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APPLICATIONS OF NEW TECHNOLOGY FOR PRODUCTION OF HIGH POWER MILLIMETER WAVES TO MAGNETIC FUSION RESEARCH

Description: Although research on magnetically confined fusion plasmas has been carried out for a half century, for most of this time control of the temperature, density and current density profiles has been limited and transient. Now, high power long pulse gyrotron systems with excellent reliability are coming on line, which can provide non-inductively driven currents and electron heating leading to higher plasma performance and continuous operation in reactor relevant regimes. The precision of the location at which heating and current drive are applied has also made it possible to suppress certain classes of plasma instabilities. Basic physics of electron cyclotron current drive and heating are understood and these new technological capabilities are being exploited in magnetic confinement devices worldwide.
Date: August 1, 2002
Creator: LOHR, J.
Partner: UNT Libraries Government Documents Department

ECE RADIOMETER UPGRADE ON THE DIII-D TOKAMAK

Description: OAK A271 ECE RADIOMETER UPGRADE ON THE DIII-D TOKAMAK. The electron cyclotron emission (ECE) heterodyne radiometer diagnostic on DIII-D has been upgraded with the addition of eight channels for a total of 40. The new, higher frequency channels allow measurements of electron temperature into the magnetic axis in discharges at maximum field, 2.15 T. The complete set now extends over the full usable range of second harmonic emission frequencies at 2.0 T covering radii from the outer edge inward to the location of third harmonic overlap on the high field side. Full coverage permits the measurement of heat pulses and magnetohydrodynamic (MHD) fluctuations on both sides of the magnetic axis. In addition, the symmetric measurements are used to fix the location of the magnetic axis in tokamak magnetic equilibrium reconstructions. Also, the new higher frequency channels have been used to determine central T{sub e} with good time resolution in low field, high density discharges using third harmonic ECE in the optically gray and optically thick regimes.
Date: August 1, 2002
Creator: AUSTIN, ME & LOHR, J
Partner: UNT Libraries Government Documents Department

DIII-D Research Operations annual report to the US Department of Energy, October 1, 1993--September 30, 1994

Description: The DIII-D tokamak research program is managed by General Atomics (GA) for the US Department of Energy (DOE). Major program participants include GA, Lawrence Livermore National Laboratory (LLNL), Oak Ridge National Laboratory (ORNL), and the University of California together with several other national laboratories and universities. The DIII-D is a moderate sized tokamak with great flexibility and extremely capable subsystems. The primary goal of the DIII-D tokamak research program is to provide data for development of a conceptual physics blueprint for a commercially attractive fusion power plant. In so doing, the DIII-D program provides physics and technology R&D output to aid the International Thermonuclear Experimental Reactor (ITER) and the Princeton Tokamak Physics Experiment (TPX) projects. Specific DIII-D objectives include the achievement of steady-state plasma current as well as the demonstration of techniques for radio frequency heating, divertor heat removal, particle exhaust and tokamak plasma control. The DIII-D program is addressing these objectives in an integrated fashion in plasmas with high beta and with high confinement. The long-range plan is organized with two principal elements, the development of an advanced divertor and the development of advanced tokamak concepts. These two elements have a common goal: an improved demonstration reactor (DEMO) with lower cost and smaller size than present DEMO concepts. In order to prepare for this long-range development, in FY94 the DIII-D research program concentrated on three major areas: Divertor and Boundary Physics, Advanced Tokamak studies, and Tokamak Physics.
Date: July 1, 1995
Creator: Lohr, J.
Partner: UNT Libraries Government Documents Department

Summary of the experimental session EC-10 workshop

Description: This review summarizes a subset of the EC-10 presentations which had been assigned by the organizing committee identification tags beginning with EX. There were fourteen presentations in this group, seven oral and seven posters. Included among the oral presentations were two invited talks. With the exception of the review of plans for electron cyclotron waves in ITER, there were all reports of physics experiments or operational experience as opposed to accounts of hardware development.
Date: June 1, 1997
Creator: Lohr, J.
Partner: UNT Libraries Government Documents Department

