Anti-DID, Anti-Solenoid and QD0: MDI Issues and Opportunities Brett Parker, BNL/SMD Anti-DID Based on Opposing Helical Coil Layers (natural “more solenoid like” coil production) Optimized, Compact Anti-Solenoid Coil Layout (look to reduce QD0 cryostat radial size) Improved QD0 Field Compensation Scheme (uses sweet spot coils, anti-solenoid compatible) Current Status and MDI Summary (QD0 prototype, SuperKEKB synergy, backup slides)

Anti-DID

A Short Anti-DID Design History Review A Detector Integrated Dipole (DID) was first proposed by A. Seryi & B. Parker† to enable use of the large crossing angle needed for the ILC Gamma-Gamma IR scheme. With the present 14 mrad crossing angle, an opposite polarity DID (Anti-DID) can be used to help guide beamstrahlung produced pairs out of the detector to reduce the background. While incorporating the DID coils with the main detector solenoid avoids introducing material inside the detector acceptance (that would adversely impact physics), coming up with a practical scheme for implementing the anti-DID coils is by no means trivial! Directly winding a complex coil structure outside the detector solenoid is challenging (production infrastructure) and wrapping a flat wound anti-DID coil around the solenoid is not easy either (anti-DID conductor stress). Coils Coils are directly wound on cylindrical surface Method A One Early Anti-DID Coil Concept Flat coils are wrapped around main solenoid †B. Parker and A. Seryi, "Novel Method of Compensation of the Effects of Detector Solenoid on the Vertical Beam Orbit in a Linear Collider," Rev. Mod. Phys. 2727(84) , April 2005. DOI: 10.1103/PhysRevSTAB.8.041001

A Different Anti-DID Production Geometry X Z Method B Consider using the helical coil† (also know as canted coil) winding technique to produce the anti-DID; this setup makes transverse field but does not couple to the main solenoid. This scheme is schematically illustrated above where we have tilted the solenoidal turns in two different radial layers in opposite directions and given them opposite currents. The longitudinal field, Bz, from the two layers cancels but the transverse field component, Bx, adds constructively to give the field profile shown (“air coil” example). We might consider winding such “solenoid like” coils on a separate structure. The coil could then be integrated with the main solenoid cold mass and independently powered. †H. Witte, et.al., "The Advantages and Challenges of Helical Coils for Small Accelerators—A Case Study," IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 22, NO. 2, APRIL 2012.

Some Anti-DID (AD) Construction Considerations The AD should not experience any net force due to the main solenoid but each AD half experiences a net torque from forces at ends. This torque leads to a bending moment in the horizontal plane. The end turn forces are reduced a bit due to magnetic interaction with yoke (image of main solenoid in the highly saturated yoke). These bending forces should be calculated if the AD structure is not supported at critical points (structure looks quite thin). Method A has pattern gaps to make radial connections to outer cryostat; the Method B coil covers most of the available surface. Interaction with “image” of solenoid coil X Z Interaction with solenoid coil Need support here! Maybe the best way to make the anti-DID is to use Method B (helical coil) and position it with a tight fit back inside the main solenoid coil (check if AD can be split into sections).

Some Anti-DID (AD) Construction Considerations With the main ILD solenoid being wound in three sections, consider also winding helical coil option (Method B) in three independent sections. This is fundamentally not possible with standard outside surface winding (Method A). Note to preserve proper anti-DID symmetry central section must be subdivided into two shorter coils. But if there is still a desire to “flatten” the central field region, this could be accomplished by swapping the center section anti- DID polarities. There is also an option to wind the anti-DID on one (or two) section(s) and then integrate it with the main solenoid by insertion after the three main sections are vertically stacked.

