摘要:

We report the results of simulating two multicusp volume negative ion sources in which plasma parameters, hydrogen vibrational spectra, and in one case the negative ion density, have been measured. We find generally good quantitative and qualitative agreement between experiment and theory for the basic discharge parameters. Good agreement is also found for atomic density, although the wall recombination coefficient &ggr;(H) is 0.05 in one source and 0.5 in the other. The calculated densities of vibrationally excited states withv‘≥5 are higher than the measured densities, but the calculated negative ion densities are lower than available measurements. Possible causes for these discrepancies are suggested. Fundamental modifications to the model may be necessary, and we have discussed two possibilities: a suprathermal rotational spectrum, and a spatial gradient in vibrational excitation (due to elastic collisions which can localize the effect of vibrational wall cooling near the wall).

ISSN:0034-6748    

DOI:10.1063/1.1144410

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Tokamak Fusion Test Reactor (TFTR) deuterium neutral beams have been operated unintentionally with significant quantities of extracted water ions. Water has been observed with an optical multichannel analyzer. These leaks were thermally induced with the contamination level increasing linearly with pulse length. Up to 6% of the beam current was attributed to water ions, corresponding to an instantaneous value of 12% at the end of a 1.5 s pulse. A similar contamination is observed during initial operation of ion sources exposed to air. Operation of new ion sources typically produces a contamination level of ∼2%, with cleanup to undetectable levels in 50–100 beam pulses. Approximately 90% of the water extracted from ion sources with water leaks was deuterated, implying that there is the potential for tritiated water production during TFTR’s forthcoming DT operation. It is concluded that isotope exchange in the plasma generator takes place rapidly, most likely as the result of surface catalysis. The primary concern is with O implanted into beam absorbers recombining with tritium, and the subsequent retention of T2O on cryopanels.

ISSN:0034-6748    

DOI:10.1063/1.1144411

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A plasma source based on an inductive breakdown of a supersonic gas puff is described. The source was developed to provide an anode plasma for an annular, extraction geometry, magnetically insulated ion diode. In this source, plasmas with densities of 1013cm−3were generated and accelerated to velocities of 20–30 cm/&mgr;s; plasma fluxes of 10–40 A/cm2were obtained. Operating the source under the diode insulating field effect, plasma fluxes above 100 A/cm2were observed. When the plasma source was used in conjunction with a magnetically insulated diode gap, intense ion beams with proton fluxes of more than 100 A/cm2, energies of 100 keV, and beam pulses longer than 1 &mgr;s were extracted.

ISSN:0034-6748    

DOI:10.1063/1.1144412

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A magnetically confined thermal electric arc gas heater of easy construction, handling, and maintenance has been designed, built, and tested as a suitable source of heat for dissociating hydrogen molecules. The plasma species in the gas discharge region are assumed to satisfy local thermodynamic equilibrium conditions. The average beam kinetic energy is determined to be 1.5 eV, leading to an arc temperature of approximately 8700 K; the dissociation rate is 0.5 atoms per molecule and the total atom beam intensity in the forward direction is 1018atoms/sr s. This novel atom source has been successfully ignited and operated with pure hydrogen during several hours of continuous performance, maintaining its characteristics and overcoming some of the difficulties previously found by researchers using other arc sources. The hyperthermal hydrogen atom beam obtained from this source is identified by MoO3chemical detectors, and analyzed and characterized by three different calorimetric sensors, Ni, Ta, and Teflon. The experimental results obtained with this dissociator agree with those published in the literature.

ISSN:0034-6748    

DOI:10.1063/1.1144413

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A relatively long‐pulse width (0.1–1 &mgr;s) intense ion beam accelerator has been built for materials processing applications. An appliedBr, magnetically insulated extraction ion diode with dielectric flashover ion source is installed directly onto the output of a 1.2 MV, 300‐kJ Marx generator. The diode is designed with the aid of multidimensional particle‐in‐cell simulations. Initial operation of the accelerator at 0.4 MV indicates satisfactory performance without the need for additional pulse shaping. The effect of a plasma opening switch on diode behavior is considered.