PERFORMANCE OF THE DIII-D SYSTEM

Description: A271 PERFORMANCE OF THE DIII-D SYSTEM. Three 110 GHz gyrotrons with nominal output power of 1 MW each have been installed and are operational on the DIII-D tokamak. All three gyrotrons were built by Communications and Power Industries (CPI). The CPI gyrotrons utilize a single disc CVD (chemical-vapor-deposition) diamond window that employs water cooling around the edge of the disc. Calculations predict that the CVD diamond window should be capable of full 1 MW cw operation, which is supported by IR camera measurements that show the window reaching equilibrium after 2.5 s. All gyrotrons are connected to the tokamak by low-loss-windowless evacuated transmission line using circular corrugated waveguide for propagation in the HE{sub 11} mode. Each waveguide system incorporates a two-mirror launcher, which can steer the rf beam poloidally from the center to the outer edge of the plasma. Results obtained using the DIII-D ECH systems will be reported.
Date: August 1, 2003
Creator: CALLIS,RW; KAJIWARA,K; LOHR,J; GORELOV,YA & PONCE,D
Partner: UNT Libraries Government Documents Department

THE MEASURED PERFORMANCE OF A MILLIMETER WAVE BEAM SPLITTER

Description: An essential component of any high power transmission system is a directional coupler that provides a sample of the forward and reflected power when this power is being delivered to the intended load. In the case of millimeter power delivered through a highly oversized corrugated waveguide, there is the much more complex issue of mode purity. It is possible to design an effective mode selective branch guide directional coupler in smooth wall overmoded waveguide. In the typical highly overmoded corrugated waveguide propagating the HE{sub 11} mode, however, obtaining an adequate coupling factor can be difficult, and branch guide attenuation and phase velocity matching over several meters become concerns. A more practical approach for large diameter corrugated waveguide is to obtain a sample of the propagating beam at a miter bend mirror. At low power, the mirror could be a thin metal screen. At the megawatt level, however, heat removal must be considered. For example, at 110 GHz at 1 MW, taking the surface resistance of copper to be 0.10 {Omega}, the dissipation on a 45{sup o} copper mirror would be 750 W or 1500 W for H or E plane reflection, respectively. With a peak to average power ratio of 3.7 for the circular HE{sub 11} mode, in 31.75 cm diameter corrugated waveguide the peak dissipation can be as high as 500 W/cm{sup 2} at the center of the mirror. An edge cooled thin metal screen is not therefore practical, but a thick plate containing a single narrow channel, at the bottom of which is a row of holes in the remaining thin wall, can be adequately water-cooled on its face. To maintain vacuum and focus the radiation from the holes, the narrow channel is filled by a fused quartz plate, the shape of which is a 45{sup o} sector ...
Date: September 1, 2002
Creator: MOELLER, C.P.; LOHR, J. & DOANE, J.L.
Partner: UNT Libraries Government Documents Department

Initial tests and operation of a 110 GHz, 1 MW gyrotron with evacuated waveguide system on the DIII-D tokamak

Description: A gyrotron producing nominally 1 MW at 110 GHz has been installed at the DIII-D tokamak and operated in a program of initial tests with a windowless evacuated transmission line. The alignment and first test operation were performed in an air environment at atmospheric pressure. Under these conditions, the tube produced rf output in excess of 800 kW for pulse lengths greater than 10 msec and power near 500 kW for pulse lengths of about 100 msec into a free space dummy load. The gyrotron was operated into evacuated corrugated waveguide in the full power parameter regime for pulse lengths of up to 500 msec injecting greater than 0.5 MW into DIII-D for a preliminary series of experiments. Generated powers greater than 900 kW were achieved. A parasitic oscillation at various frequencies between 20 and 100 MHz, which was generated during the pulsing of the gyrotron electron beam, was suppressed somewhat by a capacitive filter attached to the gyrotron itself. Addition of a magnetic shield intended to alter the magnetic field geometry below the cathode eliminated internal tube sparks. Rework of the external power and interlock circuitry to improve the immunity to electromagnetic interference was also done in parallel so that the fast interlock circuitry could be used. The latest results of the test program, the design of the free space load and other test hardware, and the transmission line will be presented.
Date: August 1, 1996
Creator: Lohr, J.; Ponce, D. & Tooker, J.F.
Partner: UNT Libraries Government Documents Department

