[en] Progress during the first year of this program has been noteworthy in both theoretical and experimental areas. Substantial improvements to the MIT CARM codes have been carried out, and the code has been successfully benchmarked against other codes, linear theory, and experimental work. CARM amplifier phase stability has been studied theoretically and found to be significantly better than that of free-electron lasers or relativistic klystrons, provided the device is properly designed. Both multimode simulations and particle-in-cell simulations have been carried out to study mode competition effects between convectively unstable and absolutely unstable modes. Improvement of the Pierce-Wiggler code for modeling the beam formation prior to the interaction region has been carried out. Experimental designs for a long-pulse, modulator-driven CARM amplifier experiment which will be carried out by the end of this fiscal year have been mostly completed. Designs for an induction-linac-driven CARM amplifier experiment, which will be carried out by the end of Year II of this program,, have also been performed. Finally, a CARM oscillator experiment is presently underway at our facility

[en] This CARM program has successfully demonstrated the first ever long-pulse CARM oscillator operation; these results demonstrate the potential of CARMs as an alternative source of millimeter waves to the gyrotron for ECRH plasma heating. The result of 1.8 MW at 27.8 GHz and 0.5 μs pulse width in the TE₁₁ mode represent a clear demonstration of the capabilities of the CARM oscillator for the production of high powers with large frequency upshift. It is hoped that this successful proof-of-principle demonstration.will lead to further development of the CARM as an ECRH source by the DOE Office of Fusion Energy, Development and Technology Division. This success is a direct outcome of this support of the Advanced Energy Projects Office of DOE in the form of this program. The CARM amplifier component of the program, although unsuccessful at obtaining CARM amplifier operation at 17 GHz, has succeeded by furthering the understanding of the limitations and difficulties that lie ahead for continued CARM amplifier development. The amplifier component of the program has successfully demonstrated a high power second and third harmonic gyro-TWT amplifier. Up to 5 MW of power at 17.1 GHz and >50dB gain have been obtained. These results should be viewed as an important contribution of this program to the development of viable microwave sources for powering the next linear collider. Indeed, the present gyro-amplifier, which resulted from this program, is presently being used in ongoing high-gradient accelerator research at MIT under a DOE High Energy Physics grant. As a result of both the oscillator and amplifier advances made during this program, the CARM and harmonic gyro-TWT have reached a significantly more mature level; their future role in specific applications of benefit to DOEs OFE and HEP offices may now be pursued

[en] The optimization of gyroklystron efficiency is investigated by employing a two-step procedure. As a first step, the prebuncher is analyzed using a small signal approximation, since the cavity(ies) here serve mainly to modulate slightly the velocities of the electrons, which will be bunched in the field-free drift section(s). It is found that the electrons entering the energy extraction cavity can be characterized entirely by only two dimensionless parameters: a bunching parameter q and a relative phase psi. The numerical simulation of the extraction cavity, based on the nonlinear pendulum equations describing the interaction between the electrons and the rf field, supplemented by the initial conditions specified by q and psi, constitutes the second step. The final result of this two-step analysis is the efficiency, eta/sub perpendicular, opt/ optimized with respect to q, psi and the magnetic detuning parameter Δ. This efficiency depends only on the normalized cavity length μ and the normalized rf field F of the energy extraction section. The efficiency as well as the conditions required to attain this optimum (q/sub opt/, Δ/sub opt/, and psi/sub opt/) are presented as contour plots on the (F, μ ) plane and can be used efficiently to design gyroklystrons of any frequency and output power

