Sep 26, 2006S. Kahn T HTS Solenoid1 A Proposal for a 50 T HTS Solenoid Steve Kahn Muons Inc. September 26, 2006

Sep 26, 2006S. Kahn T HTS Solenoid2 Alternating Solenoid Lattice for Cooling We plan to use high field solenoid magnets in the near final stages of cooling. The need for a high field can be seen by examining the formula for equilibrium emittance: The figure on the right shows a lattice for a 15 T alternating solenoid scheme previously studied.

Sep 26, 2006S. Kahn T HTS Solenoid3 From R. Palmer

Sep 26, 2006S. Kahn T HTS Solenoid4

Sep 26, 2006S. Kahn T HTS Solenoid5 A Proposal for a High Field Solenoid Magnet R&D The availability of commercial high temperature superconductor tape (HTS) should allow significantly higher field that can produce smaller emittance muon beams. HTS tape can carry significant current in the presence of high fields where Nb 3 Sn or NbTi conductors cannot. We would like to see what we can design with this commercially available HTS tape.

Sep 26, 2006S. Kahn T HTS Solenoid6 Comparison of J E for HTS Conductors We have chosen to use Bi2223 since it is available as a reinforced tape from AMSC The conductor can carry significant current at very high fields. NbTi and Nb 3 Sn can not.

Sep 26, 2006S. Kahn T HTS Solenoid7 Properties of American Superconductor’s High Temperature Superconductor Wire 6% more current per turn 10 % more turns per radial space New and Improved High Strength Plus Tape High Strength Tape used for calculations

Sep 26, 2006S. Kahn T HTS Solenoid8 Cross Sections of AMSC HTS Tape High Strength Tape High Compression Tape High Current Tape React and Wind

Sep 26, 2006S. Kahn T HTS Solenoid9 Some Mechanical Properties of Oxford BSSCO-2212 Young’s Modulus E~51-63 GPa Ultimate Strength~130 MPa Strain Degradation at 0.4% Wind and React

Sep 26, 2006S. Kahn T HTS Solenoid10 Why Do We Want to Go to Liquid Helium ? The parallel field orientation is the most relevant for a solenoid magnet. Previous calculations had used the perpendicular field. (We can view this not as a mistake, but as a contingency).

Sep 26, 2006S. Kahn T HTS Solenoid11 Current Carrying Capacity for HTS Tape in a Magnetic Field Scale Factor is relative to 77ºK with self field

Sep 26, 2006S. Kahn T HTS Solenoid12 Fit to High Field to Extrapolate Beyond 27 T We are using BSSCO 2223 which has been measured only to 27 T in the perpendicular configuration. We are using it in the parallel configuration. –We have to extrapolate to high field. We know that BSSCO 2212 has been tested to 45 T, so we think that the AMSC tape will work. –The high field measurements of BSSCO 2212 has a different falloff from BSSCO We certainly will need measurements of the AMSC tape at high field FieldQuadraticLinear

Sep 26, 2006S. Kahn T HTS Solenoid13 A Vision of a Very High Field Solenoid Design for 50 Tesla. Inner Aperture Radius: 2.5 cm. Axial Length chosen: 1 meter Use stainless steel ribbon between layers of HTS tape. –We will vary the thickness of the SS ribbon. –The SS ribbon provides additional tensile strength HTS tape has 300 MPa max tensile strength. SS-316 ribbon: choose 660 MPa (Goodfellow range for strength is MPa) Composite strength =  SS  SS + (1-  SS )  HTS (adds like parallel springs). We use the J eff associated to 50 Tesla. –We operate at 85% of the critical current. All parameters used come from American Superconductor’s Spec Sheets.