The 110 GHz ECH installation on DII-D: Status and initial experimental results

Description: Two 110 GHz gyrotrons with nominal output power of 1 MW each have been installed on the DIII-D tokamak. The gyrotrons, produced by Gycom and Communications and Power Industries, are connected to the tokamak by windowless evacuated transmission lines using circular corrugated waveguide carrying the HE{sub 11} mode. Initial experiments with the Gycom gyrotron showed good central heating efficiency at the second harmonic resonance with record central electron temperatures for DIII-D in excess of 10 keV achieved. The beam spot in the DIII-D vacuum vessel was well focused, with a diameter of approximately 8 cm, and it could be steered poloidally by a remotely adjustable mirror. The injection was at 19 deg off-perpendicular for current drive and the beams could be modulated for studies of energy transport and power deposition. The system will be described and the initial physics results will be presented. A third gyrotron, also at 110 GHz, will be installed later this year. Progress with this CPI tube will be discussed and future plans for the ECH installation and physics experiments using it will be presented.
Date: May 1997
Creator: Lohr, J.; Callis, R.W. & O`Neill, R.C.
Partner: UNT Libraries Government Documents Department

CHARACTERISTICS OF DIAMOND WINDOWS ON THE 1 MW, 110 GHz GYROTRON SYSTEMS ON THE DIII-D TOKAMAK

Description: Diamond disks made using the chemical vapor deposition (CVD) technique are now in common use as gyrotron output windows. The low millimeter wave losses and excellent thermal conductivity of diamond have made it possible to use such windows in gyrotrons with {approx}1 MW output power and pulse length up to and greater than 10 s. A ubiquitous characteristic of diamond gyrotron windows is the presence of apparent hot spots in the infrared images registered during rf pulses. Many of these spots are co-located with bright points seen in visible video images. The spots do not seem to compromise the integrity of the windows. Analysis of the infrared observations on several different gyrotrons operating at the DIII-D tokamak are reported.
Date: August 1, 2002
Creator: GORELOV, Y.A.; LOHR, J.; CALLIS, R.W. & PONCE, D.
Partner: UNT Libraries Government Documents Department

INFRARED MONITORING OF 110GHz GYROTRON WINDOWS AT DIII-D

Description: The combination of low millimeter wave losses and excellent thermal conductivity with good mechanical properties make artificial chemical vapor deposition (CVD) diamonds a compelling choice for 1 MW 110 GHz gyrotron windows. Five gyrotrons are currently operating at the DIII-D tokamak. Three Gycom gyrotrons have boron nitride (BN) ceramic windows. Due to temperature increases of the windows up to about 930 C, the pulse duration of these tubes is limited to 2 s for output power near 800 kW. Two Communications and Power Industries (CPI) gyrotrons with diamond windows are also installed and operating. The diamond disks of these windows and the construction of their water-cooling assemblies are different. This paper reviews the infrared (IR) measurements of both types of gyrotron windows, with emphasis on the two diamond designs.
Date: May 1, 2002
Creator: GORELOV, Y.; LOHR, J.; CALLIS, R.W. & PONCE, D.
Partner: UNT Libraries Government Documents Department

