## 4 Discussion  
According to the results of the calculations [4], the character of EMP distortion in plasma is determined by the total electron content (TEC) on the signal propagation path [27; 28]:  
\[\text{TEC}=\int_{0}^{L}N_{e}dl, \tag{1}\]  
where \(L\) is the total length of the propagation path. Under ionospheric conditions, it is convenient to use the TEC concept, since in most practically significant cases the plasma in the plane of the leading EMP edge can be assumed to be uniform. As a result, the effects of refraction at the transverse density gradients are not very significant, and all distortions of the EMP form along the propagation path are determined by the longitudinal \(N_{e}\) distribution only. In laboratory experiments on irradiating a large column of the laboratory plasma with EMP from a horn antenna, this approach cannot be implemented [16]. The refraction determined by the transverse \(N_{e}\) gradients leads to a significant fraction of the EMP energy leaving the plasma, and it is rereflected from the walls of the metal chamber, which, in turn, causes distortions in the form and spectrum of the pulse, which are not always predictable. The approach used here allows one to prevent these undesirable phenomena. When excited in the fundamental (transverse electromagnetic, TEM) mode, the transmitting line (in particular, coaxial line) has constant impedance characteristics in a wide frequency band, up to the zero frequency (dc). As a result, one can achieve the quasiunidimensional propagation of the EMP, which can be described using the TEC concept, both in the case of isotropic plasma [20; 21] and in the presence of an ambient magnetic field. TEC can be regarded as the scaling parameter when simulating the dispersion EMP distortion in the ionosphere [4]. For the F layer of the dayside ionosphere, TEC \(\sim\)10-40 TECu = \(10^{13}-4\times 10^{13}\) cm\({}^{-2}\) (TECu is the TEC unit, 1 TECu = \(10^{12}\) cm\({}^{-2}\)[28]). In the GCL, the typical values of TEC are \(\sim\)2 \(\times\)\(10^{-3}-0.2\) TECu = \(2\times 10^{8}-2\times 10^{11}\) cm\({}^{-2}\). When modeling the EMP propagation in the ionosphere, its propagation along a relatively short (several meters) path in a laboratory chamber with a plasma density \(N_{e}\) increased compared with ionospheric conditions. In this case, where the pulse spectrum is higher than the plasma frequency, i.e., at \(\tau_{p}<<\)\(f_{p}^{-1}\), where \(\tau_{p}\) is the pulse duration, a noticeable distortion of the waveform is possible due to the dispersion, if the following condition is fulfilled:  
\[\text{TEC}>\frac{m_{e}c}{2\pi e^{2}}\frac{1}{\tau_{p}} \tag{2}\]  
The total EMP energy is retained during propagation in this case. For a pulse with the duration \(\tau_{p}\)-1 ns, criterion (2) yields the estimation TEC \(>\) 0.02 TECu = \(2\times 10^{10}\) cm\({}^{-2}\). This value corresponds to the density of isotropic plasma in the GCL \(N_{e}\)-\(2\times 10^{8}\) cm\({}^{-3}\) along the path of about 2 m long. In a certain sense, one can state that the GCL makes it possible to simulate a segment of the ionospheric UWB EMP propagation path with a length from 0.1 to 10 km, depending on the conditions. Notwithstanding, the above TEC is an important, but not the only, modeling parameter. Particularly, the theory developed in [4] which leads to simulation criteria like (2) assumes that the pulse duration is significantly less than the period of plasma oscillations \(f_{p}^{-1}\). For longer pulses, when a significant part of the EMP frequency spectrum is on the order of and below the plasma frequency \(f_{p}\), the contribution of cutoff effects to the transformation of the EMP shape increases [16; 17]. If collision effects are considered, then pulse duration \(\tau_{p}\) should be compared to the electron collision frequency \(\
u\).