ISSN:0034-6748    

DOI:10.1063/1.1144414

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two types of fast bolometers are described for the plasma energy transport study in the Madison symmetric torus plasma confinement device. Both types use pyrocrystals of LiTaO3or LiNbO3as the sensors. One type is used for measurements of the radiated heat losses and is situated at the vacuum shell inner surface. Another type is insertable in the plasma and measures the plasma particle heat flux. The frequency response of the bolometers is measured to be in the 150–200 kHz range. The range of the measured power fluxes is 0.1 W/cm2–10 kW/cm2and can be adjusted by changing the size of the entrance aperture. The lower limit is determined by the amplifier noise and the frequency bandwidth, the higher limit by destruction of the bolometer sensor.

ISSN:0034-6748    

DOI:10.1063/1.1144478

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The count rate capability of high‐resolution neutron spectrometers for fusion plasmas is discussed. In particular, the question of the intrinsic rate limitations in neutron time‐of‐flight (TOF) spectrometers is assessed quantitatively for two design approaches where the proton recoils fromn+Hscatterings are detected with in‐beam and out‐of‐beam detectors. It is found that the count rate capability limit lies in the range 50–400 kHz for TOF depending on approach. Comparison is made with other types of neutron spectrometers for fusion experiments. It is shown, for the first time, that neutron spectrometers fall into distinct categories depending on the underlying detection methods and that this information can be used for assessing capability limits of neutron spectrometry as a diagnostic for fusion plasmas.

ISSN:0034-6748    

DOI:10.1063/1.1144415

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have developed a fast real‐time spectral analysis algorithm for space plasma three‐dimensional (3D) ion mass spectrometers that deconvolves contributions to time‐of‐flight ion mass spectra for various ion species abundances. The algorithm is composed of a set of coupled linear equations with constant coefficients. The algorithm is implemented so that in‐flight computers need only apply a predetermined number of multiplies and adds to the spectral data. The algorithm allows run times to be short and highly predictable, can accommodate the presence of background in the ion mass spectra, and can be updated to adjust to calibration changes and unexpected instrument anomalies or failures. Space plasma 3D ion mass spectrometers have the capability of generating large volumes of data and if not compressed would produce data rates that far exceed the telemetry rate usually allocated to space plasma instruments. The real‐time application of this algorithm allows one to achieve compression ratios greater than 100 for the spectral data without introducing systematic errors to the computed ion abundances. It also allows the application of other higher level data compression techniques to provide additional compression of the telemetry data. Finally, the algorithm can be thought of as a way to increase the mass resolution of the ion spectrometer.

ISSN:0034-6748    

DOI:10.1063/1.1144416

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Transverse coherent density fluctuations at the plasma cutoff layer are modeled by a rippled conducting surface. Two simulations are presented which give the reflectometer back scattered power as functions of ripple wavelength, amplitude, and phase. Results from an experimental simulation of the STOR‐M tokamak geometry and a numerical simulation using the Helmholtz integral and a paraxial Gaussian probe beam, agree in showing three ripple wavelength (&Lgr;) sensitivity regions defined by beam radius (w): Short wavelengths &Lgr;/&lgr;≪2w/&lgr; experience large Bragg scattering. Long wavelengths &Lgr;/&lgr;≫10w/&lgr; experience no scattering. Intermediate wavelengths experience complex scattering with strong modulation of reflected power at twice ripple frequency.

ISSN:0034-6748    

DOI:10.1063/1.1144417

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Modifications to a light scattering apparatus to permit study of liquid surface fluctuations of significantly higher wave number than hitherto are described. Various problems associated with the modified system are discussed. Typical results are presented for capillary wave propagation on the surface of two different fluids, demonstrating the satisfactory functioning of the spectrometer despite these problems.

ISSN:0034-6748    

DOI:10.1063/1.1144364

出版商:AIP    

年代:1993

数据来源: AIP