LAUNCHER PERFORMANCE IN THE DIII-D SYSTEM

Description: LAUNCHER PERFORMANCE IN THE DIII-D SYSTEM. The thermal performance of three different designs for the steerable mirrors on the ECH launchers installed in the DIII-D tokamak has been evaluated theoretically and experimentally. In each case the disruption forces must be minimized while providing a low loss reflecting surface. One design uses all Glidcop{reg_sign} material, but shaped so that the center is appreciably thicker than the edge. A second design is graphite with a molybdenum surface brazed to the graphite. The latest design is laminated copper/stainless steel construction with a thin copper reflecting surface. All three mirrors employ passive radiative cooling. The mirror temperatures are measured by resistance temperature devices (RTDs) which are attached at the back surfaces of the mirrors. The temperature increases are moderate for the laminated mirror, which has the best overall performance.
Date: July 1, 2003
Creator: KAJIWARA,K; BAXI,CB; LOHR,J; GORELOV,YA; GREEN,MT; PONCE,D et al.
Partner: UNT Libraries Government Documents Department

PHYSICS OF ELCTRON CYCLOTRON CURRENT DRIVE ON DIII-D

Description: OAK A271 PHYSICS OF ELCTRON CYCLOTRON CURRENT DRIVE ON DIII-D. Recent experiments on the DIII-D tokamak have focused on determining the effect of trapped particles on the electron cyclotron current drive (ECCD) efficiency. The measured ECCD efficiency increases as the deposition location is moved towards the inboard midplane or towards smaller minor radius for both co and counter injection. The measured ECCD efficiency also increases with increasing electron density and/or temperature. The experimental ECCD is compared to both the linear theory (Toray-GA) as well as a quasilinear Fokker-Planck model (CQL3D). The experimental ECCD is found to be in better agreement with the more complete Fokker-Planck calculation, especially for cases of high rf power density and/or loop voltage. The narrow width of the measured ECCD profile is consistent with only low levels of radial transport for the current carrying electrons.
Date: September 1, 2002
Creator: PETTY,CC; PRATER,R; LUCE,TC; ELLIS,RA; HARVEY,RW; KINSEY,JE et al.
Partner: UNT Libraries Government Documents Department

Current profile modification with electron cyclotron current drive in the DIII-D tokamak

Description: Proof-of-principle experiments on the suitability of electron cyclotron current drive (ECCD) for active current profile control are reported. Experiments with second harmonic extraordinary mode absorption at power levels near 1 MW have demonstrated ability to modify the current profile. This modification is manifested in changes in the internal inductance and the time at which sawteeth appear. Measurements of the local current density and internal loop voltage using high resolution motional Stark effect spectroscopy to half of the minor radius in discharges with localized deposition clearly demonstrate localized off-axis ECCD at the predicted location. Comparison with theory indicates the detrimental effect of trapped electrons on the current drive efficiency is less than predicted. Modification of the theory for finite collisionality is the leading candidate to explain the observations.
Date: November 1998
Creator: Luce, T. C.; Lin-Liu, Y. R. & Lohr, J. M.
Partner: UNT Libraries Government Documents Department

The DIII-D ECH multiple gyrotron control system

Description: DIII-D`s ECH upgrade with 1 MW, 110 GHz gyrotrons is ongoing, and with it, an upgrade of the control system. The ECH Multiple Gyrotron Control System uses software distributed among networked computers, interfaced to a programmable logic controller (PLC), the timing and pulse system, power supplies, vacuum and wave guide controls, and instrumentation. During DIII-D operations, the system will allow a chief and a co-operator to control and monitor a number of gyrotrons from different manufacturers. The software, written using LabVIEW, allows for remote and multiple operator control. Thus any supported computer can become a control station and multiple projects can be simultaneously accommodated. Each operator can be given access to the controls of all gyrotrons or to a subset of controls. Status information is also remotely available. The use of a PLC simplifies the hardware and software design. It reduces interlock and control circuitry, includes monitoring for slow analog signals, and allows one software driver to efficiently interface to a number of systems. In addition, the interlock logic can be easily changed and control points can be forced as needed. The pulse system is designed around arbitrary function generators. Various modulation schemes can be accommodated, including real-time control of the modulation. This discussion will include the hardware and software design of the control system and its current implementation.
Date: November 1, 1997
Creator: Ponce, D.; Lohr, J.; Tooker, J.F.; Cary, W.P. & Harris, T.E.
Partner: UNT Libraries Government Documents Department

