## 2 Large-Scale Coaxial Line
Duralumin tube is centered with Caprolon spokes resting against Caprolon rings. The wave impedance of the central section is \(\rho\) = 170 Ohm. The tapered transitions are made as several sections (see Figure 1c) with different flange diameters that are connected in series. The sectionalized design of the tapered transitions allows connecting EMP generators of types and classes varying the voltage amplitude and pulse duration with different output connector diameters. Solid-state generators will be used to generate nanosecond pulses with subnanosecond rise times and amplitude levels from several kilovolts to several tens of kilovolts [22; 23]. Nanosecond voltage pulses having amplitudes up to 250 kV can be generated by RADAN generators [24]. Aluminum end Sections 2-4 of the tapered transitions (see Figure 1) are made solid, which ensures the rigidity of the structure and the element manufacture precision with the requirements for the impedance transformation taken into account. In the Sections 2-4 of the tapered transitions, the inner conductor is made as a copper tapered rod, which passes into the central contact of the corresponding connector on the narrowing side. Section 4 of the tapered transition with the minimal dimensions of the outer and inner conductors acts as an adaptor for various small-size connectors including N-type connectors and customized output connectors of EMP generators. On the whole, the tapered transitions act as impedance transformers. On the excitation side, they are step-up transformers. When generators with the feeding lines having the impedance \(\rho_{0}\) = 50 Ohm are used, the EMP voltage amplitude in the uniform line section (with an impedance of 170 Ohm) increases by approximately 1.4 times. The coaxial line is filled with plasma by means of a standard pair of inductor antennas [21], brought into the gap between the outer and inner conductors (not shown in Figure 1). The maximum density of the plasma, which can be obtained in the case of a pulsed breakdown of a working gas (argon, nitrogen, or air) under a pressure of \(10^{-4}\)-\(10^{-2}\) Torr in the absence of an ambient magnetic field, exceeds \(10^{11}\) cm\({}^{-3}\)[20]. Such plasma is nontransparent for EMPs with durations about and exceeding 1 ns, which were used in the experiment. The operating background electron density ranges from \(10^{10}\) to \(10^{6}\) cm\({}^{-3}\). It is set in at the stage of the diffusion decay of the plasma in the working space  
Figure 1: (**a**) General layout of KROT plasma chamber with coaxial line installed inside it; (**b**) 3D model of the “gigantic” coaxial line; (**c**) detailed layout of tapered transition; and (**d**) photograph of the plasma chamber. of the line. For a line with the specified dimensions, the characteristic diffusion decay duration should be not less than 1 ms. Since the durations of the considered processes are significantly shorter (from fractions of a nanosecond for electromagnetic processes to tens of microseconds for plasma), it is possible to assume that the plasma is quasi-stationary. To measure pulsed electric and magnetic fields in the line directly, strip-line IPPL probes [25] and inductive TPMP probes with the rise time of the pulse characteristic being not more than 35 ps, respectively, were used. An assembly of such probes was used, e.g., to detect the shape of subnanosecond pulses generated by long spark discharges [26]. To detect the shape of an EMP after it passed through the plasma-filled line, the low-inductance dummy load with wideband attenuators was used.