12 Gev Accelerator Upgrade, 2007 Dipole and Corrector Magnet Design Summary
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JLAB-TN-07-024
12 GeV Accelerator Upgrade, 2007 Dipole and Corrector Magnet Design Summary
R. Wines, R. Michaud
Abstract:
The CEBAF beam transport magnets were designed to support 6 GeV operation of the accelerator. Design studies have been done to determine the changes required to facilitate operation of the five pass machine at 11 GeV and the addition of a sixth-pass for 12 GeV beam delivery to Hall D. Magnetic measurement and FEA modeling have been used to determine the performance of the accelerator magnets at the required specifications for 12 GEV. The accelerator dipole magnets are catagorized into regions : Arc, Hall Transport, Spreader and Recombiner, Extraction, Injection/Reinjection Chicanes, Arc10 and Hall D.
Requirements
Budget limitations of the upgrade project require the approach of reusing as many of the existing magnets in the accelerator as feasible. Engineering and design time is also minimized by use of existing designs and design principles for fabrication of new magnets. The beam transport magnets are to facilitate operation of the machine from 12 GeV settings down to 50% of this range. To reuse the power supply and control scenario the spreader and recombiner magnets will be powered by the Arc magnet power supplies, with their current settings within the use of 20A shunts. The upgrade to 12 GeV will require using existing magnets at 4x the power, thus hotter temperatures. For engineering purposes the temperature limit of dT < 40C has been set for magnets with water cooled conductors. This limit was determined from temperature and life cycle studies conducted on existing magnets. At the time of required evaluation of the upgrade magnets only the field quality specification for Arc 10 had been defined. Since this is the region with the largest beam, this specification was applied to all other regions as a conservative approach. The field quality aperture limits are defined by the size of the upstream/downstream quadrupole magnet apertures. The Arc 10 field quality specification is defined by evaluation of dB’L/BL along the curved beam trajectory with limits as defined in Figure 1.
Figure 1. Arc 10 Dipole Field Quality Specification
Arc Dipoles
The existing Arcs consist of four lines of magnets in the West and 5 lines in the East. This sums to 256 dipole magnets. The existing Arc dipole magnets use the same core cross-section and conductor size in their design, except for the BR magnet. All Arc dipoles utilize a 40 turn count coil with the magnets varying only in length. The Arcs are comprised of 1, 2 and 3 meter dipoles.
Evaluation of the existing dipoles was done by modeling the dipoles with the Vector Fields 2d and 3d FEA software. These results were then verified through measurement of prototype dipoles. The analysis results in the capability of reusing all the Arc dipole magnets with some modification. Arcs 3 through 9 will require the addition of return leg H-steel (Figure 2.) to reduce affects of saturation and allowing operation at scalable currents as exemplified in Figure 3.
Figure 2. Prototype with H-steel Figure 3. Measured reduction in
Saturation affects with H-steel
Other modifications to the existing magnets resulted from inspection of the present condition of the magnet fabrication materials and the results of a life cycle test. These modifications are shown in Figure 4.
Figure 4. Modifications to Existing Dipoles for Upgrade
The design and operating parameters for the upgrade of the Arc dipoles are summarize in Figure 5.
Figure 5. Arc Dipole Upgrade Parameters
The field quality specification defined for Arc 10 dipoles was applied to all Arc dipoles and evaluated through the use of the 3d simulations. With the limits of the quadrupole aperture applied, the Arc dipoles meet the requirements of this specification.
Figure 6. Field quality specification evaluated for Arcs 1 through 9
A sample evaluation of the field quality specification for an Arc 5 dipole at 50% activation for the upgrade requirement is shown in Figure 7.
Figure 7. Field quality specification for Arc 5 dipole at half field
Hall Transport Dipoles
The transport lines to Experimental Halls A, B and C require the use of 24 Arc style dipoles and an additional 2 BN dipoles. The Arc style dipoles again use the same core cross-section and conductor size. With the addition of H-steel these magnets will meet the requirements of the upgrade and be reused. Preliminary analysis indicates the BN magnets will have to be replaced with a new dipole design. Figure 8 summarizes the upgrade parameters of the transport line dipoles. Since Hall A through C can take any pass beam these dipoles have to operate from 1 to 11 GeV.
Figure 8. Transport Line Dipole Upgrade Parameters
The Arc 10 field quality specification was evaluated for the simulation of the transport line dipoles with passing results.