The DIII-D 3 MW, 110 GHz ECH System

Description: Three 110 GHz gyrotrons with nominal output power of 1 MW each have been installed and are operational on the DIII-D tokamak. One gyrotron is built by Gycom and has a nominal rating of 1 MW and a 2 s pulse length, with the pulse length being determined by the maximum temperature allowed on the edge cooled Boron Nitride window. The second and third gyrotrons were built by Communications and Power Industries (CPI). The first CPI gyrotron uses a double disc FC-75 cooled sapphire window which has a pulse length rating of 0.8 s at 1 MW, 2s at 0.5 MW and 10s at 0.35 MW. The second CPI gyrotron, utilizes a single disc chemical-vapor-deposition diamond window, that employs water cooling around the edge of the disc. Calculation predict that the diamond window should be capable of full 1 MW cw operation. All gyrotrons are connected to the tokamak by a low-loss-windowless evacuated transmission line using circular corrugated waveguide for propagation in the HEl 1 mode. Each waveguide system incorporates a two mirror launcher which can steer the rf beam poloidally from the center to the outer edge of the plasma. Central current drive experiments with the two gyrotrons with 1.5 MW of injected power drove about 0.17 MA. Results from using the three gyrotron systems will be reported as well as the plans to upgrade the system to 6 MW.
Date: July 1, 1999
Creator: Callis, R.W.; Lohr, J.; Ponce, D.; O'Neill, R.C.; Prater, R. & Luce, T.C.
Partner: UNT Libraries Government Documents Department

Polarization Measurements During Electron Cyclotron Heating Experiments in the DIII-D Tokamak

Description: The polarization of the launched electron cyclotron wave has been optimized for coupling to the X-mode by adjusting the inclination of grooved mirrors located in two consecutive mitre bends of the waveguide. The unwanted O-mode component of the launched beam can be positively identified by the difference in the power deposition profiles between X-mode and O-mode. The optimal polarization for X-mode launch is in good agreement with theoretical expectations.
Date: July 1, 1999
Creator: Petty, C.C.; Luce, T.C.; Austin, M.E.; Ikezi, H.; Lohr, J. & Prater, R.
Partner: UNT Libraries Government Documents Department

The Upgrade of the DIII-D GHz ECH System to 6 MW

Description: ECH power has proven capabilities to both heat and drive current in energetic plasmas. Recent developments in high power sources have made the use of these capabilities in energetic plasmas feasible. For the second phase of ECH power on DIII-D, there will be three 1 MW sources added to the existing 3 MW for a total generated power of 6 MW. The upgrade is based on the use of single disc CVD (chemical vapor deposition) diamond windows on 1 MW gyrotrons developed by CPI. AU gyrotrons are connected to the tokamak by low-loss-windowless evacuated transmission lines using circular corrugated waveguide for propagation in the HE{sub 11} mode. Each waveguide system incorporates a two-mirror launcher which can steer the rf beam poloidally from the center to the outer edge of the plasma and toroidally for either co- or counter-current drive. The total system overview and integration with existing systems will be discussed along with the new aspects of the upgrade from building modifications to the new launchers. Much of the upgrade is comprised of existing designs, which will need only slight modifications, while some components have required new designs because of longer pulse lengths.
Date: November 1, 1999
Creator: Cary, W.P.; Callis, R.W.; Lohr, J.M.; Ponce, D. & Legg, R.A.
Partner: UNT Libraries Government Documents Department

