Multi-beam gun design for an S-band klystron
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This paper introduces the detailed design scheme of a multi-beam electron gun applied to an S-band high power multi-beam klystron. The multi-beam gun adopts a coaxial cavity arrangement, and the total number of electron beams are 40 (19 in the inner layer and 21 in the outer layer). The working voltage of the electron gun is 60 kV, the total current is 300 A (evenly distributed on 40 electron beams), and the single beam perveance is 0.51 μP. The total perveance is 20.4 μP. The cathode loading of the gun is 12 A/cm2, which can meet the requirements of cathode operational lifetime. The beam focusing system uses a periodic reversal permanent magnet to realize miniaturization of the klystron.Keywords:
Perveance
Klystron
Electron gun
The report presents synthesis method of modeling the electron-focusing systems that formed compressed sheet electron beam with supporting the beam magnetic field and field-emission cathode. Results of calculating by synthesis and analysis method of the electron gun with linear compression of the beam 10, micro-perveance of Pμ = 0.035 and 100 mA current are performed. The electron gun forms a sheet beam with a 0.125mm thickness, and 0.7 mm width.
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The bandwidth of a klystron output cavity scales (approximately) as p/sup 0.8/P/sup 0.2/, where p is the beam perveance and P is the beam power. For high-perveance (p>10 /spl mu/pervs) high-power (P>10 kW) electron beams, it is relatively straightforward to design a broad-band output cavity. However, the design of the input cavity of the broad-band klystron is in some ways more difficult. The purpose of the input cavity is to produce a velocity-modulated electron beam with a frequency-dependent modulation amplitude that will optimize the bandwidth of the entire klystron system, while providing a magnitude of velocity modulation large enough to minimize the length of the klystron. This paper shows how a multiplet (multiple cavity) buncher cavity can be designed to provide broad-band (>20%) operation while keeping short the drift section length of the klystron.
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This paper describes the development of an electron gun for a sheet beam klystron. Initially intended for accelerator applications, the gun can operate at a higher perveance than one with a cylindrically symmetric beam. Results of 2D and 3D simulations are discussed.
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The high power klystron-modulator (K&M) system is a main pulse and microwave source for the PLS linac. The peak powers of the modulator and the klystron have 200 MW and 80 MW, respectively. The total heater run time of an oldest klystron system has been accumulated over 75,000-hours as of now. This klystron must operate efficiently and stably in the linear gain region within a band of frequencies. The micro-perveance will change as the tube ages. It is believed that a change in the perveance of the klystron may be a predictor of when a klystron is about to fail. Therefore, it is necessary to monitor the klystron operational status for stable beam operation. It can be achieved by measuring the klystron micro- perveance to diagnose characteristics of klystron. Up to now, the operator manually performs it. The prototype perveance monitor system has been designed by processing the sensing signal of a beam voltage and current of the klystron. In this paper, the design concept and experimental results for application will be presented.
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The bandwidth of a klystron output cavity scale (approximately) as...0.8P0.2, where p is the beam perveance and P is the beam power. For high-perveance (p > 10 (mu) pervs), high-power (P > 10 kW) electron beams, it is relatively straightforward to design a broadband output cavity. However, the design of the input cavity of the broadband klystron is more difficult. The purpose of the input cavity is to produce a velocity-moldulated electron beam with a frequency-dependant modulation amplitude that will optimize the bandwidth of the entire klystron system, while providing a large enough magnitude of velocity modulation to minimize the length of the klystron. This paper shows how a multiplet (multiple cavity) buncher cavity can be designed to provide broadband (> 20%) operation while keeping the drift length of the klystron short.
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Long life high performance grid-controlled electron gun has been great extensive used in multi-beam klystron. High performance grid-controlled electron gun is the base of modern high power and broadband multi-beam klystron. We developed a tight and efficient electron gun; its perveance can be more than 0.5 micro-perveance of only one cathode.The whole electron gun has 28 independent small cathodes. The total of whole gun's perveance can be more than 18 micro-perveance. The characteristics of the gun are given in this article.
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In multi-beam Klystron (MBK), several electron beams are used to interact with the RF signal in a single interaction structure. MBK has a number of advantages over single beam klystron. As it uses several low perveance beams, for the same overall perveance, the beam voltage is substantially lower than single beam klystron for same RF output power.
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Abstract This paper has completed the simulation of the X-band 1 MW klystron electronic optical system, and optimized the electron gun and focusing system respectively. The electron gun adopts a single electron beam scheme. The voltage and current of the beam is 80 kV and 45 A respectively, the perveance is about 2.0 μP , and the average emission current density of the cathode is 6.81 A / cm 2 . The focusing system adopts the design of electromagnetic focusing, and the maximum magnetic field in the uniform area is about 0.33 T. The calculation results show that the distribution of the electric field lines in the electron gun area is uniform, the fluctuation of the electron beam is uniform, and the DC pass rate of the electron beam reaches 100%, which meets the design requirements.
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Successful operation of the BNL EBIS with electron current up to 10 A provides optimism that EBIS operation with even higher electron current should be possible. We are now considering key aspects of the design for an EBIS operating with electron current 20 A. Several technical problems need to be resolved, including generation of a 20 A electron beam and dissipation of this electron beam power on the electron collector. Since we already have a tested concept of electron beam generation with the gun immersed in a magnetic field and subsequent purely magnetic compression of the electron beam, it makes sense to develop the new electron gun with immersed cathode but with higher perveance. To distribute the electron beam power on the surface of the electron collector more evenly, the emission current density from the cathode can be made bell-shaped with minimum close to zero on the periphery of the electron beam. With the already high requirements to the emission current density, and since such shaping of the electron beam makes these requirements even higher, perhaps the only available cathode material that can satisfy these requirements is IrCe. The problems of power dissipation on the electron collector (EC) include heat removal with cooling water and fatigue of the EC material. The first step in the EC design was electron beam transmission simulation with the goal to reduce `spikes' of power density on EC surface as much as possible. With the geometry of EC thus defined, the conditions of heat exchange for several modes of EBIS operation have been analyzed and cooling parameters, which provide adequate heat removal were found. The last step was stress analysis of several EC materials with ANSYS to find the material suitable for this application. Details of the 20 A electron gun and collector are presented.
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Total 12 units of high power klystron-modulator systems are under continuous operation in the Pohang Light Source (PLS) linac. The peak powers of the modulator and the klystron are 200 MW and 80 MW, respectively. The total heater run time of an oldest klystron system has been accumulated over 75,000-hours as of now. Therefore, it is necessary to monitor the klystron operational status for stable beam operation. It can be achieved by measuring the klystron perveance to diagnose characteristics of klystron. Up to now, the operator manually performs it. We have designed the perveance monitor by processing the sensing signal of a beam voltage and current of the klystron. It takes advantage of the time saving in diagnosing klystron performance. In addition, a highly accurate current and voltage sensor is one of the critical components of the measuring system. This paper presents the design concepts and initial test results of the perveance monitor to diagnose characteristics of klystron.
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