摘要:

Progress in the modeling of D−sources is discussed from the point of view of either elementary processes or whole modeling. Recent results obtained in both aspects are presented and discussed.

ISSN:0094-243X    

DOI:10.1063/1.44778

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A post‐discharge peak in both extracted negative ion current and negative ion density has been observed in volume hydrogen negative ion sources. This peak is closely related to the principle of the pulsed volume source. To understand the physical mechanisms involved, we have studied the post‐discharge peak in a medium‐sized negative ion source with a numerical simulation code. The simulation shows a post‐discharge peak in H−density, which is most important at high discharge current and low gas pressure. The post‐discharge peak in H−density which we find is principally due to the reduced destruction of H−by electron detachment. The peak size and duration is limited by the decay of plasma densityneand plasma potentialVp. The decay ofnerapidly reduces H−production by dissociative attachment, and the decay ofVpreduces the electrostatic confinement of H−. We find that electron energy loss is principally due to the energy carried out of the plasma by lost electrons. In this casene,Te, andVpall decay on the ion confinement time scale, which determines the length of the H−post‐discharge peak. A significantly longer ion confinement time would increase the length and magnitude of the H−peak.

ISSN:0094-243X    

DOI:10.1063/1.44779

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss the atomic collision processes that are of major importance for the destruction of the vibrationally excited molecules generated in the discharge, processes that are essential to the valuation of the optimization procedure. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.44780

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We propose a variation on the single‐chamber and tandem systems that employs a single‐chamber, pulsed discharge. Following the discharge pulse, the transient variation of the electron energy distribution allows for a more optimal generation of negative ions than does the static single‐chamber system. Some of the limitations of this system when compared with steady‐state tandem system are discussed. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.44781

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Employing the crossed‐beams technique, we have measured absolute cross sections for mutual electron detachment in collisions between two negative ionsH−+X−→H0+X0+2e−(X−:B−,H−,Cu−,O−,Au−,F−) in the CM‐energy range between a few keV and about 100 keV. The results obtained appear not to obey a simple scaling with negative ion binding energies. For H−+H−‐collisions also the single detachment reactionH−+H−→H0+... has been investigated.

ISSN:0094-243X    

DOI:10.1063/1.44774

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The production of negative ion beams for use in neutral beam injection heating has become an important area of research in recent years. This paper discusses the negative ion densities measured in a pulsed multicusp volume ion source using photodetachment diagnostic technique. A pulse modulated negative ion source is being used as an alternative to the tandem source and an increase in negative ion extracted current has previously been observed by Hopkins and Mellon. Work with photodetachment quoted in this paper shows an increase in negative ion density during the post discharge similar to previous results obtained using an accelerator to extract the negative ions.

ISSN:0094-243X    

DOI:10.1063/1.44775

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

To examine the problem that the measured population distributions taken against the background of the modelling solutions would seem to imply alternate sources of H−production other than dissociative attachment, we have generated new modelling solutions for compression with the data of Eenshuistraet al. Employing modern values for cross sections and rates in our previous works and calculating both the vibrational distributions and the H−concentrations. We have compared and contrasted these solutions with those of Gorseet al. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.44783

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The numerical simulation of kinetic processes in the negative hydrogen ion (H−) sources was carried out with reflector‐type discharge being performed under high specific power. It was shown that at lower specific power (P≤100 W/cm3) the concentration of negative hydrogen ions (NH−) is proportional to the discharge current (I), but as the specific power increases the NH−is proportional to &sqrt;I. The aforementioned circumstance leads to the H−density saturation at P≳500 W/cm3.

ISSN:0094-243X    

DOI:10.1063/1.44784

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present the results of a numerical study of isotope effects in volume negative ion sources. We have studied both hydrogen and deuterium discharges over a range of discharge current. For basic plasma parameters, the model reproduces the behavior measured in the discharge region of a multicusp source. A predicted peak in negative ion production Te‐opt≊0.6–0.8 eV finds support from our analysis of D−and H−densities measured in a hybrid multicusp source. The most significant isotope effect suggested by this modeling effort is a stronger V–T cooling of the vibrational distribution in deuterium, which reduces negative ion production in high power deuterium discharges below that in equivalent hydrogen discharges.

ISSN:0094-243X    

DOI:10.1063/1.44785

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Theory of low‐voltage (LV) Cs–H2discharge is presented. LV arc plasma is created in consequence of ionization of small Cs amount (NCs/NH2≲10−2), hydrogen being non ionized and slightly dissociated. In dense LV plasma the cathode beam relaxation and thermal electron heating occur because of pair Coulomb collisions between beam and plasma electrons. The volume H−generation occurs because of dissociation attachment of heated thermal electrons to vibrationally excited H2molecules. It is shown theoretically that high H−concentration (NH−≳1013cm−3) may be achieved in dense plasma of LV Cs–H2discharge. The high rate of H−generation is explained by optimum value of thermal electron temperature (Te≳1 eV), high electron concentration (n∼1014cm−3) and high hydrogen pressure (PH2≳1 Torr), that causes rapid v‐v pumping of vibrationally excited H2levels. Results of the first experimental investigation of LV Cs–H2discharge are presented. It is shown that LV discharge exists at comparatively small anode voltage (Ua≳1 V) and sufficiently high electron temperature and concentration. Preliminary comparison between theoretical and experimental data is fulfilled. Experimental plasma parameters agree satisfactory with theoretical ones.

ISSN:0094-243X    

DOI:10.1063/1.44786

出版商:AIP    

年代:1992

数据来源: AIP