Multiple-charge beam dynamics in an ion linac

Abstract

An advanced facility for the production of nuclei far from stability could be based on a high-power driver accelerator providing ion beams over the full mass range from protons to uranium. A beam power of several hundred kilowatts is highly desirable for this application. At present, however, the beam power available for the heavier ions would be limited by ion source capabilities. A simple and cost-effective method to enhance the available beam current would be to accelerate multiple charge states through a superconducting ion linac. This paper presents results of numerical simulation of multiple charge state beams through a 1.3 GeV ion linac, the design of which is based on current state-of-the-art superconducting elements. The dynamics of multiple charge state beams are detailed, including the effects of possible errors in rf field parameters and misalignments of transverse focusing elements. The results indicate that operation with multiple charge state beams is not only feasible but straightforward and can increase the beam current by a factor of 3 or more.

Heavy-ion LINAC development for the US RIA project

“…As was discussed in ref. [6,7] multi-q beam requires corrective steering in order to avoid appreciable emittance growth. Therefore our simulation was done in the presence of steering elements along the linac.…”

“…As discussed in ref. [6,7], full 3D numerical simulations show such operation to be straightforward, entailing a modest increase of longitudinal and transverse emittance, which remains well within the linac acceptance. Also, it should be noted that the feasibility of multiple charge-state (multi-q) beam acceleration has been experimentally established in a series of tests with the existing SC ion accelerator ATLAS [8,9].…”

“…Such an immense margin for emittance growth makes possible a novel operating mode for the linac, in which the beam contains multiple charge-states [6,7]. By simultaneously accelerating several of the multiple charge states resulting from stripping the beam, a much higher portion of the stripped beam can be utilized.…”

The US Rare Isotope Accelerator project

“…While this is achievable with standard techniques for light ions, for the heaviest ions such as uranium, the present performance of even the best existing ECR sources would limit conventional accelerators to power well below that. This limitation is overcome in the RIA driver by accelerating multiple charge states [1] of the heavy ions of interest through the linac making use of the large acceptance of the superconducting linac. Taking as an example the most difficult beam, uranium at 400 MeV/u, we would find two charge states of uranium from an advanced ECR source [2], 28+ and 29+, transported from the ion source platform, bunched at 28.7 MHz and the 2 charge states loaded into successives buckets of the 57.5 MHz RFQ.…”

The LIDOS.RFQ.Designer development

“…Concurrently simulation of different ion types is topical for generation of advanced facility for the production of nuclei far from stability [2]. Optimization problems are currently central generation superpower accelerations for ADT applications, as example, which must be practically free of beam losses.…”