High-power X-band traveling-wave tube amplifiers (TWTs) have been fabricated and tested. The tubes have gains ranging from 13 to 35 dB at 8.76 GHz and output powers ranging from 3 to 100 MW. The amplifiers are driven by the interaction of a slow space-charge wave, propagating on an electron beam, with an electromagnetic wave supported by the structure. The electron beam, which is produced from a magnetic-field-immersed field-emission cathode, has an energy of 850 keV, a current in the 1-kA range, and a pulse duration of 100 ns. The amplifiers are designed to operate as narrow-band devices in the TM/sub 01/ mode. A report is presented on the amplifier characteristics, and their performance is compared with calculated performance using conventional TWT theory. The scaling of the gain and bandwidth with the beam current are approximately as expected from theory, but the absolute magnitude of the gain is somewhat greater than expected. >

A high-power, traveling wave tube amplifier

With the advent of the SLAC electron-positron linear collider (SLC) in the 100 GeV center-of-mass energy range, research and development work on even higher energy machines of this type has started in several laboratories in the United States, Europe, the Soviet Union and Japan. These linear colliders appear to provide the only promising approach to studying e/sup /plus//e/sup /minus// physics at center-of-mass energies approaching 1 TeV. This thesis concerns itself with the study of radio frequency properties of periodic accelerating structures for linear colliders and their interaction with bunched beams. The topics that have been investigated are: experimental measurements of the energy loss of single bunches to longitudinal modes in two types of structures, using an equivalent signal on a coaxial wire to simulate the beam; a method of canceling the energy spread created within a single bunch by longitudinal wakefields, through appropriate shaping of the longitudinal charge distribution of the bunch; derivation of the complete transient beam-loading equation for a train of bunches passing through a constant-gradient accelerator section, with application to the calculation and minimization of multi-bunch energy spread; detailed study of field emission and radio frequency breakdown in disk-loaded structures at S-, C- and X-band frequencies under more » extremely high-gradient conditions, with special attention to thermal effects, radiation, sparking, emission of gases, surface damage through explosive emission and its possible control through RF-gas processing. 53 refs., 49 figs., 9 tabs. « less

/pdf/rf-properties-of-periodic-accelerating-structures-for-linear-5fj0hzmgu0.pdf

RF Properties of Periodic Accelerating Structures for Linear Colliders

The authors discuss the design and construction features of a high-power RF generator comprising a 5.7-GHz chopping system and 11.4-GHz high group velocity, traveling-wave structures. The device is designed for operation with high current megavoltage beams and has been developed in support of the Relativistic Klystron High Gradient Accelerator program. The RF chopping system operates under immersed beam conditions with an axial magnetic field matched to the beam emittance and betatron resonance requirements so that the 11.4-GHz RF current is maximized. The TW circuit shunt impedance was chosen to enable high levels of beam-induced RF power to be generated without exceeding safe E-field values. The use of high group velocity structures having a short interaction region enabled an RF filling time of only 1050 ps to be achieved, thereby providing a broadband, phase- and temperature-insensitive circuit having fast response characteristics consistent with the intended 1000-A 40-ns beam pulse operation. >

Design and construction of a chopper driven 11.4 GHz traveling wave RF generator

This paper describes the experimental development of a long pulse high current relativistic klystron amplifier (RKA). The desired performance parameters are 1 GW output power and 1 /spl mu/s pulse length with an operating frequency of 1.3 GHz. Peak powers approaching 500 MW have been achieved in pulses of 1 /spl mu/s nominal baseline-to-baseline duration. The half power pulse width is 0.5 /spl mu/s. These pulses contain an energy of about 160 J. RF output rises linearly in concert with the beam current pulse, and terminates abruptly just before the highest part of the pulsed voltage curve is reached. A possible explanation, not yet experimentally confirmed, for the premature termination of the RF pulse is an output cavity gap voltage that is too high, causing electron reflection at the gap and RF breakdown across the gap. A new output cavity has been designed with a much lower shunt impedance and a loaded Q of 4. >

A 500 MW, 1 /spl mu/s pulse length, high current relativistic klystron

This paper presents a status report on rf field emission and high-gradient breakdown studies in linac structures at SLAC. The motivation behind these studies, begun in 1984, is to determine the maximum accelerating field gradients that could be used safely in future e/sup /plus minus// colliders, to contribute to the basic understanding of the rf breakdown mechanism, and to discover if special surface treatments might make it possible to shorten the time needed for rf processing and to supersede the field limits presently reachable in room temperature copper structures. Both theoretical ideas and experimental results are discussed. 8 refs., 3 figs., 1 tab.

/pdf/field-emission-and-rf-breakdown-in-copper-linac-structures-gyq0eva8v4.pdf

Field emission and rf breakdown in copper linac structures

There are now 200 new, high power 5045 klystrons installed on the two-mile Stanford Linear Accelerator. Peak power per klystron averages over 63 MW. Average energy contribution is above 240 MeV per station. Electron beam energy has been measured as high as 53 GeV. Energy instability due to klystron malfunction is less than 0.2%. The installed klystrons have logged over one million operating hours with close to 20,000 klystron hours cumulative operating time between failures. Data are being accumulated on klystron operation and failure modes with failure signatures starting to become apparent. To date, no wholesale failure modes have surfaced that would impair the SLAC Linear Collider (SLC) program.

Performance of the SLAC Linear Collider klystrons

The next generation of linear colliders requires peak power sources of over 200 MW per meter at frequencies above 10 GHz at pulse widths of less than 100 nsec. Several power sources are under active development, including a conventional klystron with rf pulse compression, a relativistic klystron (RK) and a crossed-field amplifier. Power from one of these has energized a 0.5 meter two- section High Gradient Accelerator (HGA) and accelerated a beam at over 80 MeV meter. Results of tests with these experimental devices are presented here.

/pdf/rf-power-sources-for-linear-colliders-3env5z6e2n.pdf

Rf power sources for linear colliders

Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron--positron colliders, compact accelerators, and FEL sources We have attained 200MW peak power at 114 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 114 GHz accelerator section We report here on the design of our first klystrons, the results of our experiments so far, and some of our plans for the near future 5 refs, 7 figs

Relativistic klystron research for high gradient accelerators

Experimental work is now under way by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. We have learned how to overcome our previously reported problem of high-power rf pulse shortening and have achieved peak rf power levels of 290 MW. We have used the rf from a relativistic klystron to power a short, 11.4-GHz high-gradient accelerator. The measured momentum spectrum of the accelerated electron beam corresponds to an accelerating gradient of 84 MV/m. 5 refs., 7 figs.

/pdf/recent-progress-in-relativistic-klystron-research-suize6yb77.pdf

Recent progress in relativistic klystron research

The SLAC Linear Collider (SLC) must reach a nominal center-of-mass energy of 100 GeV to fulfill its high energy physics goals This paper describes the energy upgrade program that is being implemented on the SLAC linear accelerator to meet these goals It includes a discussion of the design requirements and available technical options, the rationale for the adopted solution, and the technical problems involved in the engineering and production of klystrons and modulators

SLC Energy Upgrade Program at SLAC

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