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Conceptual Design of Highly-Constrained Splitters for the FFA@CEBAF Energy Upgrade Study

Ryan Bodenstein, Jay Benesch, Alexander Coxe, Kirsten Deitrick, Brian Freeman, Randika Gamage, Reza Kazimi, Donish Khan, Katheryne Price, Ben Schaumloffel

Abstract

The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab is investigating a significant energy upgrade utilizing Fixed-Field Alternating-gradient (FFA) recirculating arcs. This upgrade requires the design of complex horizontal beam splitters to manage up to six concurrent beam passes. This paper presents the conceptual design of these splitters, which are subject to severe physical constraints imposed by the existing accelerator tunnel and multifaceted beam dynamics requirements for matching into the permanent-magnet FFA arcs. The design methodology, centered on multi-pass simulations in the Bmad toolkit, is detailed from the initial geometric layout through the advanced optics matching. Key results include a robust geometric arrangement that fits within the spatial boundaries and the development of multiple, flexible optics matching solutions. Furthermore, the design integrates a viable scheme for extracting high-energy beams for the experimental halls, a critical operational requirement. This work establishes a comprehensive and viable conceptual design, forming a baseline for future engineering and performance optimization studies.

Conceptual Design of Highly-Constrained Splitters for the FFA@CEBAF Energy Upgrade Study

Abstract

The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab is investigating a significant energy upgrade utilizing Fixed-Field Alternating-gradient (FFA) recirculating arcs. This upgrade requires the design of complex horizontal beam splitters to manage up to six concurrent beam passes. This paper presents the conceptual design of these splitters, which are subject to severe physical constraints imposed by the existing accelerator tunnel and multifaceted beam dynamics requirements for matching into the permanent-magnet FFA arcs. The design methodology, centered on multi-pass simulations in the Bmad toolkit, is detailed from the initial geometric layout through the advanced optics matching. Key results include a robust geometric arrangement that fits within the spatial boundaries and the development of multiple, flexible optics matching solutions. Furthermore, the design integrates a viable scheme for extracting high-energy beams for the experimental halls, a critical operational requirement. This work establishes a comprehensive and viable conceptual design, forming a baseline for future engineering and performance optimization studies.
Paper Structure (45 sections, 2 equations, 14 figures, 6 tables)

This paper contains 45 sections, 2 equations, 14 figures, 6 tables.

Table of Contents

  1. Introduction
  2. CEBAF Background
  3. The FFA@CEBAF Energy Upgrade
  4. The Need for a Horizontal Splitter
  5. Design Philosophy and Approach
  6. Scope of this Paper
  7. Design Constraints and Requirements
  8. Physical and Geometrical Constraints
  9. Beam Dynamics Requirements
  10. Operational Requirements
  11. Geometric Layout
  12. Magnet and Component Design
  13. Multi-Pass Separation Scheme
  14. Time-of-Flight and $R_{56}$ Management
  15. Recombination and Matching Section
  16. ...and 30 more sections

Figures (14)

  • Figure 1: Diagram of the transverse constraints in the CEBAF tunnel.
  • Figure 2: Diagram of the proposed mechanical movers that may or may not be required for path length correction.
  • Figure 3: Overhead view of splitter floor plan. Note unequal scales. Dipoles (blue), extraction dipoles (orange), and quadrupoles (red) shown with real dimensions. Horizontal orange lines show transverse spatial limitations with the physical wall at the top and the walkway at the bottom. The aisle-side wall is not shown in this image. Beam travels left to right.
  • Figure 4: Splitters shown in place in the CEBAF engineering diagram, scaled appropriately. They are located in the northeast and southwest corners. North is up in this image.
  • Figure 5: An FFA Cell, including the segmented Bending-Defocusing (left) and Bending-Focusing (right) magnets. $\beta$-functions for each energy pass shown. The match points used for this work are at the beginning of this cell (far left, at the drift indicated by the red arrows), and in the center of the first magnet (after three segments in the first magnet, indicated by the blue arrows).
  • ...and 9 more figures