Journal Article/Contribution to a conference proceedings

PUBDB-2025-02026

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Modelling two-phase He II flow for heat load limits in XFEL Cryomodules for CW operation

Dhillon, A. K. (Corresponding author)DESY* ; Barbanotti, S.DESY* ; Bozhko, Y.DESY* ; Jensch, K.DESY* ; Ramalingam, R.DESY* ; Abassi, E.DESY* ; Schnautz, T.DESY*

2025

Abstract: The European XFEL (EuXFEL) is under consideration for a High Duty Cycle (HDC) upgrade to enhance the user’s operational range by enabling short pulse, long pulse, and Continuous Wave (CW) operation. Therefore, the EuXFEL shall be extended by new CW optimized cryomodules (CMs) that will be installed at the beginning of the EuXFEL linac. These new CMs will be followed by the already existing CMs, which have to be operated at respectively higher 2 K dynamic heat loads at various operating modes. One of the key challenges for this upgrade is the design of the CW-optimized CMs. Furthermore, the heat load limit of the existing EuXFEL CMs has to be identified with respect to operational stability. Measures must be implemented to increase the heat load limit to meet the requirements of the HDC upgrade. Referring to operational stability, the flow conditions in the two-phase pipe within the CMs play a critical role to prevent vibrations and microphonic effects with undesirable impacts on RF operation. To address these challenges, a simulation model has been developed to analyze the two-phase flow behavior of superfluid helium in EuXFEL-like CMs installed on the cryomodule test stands in the Accelerator Module Test Facility (AMTF). This model incorporates the Taitel-Dukler criterion to evaluate the transition from stratified smooth to stratified wavy flow in the two-phase pipe under varying heat loads. The findings provide path for the CW optimized CM design and JT valve arrangement, ensuring stable operation under increased heat loads. Validation tests planned at AMTF will further establish the predictive accuracy of the model and support its future use in XFEL HDC upgrades.

Note: online first

---

Contributing Institute(s):

1. Kryogenik (MKS1)

Research Program(s):

1. 621 - Accelerator Research and Development (POF4-621) (POF4-621)

Experiment(s):

1. Facility (machine) XFEL

Appears in the scientific report 2025

---