Now Correct One Anti-DID Mistaken Impression... Figure 16 Figure 17 “Air Coil” Anti-DID Same Anti-DID Coil with Magnetic Yoke X Can flatten the field but you have to readjust the coils! Z I recently became aware of Linear Collider Report LC-DET-2012-08, “Conceptual Design of the ILD Detector Magnet System,” where the implication seems to be that one cannot flatten the central-most anti-DID field in the ILD detector when the yoke is included. While I actually agree with the conclusion that the added complexity of the anti-DID coil needed to flatten the central field is not worthwhile, the above example given in the report is a bit misleading. For field optimization the “air coil” design was only used to get an approximate anti-DID coil geometry; then when this coil is put with the main solenoid in the yoke, the anti-DID (in my case the coil currents) must be re-optimized to achieve the desired field shape. You certainly should be able to reduce the anti-DID field perturbation in the central region; however, the resulting solution will be sensitive to small errors and yes I would advise against the added complexity if you can live without it.

Anti-Solenoid

A Short Anti-Solenoid Design History Review Huge The accelerator physics formalism and first ILC specific designs for the anti-solenoid (AS) were presented by Y. Nosochkov & A. Seryi†. But a 62 ton AS longitudinal coil force can not reasonably be accommodated in the QD0 cryostat; the AS had to be integrated with the detector (i.e. major field and design impacts). For the ILC RDR/TDR we developed a force neutral AS concept where two solenoids of different radii but opposite polarity are used to largely cancel the longitudinal force yet maintain a net field at the beam position. The efficiency of the two coil, force neutral AS configuration improves as the radial separation between the inner and outer coils increases. The size of the outer AS coil then becomes the determining factor (followed by the QD0 interconnect size) for setting the QD0 cryostat radial envelope. Huge repulsive coil force! Huge impact on detector! †Yuri Nosochkov and Andrei Seryi, "Compensation of detector solenoid effects on the beam size in a linear collider," Rev. Mod. Phys. 8(2) , February 2005.

A Compact Anti-Solenoid Concept for QD0 Inner anti-solenoid coil for use in ILD New anti-solenoid has little impact on detector field quality. Outer anti-solenoid coil for use in ILD We look to reduce the anti-solenoid diameter via this new coil geometry (with the old QD0 layout the active shield coil was in the way). We can roughly balance repulsion between the anti- and detector solenoids via a second opposite polarity coil powered in a 2:1 ratio. Thus we can use the net anti-solenoidal field for optics compensation without then having to pass any large longitudinal force from the cold mass out to the warm support structure. Inner/outer anti-solenoid coils are nested with QD0 and the sweet spot coils.

QD0

Short QD0 External Field Compensation History Review The ILC QD0 RDR/TDT baseline has an outer reverse-polarity quadrupole coil to cancel the main QD0 external field. The main coil gives 148 T/m, outer -8 T/m for 140 T/m net gradient. A short prototype was made that performed well; then a 2.2 m full length coil was wound. Field harmonic measurements of the 2.2 m coil showed that we had not adequately controlled the mid-point centering during coil winding. So we split QD0 in order to add a middle support. Splitting QD0 into two independently powered sections is also useful for optics flexibility to accommodate low CM energy physics running. QD0 Split Coils Mid-Coil Support

A Sweet Spot Coil Concept for QD0 QD0 with L*=4.1 m & Lmag = 1.3 m Sweet Spot Coil QD0 Extraction Beam Line ILC Layout has 14 mrad Total Crossing Angle Combined Field at Extraction Line By (T) at Extraction Line QD0 Magnetic Length Covers 4100-5400 mm This sweet spot coil has dipole and quad windings, offset but parallel to QD0, that are powered in series such that their fields cancel at QD0 and add at the extraction beam line. QD0 Midpoint

Current Status and MDI Summary

QD0 Magnet Cryotat Coils Multiple main magnet and corrector coils were produced on common support tubes. These tubes are themselves supported from a rigid sled structure inside the cold mass. QD0 Split Coil Winding Lead End Extraction Line Quadrupole Main coils & correctors are wound on common support tube. Main Sextupole, and Octupole Coil Package View Inside QD0 Cryostat to Show Coil Positions and Support Infrastructure R&D Geophone Split QD0 Half Coils (anti-solenoid is not shown) IP End

QD0 R&D Magnet Cryostat. The ILC QD0 R&D magnet prototype cryostat is 90% complete and almost ready for insertion of the magnet coils on the “sled assembly.” Finishing the Magnet Cryostat was given higher priority than manufacturing the transfer line parts. ILC QD0 R&D Magnet Cryostat Assembly

ILC Service Cryostat R&D. Final assembly of the R&D Service Cryostat is now proceeding. Plan was to test it using a dummy heat load attached to where the transfer line exists. We would like to mount a geophone alongside the dummy load to characterize sources of vibration. Transfer line parts drawings do exist but all work has remained stopped due lack of funds. ILC Service Cryostat undergoing final leak testing before assembly with outer vessel.

