Claus Rode

Spallation neutron source cryomodule heat loads and thermal design

When complete, the Spallation Neutron Source (SNS) will provide a 1 GeV, 2 MW beam for experiments. One portion of the machine’s linac consists of over 80 Superconducting Radio Frequency (SRF) 805 MHz cavities housed in a minimum of 23 cryomodules operating at a saturation temperature of 2.1 K. Minimization of the total heat load is critical to machine performance and for efficient operation of the system. The total heat load of the cryomodules consists of the fixed static load and the dynamic load, which is proportional to the cavity performance. The helium refrigerator supports mainly the cryomodule loads and to a lesser extent the distribution system loads. The estimated heat loads and calculated thermal performance are discussed along with two unique features of this design: the helium heat exchanger housed in the cryomodule return end can and the helium gas cooled fundamental power coupler.

Thermal Performance of the Cebaf Superconducting Linac Cryomodule

When complete, the Continuous Electron Beam Accelerator Facility (CEBAF) will be centered on a 4 GeV recirculating linac. Each of the two linacs contains 160 superconducting radio frequency (SRF) 1497 MHz niobium cavities1 in 20 cryomodules operating between 2 and 2.3 K. Minimization of the total heat load is critical to machine performance, since the refrigeration capacity is fixed. The total heat load of the cryomodule consists of the static load (fixed heat leak) and the dynamic load (proportional to the cavity performance Qo, or quality factor). The heat load of the cryomodules is the single largest load to both the primary and secondary cooling circuits of the refrigerator. The optimization of the thermal performance of the cryomodule considers recent test data of multilayer insulation (MLI) systems developed for the SSC, in addition to the effect of the dynamic heat load on the design of the cryostat. The design of the cryomodule and the measured thermal performance of the installed north and south linac cryomodules are discussed. The performance to date is shown to meet the design heat loads for the accelerator.

FMEA on the Superconducting Torus for the Jefferson Lab 12 GeV Accelerator Upgrade

As part of the Jefferson Lab 12 GeV accelerator upgrade project, Hall B requires two conduction cooled superconducting magnets. One is a magnet system consisting of six superconducting trapezoidal racetrack-type coils assembled in a toroidal configuration and the second is an actively shielded solenoidal magnet system consisting of five coils. Both magnets are to be wound with Superconducting Super Collider-36 NbTi strand Rutherford cable soldered into a copper channel. This paper describes This paper describes a failure modes and effects analysis (FMEA) that was done on these magnets to identify their various failure modes, which were assessed in terms of their Risk Priority Numbers (RPN). Mitigating actions were identified that would reduce the RPNs to acceptable values.

Temperature optimization for superconducting cavities

Since our previous analysis of optimized operating temperature of superconducting cavities in an accelerator a decade ago, significant additional information has been discovered about SRF cavities. The most significant is the Q/sub 0/ (quality factor) shift across the Lambda line at higher gradients as a result of a slope in Q/sub 0/ vs. E/sub acc/ above Lambda. This is a result of the changing heat conduction conditions. We discuss temperature optimizations as a function of gradient and frequency. The refrigeration hardware impacts and changes in cycle efficiency are presented.

Electromagnetic and Mechanical Analysis of the Coil Structure for the CLAS12 Torus for 12 GeV Upgrade

The torus magnet for the CLAS12 spectrometer is a 3.6-T superconducting magnet being designed and built as part of the Jefferson Lab 12-GeV upgrade. The magnet consists of six coil case (enclosed in a vacuum-impregnated coil pack) assemblies mounted to a cold central hub. The coil pack consists of a 117-turn double-pancake winding wrapped with two layers of 0.635-mm-thick copper cooling sheets. The coil case assembly is cooled by supercritical helium at 4.6 K. This presents the electromagnetic and structural analysis of the coil case assembly and the assessment of the coil pack stresses. For the normal operation of the torus magnet, the coil case assembly was analyzed for cool down to 4.6 K and the Lorentz forces at normal operating current. In addition to the normal operating configuration, the coil case assembly was analyzed for Lorentz forces arising from coil misalignment and current imbalances. Primary stresses were limited to the lesser of 2/3 times the yield strength or 1/3 times the ultimate tensile strength. Primary plus secondary stresses were limited to 3 times the primary stress allowable. The analysis was performed using ANSYS Maxwell and ANSYS Mechanical to calculate the magnetostatic loads and calculate the stresses.

The CLAS12 torus detector magnet at Jefferson Laboratory

The CLAS12 Torus is a toroidal superconducting magnet, which is part of the detector for the 12-GeV accelerator upgrade at Jefferson Laboratory (JLab). The coils were wound/fabricated by Fermilab, with JLab responsible for all other parts of the project scope, including design, integration, cryostating the individual coils, installation, cryogenics, I&C, etc. This paper provides an overview of the CLAS12 Torus magnet features and serves as a status report of its installation in the experimental hall. Completion and commissioning of the magnet is expected in 2016.

Gradient optimization for SC CW accelerators

The proposed rare isotope accelerator (RIA) design consists of a normally conducting radio frequency quadruple (RFQ) section, a superconducting (SC) drift tube cavity section, a SC elliptical multi-cell cavity section and two charge strippers with associated charge state selection and beam matching optics. The SC elliptical section uses two or three multi-cell beta cavity types installed into cryomodules to span the energy region of about 84.5 MeV/nucleon up to 400 MeV/nucleon. This paper focuses on the gradient optimization of these SC elliptical cavities that provide a significant portion of the total acceleration to the beam. The choice of gradient coupled with the cavity quality factor has a strong affect on the overall cost of the accelerator. The paper describes the optimization of the capital and operating cost associated with the RIA elliptical cavity cryomodules.

Structural Analysis of Thermal Shields During a Quench of a Torus Magnet for the 12 GeV Upgrade

A toroidal magnet system consisting of six superconducting coils is being built for the Jefferson Lab 12 GeV accelerator upgrade project. This paper details the analysis of eddy current effects during a quench event on the aluminum thermal shield. The shield has been analyzed for mechanical stresses induced as a result of a coil quench as well as a fast discharge of the complete magnet system. The shield has been designed to reduce the eddy current effects and result in stresses within allowable limits.

Large superconducting radio frequency construction projects

The SRF achievements of the last two decades will be reviewed; concentrating on the CEBAF, LEP, and SNS projects. The near term new SRF initiatives will also be presented.

Thermal Performance of the SNS Cryomodule

When complete, the Spallation Neutron Source (SNS) will provide a 1 GeV, 2 MW beam for experiments. One portion of the machine’s linac consists of over 80 Superconducting Radio‐Frequency (SRF) 805 MHz cavities housed in a total of 23 cryomodules (CMs) operating at 2.1 K. Minimization of the total heat load is critical to machine performance since the refrigerator capacity is fixed. The total heat load of the cryomodules consists of the fixed static load and the dynamic heat load, which is proportional to the cavity performance. The heat load of the cryomodules is the single largest load to the cooling circuits of the refrigerator. During acceptance testing at Jefferson Lab, a series of measurements have been taken on the prototype and first three production CMs. Calorimetric measurements of the primary heat load and shield heat load are presented and discussed. Temperature measurements taken allow a comparison between actual and predicted thermal performance of two components unique to this cryomodule des...