Multi-megawatt 110 GHz ECH system for the DIII-D tokamak

Description: Two 110 GHz gyrotrons with nominal output power of 1 MW each have been installed on the DIII-D tokamak. The first 110 GHz gyrotron built by Gycom has a nominal rating of 1 MW and a 2s pulse length, with the pulse length being determined by the maximum temperature allowed on the edge cooled boron nitride window. This gyrotron was first operated into the DIII-D tokamak in late 1996. The second gyrotron was built by Communications and Power Industries (CPI) was commissioned during the spring of 1997. The CPI gyrotron uses a double disc FC-75 cooled sapphire window which has a pulse length rating of 0.8s at 1 MW, 2s at 0.5 MW and 10s at 0.2 MW. Both gyrotrons are connected to the tokamak by a low-loss-windowless evacuated transmission line using circular corrugated waveguide for propagation in the HE(11) mode. Using short pulse lengths to avoid breakdown inside the air filled waveguide, the microwave beam has been measured inside the DIII-D vacuum vessel using a paper target and an IR camera. The resultant microwave beam was found to be well focused with a spot size of approximately 8 cm. The beam can be steered poloidially from the center to the outer edge of the plasma. The initial operation of the Gycom gyrotron with about 0.5 MW delivered to a low density plasma for 0.5 s showed good central electron heating, with peak temperature in excess of 10 keV. A third gyrotron, being built by CPI, will be installed later this year. Progress with the first CPI tube will also be discussed and future plans for the ECH installation and physics experiments will be presented.
Date: November 1, 1997
Creator: Callis, R.W.; Lohr, J.; O`Neill, R.C.; Ponce, D. & Prater, R.
Partner: UNT Libraries Government Documents Department

THE 110 GHz MICROWAVE HEATING SYSTEM ON THE DIII-D TOKAMAK

Description: OAK-B135 Six 110 GHz gyrotrons in the 1 MW class are operational on DIII-D. Source power is > 4.0 MW for pulse lengths {le} 2.1 s and {approx} 2.8 MW for 5.0 s. The rf beams can be steered poloidally across the tokamak upper half plane at off-perpendicular injection angles in the toroidal direction up to {+-} 20{sup o}. measured transmission line loss is about -1 dB for the longest line, which is 92 m long with 11 miter bends. Coupling efficiency into the waveguide is {approx} 93% for the Gaussian rf beams. The transmission lines are evacuated and windowless except for the gyrotron output window and include flexible control of the elliptical polarization of the injected rf beam with remote controlled grooved mirrors in two of the miter bends on each line. The injected power can be modulated according to a predetermined program or controlled by the DIII-D plasma control system using real time feedback based on diagnostic signals obtained during the plasma pulse. Three gyrotrons have operated at 1.0 MW output power for 5.0 s. Peak central temperatures of the artificially grown diamond gyrotron output windows are < 180 C at equilibrium.
Date: July 2003
Creator: Lohr, J.; Callis, R. W.; Doane, J. L.; Ellis, R. A.; Gorelov, Ya; Kajiwara, K. et al.
Partner: UNT Libraries Government Documents Department

STABILITY OF HIGH VOLTAGE MODULATORS FOR NONLINEAR LOADS

Description: OAK-B135 Gyrotrons have a nonlinear voltage--current characteristic such that the small signal or ac impedance changes as operational voltage and currents are reached. The ac impedance determines the stability of a voltage or current control system. this can become particularly challenging when several gyrotron are connected in parallel to a single modulator. With all gyrotrons hooked to a common ground, large current loops can be generated as well as non-canceling currents in individual coaxial lines. These inequalities can provide the required feedback impulse to start an oscillation condition in the power system for the tubes. Recent operation of two CPI 110 GHz gyrotrons in the MN class from a single modulator on DIII-D has shown instability in the power system. An oscillation in the drive current occurs at various points in the ramp up and flat top portions of the 80 kV voltage pulse with each tube drawing 40 A at full voltage. Efforts to stabilize these instabilities are presented along with some modeling and examination of the issues for gyrotron modulators.
Date: October 1, 2003
Creator: PAWLEY,J.C; TOOKER,J; PEAVY,J; CARY,W.P; NEREM,A; HOYT,D et al.
Partner: UNT Libraries Government Documents Department

