B. Stockwell

8.3: A high aspect ratio, high current density sheet beam electron gun

A beamstick for demonstration of a 25∶1 aspect ratio, 750 A/cm² current density sheet beam for DARPAs HiFIVE project will be described.

Development of a megawatt C-band klystron for radar

An air cooled, 1 MW klystron with an instantaneous bandwidth of 50 MHz centered about 5625 MHz has been developed for radar applications. Details of the design and test results are presented.

P4-2: Permanent magnet for HiFIVE sheet beam transport

A permanent magnet structure has been successfully designed and fabricated for the HiFIVE program. The design produces a peak field of 0.75 T within a gap length of 2.5 cm.

Design and operation of a 2.5 MW, PPM focused X-band klystron

PPM focusing has been used in a 2.5 MW, 9300 MHz klystron. The design will be discussed and test results for three klystrons presented.

5.1: Validation of TESLA for widely varying klystron designs

Comparison between predictions of the 2.5D large signal code TESLA and measured data for three different klystrons are presented. The klystrons cover an operating frequency range from P-band to X-band, micro-perveance between 1.1 to 2.0, parameter ga between 0.53 to 0.87 and efficiency between 43% to 62%. Two of the three devices are CPI legacy tubes that are solenoid-focused. Thousands of one type have been successfully built in CPI production lines over the last thirty years. The third device is a state-of-the-art PPM-focused klystron that was designed and manufactured recently.

Test results from a 1.3 GHZ, 10 MW, high efficiency multiple beam klystron for XFEL

Large particle accelerator projects like the European X-ray Free Electron LASER (XFEL), which is under construction at DESY in Hamburg (Germany), or like the planned International Linear Collider (ILC) favor MBKs for their ability to generate high rf output powers at moderate electron beam energies. For the XFEL, Deutsches Electronen Synchrotron (DESY) ordered a prototype of a horizontally oriented, high-power MBK operating at 1300 MHz. This is CPGammas second generation 10 MW, L-band MBK, designated the VKL-8301B. The klystron is required to provide at least 65% efficiency at 10 MW peak rf output and more than 3 MHz instantaneous -l dB bandwidth. Average power and rf pulse length are 150 kW and 1.5 ms, respectively. Our design uses six off-axis electron beams for low cathode current density and thus longer cathode life. For the rf cavities we are utilizing fundamental-mode ring resonators. This ensures sufficient beam separation while still keeping the overall diameter of the device small in order to reduce cost. A more in-depth report on our design process and the tools we used was presented at the 2008 ICOPS. At the time of submission of this paper, initial rf hot test data were taken at reduced duty and pulse width while operating into well-matched output loads. At 0.42% rf duty, a peak rf output power as high as 11.2 MW was achieved, which corresponds to a 74% efficiency. The electron beam interception at and close to saturation was fairly high. Preliminary measurements of body power and the high efficiency indicate that mostly low-energy electrons past the output cavity gaps are involved in the klystron body interception in that operating condition. Initial optimization of the electromagnet for lower interception resulted in a 70% reduction of the rf body current, but this was accompanied by a noticeable drop in rf output power, efficiency (down to 67%) and gain. The klystron performance was stable for all operating conditions encountered so far. Further optimization of the magnetic field balance still has to be carried out for low body current and high efficiency at all required operating conditions, including operation into an output mismatch up to 1.2:1 VSWR. A more complete set of data taken after optimization and tuning will be presented at the conference.

Development of a 1.3 GHz, 10 MW, 65% efficiency multi-beam klystron for XFEL

CPIs second generation, 10 MW, 1300 MHz multiple beam klystron (MBK), designated the VKL-8301B, has been developed and is being built for the European X-ray free electron laser (XFEL), which is under construction at DESY in Hamburg (Germany). At 10 MW peak rf output the MBK is required to provide at least 65% efficiency and more than 3 MHz instantaneous -1 dB bandwidth. Average power and rf pulse length are 150 kW and 1.5 ms, respectively. MBKs have the advantage of generating high rf output powers at moderate electron beam energies. For our design, six off-axis electron beams enable low cathode current density for longer cathode life. Compared to our first- generation design, where higher-order-mode cylindrical cavities were used, we are utilizing ring resonators operating in the fundamental-mode. This ensures sufficient beam separation while still keeping the overall diameter of the device small in order to reduce cost. Our in-house 1D large-signal rf code (LSCEX) was used to come up with the initial rf design. The 2.5D rf code TESLA enabled us to verify and refine the design. For the cavity design we utilized the commercially available 3D codes MAFIA and HFSS. The baseline beam optics design was created using our in-house 2.5D code XGun. With state-of- the-art 3D modeling software for beam optics (MICHELLE) and magnetics (MagNet) we then validated and optimized the design. Most of the mechanical design is completed. Material for the prototype is currently being procured and we will start building the klystron by the end of February 2008. We are going to present simulated data showing the expected performance of the device. The simulations exceed the requirements by a healthy margin. Measured data will be presented as they become available throughout the assembly process.

Use of state of the art computer-aided design tools at CPI

This paper presents results from some of the tools currently used at CPI for design of helix TWTs, coupled-cavity TWTs and klystrons. HFSS, a commercial 3D electromagnetic code, and CTLSS, a 3D electromagnetic code, are currently used to predict helix circuit dispersion and impedance characteristics. CTLSS and HFSS are the first tools available that allow us to perform completely cold-test-free helix TWT design. HFSS is also used to predict CC-TWT circuit dispersion characteristics and to design waveguide transformers, windows and severs.

Design of a multiple beam klystron for TESLA

In this paper, we reported on the design of a 10 MW, 1300 MHz multiple beam klystron for TESLA superconducting linear accelerator. The multiple beam klystron is used in the accelerator because of its ability to produce high RF output power at moderate electron beam energies. The beam optics design has been verified by fully 3D simulations using the codes Michelle and Mafia. Electron trajectories in the gun region as calculated from Mafia codes.

Multiple beam klystron development for TESLA

Summary form only given, as follows. Progress to date is reported on the development of a 10 MW, 1300 MHz multiple beam klystron for the TESLA superconducting linear accelerator. A multiple beam klystron will be used because of its ability to produce high rf output powers A moderate electron beam energies. In this device, low cathode current density loading and hence longer cathode life is achieved by the use of off-axis electron beams. Beam bunching occurs in a series of separate fundamental mode klystron cavities whereas drive power input and output power extraction occur in large over-moded cavities for power combination reasons. The essential parameters of the device are 114 kV beam energy, 131 A beam current (21.8 A per beam), 65% efficiency, 50 dB gain and 150 kW of average rf output power.