摘要:

During the last 10 to 15 years, significant progress has been made worldwide in the area of pellet injection technology. This specialized field of research originated as a possible solution to the problem of depositing atoms of fuel deep within magnetically confined, hot plasmas for refueling of fusion power reactors. Using pellet injection systems, frozen macroscopic (millimeter‐size) pellets composed of the isotopes of hydrogen are formed, accelerated, and transported to the plasma for fueling. The process and benefits of plasma fueling by this approach have been demonstrated conclusively on a number of toroidal magnetic confinement configurations; consequently, pellet injection is the leading technology for deep fueling of magnetically confined plasmas for controlled thermonuclear fusion research. Hydrogen pellet injection devices operate at very low temperatures (&bartil;10 K) at which solid hydrogen ice can be formed and sustained. Most injectors use conventional pneumatic (light gas gun) or centrifuge (mechanical) acceleration concepts to inject hydrogen or deuterium pellets at speeds of &bartil;1–2 km/s. Pellet injectors that can operate at quasi‐steady state (pellet delivery rates of 1–40 Hz) have been developed for long‐pulse fueling. The design and operation of injectors with the heaviest hydrogen isotope, tritium, offer some special problems because of tritium’s radioactivity. To address these problems, a proof‐of‐principle experiment was carried out in which tritium pellets were formed and accelerated to speeds of 1.4 km/s. Tritium pellet injection is scheduled on major fusion research devices within the next few years. Several advanced accelerator concepts are under development to increase the pellet velocity. One of these is the two‐stage light gas gun, for which speeds of slightly over 4 km/s have already been reported in laboratory experiments with deuterium ice. A few two‐stage pneumatic systems (single‐shot) have recently been installed on tokamak experiments. This article reviews the equipment and instruments that have been developed for pellet injection with emphasis on recent advances. Prospects for future development are addressed, as are possible applications of this technology to other areas of research.

ISSN:0034-6748    

DOI:10.1063/1.1143995

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two different electron density reconstruction methods for 8‐keV neutral lithium beam probing have been developed for the Compact Helical System (CHS). Density dependences on emission and ionization processes are included by using effective rate coefficients obtained from the collisional radiative model. Since the two methods differ in the way the local beam density in the plasma is determined, the methods have different applicable electron densities. The beam attenuation is calculated by iteration from the electron density profile in method I. In method II, the beam remainder at the observation pointzis determined by integrating the Li iemission intensity fromztoward the position of emission tail‐off. At the emission tail‐off, the fast lithium beam is completely attenuated. Selecting an appropriate method enables us to obtain edge electron density profile well inside the last closed flux surface for various ranges of plasma densities (1012–5×1013cm−3). The electron density profiles reconstructed by these two different methods are in good agreement with each other and are consistent with results from ruby laser Thomson scattering.

ISSN:0034-6748    

DOI:10.1063/1.1143996

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Frequency shifts in the megahertz region, as required under certain conditions in far‐infrared diagnostics of magnetically confined fusion plasmas, can be achieved via multiple diffraction by a cylindrical diffraction grating rotating at moderate speed. We present a compact modular concept to correct the beam distortion at the grating. The concept is based on two elliptical mirrors and a sequence of (n−1) identical concave mirrors forndiffractions. Design parameters are derived for &lgr;=119 &mgr;m (H2O laser), &lgr;=195 &mgr;m (DCN laser), and &lgr;=337 &mgr;m (HCN laser). The concept was successfully realized for &lgr;=119 &mgr;m using four diffractions. A frequency shift of 3 MHz was achieved with a grating driven by an electric micromotor. The quality of the beam exiting from the grating was excellent. The total efficiency after four diffractions was measured as 64%, corresponding to an overall efficiency (i.e., mirror and other losses included) of 0.641/4=89% per diffraction.  

ISSN:0034-6748    

DOI:10.1063/1.1143997

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new, fast, and very sensitive semiconductor bolometer has been designed and developed for the measurement of radiative energy losses in fusion devices in which the hard radiation level is not too high. Special care was taken in the design of the bolometer to simplify both the construction technology and the installation in fusion devices. The major novelty of this bolometer is the use of a low thermal conductivity rigid substrate, instead of the typical thin foil stretched on a rigid frame. In spite of large detector‐substrate contact area, the cooling time constant reaches values as high as 150 ms. The rigid substrate allows the detector to be very robust and reliable; moreover, the monolithic integration of array structures is straightforward. The detector has been fabricated with a thin‐film multilayer technology achieving very low thermal capacitance (<2 mJ/K) and very low response time (<5 &mgr;s). High responsivity (20 V/W) is obtained using GeOxthin film with a high thermal coefficient of the electrical resistance (−4.5%/K) as sensing thermistor.

