DEVELOPMENT OF SSR2 FOCUSING LENSES FOR PIP-II Electromagnetic - - PowerPoint PPT Presentation

DEVELOPMENT OF SSR2 FOCUSING LENSES FOR PIP-II

Electromagnetic Application Section Electromagnetic Applications & Instrumentation Division

Team members: Kumud Singh, Janvin Itteera, Mahima, R R Singh , Rajesh Jalan & Sanjay Malhotra

OUTLINE

• Design Work carried out for PIP-II superconducting focusing lenses for Spoke

resonator cryomodule (SSR2).

• EM design of SSR2 superconducting focusing lens.
• Quench Analysis.
• Engineering development

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

Parameters Values Focusing Strength 5 T2m Bending strength of Dipole correctors 5 mT-m Beam pipe aperture 40 mm Uncertainty in the location of magnetic axis w.r.t Reference points (Transverse and angular alignment) <0.1mm RMS <0.5 mrad RMS Effective length of solenoid (FWHM) <15 cm Active magnetic shielding requirements 0.5Q0 criterion Maximum current in the solenoid 100A Maximum current in the dipole correctors 50 A

• A new design is suggested and verified to meet

the main requirements because of increased beam aperture and focusing strength for SSR2.

• Focusing strength and Fringe field on the SSR2

cavity surface has been optimized for PIP-II requirements.

FUNCTIONAL REQUIRMENT SPECIFICATIONS

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

EM DESIGN AND PARAMETERS (Design date: Jan’2016)

60.6 mm

44.4mm 44.4mm

50 mm 145 mm 169 mm

Beam pipe aperture 40 mm

105.5 mm

150 mm

Objective function : 𝐶𝑨

2 . 𝑒𝑨 ≥ 5 T2m

Minimize 𝐶. 𝑒𝑚

𝑠=0.3 𝑠=0

at z= 0.5m Constraints:

𝐶𝑨∗𝑒𝑨 𝐶0

≤ 150 cm I exc < 100A Optimization Parameters: Nmain, L main , R main NBC, L MC , R MC , Z center-BC

• Sr. no

Parameter Value Unit

1.

Designed value of focusing strength 5.33 T2m

2.

Magnetic Field Integral 1.01 T-m

3.

Peak transverse Magnetic field in the lens aperture 6.22 T

4.

Peak Magnetic field on the wire strand 6.878 T

5.

Nominal current 77.4 A

6.

Nominal Current Density 260 A/mm2

7.

B max at the cavity Surface 0.179 Gauss

8.

Field Integral (along the radial line 0 to 0.3m) at axial Distance of 0.5 mm 3.9 G-cm

52.5 mm

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

ACTIVE MAGNETIC SHIELDING REQUIRMENTS

• Power loss in superconducting RF cavities is a major source of heat influx in the cryomodules.
• Power loss can be affected by magnetic field trapped in superconducting walls of the cavities.
• Diamagnetism of superconducting niobium shield the cavities . But this protection is broken when the cavity

quenches as part of its surface warms up above the superconductivity threshold .

• During quenching, magnetic flux penetrates inside the cavity through the normally conducting opening and

becomes trapped in the cavity Trapped magnetic flux that reduces the unloaded quality factor of a cavity Q0 to the level Q1 = η∙Q0 (η≤1) can be calculated as Φtr= 2μ0Φ0 (Rs∙ ξ0

2) * f∙V

(ΛQ0)

*(1−η) η

μ0=4π∙10-7H/m is the permeability of empty space ; Φ0=2∙10-15Wb is the magnetic flux quant, ξ0=3.9∙10-8 m is the coherent length in Nb, f is the frequency of the cavity, Rs is the surface resistance of Nb at this frequency, V is the volume of the cavity, and Λ is a dimension-free coefficient that defines magnetic energy density at the location of the quench relative to the average energy density in the cavity

First multiplier is fully defined by the properties of superconducting material. The second one is cavity specific with Λ depending on quench location. The last multiplier relates the acceptable degree of degradation η with allowed amount of the trapped flux. Corresponding choice of η can be made taking into account available cooling power and distribution of RF magnetic field (or the energy density factor Λ ) and expected static magnetic field on the cavity surface. (0.5Q0 for PIP-II SSR cavities)

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

FRINGE FIELD ON CAVITY SURFACE

The magnetic field generated by magnetic elements inside cryomodule must be sufficiently small to limit the degradation in Q .

