Volume 77, Issue 11, November 2006
Index of content:
- NUCLEAR PHYSICS, FUSION AND PLASMAS
77(2006); http://dx.doi.org/10.1063/1.2364133View Description Hide Description
A novel design of three-step Langmuir probe (TSLP) array has been developed for zonal flow (ZF) studies in the HL-2A tokamak. Three TSLP arrays are used to determine three-dimensional (3D) features of the ZFs. Two TSLP arrays are located in the same poloidal plane at a separation, while the third TSLP array is separated toroidally by . A fourth TSLP array driven by pneumatically reciprocating system is applied for boundary parameter profile measurements within . The TSLP structure is described in detail. The measured 3D properties of the geodesic acoustic mode (GAM) ZFs are described and the poloidal and toroidalmode numbers are simultaneously determined in the HL-2A tokamak for the first time. The radial wave vector at the GAM frequency is estimated as , corresponding to radial scale length of .
77(2006); http://dx.doi.org/10.1063/1.2372735View Description Hide Description
This article presents designs for a single-shot x-ray compatible wave-front sensor and visible light demonstrations of such a wave-front sensor based on a novel implementation of the method of phase retrieval. This wave-front sensor may be used with a soft x-ray laser, as well as with incoherent line emission at multikilovolt x-ray energies. This approach could be used to characterize line-integrated electron density gradients formed in laser-produced and -pinch plasma experiments, as well as for at wavelength testing of extreme ultraviolet lithography components and x-ray phase imaging of biological specimens. The phase retrievaldiagnostic is experimentally demonstrated in the visible region using a liquid-crystal spatial light modulator to provide a simulated phase profile, representing the phase that would be incurred by an x-ray probe passing through an exploding foil plasma. The visible light phase retrievaldiagnostic represents the first experimental test of this phase retrieval algorithm, and the results are compared with an interferometric measurement and shown to be in close agreement. The merits of this diagnostic include a wide dynamic range, broadband or low coherence length light capability, high x-ray efficiency, two-dimensional gradient determination, and experimental simplicity.
electron cyclotron resonance plasma source using cylindrically comb-shaped magnetic-field configuration for broad ion-beam processing77(2006); http://dx.doi.org/10.1063/1.2387885View Description Hide Description
An electron cyclotron resonance (ECR) plasma source for broad ion-beam processing has been upgraded by a cylindrically comb-shaped magnetic-field configuration and frequency microwaves. A pair of comb-shaped magnets surrounds a large-bore discharge chamber. The magnetic field well confines plasmas with suppressing diffusion toward the axial direction of the cylindrical chamber. The magnetic field is constructed with a multipole and two quasiring permanent magnets. The plasma density clearly increases as compared with that in a simple multipole magnetic-field configuration. The frequency of microwaves output from the traveling-wave tube amplifier can be easily changed with an input signal source. The plasma density for is higher than that for . The maximum plasma density has reached approximately at a microwave power of only and a pressure of . The enhancement of plasma generation by second-harmonic resonance and microwave modes has been investigated. The plasma density and the electron temperature are raised around the second-harmonic resonance zone. And then, the ion saturation current is periodically increased with varying the position of the plate tuner. The distance between the peaks is nearly equal to half of the free-space wavelength of microwave. The efficiency of ECR has been improved by using the comb-shaped magnetic field and raising microwave frequency, and then the high-density plasma source has been accomplished at low microwave power.
77(2006); http://dx.doi.org/10.1063/1.2393164View Description Hide Description
A radio frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface has been constructed. All of the random electron flux incident on an exit aperture is extracted through an electron sheath resulting in total nonambipolar flow within the device when the ratio of the ion loss area to the electron loss area is approximately equal to the square root of the ratio of the ion mass to the electron mass, and the ion sheath potential drop at the chamber walls is much larger than . The nonambipolar electron source (NES) has an axisymmetric magnetic field of at the extraction aperture that results in a uniform plasma potential across the aperture, allowing the extraction of all the incident electron flux without the use of grids. A prototype NES has produced of continuous electron current, using (SCCM denotes cubic centimeter per minute at STP) Ar, rf power at , and 6 times gas utilization. Alternatively of electron current can be produced, using Ar at rf and 20 times gas utilization. NES could replace hollow cathodeelectron sources in a wide variety of applications.