ISSN:0034-6748    

DOI:10.1063/1.1143998

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

LiF (200) crystals were heated with the x rays produced when a 30 J, 0.35 &mgr;m laser pulse of 0.6 ns duration was incident on a gold‐coated titanium target at an irradiance of 2.5×1015W cm−2. A filter arrangement allowed half of the crystal to be heated by the broad band x radiation from the gold plasma, whilst effectively shielding the other half of the crystal. The reflectivity of both x‐ray heated and unheated portions of the crystal was monitored by diffracting He‐&agr; radiation from the underlying titanium from both parts of the crystal. Significant increases in the integrated reflectivity (36%) of the heated crystal were found.

ISSN:0034-6748    

DOI:10.1063/1.1143999

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The absolute x‐ray response of three X‐UV photodiodes was measured over an energy range of 1.5–17.5 keV so that they could be used to calibrate x‐ray imaging systems for the ASCA satellite mission. An intense electron‐beam x‐ray generator was used to test both the dc and ac x‐ray response at 1.5, 4.5, 8.0, and 17.5 keV, and an55Fe source was used to examine one of the photodiodes at 5.9 keV. The x‐ray response was determined by comparing the X‐UV diode signal to that of a previously calibrated silicon surface barrier diode (SBD). The X‐UV detector response was similar to the SBD response at low energies (1.5 and 4.5 keV). At 8 keV, the X‐UV detectors exhibited about 70% of the SBD response, and at 17.5 keV, about 50%. This result is surprising, because the X‐UV diodes actually have a greater silicon thickness than the SBD. In contrast to our findings for SBDs in the past, this implies that not the entire physical volume of these detectors comprises the active volume. The X‐UV detector x‐ray response was also examined as a function of the applied bias voltage. No significant bias voltage dependence of the x‐ray signal was found, which indicates that the depletion layer thickness does not determine the active volume either. However, the detector noise was found to decrease substantially as the applied bias was raised from zero to a few volts. Response of these detectors, operated in pulse mode, to226Ra &agr; particles indicated large charge carrier recombination in the bulk silicon. This feature renders these detectors unsuitable for most charged‐particle spectroscopy applications.

ISSN:0034-6748    

DOI:10.1063/1.1144000

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For the purpose of new applications of thermal and recombining plasma, an apparatus is developed which continuously produces ‘‘arc‐heated and magnetically trapped expanding plasma jet.’’ In this apparatus, arc‐heated thermal helium plasma of atmospheric pressure is spouted from a nozzle of 1.2 mm inner diameter into a rarefied gas wind tunnel of about 3–20 Pa with a parallel magnetic field of 0.025–0.16 T. Investigations about the plasma are carried out and stationary inverted populations are observed downstream along this plasma jet. The magnetic field establishes stable arc discharge. Electron temperatureTe, ion temperatureTi, and electron densityneof the plasma are about 0.1–1, 0.1–0.8 eV, and 1×1012–2×1013cm−3, respectively. Two examples of applications of this apparatus are discussed. One is a potential active laser medium, and the other is a cluster preparer.

ISSN:0034-6748    

DOI:10.1063/1.1144001

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A technique is demonstrated whereby the delivered mass and flow rate versus time of a short rise‐time gas delivery system may be accurately determined. The gas massMthat flows past a point in a gas delivery system by an arbitrary timet=tpmay be accurately measured if that point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values oftp, and assuming reproducibility, the injected mass time historyM(t) characteristic of the systemwithoutthe fast closing valve may be determined. The flow rate versus timedM(t)/dtmay then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2‐mm‐i.d., 0.76‐mm‐thick copper tube is isolated by imploding (&thgr; pinching) the tube using a single turn tungsten magnetic‐field coil. Optical measurements of the tube’s internal area versus time indicate that the tube is sealed in 7 &mgr;s. Results are correlated with piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the &thgr; pinch process.

ISSN:0034-6748    

DOI:10.1063/1.1144002

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A method using nuclear scattering with an ion beam microprobe for characterizing the spatial and temporal density profile of a supersonic gas jet is described. The technique was applied to Ar and N2gas jets from an axially symmetric DeLaval nozzle and the results are presented.

ISSN:0034-6748    

DOI:10.1063/1.1144003

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe an ion source based on the spontaneous desorption process. The production, acceleration, and separation processes allow for the production of keV energy polyatomic ions while maintaining a high signal‐to‐background ratio. Both atomic and polyatomic ions with up to 37 keV energy were generated. Because the spontaneous desorption process is naturally pulsed, the ion source was attached to a dual time‐of‐flight mass spectrometer for secondary ion mass spectrometry experiments. In this article, we describe the design of both the polyatomic ion source and the mass spectrometer.

ISSN:0034-6748    

DOI:10.1063/1.1144004

出版商:AIP    

年代:1993

数据来源: AIP