An FEL-based microwave system for fusion

Stone, R.R.; Jong, R.A.; Orzechowski, T. J.; Scharlemann, E.T.; Throop, A.L.; Kulke, B.; Thomassen, K.I.; Stallard, B. W.

doi:10.1007/bf01057323

Cited by 9 publications

(6 citation statements)

References 18 publications

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“…In the case of a spacially periodic magnetic or electric field (undulator/wiggler), the oscillation frequency nb (bounce frequency) is proportional to the ratio of the electron beam velocity Vz to the field spatial period 'Aw. Thus, (3) The operating frequency of such devices, an example of which is the FEM [13][14][15], is detennined by the condition that an electron in its rest frame "observes" both the radiation and the periodic external force at the same frequency. If the electron beam is highly relativistic, (vph = Vz = c) the radiationwill have a much shorter wavelength than the external force in the laboratory frame ('A = 'Awf2y2 so that ro = 2y 2 Ob).…”

mentioning

confidence: 99%

State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

Thumm

2020

J Infrared Milli Terahz Waves

291

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STATE-OF-THE-ART OF HIGH POWER GYRO-DEVICES AND FREE ELECTRON MASERSAt present, gyrotron oscillators are mainly used as high power millimeter wave sources for electron cyclotron resonance heating (ECRH) and diagnostics of magnetically confmed plasmas for generation of energy by controlled thermonuclear fusion. 140 GHz gyrotrons with output power Pout = 0.58 MW, pulse length 't = 2.0 s and efficiency 11 = 34 % are commercially available. Diagnostic gyrotrons deliver P out = 40 kW with 't = 40 J-lS at frequencies up to 650 GHz (11 2_ 4 %). Recently, gyrotron oscillators have also been successfully used in matedal processing and plasma chemistry. Such technological applications require gyrotrons with the following parameters: f 2. 28 GHz , Pout = 10-30 kW, CW, 11 2. 30 %. This paper reports on achievements and problems related to the development of very high power mm-wave gyrotrons for long pulse or CW operation and describes the microwave technological pecularities of the different development steps. In addition, this work gives a short overview of the present development of gyrotrons for technological applications, quasi-optical gyrotrons, cyclotron autoresonance masers (CARMs), gyro-ldystrons, gyro-TWT amplifiers, gyro-BWO's and free electron masers (FEMs). The most impressive FEM output parameters are: Pout = 2GW, 't = 20 ns, 11 = 13 % at 140 GHz (LLNL) and Pout = 15 kW, 't = 20 J-tS, 11 = 5 % in the range from 120 to 900 GHz (UCSB). ENTWICKLUNGSSTAND VON HOCHLEISTUNGS-GYRO-RÖHREN UND FREI-ELEKTRONEN-MASERN Übersiebt Gyrotronoszillatoren werden derzeit vorwiegend als Hochleistungsmillimeterwellenquellen für die Elektron-Zyklotron-Resonanzheizung (ECRH) und Diagnostik von magnetisch eingeschlossenen Plasmen zur Erforschung der Energiegewinnung durch kontrollierte Kernfusion eingesetzt. 140 GHz Gyrotrons mit einer Ausgangsleistung von Pout = 0.58 MW bei Pulslängen von 't = 2.0 s und Wirkungsgraden von • 11 = 34% sind kommerziell erhältlich. Gyrotrons zur Plasmadiagnostik erreichen Frequenzen bis zu 650 GHz bei P out = 40 kW und 't = 40 ~-ts (11 2. 4 %). In jüngster Zeit jedoch finden Gyrotronoszillatoren auch für technologische Prozesse und in der Plasmachemie erfolgreich Verwendung. Dabei werden Röhren mit folgenden Parametern eingesetzt: f 2_ 28 GHz, Pout = 10-30 kW, CW, 11 2. 30 %. In diesem Beitrag wird auf den aktuellen Stand und die Probleme bei der Entwicklung von Hochleistungs-mm-Wellen-Gyrotrons für Langpuls-und Dauerstrichbetrieb sowie auf die mikrowellentechnischen Besonderheiten der einzelnen Entwicklungsphasen eingegangen: Außerdem wird auch kurz über den neuesten Stand der Entwicklung von Gyrotrons für technologische Anwendungen, quasi-optischen Gyrotrons, Zyklotron-Autoresonanz-Masern (CARMs), Gyroklystrons, Gyro-TWT-Verstärkern, Gyro-Rückwärtswellenoszillatoren (BWOs) und Frei-Elektronen-Maser (FEM) berichtet. FEM-Rekordausgangsparameter sind hier: Pout = 2 GW, 't = 20 ns, 11 = 13 % bei 140 GHz (LLNL) und Pout = 15 kW, 't = 20 J-lS, 11 = 5 % im Bereich von 120 bis 900 GHz (UCSB). Contents

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confidence: 99%

State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

Thumm

2020

J Infrared Milli Terahz Waves

291

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“…ICflLl = o ~ 7T c ° 1 8 i n *° "*" "n? c o s *°) (39) of the power is lost to the excitation of the undesired L/O mode. The same formula is applicable to the evaluation of the losses, when a pure LCP field is used to excite the L/O mode, because \c RL \ 2 = Ic/jjl 2 .…”

Section: Beam Input Parametersmentioning

confidence: 99%

High frequency Raman current drive

Karttunen

Pättikangas²,

Salomaa³

et al. 1991

Nucl. Fusion

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Current drive in reactor grade tokamak plasmas with a pulsed, high power free electron laser (FEL) is investigated. The stimulated Raman process generates fast, longitudinal electron plasma waves which accelerate electrons to relativistic energies. The fast electrons with vi ≫ v⊥ are not trapped toroidally and the resulting current decays slowly. The paper presents a systematic study on different combinations of Raman forward and backward scattering and FEL polarization. The optimal FEL frequencies fall within the range 2.2-4.0ωp (left circularly polarized case) and 3.8-7.0ωp (right circularly polarized case) in a typical tokamak plasma with Ωe ≃ 1.5ωp In a reactor grade plasma the best current drive efficiency, 5 × 10l9 A/W⋅m2, is obtained by using the stimulated Raman forward process and a left circularly polarized FEL beam. The FEL driven current can be localized to the plasma centre and amplified by the bootstrap effect to further enhance the overall efficiency. Raman current drive in high temperature reactor plasmas is quite different from small scale experiments with Te ∼ 1 keV, where the Raman backward process dominates and the current drive efficiency remains rather low.

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“…Designs for a 280 GHz, 10 MW FEL to be used to heat the CIT have been completed 6 , and these are based on the technology to be demonstrated on MTX. The repetition rate was increased a factor of two, the beam energy raised about 40%, and the pulse length increased from 50 to 70 ns in comparison with the MTX system.…”

Section: Microwave Fel Progressmentioning

confidence: 99%

“…In the Compact Ignition Tokamak (CIT) under design at Princeton a microwave heating system at about 300 GHz is being considered. System designs using both gyrotrons 5 and FEL's 6 have been done. The availability of sources at twice the above frequencies could easily change these "requirements" in order to use second harmonic waves thai allow higher density operation and shorten the absorption depths.…”

Section: Pyhsics Applicationsmentioning

confidence: 99%