𝑆𝑡𝑣𝑠𝑔 = 𝑆𝐶𝐷𝑇 (ν, 𝑈) + 𝑆𝑠𝑓𝑡 + 𝑆𝑛𝑏𝑕 (𝐼𝑓𝑦𝑢)

External DC magnetic field on the cavity surface due to fringing field of the solenoid magnet has been restricted to below 1 mT (10 Gauss).

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

TOLERANCE STUDIES ON BUCKING COIL GEOMETRICAL PARAMETERS

• Tight tolerance is required for the bucking coil winding dimensions and its placement w.r.t main coil.
• The positional inaccuracy of the Bucking coil effects the fringe magnetic field on the cavity surface.

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

OPERATING CURVE FOR THE SSR2 FOCUSING LENS

43 93 143 193 243 293

4 5 6 7 8 9 10 Current [A]

Max magnetic Field on Sc strand [T]

Predicted performance of main coil for SSR2 Magnets

2K 4K Operating curve

we expect the magnet to go resistive 'quench' where the peak field load line crosses the critical current line

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

DIPOLE CORRECTOR COIL

• Sr. no

Parameter Value Unit 1. Designed value of Bending strength of corrector coils 5.25 mT-m 2. Designed value of integrated Gradient of focusing quadrupole 0.2 T 3. Nominal current ~39.2 A January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

COMBINED FIELD SIMULATION

Fringe field on the cavity surface increases slightly when DC coil powered on with MC coil but field values are still within the acceptable limits

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

WINDING CONDUCTOR

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

• LUVATA make OK 54 Conductor
• Wire Specifications:
• Magnetization measurements have been carried out on the wire samples to derive critical current

density data. Measured data shall be fitted to Bottura fit. Wire DC resistivity vs temperature is being measured to fit the measured data into simulations.

• Sr. No.

Parameter Value 1. Diameter, nominal 0.540 ± 0.15 2. Diameter (bare ,nominal) 0.5 mm 3. Insulation PVA, Formvar 4. Number of filaments 54 (filament dia : 45 µm) 5. Cu/Sc (nominal) 1.3 6. Critical Currents Ic (A) Jc (A/mm2) @3T 252 3645 @6T 134 2173

WINDING CONDUCTOR

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

The magnetization was measured at various temperature and magnetization data were normalised to the volume of sample calculated from mass and the density of wire. For calibration of the magnetometer nickel standard sample is used. Factors which influence the magnetization can be derived from the Bean Model. According to this the magnetization of a strand in the hysteresis loop is: 𝑁 =

2 3𝜌 λ3/2 √𝑂𝑔 𝐾𝑑 d , 𝑝𝑠 2 3𝜌 λ3/2 √𝑂𝑔 𝐾𝑑 D

M = magnetic moment per unit volume, λ = Ratio of superconductor to strand volume, Jc = Critical current density, 𝑂

𝑔= Number of filaments,

d = Filament diameter D = Strand diameter

QUENCH ANALYSIS

• Although the total stored magnet Energy of 14KJ is small, the Quench analysis needs to be carried
• ut to verify the maximum hot spot temperature and the maximum coil to ground voltage are within

safe limits.

• A quench circuit is defined to include main coil, bucking coils, dump resistance and coil-diodes. An

inductance matrix is needed in the quench circuit for QUENCH analysis.

