher frequency operations are also discussed.

A design for a novel H− ion source based on electron cyclotron resonance plasma heating and surface ionization is presented. The plasma chamber of the source is an rf‐cavity designed for TE111 eigenmode at 2.45 GHz. The desired mode is excited with a loop antenna. The ionization process takes place on a cesiated surface of a biased converter electrode. The H− ion beam is further “self‐extracted” through the plasma region. The magnetic field of the source is optimized for plasma generation by electron cyclotron resonance heating, and beam extraction. The design features of the source are discussed in detail and the attainable H− ion current, beam emittance and duty factor of the novel source are estimated.

Presently, the Los Alamos National Laboratory is in the process of planning a refurbishment of various subsystems within its Los Alamos Neutron Science Center accelerator facility. A part of this LANSCE facility refurbishment will include some replacement of and improvement to existing older beam-diagnostics instrumentation. While plans are still being discussed, some instrumentation that is under improvement or replacement consideration are beam phase and position measurements within the 805-MHz side-coupled cavity linac, slow wire profile measurements, typically known as wire scanners, and possibly additional installation of fast ionization-chamber loss monitors. This paper will briefly describe the requirements for these beam measurements, what we have done thus far to answer these requirements, and some of the technical issues related to the implementation of the instrumentation.

There is presently an ongoing effort to develop beam position and phase measurements for the Los Alamos Neutron Science Center (LANSCE) linac associated with an improvement project known as the LANSCE Refurbishment. This non-interceptive measurement's purpose is to provide both measurements of beam phase for determining RF-cavity phase and amplitude set points, and position for determining the 805-MHz linac input beam transverse position and trajectories. The measurement components consist of a four-electrode beam-position and phase monitor (BPPM), a cable plant that transports the 201.25-MHz signals, electronics capable of detecting phase and amplitude signals, and associated software that communicates with a mature LANSCE control system. This paper describes measurement requirements, proposed beam line device, initial concepts for the associated electronics, and some of the issues developing beam measurements for an operational facility.

Los Alamos completed design, fabrication, procurement, and initial testing (without beam) of the SNS medium-energy beam-transport (MEBT) chopper, including the meander-line traveling-wave structure and the electrical-pulser system. This report reviews the design parameters and discusses the fabrication process for the chopper structures, including measurements of the impedance and rise time. (The MEBT vacuum system and chopper-target beam stop were developed at and reported by LBNL.) We discuss the specifications for the pulse generator and its fabrication and testing at Directed Energy, Inc. of Ft. Collins, CO. Experimental tests of the chopper system are currently being performed at the SNS site at ORNL and will be reported separately.

Los Alamos National Laboratory is building room-temperature rf accelerating structures for the Spallation Neutron Source (SNS). These structures, for Hions, consist of six 402.5 MHz, 2 MW drift-tube linac (DTL) tanks from 2.5 to 87 MeV followed by four 805 MHz, 4 MW coupled-cavity linac (CCL) modules to 186 MeV. The DTL uses permanent magnet quadrupoles inside the drift tubes arranged in a 6βλ FFODDO lattice with every third drift tube available for diagnostics and steering. The CCL uses a 13βλ FODO electromagnetic quadrupole lattice. Diagnostics and magnets occupy the 2.5βλ spaces between 8-cavity segments. This paper discusses design of the RF cavities and low-power modeling work

The Spallation Neutron Source (SNS) linac accelerates 52-mA peak of pulsed H- particles to over 800 MeV. There are three types of accelerating structure in which the beam position must be measured: the drift-tube-linac (DTL); cavity-coupled-linac (CCL); and superconducting-linac (SCL)[1, 2]. Beam with a 402.5-MHz structure is injected into a 402.5 MHz DTL, followed by 805-MHz CCL and SCL structures. The position monitor pickups are all of the shorted-microstrip type with apertures of 2.5-cm, 3-cm and 7.3-cm-dia. In all cases, we down convert signals from the beam position pickups to a 50-MHz intermediate frequency (IF) for processing. We use the sampled in-phase and quadrature-phase (I&Q) processing technique to obtain the amplitude and phase information of the IF signals. All of the electronics are PCI-based hardware installed in PC computers employing standard technologies. LabVIEW/sup TM/ is used for all of the acquisition, processing, and serving of the data to ethernet, and hence, the control system. The design of this beam position system hardware is described herein.