[en] The design parameters of a 120 GHz gyromonotron capable of output powers in excess of 1 MW are determined. A nonlinear model of the interaction between the beam and rf field is used in which the efficiency is a function of only three normalized variables. By expressing the technological constraints in terms of these variables, permissible design parameters yielding high efficiency operation can be calculated. Constraints that are considered include ohmic heating of the walls, voltage depression of the beam, reduced coupling between the beam and rf field due to beam thickness, and efficiency degradation due to space charge forces within the beam. An analysis of the tradeoffs between current and voltage at the 1 MW level indicates that lower order modes can be utilized at lower voltages, but the constraints based on current limitations are difficult to satisfy. An 80 kV, 29 A design is presented that achieves a total efficiency of 44%. The primary uncertainty of these designs is the severity of competition due to parasitic modes. However, a number of isolated asymmetric modes appear capable of single mode emission at 1 MW based on present experimental results. Multimegawatt operation is also considered. It is shown that powers exceeding 20 MW are possible if single mode operation can be achieved in very high order modes. The methodology presented in this paper is general and can be easily adapted to other frequencies and output powers

[en] The MIT Lincoln Laboratory is investigating the possibility of building a free electron laser (FEL) operating at an average power of about 7 kW at wavelengths of 500--600 nm. Additional specifications for the FEL include a bandwidth of less than 0.1 cm^-1 and a micropulse separation of less than 10 ns. The design study has investigated the basic design parameters of the FEL including an analysis of the electron accelerator, beam line, wiggler and optical cavity. A nonlinear model of the FEL has been used to calculate the FEL gain and efficiency. The required output power appears achievable from an FEL operating at more than 1% efficiency with a conventional RF accelerator. Details of the FEL design are presented in this report which represent the final report for the year from September 1, 1989 to August 31, 1990. 28 refs., 13 figs., 5 tabs

[en] Power and bandwidth studies for a high power W-band (∼94 GHz) FEM amplifier is presented for a helical wiggler/cylindrical waveguide configuration using 3D ARACHNE simulation code (H.P. Freund, T.M. Antonsen, Jr., Principles of Free-electron Lasers, 2nd edn., Chapman and Hall, London, 1996, Ch. 5). Using a 300 kV/20 A electron beam with a normalized emittance of 95 mm mrad, a 600 G wiggler field with a 0.88 cm period, and a strong guide field of 20 kG, efficiencies of greater than 8% are possible with a FWHM bandwidth of 4.5 GHz

[en] The physics and technological issues involved in high gradient particle acceleration at high microwave (RF) frequencies are under study at MIT. The 17 GHz photocathode RF gun has a 1 1/2 cell (π mode) room temperature cooper cavity. High power tests have been conducted at 5-10 MW levels with 100 ns pulses. A maximum surface electric field of 250 MV/m was achieved. This corresponds to an average on-axis gradient of 150 MeV/m. The gradient was also verified by a preliminary electron beam energy measurement. Even high gradients are expected in our next cavity design

[en] The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as a function of generalized parameters for the second through fifth harmonics. The numerical results are valid for a wide range of operating conditions, including voltage, current, beam radius, cavity dimensions, and operating mode. Relatively high efficiencies are found even at high harmonics; the maximum transverse efficiencies for harmonics 2, 3, 4, and 5 are 0.72, 0.57, 0.45, and 0.36, respectively. The calculation of the efficiency in terms of generalized parameters allows the straightforward design and optimization of harmonic gyrotrons. The influence of the axial profile of the rf field in the gyrotron cavity on the efficiency is also investigated. Improved efficiency can be achieved with asymmetric field profiles. The implications of these results for the generation of millimeter and submillimeter wave radiation by harmonic emission are discussed

[en] Future linear colliders will require high peak power RF sources at high frequencies which are significantly beyond present source technology. Considerable progress has been made during the past several years in this direction. This paper summarizes the present state of high power RF source technology, and identifies the critical remaining technical issues. copyright 1995 American Institute of Physics

[en] A new compact high-gradient (60 MeV/m) high-frequency (17.136 GHz) RF linac is presently under construction by Haimson Research Corp. (HRC) for installation at the MIT Plasma Fusion Center in the High-Gradient Accelerator and High Power Microwave Laboratory. This accelerator will utilize an existing traveling-wave relativistic klystron (TWRK) which is now operation at MIT with 25 MW power, 67 dB gain, and 52% efficiency at 17.136 GHz