Zhaochuan Zhang

Investigation of the Failure Mechanism for an S-Band Pillbox Output Window Applied in High-Average-Power Klystrons

On the basis of the results of X-ray photoelectron spectroscopy, theoretical analyses, and numerical simulations, the failure mechanism of an S-band pillbox output window applied in a high-average-power klystron is discussed. The influence of the high-order cylindrical-guide modes on the microwave power loss, the direction of the power flow and the window disk cracking are investigated. The high-order cylindrical-guide TM11 mode existing on the surface of the window ceramic disk may cause the carbon film deposition and excessive radio frequency losses on the disk and lead to the breakdown of the window.

Magnetic reconnection driven by Gekko XII lasers with a Helmholtz capacitor-coil target

We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 1018 cm−3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications.

3.3: C-band broadband Multi-Beam Klystron with bandwidth of 8%

The research progress on C-band Broadband Multi-Beam Klystron at IECAS were presented in this paper. The relative bandwidth of 8.1% and 8.5% for C-band Broadband MBKs KC4137 and KC4148 were obtained on the power level of 100kW and 160kW with efficiency of 29% and 32.5%. The reason of higher parasitic output was analysis, and the method for surpressing it was discuseed.

Development of an S-band 50-kW-Average-Power Klystron

This paper reports the design considerations, simulation results, and test results of an S-band 70-MHz-instantaneous-bandwidth 50-kW-average-power klystron, which was developed by the Institute of Electronics, Chinese Academy of Sciences, from January 2004 to August 2007. The typical result is a 50-kW average output power with an 89-mus RF pulsewidth and a 300-Hz repetition rate during 8 h of continuous reliability testing. A cracked output window is also discussed.

A New Impregnated Dispenser Cathode

We put forward a new type impregnated dispenser cathode, which impregnates the active salt of BaO/SrO/Sc₂O₃. At 1100□_B, the pulse current density of the cathode is up to 86.2A/cm², 2.7 times of the value of a traditional M-type cathode. It is proposed that, the emission of pores and pore edges caused by Sc₂O₃ and SrO is the main reason that the new cathode has excellent emission performance.

Research progress on the S-band high-power broadband multi-beam klystrons

Two types (type-A and type-B) of the S-band high-power broadband multi-beam klystrons are being developed in the Institute of Electronics, Chinese Academy of Sciences (IECAS). Type-A adopts a coil focusing system, and type-B has a Periodic Reverse Permanent Magnet (PRPM) focusing system. Five tubes have been manufactured and tested to date. Test results show that both MBKs have the RF peak output power of more than 1 MW, and the RF average output power of more than 20 kW with the 200 MHz instantaneous bandwidth. The design considerations, simulation results and test specifications will be presented in conference. The technical problems met during the development of the MBKs will also be discussed.

Suppression of high order mode oscillation and parasitic RF output in multi-beam klystrons

The high order mode oscillation and parasitic RF output have serious influence on the normal operation and the purity of the output spectrum of MBKs. A new method to suppress the high order modes will be introduced in this paper. By putting selective absorbing material on coupling slot of the double-gap coupling cavity, all the high order modes with π mode field structure can be suppressed effectively. This method has been applied to C-band MBKs successfully

Development of an S-band 22-kW-Average-Power-Klystron With 7.14% Relative Bandwidth

This paper presents the design considerations, simulation results, and test results for an S-band 22-kW-average-power 7.14%-relative-bandwidth klystron design with 4-min startup, which was developed in the Institute of Electronics, Chinese Academy of Sciences (IECAS) before December 2009. Ten klystrons were built and tested. Over 1.1-MW peak output power with 7.14% relative bandwidth was measured at a 2% radio-frequency (RF) duty cycle. The measured startup time is 4 min. A method of supplying the heater with electricity is proposed, the manner of improving the RF output performance is also described, and both of them have been validated through the further experiments with a specialized electron gun and the hot-test results of the klystron, respectively.

Development of a C-Band Klystron With a 360-MHz Instantaneous Bandwidth

This paper presents the design considerations, the simulation results, and the test results for a C-band klystron design with a 360-MHz instantaneous bandwidth, which was developed from March 2005 to June 2008. Five klystrons were built and tested. Over 800 kW peak output power with a 400-MHz instantaneous bandwidth (constant RF input drive over frequency) was measured at a 0.525% RF duty cycle. The measured electron beam-to-RF conversion efficiency is 30%, and the output power fluctuation over frequency is less than ±0.75 dB. The technological problems, including gain/power dip over frequency and low electron-beam transmission, are also discussed.

Theoretical Investigation and Simulation of Resonant System of Sector and Hole-and-Slot Resonator Type Rising-Sun Magnetron

In this paper, a sector-step approximation (SSA) model is introduced. With step admittance recurrence and field matching relation, the dispersion equation of rising-sun magnetron (RSM) with arbitrary resonators is derived. By this model, resonant frequencies of a 10-resonator sector and hole-and-slot resonator type RSM (SHSRSM) are theoretically calculated. In addition, computer simulation is performed to verify the accuracy of the theory. Besides, the effects of the hole radius on magnetrons main characteristic parameters are analyzed, such as π-mode resonant frequency, mode separation, and quality factor. The optimized SHSRSM is compared with two common kinds of RSMs, such as sector resonator type RSM (SRSM) and sector-and-slot resonator type RSM (SSRSM). The results show that the theoretical results are well consistent with the simulation results, and the maximum relative error is less than 3%, which verifies the accuracy and feasibility of the SSA model. Compared with SRSM and SSRSM, SHSRSM has greater mode separation and quality factor, which improves the stability and the energy storage of RSM.