摘要:

A Penning trap system has been set up for storing and investigating cluster ions over time ranges from microseconds up to minutes. This enables studies of cluster reactions with extremely low cross sections and the observation of their time dependence in a new regime. The ions are created externally by laser vaporization, cooled by adiabatic expansion of a supersonic beam, and injected into the Penning trap. Detection of reaction products is achieved by combining the advantages of two complementary approaches, viz. the high resolution of Fourier transform mass spectrometry and the high sensitivity of single‐ion counting with a time‐of‐flight mass spectrometer. The performance of the apparatus is illustrated by results of recent cluster experiments. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146172

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A volume production type microwave negative ion source has been developed for negative ion beam processes such as ion implantation and ion beam deposition, etc. In order to increase efficiency of negative oxygen ion production, we employed a double plasma cell system in which two plasma cells were connected to each other. A high density primary plasma was generated in the first plasma cell with 2.45 GHz microwave power and negative ions were effectively generated in the second plasma cell. A filter magnetic field of about 0.1 T was applied on the second plasma cell to prevent diffusion of high energy electrons from the first plasma cell. Oxygen negative ion beams were generated by this method and the maximum oxygen (O−) ion current of 142 &mgr;A (current density: 325 &mgr;A/cm2) was extracted continuously from the ion source at an extraction voltage of 30 kV and a microwave power of 500 W. This value was three orders larger than that obtained by a single plasma cell system without the filter magnetic field. Molecular oxygen ions (O−2and O−3) were also obtained at percentages of about 20% and 2% of the major O−ion intensity. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146173

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A tabletop high‐brightness line‐emitting laser‐plasma soft x‐ray source utilizing single microscopic droplets as target is shown to produce several orders of magnitude less debris than conventional‐target sources. Quantitative measurements of debris deposition rates and x‐ray flux at different directions around the droplet plasma are presented. With ethanol droplets and a 10 Hz, 70 mJ/pulse laser, typically ∼1×1012photons/(sr⋅pulse⋅line) are emitted from the C V and C VI lines in the water window. The debris deposition is further reduced with a small, localized gas jet shield, which is transparent to the x‐rays. The deposition rate through the gas shield has been determined to be ∼0.2 pg/(sr⋅pulse). Thus, this droplet‐target laser‐plasma x‐ray source is four orders‐of‐magnitude cleaner than a low‐debris plastic tape target laser plasma of similar brightness, making it useful for x‐ray microscopy and lithography. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146174

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The article presents a novel vertical‐dispersion variant of the Johann spectrograph. Very good focusing properties, extremely high spectral resolution, and one‐dimensional spatial resolution of this instrument open new possibilities in x‐ray spectroscopy, especially in x‐ray diagnostics of high‐temperature plasmas. Basic characteristics of the spectrograph scheme are analyzed in detail by using ray tracing procedure. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146175

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The standard photodetachment method was applied for the diagnostic of negative ions in a cesium–hydrogen plasma. The plasma generator studied is a steady‐state source of hydrogen negative ions with a cesium hollow cathode and a radial magnetic field. We demonstrate the possibility of using the photodetachment method for the diagnostics of cesium–hydrogen plasma. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146176

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A novel end‐loss ion‐energy spectrometer is designed for plasma‐ion diagnostics in open‐ended plasma‐confinement devices. This analyzer significantly upgrades a previous slanted grid end‐loss analyzer (SELA) to essentially eliminate secondary‐electron current, and to provide a differential‐spectrum mode of operation, in addition to the usual integral‐spectrum operation of gridded ion‐energy analyzers. The upgraded SELA does not perturb the ambient magnetic field due to its electrostatic operation. Either the differential or integral spectra are obtained by a time sweep of grid voltages, collecting the ion current on a single‐channel plate. Because the angular alignment of the SELA is not critical, it can be used as a spatially scannable diagnostic of ion‐energy distributions and plasma potentials. It is characterized using computer simulations of ion trajectories, monoenergetic ion beams, and end‐loss plasma from the world’s largest tandem mirror—GAMMA 10. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146177

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The contribution of the initial plasma to density profiles reconstructed from thed&fgr;/dfvsfcurve obtained with reflectometry is studied. It is shown that the initial phase information determines to a great extent the accuracy of the inverted profiles at the edge. As it is difficult to measure the edge contribution models are required to initialize the profile evaluation. A novel method is presented that uses the phase information from the lowest frequency waves to obtaind&fgr;/dfbelow the first probing frequencyF1, by imposing the continuity with the measuredd&fgr;/dfcharacteristic and its derivative atF1. An approximate shape of the edge profile is obtained because low‐frequency waves are sensitive to the initial plasma where they propagate without reflection. The accuracy of the inverted profiles is thereby improved, as shown by simulation studies performed for profiles with an exponential‐like decay and with an edge density plateau (typical ofH‐mode regimes during ELMs). It is found that the contribution from the initial plasma decreases with density (or frequency); for densities of the order of 10× the first probed densityne1it is reduced to values less than 10% in the case of a profile with a flat edge and 2% for a peaked one. Forne≳10ne1the profiles can be absolutely calibrated from reflectometry data alone with an accuracy of ±2 mm independent of the initialization model. The numerical study also shows that profile deviations resulting from insufficient phase derivative data, e.g., due to discrete probing, can be more significant than those originated by the initialization process. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146178

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have created a detector to image the neutrons emitted by imploded inertial‐confinement fusion targets. The 14 MeV neutrons, which are produced by deuterium–tritium fusion events in the target, pass through an aperture to create an image on the detector. The neutron radiation is converted to blue light (430 nm) with a 20 cm2array of plastic scintillating fibers. Each fiber is 10 cm long with a 1 mm2cross section; approximately 35 000 fibers make up the array. The resulting blue‐light image is reduced in size and amplified by a sequence of fiber‐optic tapers and image intensifiers, then acquired by a charge‐coupled device camera. The fiber‐optic readout system was tested separately for overall throughput and spatial resolution; the throughput was 0.22 electrons/photon, and the resolution was 0.8 mm. We also characterized the overall efficiency of the detector using the DT‐fusion neutrons emitted by inertial confinement targets; the measured value was 14 electrons/pixel/neutron. Several neutron images of laser‐fusion targets have been obtained with the detector. We describe the detector, present characterization results, and give examples of the neutron images. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146179

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The design of a six‐channel one‐dimensional neutron/x‐ray camera (multicollimator) for the Frascati tokamak upgrade (FTU) machine is described only with regard to the aspects concerning the neutron measurements. The multicollimator, viewing a poloidal cross section of FTU, provides the radial profile of neutron emission from D–D plasmas. The ion temperature profile can be derived in ohmic plasmas if independent data on density are available, while energetic ion tails can be located in the presence of additional rf heating. Information on the position and shape of FTU circular plasmas can also be obtained. The constraints imposed on the collimation and shielding by the compactness of FTU and the expected neutron fluxes are analyzed in detail. The detection system and the performance of the multicollimator are also discussed. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146478

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An optical fiber detector is developed to measure simply and accurately the axial speed of the plasma sheath in a plasma focus device. Using a suitable model, self‐consistent information on the distribution of ionized mass and current inside the structure of the plasma sheath may also be inferred. The thickness of the sheath is also obtained. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146180

出版商:AIP    

年代:1995

数据来源: AIP