Figure 9. Hall A & C dipole specification results Figure 10. Hall B dipole specification results
Synchrotron Radiation Compensation Coils
Energy loss is found to occur in the simulation of the higher energy Arcs and Hall Transport Lines due to synchrotron radiation. To keep the beam on magnetic center of the magnet through these regions compensation coils are required to trim the field. The conceptual design consists of two 8 turn, #14 AWG wire, coils wound around the poles of each dipole in Arcs 8, 9 , 10 and the transport lines. The turns of the coils will be energized such that the magnitude of the field is increased or decreased as needed to center the beam through the trajectory of the magnets. All compensation coils in each Arc will be powered in series to give an adjustment “knob” for each Arc.
Spreader and Recombiner Dipoles
The Spreader and Recombiner magnets carry the beam to and from the Linac regions. These 4 regions are dominated by space restrictions resulting in the use of primarily 1 meter C-style dipoles. The existing 1 meter dipoles utilize 2 core designs; a 4” pole width and a 5” pole width. Their coils are configured from the use of 2 coil designs; an 8 turn count and a 10 turn count. Various modifications to the existing 1 meter dipoles were simulated and tested to achieve the upgrade requirements. The 1 meter dipoles will be modified by adding H-steel, changing the turn count to match power supply requirements and adding shims to the pole ends to achieve the field quality specifications. The Spreader and Recombiner dipole magnets are powered by the Arc string power supplies. Shunts are used to reduce the Arc current settings to the corresponding pass Prototype testing results of these modifications is compared with the Arc 10 field quality specification in Figure 11.
Figure 11. 1 meter prototype field quality comparison with modifications
The 1 meter dipoles for the upgrade requirements are summarized in Figure 12. The turn counts have been changed such that no new coils will need to be purchased with the use of existing spare coils.
Figure 12. 1 meter Spreader and Recombiner upgrade parameters
The entrance/exit to the Spreader and Recombiner regions utilizes 2 H-style magnets, referred to as BCOM magnets. Simulation of these dipoles indicates only the trapezoid dipole in these regions will need to be modified for the upgrade. The 2d analysis resulted in the addition of 6” of steel to the return leg of the trapezoid magnet to reduce the affects of saturation from the upgrade requirements as shown in Figure 13. The field uniformity is shown to be within 10-4 range over 12 cm which encompasses the affected trajectories.
Figure 13. BCOM dipole layout with 6” steel addition and field uniformity
The 3d simulation results for the rectangular BCOMS using the most stringent beam trajectory requirements are shown in Figures 14 and 15 as compared to the Arc 10 field quality specification.
Figure 14. AQ field quality specification Figure 15. AW field quality specification
(rectangular BCOM) (rectangular BCOM)
The upgrade parameters of the BCOM magnets are summarized in Figure 16.
Figure 16. BCOM dipole upgrade parameters
The Spreader and Recombiner Septa magnet parameters are summarized in Figure 17. The 2d simulations indicate 3 of 2 meter Septas can be reused with modification. The 2 meter septas will need new coils to accommodate beam clearance through these magnets. A new 3 meter septa design will be used in all other required locations. The new design utilizes the existing 2 meter design with the addition of a wider pole. Figure 18 depicts the field uniformity of the 3 meter septa.
Figure 17. Septa magnet upgrade parameters
Figure 18. Field uniformity of the 3 meter septa
Due to space limitations the Spreader and Recombiner regions require the use of curved dipoles in some portions of the beam transport. The curved dipoles are configured with the coils wound around the return leg of the core rather than the pole. Analysis results indicate these magnets cannot be modified for reuse in the upgrade. The design of the new curved dipoles is based on adding 1” of steel to the core of the existing design, widening the pole by ½”, changing the curvature to match the beam path and changing the turn count of the coils. Figures 19 and 20 show the 2d simulation results to be within 10-4 range over 3 cm for these modifications.
Figure 19. AU modified Figure 20. Field uniformity for AU modified
The upgrade parameters for the curved dipoles is summarized in Figure 21.
Figure 21. Upgrade parameters of the curved dipoles
The 5th pass line to Arc 10 and the line to Hall D require additional 2 meter magnets (XH, XK) not present in the current machine. The design of these dipoles uses the same conductor and turn count coils as the existing Arc magnets. The core is similar to the Arc BR magnet with a 5.125” pole width. The 3d analysis gives the field quality specification results as shown in Figure 22 and 23 compared to the Arc 10 dipole specification.
