Reconstruction of FXR beam conditions

Abstract

Abstract:Beam-envelope radius, envelope angle, and beam emittance can be derived from measurements of beam radius for at least three different transport conditions. We have used this technique to reconstruct exit parameters from the FXR injector and accelerator. We use a diamagnetic loop (DML) to measure the magnetic moment of the high current beam. With no assumptions about radial profile, we can derive the beam mean squire radius from the moment under certain easily met conditions. Since it is this parameter which is required for the reconstruction, it is evident that the DML is the ideal diagnostic for this technique. The simplest application of this technique requires at least three shots for a reconstruction but in reality requires averaging over many more shots because of shot to shot variation. Since DML measurements do not interfere with the beam, single shot time resolved measurements of the beam parameters appear feasible if one uses an array of at least three DMLs separated by known transport conditions.

Particle Beam Radiography

“…Efforts to improve FXR beam quality and accelerator reliability have continued [80][81][82][83][84][85][86][87]. They include retuning the LIA to minimize emittance growth [84] and further reducing the temporal variation of the energy, thereby reducing the corkscrew [83,86].…”

“…They include retuning the LIA to minimize emittance growth [84] and further reducing the temporal variation of the energy, thereby reducing the corkscrew [83,86]. Many of the FXR beam optimization experiments have been made possible through implementation of advanced beam diagnostics [80][81][82]84].…”

FXR LIA Optimization - Time-resolved OTR Emittance Measurement

“…Average Normalized RMS Emittance (cm-mr) Magnet scan [6] 400 OTR (G. LeSage [7]) 370 OTR (J. Jacob et. al.)…”

“…A variety of emittance measurement techniques are employed on particle accelerators today, including collimation of the beam with an array of small apertures ("pepper-pot" technique) [4], magnet scan techniques in which the beam profile is characterized as a function of varying focusing parameters [5], and multi-profile techniques in which the beam profile is characterized simultaneously at several locations [6]. Optical Transition Radiation (OTR) provides an attractive alternative to these methods and avoids many of the potential pitfalls that make other measurement techniques difficult to implement on a high-current, high-energy beam --magnet scan techniques are influenced by space charge effects (especially with solenoid focusing magnets), and the high energy at the exit of the accelerator requires pepper-pot grids of an unreasonable thickness to effectively stop the beam.…”

Flash X-Ray (FXR) Accelerator Optimization Electronic Time-Resolved Measurement of X-Ray Source Size

“…A single-cell test stand has been constructed to investigate cell voltage variations and test improvements to the pulsed power system, as well as to investigate and compensate for beamloading effects in the accelerator cells, which should markedly improve the energy stability of the beam [4,5]. In addition, transverse emittance has been measured using magnet scan [6] and pepper-pot techniques [7] as well as a time-resolved OTR (optical transition radiation) emittance measurement diagnostic [8]. Combined with time-resolved xray spot size data and beam modeling efforts, we should be able to identify key limiting factors and implement an overall plan to improve the x-ray spot size.…”