LAUNCHER PERFORMANCE AND THERMAL CAPABILITY OF THE DIII-D ECH SYSTEM

Description: OAK-B135 The temperatures of components of DIII-D ECH launchers were observed during 2003 tokamak operation. The injected power was typically 500-700 kW and the pulse length was typically 2s. Plasma shots were performed at intervals of about 17 min from 9 a.m. to 5 p.m. The temperatures of a movable mirror, a fixed mirror and a launcher reached an equilibrium after about six hours of repetitive pulsing. The saturation temperature depends to some extent on the plasma stored energy. However, even in high {beta} plasma, the temperatures plateaued at acceptable values.
Date: October 1, 2003
Creator: KAJIWARA,K; LOHR,J; GORELOV,I.A; GREEN,M.T; PONCE,D; CALLIS,R.W et al.
Partner: UNT Libraries Government Documents Department

RECENT DEVELOPMENTS ON THE 110 GHZ ELECTRON CYCLOTRON INSTATLLATION ON THE DIII-D TOKAMAK

Description: OAK A271 RECENT DEVELOPMENTS ON THE 110 GHZ ELECTRON CYCLOTRON INSTALLATION ON THE DIII-D TOKAMAK. Significant improvements are being implement4ed to the capability of the 110 GHz electron cyclotron system on the DIII-D tokamak. Chief among these is the addition of the fifth and sixth 1 MW class gyrotrons, increasing the power available for auxiliary heating and current drive by nearly 60%. These tubes use artificially grown diamond rf output windows to obtain high power with long pulse capability. The beams from these tubes are nearly Gaussian, facilitating coupling to the waveguide. A new fully articulating dual launcher capable of high speed spatial scanning has been designed and tested. The launcher has two axis independent steering for each waveguide. the mirrors can be rotated at up to 100{sup o}/s. A new feedback system linking the DIII-D Plasma Control System (PCS) with the gyrotron beam voltage waveform generators permits real-time feedback control of some plasma properties such as electron temperature. The PCS can use a variety of plasma monitors to generate its control signal, including electron cyclotron emission and Mirnov probes. Electron cyclotron heating and electron cyclotron current drive (ECH and ECCD) were used during this year's DIII-D experimental campaign to control electron temperature, density, and q profiles, induce an ELM-free H-mode, and suppress the m=2/n=1 neoclassical tearing mode. The new capabilities have expanded the role of EC systems in tokamak plasma control.
Date: October 1, 2002
Creator: PONCE,D; CALLIS,RW; CARY,WP; FERRON,JR; GREEN,M; GRUNLOH,HJ et al.
Partner: UNT Libraries Government Documents Department

PHYSICS OF OFF-AXIS ELECTRON CYCLOTRON CURRENT DRIVE

Description: Electron cyclotron current drive is a key option for driving current off-axis in a tokamak, as needed for example for current profile control or for suppression of neoclassical tearing modes. Experiments in DIII-D at low beta have shown that the partial cancellation of the Fisch-Boozer co-current by the Ohkawa counter-current can cause strong deterioration of the current drive efficiency at larger minor radius. However, more recent experiments at higher power have shown that the loss in efficiency can be mostly recovered if the target plasma has higher electron beta, {beta}{sub e}. The improvement in efficiency with beta can be understood from a theoretical viewpoint by applying the Fokker-Planck code CQL3D, which shows excellent agreement with experiment over a wide range of parameters, thereby validating the code as an effective means of predicting the ECCD.
Date: July 1, 2002
Creator: PRATER, R.; PETTY, C.C.; HARVEY, R.; LIN-LIU, Y.R.; LOHR, J.M. & LUCE, T.C.
Partner: UNT Libraries Government Documents Department

FEEDBACK CONTROL OF THE DIII-D ECH SYSTEM

Description: The output power of the DIII-D gyrotron complex has been modulated by the plasma control system using feedback on the difference between a desired electron temperature and the ECE measurement. Operation was stable and permitted control of the flux penetration during initiation of the discharge.
Date: August 1, 2002
Creator: LOHR, J.; FERRON, J.R.; GORELOV, Y.A.; KAJIWARA, K.; PONCE, D. & WADE, M.R.
Partner: UNT Libraries Government Documents Department