Sep 26, 2006S. Kahn T HTS Solenoid14 Constraining Each Layer With A Stainless Steel Strip Instead of constraining the forces as a single outer shell where the radial forces build up to the compressive strain limit, we can put a mini-shell with each layer. Suggested by R. Palmer, but actually implemented previously by BNL’s Magnet Division for RIA magnet. (See photo)

Sep 26, 2006S. Kahn T HTS Solenoid15 A Slightly More Aggressive Approach We can vary the amount of stainless steel interleafing as a function of radius to achieve 0.4% strain. –At small radius where we have smaller stress, we could use a smaller fraction of stainless steel. (See previous slide) –In the middle radial region we would use more stainless where the tensile strength is largest. Following this approach we can build a 50 Tesla solenoid. Case 3: 50 Tesla solenoid with SS interleaving varied to achieve 0.4% strain throughout. A 60 Tesla solenoid may be achieved by increasing the current as the field falls off with radius by using independent power supplies for different radial regions.

Sep 26, 2006S. Kahn T HTS Solenoid16 Varying SS Interleaving to Achieve Maximum Strain The thickness of the stainless steel interleaving is varied as a function of radius so as to reach the maximum allowable strain through out the magnet. –This minimizes the outer solenoid radius (and consequently the conductor costs). –This also brings the center of current closer to the axis and reduces the stored energy. –This is likely to increase the mechanical problems.

Sep 26, 2006S. Kahn T HTS Solenoid17 Case Comparisons The tables on the left summarize the parameters and results of the three cases presented. –The analysis assumes the solenoid length is 70 cm (We are now using a 1 m length.) –The top table shows the dimensional parameters: Inner/outer radius Conductor length and amp-turns. –The bottom table shows the results from the magnetic properties: Stored energy Radial and Axial Forces

Sep 26, 2006S. Kahn T HTS Solenoid18 Comments on Stored Energy The 70 cm length was chosen to be consistent with the range of ~100 MeV muon. It is also the minimum solenoid length where there is some “non-fringing” central field. The stored energy of the 50 Tesla magnet (case 3) is 20 Mega- Joules (for 70 cm). –This can be compared to 7 Mega-Joules for the 10 m long LHC 2-in-one dipole. The LHC quench protection system actually handles a string of dipoles in a sextant (?). There are differences between HTS and NbTi that need to be considered for quench protection. –HTS goes resistive at a slower rate than NbTi. –A quench propagates at a slower velocity in HTS than for NbTi. –We will have to perform computer simulations of quench protection for the HTS system to determine how to protect the magnet in case of an incident.

Sep 26, 2006S. Kahn T HTS Solenoid19 What about Axial Forces? There is a significant contribution to the axial forces from the fringing radial fields at the ends. –In the 50 Tesla solenoid shown we will see a fringing field of 9 Tesla –We have seen that there is a total axial compressive force at the center of ~30 Mega-Newtons.

Sep 26, 2006S. Kahn T HTS Solenoid20 More on Compressive Forces The top figure shows the Lorentz force density at the end of the solenoid as a function of radius for the three cases. –The axial pressure on the end is P=J  B r  t where t is the tape width. This peaks at 10 MPa. The lower figure shows the Lorentz force density along the length for the peak radial position. –It is largest at the end and falls to zero at center as expected. These stresses are not large. Do we have to worry about compressive strain along the axial direction? –The maximum allowable compressive strain for the tape is 0.15%.

Sep 26, 2006S. Kahn T HTS Solenoid21 Formulate R&D Plan Initial measurements of material properties. –J C measurements under tensile and compressive strain. –Modulus measurements of conductor. –Thermal cycling to 4  K. Formulate and prepare inserts for high field tests. –Design insert for test in 30 Tesla magnet. This magnet has a reasonable size aperture. –At 30 Tesla, some part of the insert should be at the strain limit. –Program for conductor tests at 45 Tesla. 45 Tesla magnet has limited aperture (3.1 cm). It has a warm aperture. There is a 38 Tesla facility in Japan that could be used if the 45 Tesla facility is not available.

Sep 26, 2006S. Kahn T HTS Solenoid22 Preliminary Calculations for Quench Protection I am presenting some preliminary calculations using the quench calculation program QUENCH. –This program was written by Martin Wilson at Rutherford Lab in the 1970’s. The current version of the program is marketed by B. Hassenzahl of Advanced Energy Analysis. BNL has a license to use it. There are other codes available: –QUENCHPRO at FNAL Technical Division. –SPQR from CERN. –Vector Fields is developing a quench propagation code ??

