## 1 Introduction  
Imaging is a crucial factor in a fundamental understanding of the environment surrounding us as well as the insight of ourselves. New imaging methods have been explored during the last couple of decades to continue research in cell biology. One of the emerging imaging methods for cell biology is soft X-ray microcopy with its spatial resolution in the order of tens nm covering the gap between transmission electron microscopy (TEM) and visible light microscopy. The soft X-ray microscopic images captured by employing the Fresnel zone plate as the objective optics with 10 nm spatial resolution have been presented [1], and the soft X-ray ptychographic microscope demonstrated spatial resolution below 5 nm [2] as ptychography removed the resolution limit imposed by the characteristics of the X-ray optics. Soft X-ray microscopes typically operate within the \"water-window\" spectral region, between the K-absorption edges of oxygen (2.34 nm; 530 eV) and carbon (4.4 nm; 280 eV) [3,4] and have three advantages over light and electron microscopes. Firstly, SXR radiation penetrates biological materials much more easily than electrons, which allows specimens up to 10 \(\upmu\)m thick to be imaged. Unlike electron microscopy, there is no need for sectioning eukaryotic cells with an ultramicrotome before imaging [5]. Secondly, the short-wavelength allows image cells with higher spatial resolution to be compared to light sources [4]. Finally, image contrast is obtained from the absorption of X-rays by the specimen [5]; thus, there is no need to insert any fluorescence markers or other substances into the sample. This absorption is described by the Beer-Lambert Law, therefore is linear with thickness and concentration [4]. By imaging in the \"water-window,\" organic matter containing carbon and nitrogen absorbs photons at an order of magnitude more than water, which creates inherent contrast to visualize cellular structure [6]. The in-depth comparison between images taken by the soft X-ray microscope (scanning transmission X-ray and X-ray ptychography) and the electron microscope can be found in [7]. A major part of SXR microscopes is based on large-scale facilities such as synchrotron or free-electron lasers, and their advantage is a short exposure time and high spatial resolution contrary to their vastness and the price demands (construction and operation), which does not allow access to this imaging technique for the broader scientific community. Therefore, in the mid-1990s the first effort to develop a compact, laboratory-scale source appeared. In recent years, considerable progress has been achieved, and several transmission SXR microscopes operating in the water-window region based on table-top sources were reported. Compact transmission SXR microscopic systems based on laser-produced plasma sources--using liquid-jet target [8; 9; 10], gaseous target [11; 12], double-stream gas target [13; 14; 15], or ultra-thin metal target [16]--were developed. The second branch of laboratory-scale transmission SXR microscopes are based on discharge-produced plasma sources using pseudo sparks such as electrode geometry [17], an electrode-less design (Energetiq, Inc., WI, MA, USA) [18; 19], or Z-pinching capillary discharge [20]. A compact transmission SXR microscope based on an electron-impact source, utilizing the oxygen K-alpha emission line at 525 eV (2.36 nm), was reported [21]. Nevertheless, the reported photon flux of these sources is about a few orders lower compare to laser-produced and discharge-produced plasma sources. Coherent laboratory sources such as plasma-based X-ray lasers (XRLs), sources based on high harmonics generation (HHG), or betatron radiation produced by laser-wakefield accelerators (LWFAs) are due to the high spatial coherence more suitable for other imaging techniques than transmission water-window microscopy, such as coherent diffraction imaging, ptychography, etc. [22].