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Volker Ziemann

Publications and source records attributed to Volker Ziemann.

21 records · Page 2Linked to original sources
arXiv2021

MATLAB Simulations of the Helium Liquefier in the FREIA Laboratory

We describe simulations that track a state vector with pressure, temperature, and gas flow through the helium liquefier in the FREIA laboratory. Most components, including threeway heat exchangers, are represented by matrices that allow us to track the state through the system. The only non-linear element is the Joule-Thomson valve, which is represented by a non-linear map for the state variables. Realistic properties for the enthalpy and other thermodynamic quantities are taken into account with the help of the CoolProp library. The resulting system of equations is rapidly solved by iteration and shows good agreement with the observed LHe yield with and without liquid nitrogen pre-cooling.

physics.ins-det↗
arXiv2019

Envelope Dynamics and Stability with non-linear Space-Charge Forces

We developed a model to calculate the stability of Gaussian beam distributions with non-linear space-charge forces in the presence of random and skew-quadrupole errors. The effect of the space-charge force on the beam matrix is calculated analytically including full cross-plane coupling in 4D phase space, which allows us to perform fast parameter studies. For stability analysis, we find the fixed points of the beam including the space-charge forces and construct a Jacobi-matrix by slightly perturbing the periodic solution. The stability of envelope oscillations is inferred by eigenvalue analysis. Furthermore, we employ envelope tracking as a complementary method and compare the results of the eigenvalue analysis with FFT data from the tracked envelope. The non-linearity of the space-charge force in combination with lattice errors and beam coupling opens up for envelope-lattice resonances and envelope coupling resonances. Hitting these resonances leads to envelope blow-up, causing an effective beam mismatch. Therefore, we finally examine the effect of beam mismatch on the envelope tune-shift and its stability.

physics.acc-ph↗