Sep 26, 2006S. Kahn T HTS Solenoid23 Conductor and Insulator Description The conductor is BSCCO 2223 which is 30% HTS filaments and 70% Ag matrix and Ag-Mg sheath (for strength). We assume the matrix/sheath is all Ag for the calculation. The insulator is assumed to be the Stainless Steel interleaving. A minimum thickness (0.07 mm) is used since we are describing the inner layers. –In practice we will likely add a ceramic coating or kapton wrap as insulator. This will inhibit the transverse quench propagation. ComponentAreaFraction HTS conductor mm Ag matrix/sheath mm SS Insulator0.301 mm

Sep 26, 2006S. Kahn T HTS Solenoid24 Conductor Material Properties Necessary for Quench Protection We need the material properties of all the components of the conductor and insulation. The important properties are –Heat capacitance (Specific Heat) –Resistivity –Thermal conductance Obtained from resistivity with Wiedemann-Frantz law. C V and  are parameterized as in up to four temperature ranges:

Sep 26, 2006S. Kahn T HTS Solenoid25 Critical Current Measurements Measurements of critical current as a function of B and temperature are from EHTS (another provider of BSSCO 2223). The measured data is used to determine parameters of the following equation: Used only high field part of data to determine B c20

Sep 26, 2006S. Kahn T HTS Solenoid26 Quench Propagation Velocity Quench protection calculations depend on the quench propagation velocity. The quench propagation velocity can be calculated from the formula below. –This is what I did. –Experience for NbTi shows that the formula does not reproduce the measurements. Typically the experimentally determined value is used. –We need to measure this for HTS. –One of the weaknesses of the velocity calculation is that the specific heat (  C V ) varies as T 3 and is rapidly varying at the quench front. TsTs T0T0 T1T1 Lorentz Number

Sep 26, 2006S. Kahn T HTS Solenoid27 Circuit for Quench Energy Extraction Quench circuit components: –Solenoid represented by inductance L. Also there is an internal resistance (not shown) which is about 10 ohm. –R PR represents the energy extraction resistance. This will take the large share of quench energy. –Switch will be activated by quench detection system. Could even be a diode system. –R EXT represents the resistance associated to leads, power supply, etc. R EXT LR PR R SW Power Supply Solenoid Magnet

Sep 26, 2006S. Kahn T HTS Solenoid28 Circuit Parameters QUENCH treats the whole magnet. It does not provide for segmenting the magnet into separate coupled systems. –The total inductance can be calculated from the stored energy: U=½LI 2 where U=20 Mega-Joules and I is the total amp- turns(=2.97  10 7 ). There are 444 layers  175 turns/layer = turns. This gives 280 henrys (big!) –The resistance associated with 61 km of Ag is 8 ohms. We certainly will need to trigger an external resistance into the circuit with a quench is detected.

Sep 26, 2006S. Kahn T HTS Solenoid29 Quench Parameters as a Function of External Resistance The figures show the following parameters as a function of an external resistance for energy extraction. Maximum temperature on conductor Time constant for decay External voltage on external resistance Note that as one increases the external resistance one decreases temperature, but increases the external voltage.

Sep 26, 2006S. Kahn T HTS Solenoid30 A Better Approach It may be a better approach to divide the magnet radial into separate thermally and electrically isolated systems on separate power supplies. These systems would be coupled through mutual inductance. –Each system would contain less stored energy and could have different time constants and different start times. –Different sub-systems would have different critical currents since they are at different magnetic fields. Some may not quench at all. QUNECH can not simply handle this complex system. –Do the other codes handle this or do we have to write our own? –Fermilab people may have thought about this.

Sep 26, 2006S. Kahn T HTS Solenoid31 What Do We Need to Measure? It is clear from this initial calculation that some parameters are not well known. We should try to measure them. –Electrical resistivity and heat capacity of HTS conductor as a function of temperature. This should be done above critical current. –Same measurements of Silver as a control. –Determine I c (B) at high field. Verify that the critical current relation that we used (which was developed for NbTi, Nb 3 Sn) works for HTS. –Measure the quench propagation velocity. This is important.