摘要:

Two fast scanning heterodyne receivers, swept between 75–110 and 110–170 GHz in 2 ms every 4 ms, were developed to measure the electron cyclotron emission on the horizontal midplane of the Tokamak Fusion Test Reactor (TFTR) plasma. An absolute,insitucalibration technique enables the determination of the profile of the plasma electron temperature from the cyclotron emission intensity. The 4‐ms repetition rate of the receiver allowed the resolution of ‘‘sawtooth’’ fluctuations of temperature, whose period was 10–100 ms, in profiles with central temperatures of 1–2.5 keV.

ISSN:0034-6748    

DOI:10.1063/1.1137668

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A hollow cathode discharge fed plasma neutralizer has been built and was used to neutralize 3‐MeV Li−, C−, and Si−ions. Initial results indicate that the performance of an unoptimized plasma neutralizer is better than gas stripping. Since hollow cathodes produce plasma targets with high efficiency, this type of plasma neutralizer can improve the overall efficiency of a neutral beam line.

ISSN:0034-6748    

DOI:10.1063/1.1137669

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A diagnostic has been developed to simultaneously determine the magnetic field and space potential in fusion‐like plasmas. Initial tests have demonstrated the ability to measure an absolute change of 17 G in the magnetic field strength; under the same test conditions a 6‐V change in space potential could have been detected. The spatial resolution in these tests is a volume of 0.25 cm3. The magnetic field is determined by a measurement of the Zeeman resonance absorption pattern with a frequency scanning narrow‐band laser of an energetic (<50 keV), low current (∼10 &mgr;A) barium ion beam. The laser is injected tangentially to the ion beam to take advantage of the narrow Doppler spread in the direction of the beam. Space potentials are determined by a measurement of the Doppler shift due to a change in beam energyE=E0−e&Jgr;. The diagnostic will be used initially on the TRW STM device to measure diamagnetic depression of the ELMO rings in STM.

ISSN:0034-6748    

DOI:10.1063/1.1137670

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

This paper presents a characterization of a commercially available position‐sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position‐encoding anode. The work includes measurement of absolute efficiencies of H+, He+, and O+ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

ISSN:0034-6748    

DOI:10.1063/1.1137671

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An ion source capable of producing a wide variety of ion species from elemental materials is described. Ion beams of metals can be produced by sputtering a disk, made of the materials to be ionized, placed on the cathode. In order to raise the rate of ionization of the sputtered materials an rf discharge is superimposed on the dc sputtering. Ions of refractory metals, such as Nb, can be easily produced without using halides.

ISSN:0034-6748    

DOI:10.1063/1.1137672

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Molecular beam epitaxy (MBE) is a crystal growth technique capable of growing ultrathin layered heterostructures for basic studies, and devices such as modulation doped field‐effect transistors (MODFET’s), heterojunction lasers, heterojunction bipolar transistors (HBT’s), and superlattices. By using a dimeric arsenic source to grow GaAs and AlGaAs layers, the crystalline quality of these devices and structures may be improved, ultimately improving device performance. The design of a novel large capacity effusion cell (capable of producing about 700 &mgr;m GaAs growth) for cracking tetrameric arsenic into dimeric arsenic and the results of its use are described.

ISSN:0034-6748    

DOI:10.1063/1.1137654

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

This paper describes a 280‐kV constant‐gradient positive‐ion acceleration tube in which the interelectrode voltage is established with a voltage divider chain of resistors that is mounted inside the vacuum of the tube. A single glass pipe serves as the vacuum envelope, flat aluminum disks are used for the tube electrodes, and resistance‐paint‐coated plastic cylinders compose the voltage divider chain. These construction features simplify tube construction and keep manufacturing costs low. During high‐voltage tests, interelectrode voltage was estimated to deviate less than ±6% from uniformity, heat was adequately dissipated from the vacuum‐mounted resistors, and the maximum design acceleration voltage of 280 kV was held. Furthermore, preliminary ion acceleration trials yielded from 0.7 &mgr;A of N+2at 50 kV to 1.5 &mgr;A at 280 kV. The accelerated‐beam cross section, as viewed on a ground quartz screen, remained stationary during those trials, indicating that the tube configuration provided adequate shielding of the beam from asymmetric charges on the interior insulating walls of the tube.

ISSN:0034-6748    

DOI:10.1063/1.1137655

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Instrumentation and procedures for performing pulsed laser‐induced thermal desorption experiments are described. The influence of various instrumental parameters on the measured desorption signals is discussed. Proper conditioning of the desorption flux is shown to be a critical factor for obtaining desorption signals undistorted by the finite pumping speed of the apparatus. Instrumental effects are illustrated using data for pulsed laser desorption of CO from clean copper surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1137656

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Construction and performance of a low‐cost easy‐to‐build CO2laser beam profile monitor are described. Its specifications correspond to those of commercial devices. In this monitor a small slit covered by a temperature dependent fluorescent surface is imaged on a photodiode. A rotating mirror scans the spatial intensity distribution over the slit. This allows one to avoid an expensive photodiode array. The signal‐to‐noise ratio is improved by repetitive sampling with a low‐cost digital processing unit. The dynamic range of measurement is 7 to 1 and the linearity is 10% within this range.

ISSN:0034-6748    

DOI:10.1063/1.1137657

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The temperature evolution and profile of metal field ion emitters under pulsed laser irradiation are solved numerically using an implicit alternating direction method. The temperature profile along the emitter axis at selected times and the temperature evolution curve at the emitter apex during and after the pulsed‐laser irradiation have been obtained. This numerical result shows that the emitter can cool down from the peak temperature by ∼20 K in less than 5 ns, and the heated region is very much localized to the irradiated part of the emitter. The cooling rate is higher for specimens of larger thermal diffusivity, and also if the laser pulse width is narrower and the laser heating is better localized. The peak temperature of the tip apex reached depends almost linearly on the incident flux of the laser beam.

ISSN:0034-6748    

DOI:10.1063/1.1137658

出版商:AIP    

年代:1984

数据来源: AIP