Focusing Lens for the SSR1 Section of PXIE with Active Shielding

1. Focusing Lens for the SSR1 Section of PXIE with Active Shielding Continuing Discussion I. Terechkine

2. Requirements Main Coil • Minimum beam bore diameter 30 mm • Maximum allowed longitudinal real estate 170 mm • Nominal temperature 2 K Main concept approaches reviewed: 1. Lens is not mechanically connected to the beam pipe; passive shielding; 2. Lens is mechanically connected to the beam pipe; passive shielding; 3. Lens is mechanically connected to the beam pipe; active shielding. Correctors Required strength 0.0025 T-m – 2-9-12 Design options: 1 mrad error of solenoid alignment excites betatron oscillations of about 1.5 mm I. Terechkine

3. Strand Oxford Instruments, 54/50 NbTi strand at 4.2 K I. Terechkine

4. Active Shield Lens ANL Lens -Wire: NbTi, - Operating temperature: 1.8-4.6 K, - Magnetic field integral: ∫Bzdz= 0.75 T-m, - Operating current: ~79 amps, - Inductance: 1.1 Henries, - Shielding: B < 100G: z >= 15cm, - Steering coils: 0.2 T, 30 T-mm, - Bore diameter: 35 mm. Residual field requirement (warm) – 3 µT Wall field – less than 40 G Focusing Strength – 4.3 T2m Because no drawings are available, a reverse engineering approach was used to guess the coil parameters and to attempt some optimization I. Terechkine

5. SSR0 Lens (ANL): Reverse Engineering The need for optimization: Existing design was optimized for the smallest field on the axis, not on the surface; The lens on the opposite side of the cavity was not taken into account. • Initial set of the lens design parameters: • Round 0.35 mm NbTi strand, • Coil length - 130 mm, • Inner radius of the main coil – 20 mm, • Outer radius of the main coil – 32.5 mm, • Compaction factor in the main coil – 0.65, • Number of turns in the main coil – 10978 • Inner radius of the flux return coil – 70.4 mm, • Outer radius of the flux return coil – 72.7 mm, • Compaction factor in the flux return coil – 0.6, • Number of turns in the flux return coil – 1865, • Quench current - 75 A. • Focusing strength – 4.5 T2m • Field integral – 0.87 T-m • New number of turns in the flux return coil – 1550 |B| [T] at Z = 150 mm I. Terechkine

6. SSR0 Lens in the SSR1 Cryomodule Parameters of optimization: Radial position of the flux return coil; Number of turns in the FRC; The next adjustments were made to the original concept: Inner position of the steering coils; N*I in the active shield (flux return coil) was increased to reduce the field on the cavity wall at R ~ 150 mm; • Lens parameters near local minimum point: • Round 0.35 mm NbTi strand is used to wind both coils, • Coil length - 130 mm, • Inner radius of the main coil – 22.5 mm, • Outer radius of the main coil –35.5 mm, • Compaction factor in the main coil – 0.65, • Number of turns in the main coil – 11418 • Inner radius of the flux return coil – 65 mm, • Outer radius of the flux return coil – 67.5 mm, • Compaction factor in the flux return coil – 0.65, • Number of turns in the flux return coil – 2284, • Quench current - 75 A. • Focusing strength – 4.35 T2m • Field integral – 0.86 T-m Wall field less than 10 G (R = 100 mm) Outer border field less than 3 G I. Terechkine

7. Field Graphs: Resistive Cavity Walls Along the line Z = 250 mm Along the line R = 250 mm I. Terechkine

8. Field distribution along the axis and along the cavity wall (cold) Along the line Z = 249 mm Along the line R = 254 mm I. Terechkine

9. Actively Shielded Lens in SSR1 Cryomodule I. Terechkine

10. Summary Actively shielded SSR0 lens can be optimize to reduce the fringe field; With some modification, it can be used in the SSR1 cryomodule; Fringe field requirements still needs to be better understood; Alignment precision and reproducibility needs to be studied; If this direction is chosen, an RFP can be generated; Design study can continue with the goal to better adjust the lens design for placement in the cryomodule and to provide a chosen vendor with better specifications; Acceptance tests, accompanied by magnetic measurements, can be made in the 4 K cryostat of the Test Stand 3 in IB1. I. Terechkine