ILC Service Cryostat R&D QD0 R&D Service Cryostat Dummy Heat Load for Testing Current Leads, Valves etc. Internal Plumbing These pictures were taken in 2014; no additional work since then.

Synergy Between SupeKEKB and ILC Vibration Work IR Magnet for SuperKEKB FF vibrational stability is an important issue for the ILC; with BNL work on the QD0 R&D Prototype stopped, we should look to other means for gaining some information.. The roughly 35 nm vertical stability needed for the SuperKEKB FF is not so far from the ILC requirements. So we look to apply some of the preliminary vibration stability work started for the ILC QD0 R&D Prototype to a SuperKEKB stability measurement program within the context of US-Japan collaboration. Unfortunately with current schedules and fiscal plans this work must be stretched out in time as funding has not been available early as originally proposed. There has also been significant personnel change at the BNL side. Need to discuss with Ohuchi-san et.al. how best to proceed with this important work. Early work at KEK aimed at comparing calculations for the SuperKEKB magnets to lab experimental results. From H. Yamaoka, “Result of QCSL Modal Test,” presentation at KEK-BNL SeeVogh meeting, 2016.02.04.

End of Main Presentation Thank you!

Backup Slides

Consider This Simple Coil Layout Thought Experiment Quadrupole and Dipole Coils (powered in series) Overlay a dipole coil with field, Bo, and a second quadrupole coil that has gradient , Go. Define the distance, Xo = Bo/Go Then B(-Xo)= 0 and B(Xo)= 2Bo Thus if QD0 is centered at the B=0 field point of the combined dipole and quadrupole coils, we can create an arbitrary field at some point outside QD0 without shifting QD0’s field center. † QD0 -Xo Xo By=2Bo By=0 †Brett Parker, "SWEET SPOT DESIGNS FOR INTERACTION REGION SEPTUM MAGNETS," Contribution TUPMB042 to Proceedings of IPAC2016, Busan, Korea, May 2016, ISBN 978-3-95450-147-2, pp. 1196-1198. See URL: http://accelconf.web.cern.ch/AccelConf/ipac2016/papers/tupmb042.pdf

A Sweet Spot Coil Concept for QD0 Combined Field at Extraction Beam Line Sweet spot coil is offset -33.05 mm with respect to QD0 which is the place where the dipole and quadrupole fields cancel. So the sweet spot coil can be adjusted without changing the QD0 field center. Original QD0 gradient is 124.66 T/m and with sweet spot coil energized, to buck QD0’s integrated external field, the gradient goes up 0.44% to 125.212 T/m A simple sweet spot coil, with constant dipole and quad fields, under corrects at QD0’s front and over shoots at the end. It should be possible to tailor the fields shapes, as was done for SuperKEKB, to improve the local field cancellation. There is small residual weak focusing at the extraction beam line next to QD0 with this sweet spot magnet geometry. By (T) at Extraction Line QD0 Magnetic Length Covers 4100-5400 mm QD0 Midpoint Combined Field at QD0 Center Projection Region for the Extracted Beam QD0 Axis

Repurpose ATF2 FF Coils for a Sweet Spot Prototype Measured Magnetic Field Harmonics for the ATF2 FF Coil Package Sweet Spot Quadrupole Concept for eRHIC The ATF2 FF coil diameter is similar to what is needed for eRHIC. By adding racetrack and outer coils we can rather easily create a Sweet Spot quadrupole prototype, similar to those needed for the eRHIC IR, to test the Sweet Spot concept. Unless there is significant interest (and new funding) it does not seem we will use the present coils at ATF2.