• Inductance matrix of the sub-coils
• 𝐽 =

4.82𝐼 −0.59𝐼 −0.59𝐼 −0.59𝐼 0.694𝐼 0.082𝐼 −0.59𝐼 0.082𝐼 0.694𝐼

• To compute the maximum temperature after quench, a heat flux is introduced at the point of

maximum magnetic field to initialize a quench.

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH ANALYSIS

• Material properties for quench analysis:
• In the present case an external heat source has been defined at peak magnetic field location to

study the effect of quench.

• Resistance growth and peak voltage was derived from the loops defined in the circuit.
• To simplify quench analysis, existence of liquid helium, insulation between the bobbin and the coil,

and the stainless steel keys around the coil were ignored, which is a conservative assumption because in reality they will absorb heat from the coil when quench happens. The actual maximum temperature due to quench should be lower than calculated. In the event of quench, the coil is protected by an external dump resistor. The dump resistance is 0.010 Ω for both the main coil and the bucking coil. The overall resistance of the connections, including the internal bus bars, current leads, and external connections with the dump resistor, is assumed to be 2.0x 10-4 Ω.

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN MAIN COIL

Quench initiated at t=0.1s Quench propagation at t=0.175s Quench propagation at t=0.105s Quench propagation at t=0.3s Quench propagation at t=0.5s Quench propagation at t= 20 s

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN MAIN COIL

Temperature rise in main coil after quench initiation Energy Dissipation in main coil

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN MAIN COIL

Coil resistance growth in main coil after quench initiation di/dt across main coil and bucking coil after quench initiation

Vmc = Ldimain/dt = 744Volts Vbc = LdiBC/dt = 79.35V (Voltages appear top be less in revised simulations)

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN BUCKING COIL

Most severe quenching scenario takes place when the quench is initiated in Bucking coil and a large dI/dT introduces interlayer voltage in the main coil.

Quench initiated at t=0.1s Quench propagation at t=0.125s Quench propagation at t= 0.3 s Quench propagation at t= 10s Quench propagation at t= 20 s

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN BUCKING COIL

Temperature Rise in Bucking coil after quench initiation Quench Energy released in form of heat

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

QUENCH INITIATED IN BUCKING COIL

Coil resistance growth in Bucking coil after quench initiation di/dt across main coil and bucking coil after quench initiation

Vmc = Ldimain/dt = 1080 Volts Vbc = LdiBC/dt = 34.5V

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

(Voltages appear top be less in revised simulations)

ENGINEERING DEVELOPMENT

Solid Works Model for SSR2 Solenoid lens 2D Drawings for SSR2 Solenoid Lenses

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

ENGINEERING DEVELOPMENT (Fabrication)

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

• Sr. No

Parameter Value 1.

• No. of Turns in Main Coil

8325 2.

• No. of Turns in Corrector Coil

100 3.

• No. of Turns in Bucking Coil

1066 4. Overall Magnet length (including bobbin) 206.7mm 5. Overall magnet diameter 190 mm

ENGINEERING DEVELOPMENT (Testing)

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

SCOPE & SCHEDULE – SSR2 SOLENOID MAGNETS

Technical Deliverables (as part of PIP-II IIFC collaboration) SSR2 Focusing Solenoids

– Electromagnetic/Mechanical and quench protection design of solenoid – 4 no's of SSR2 solenoids to be delivered in R&D phase (CY 2019).

Deliverables under Addendum II

– TRS for SSR2 magnets – Preliminary/Final design review documents

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

SUMMARY

• To compare the results for quench results from two independent software common material

properties & initial conditions shall be defined.

• A brief report summarizing the material properties, quench conditions and results to be

recorded shall be documented for records. It can be compared to experimental results.

• Quench training and Magnetic qualification of 1 No. of fabricated SSR2 magnet targeted to

be completed by March-2019

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II

Thank You for your kind attention

January 31, 2019 IIFC Magnet meeting presentation | SSR2 lenses For PIP-II