Figure 22. XH 2meter field quality specification Figure 23. XK 2 meter field quality specification
The XH and XK 2 meter magnets use the same core cross-section and conductor differing only in total turn count. The parameters of the new 2 meters are summarized in Figure 24.
Figure 24. New 2 meter XH and XK upgrade parameters.
The 1st pass of these regions utilizes a 1 meter dipole with the coils configured around the return leg of the core. Simulation shows this magnet design will meet the requirements of the upgrade by lengthening it to a 1.5 meter magnet, referenced as the XL. The 2d analysis shows the field uniformity to be within 10-4 over 5 cm for the geometry of this magnet as shown in Figure 25.
Figure 25. XL 1.5 meter cross-section and field uniformity
Figure 26 summarizes the upgrade parameters for the 1.5 meter XL dipole.
Figure 26. XL dipole upgrade parameters
Extraction Dipoles
The upgrade of the Extraction region will reuse existing magnets. Additional BP and YA magnets will be added to the lines to meet the upgrade requirements. Two meter YR magnets will be relocated from other regions of the machine to be reused in the Extraction upgrade. The upgrade Extraction region configuration is shown in Figure 27.
Figure 27. Upgrade Extraction region configuration
The 1st and 2nd passes are unchanged from the existing machine. The operating parameters of the extraction magnets are within the tested limits of the existing magnets, except for the 5th pass BP. Simulation of the BP indicates the field integral can be achieved with this higher current. Energy requirements of the Extraction region are summarized in Figure 28.
Figure 28. Extraction region upgrade requirements
The Extraction region requires a 3 channel septa magnet for extraction of beam to the 3 experimental halls. The 3 channel septa, Lambertson, bends 2 beams with the center beam unaffected. Thermal analysis results in the recommendation of replacing the existing coils in this magnet with a new 24 turn/coil to lower the dT below 40C. The additional turns will require the core to be machined out. The magnetic performance of B = 4.9 kG has been verified by 2d simulations.
Injection and Reinjection Chicane Dipoles
The Injection/Reinjection region consists of chicane and mini-chicane regions. The upgrade of the chicane will reuse the existing 3 BL magnets plus a new fourth one. Figure 29. compares the parameters of the existing to the upgrade BL magnet requirements.
Figure 29. BL magnet comparison
The upgrade mini-chicane requirements are achieved by replacing the existing magnets with 3 new CB magnets and use the Chicane BL magnet, as shown in Figure 30. The CB magnet design is based on lengthening the existing BK magnet design and using a 20A supply with a dT in the coil of 8C. The mini-chicane parameters are summarized in Figure 31.
Figure 30. Mini-Chicane Upgrade layout
Figure 31. Mini-Chicane magnet parameter comparison
Arc 10 and Hall D Dipoles
The addition of Arc 10 requires 32 new 4 meter dipoles. Simulation results achieve the specification requirements of field integral of 3600 kG-cm with a H-style dipole, as depicted in Figure 32. The coil is configured as four 10 turn pancakes operating at 460A and a dT of 38C. The transport line to Hall D utilizes two more of this design to bend the beam up to Hall D. Figure 33 shows the field quality specification of the 4 meter dipole.
Figure 32. 4 meter dipole simulation Figure. 33 4 meter dipole field quality
Correctors
Given the upgrade field integral and location requirements for corrector magnets, existing corrector capabilities is evaluated. Figure 34 and 35 summarize the upgrade requirements and existing corrector designs.
Figure 34. Corrector upgrade parameters.
From the evaluation three complications exist with the corrector solution in the transport recombiner region; MBD 6T09V, 8T07V and 8T09V. The 6T09V solution is to replace the BD magnet with a new CB magnet as used in the mini-chicane. The 8T07V solution is to add a 2nd BD magnet in series. The 8T09V solution is to replace the BD with a new CB magnet.
The upgrade requires the addition of 4 girders in the Injection region and 5 new girders in each of the North and South Linacs. 19 new FEL style horizontal and vertical correctors will be used in these region.
Arc 10 and Hall D will utilize 136 new BD correctors to meet the requirements of the upgrade.
Summary
Figure 35. summarizes the modifications and requirements for new dipole magnets to meet the specifications of the 12 GeV upgrade.
Figure 35. Summary of new and modified dipole upgrade magnet
References
- Leigh Harwood and Ken Baggett, Analysis of field quality specification and magnet measurement data spreadsheet data.
- Mike Spata, Scope of Extraction region for 12GeV upgrade.
- 2006 and 2007 Beam Transport 12GeV Upgrade design reviews of each region, powerpoint presentations.