$X$-band two-stage rf pulse compression system with correction cavity chain

A compact $X$-band two-stage rf pulse compression system has been successfully designed, fabricated, and tested at Tsinghua $X$-band high-power test stand. The pulse compression system consists of a correction cavity chain, a first-stage, and a second-stage storage cavity. The correction cavity chain adopts a new design whose transmission loss and length are reduced by half compared with the old one. A detuning device is applied to the second-stage storage cavity so that the system can work in one-stage or alternatively two-stage compression mode. In the one-stage compression mode, a 150-ns, 70-MW flattop output, with a standard deviation of 1.5% in amplitude and 1° in phase, was generated with a gain factor of 3. In the two-stage compression mode, a first two-stage pulse compression experiment with correction cavities in the $X$ band was performed. A peak power of 320 MW was achieved with a gain factor of 9.7 and full-width at half-maximum pulse durations of 53 ns.

Figure 1

Vacuum model of the $X$-band two-stage pulse compression system.

Figure 2

Geometry of the expanded polarizer and the transient E-field distribution with 1-W input power fed from port 1.

Figure 3

Transmission spectra of the expanded polarizer with two cavities at different frequencies compared with two cascaded normal polarizers with the same cavities.

Figure 4

Calculated power gains with different coupling factors and waveforms of one-stage and two-stage pulse compression. (a) Power gain of one-stage pulse compression versus coupling factor of the first storage cavity. (b) Input and output waveforms of the one-stage pulse compression with ${\beta }_{s1}=4.0$ in the case with and without amplitude modification. (c) Power gain of the two-stage pulse compression versus coupling factor of the first and second storage cavities. (d) Input and output waveforms of the two-stage pulse compression with ${\beta }_{s1}=4.0$, ${\beta }_{s2}=30$. Red circles in (a) and (c) indicate the optimized coupling factor.

Figure 5

Vacuum model and simulated transmission spectrum of CC. The dotted boxes show the correspondence between cavity pairs and resonant peaks.

Figure 6

Surface field of storage cavities. (a)–(c) are surface electric field, magnetic field, and modified Poynting vector of SC1. (d)–(f) are surface electric field, magnetic field, and modified Poynting vector of SC2. Arrows point to maximum locations.

Figure 7

Mechanical design of the correction cavity chain and storage cavities.

Figure 8

Microwave measurement of the correction cavity chain during tuning.

Figure 9

$S$-parameters of the correction cavity chain (a) before and (b) after tuning. The transmission loss after tuning is $-0.24\mathrm{dB}$.

Figure 10

Microwave measurement of the storage cavity during tuning with the correction cavity chain measured simultaneously.

Figure 11

Transmission (a) and reflection spectrum (b) of the storage cavities after tuning.

Figure 12

System diagram of Tsinghua high-power test stand (TPOT-X) with the two-stage pulse compression system installed.

Figure 13

Photograph of the pulse compression system with four stainless steel loads after installation.

Figure 14

Condition history of the two-stage pulse compression system at TPOT-X.

Figure 15

Waveforms of the two-stage pulse compression high-power test. (a) Measured waveforms of the input, first-stage output, and second-stage output. (b) Measured waveforms of the input and calculated waveforms of the first- and second-stage output.

Figure 16

Waveforms of the pulse compression system (a) with and (b) without amplitude modification when the second-stage storage cavity was detuned.

Figure 17

Phase information of the one-stage pulse compression.

Figure 18

Equivalent circuit of a storage cavity feed by a generator through a transmission line.

Figure 19

Scheme of the pulse compressor with an elliptical cavity. Mode $\mathrm{P}i$ denotes the port modes of the waveguide, and mode $\mathrm{C}i$ denotes the polarized eigenmodes of the cavity.

Figure 20

Schematic diagram of a cavity with a cylinder waveguide working at the polarized degenerate mode.

Figure 21

Simulation of a pulse compressor with an elliptical cavity and reconstruction of reflection spectrum for each polarized mode. (a) Simulated transmission and reflection spectra of a pulse compressor with the elliptical cavity. (b) Polar plot of (a). (c) Reconstructed reflection spectra of two eigenmodes in the elliptical cavity. (d) Polar plot of (c).