The Thermionic Current between Parallel Plane Electrodes; Velocities of Emission Distributed According to Maxwell's Law

Fry, Thornton C.

doi:10.1103/physrev.17.441

Cited by 89 publications

(27 citation statements)

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“…The thermionic emission model used to generate electrons from the cathode surface for the new electron gun geometry optimization was based on the LangmuirFry law. 15,16 This thermionic model is realistic enough to match experimental data according to Ref. 17 and at the same time it is not too computationally intensive.…”

Section: E Software Packages Used In Simulationsmentioning

confidence: 80%

A novel electron gun for inline MRI‐linac configurations

et al. 2014

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Purpose: This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Methods: Simple electron gun geometry modifications of a Varian 600C electron gun are considered and solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Results: Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5• , and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ±15 cm along the axis of the 0.5 T magnet without capture efficiency reduction below the experimental value in zero field. In this range of linac displacements, the electron beam generated by the new gun geometry is more effectively injected into the linac in the presence of an external magnetic field, resulting in approximately 20% increase of the target current compared to the original gun geometry behavior at zero field. The new gun geometry can generate and accelerate electron beams in external magnetic fields without current loss for fields higher than 0.11 T. The new electron-gun geometry is robust enough to function in the fringe fields of the other two magnets with a target current loss of no more than 16% with respect to the current obtained with no external magnetic fields. Conclusions: In this work, a specially designed electron gun was presented which can operate in the presence of axisymmetric strong magnetic fringe fields of MRI magnets. Computer simulations show that the electron gun can produce high quality beams which can be injected into a straight through linac such as Va...

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Section: E Software Packages Used In Simulationsmentioning

confidence: 80%

A novel electron gun for inline MRI‐linac configurations

et al. 2014

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“…In reality the injected ion flows in non-monokinetic and there is some discrepancy in ion energy values, [53][54][55] allowing for evaluation of the virtual emitter thickness (the length scale of ion density variation). Thus, the emitter thickness depends on kT i for Maxwellian ion energy distribution: …”

Section: -12mentioning

confidence: 99%

Spatial distribution of the electrical potential and ion concentration in the downstream area of atmospheric pressure remote plasma

et al. 2014

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This paper presents the results from an experimental study of the ion flux characteristics behind the remote plasma zone in a vertical tube reaction chamber for atmospheric pressure plasma enhanced chemical vapor deposition. Capacitively coupled radio frequency plasma was generated in pure He and gas mixtures: He–Ar, He–O2, He–TEOS. We previously used the reaction system He–TEOS for the synthesis of self-assembled structures of silicon dioxide nanoparticles. It is likely that the electrical parameters of the area, where nanoparticles have been transported from the synthesis zone to the substrate, play a significant role in the self-organization processes both in the vapor phase and on the substrate surface. The results from the spatial distribution of the electrical potential and ion concentration in the discharge downstream area measured by means of the external probe of original design and the special data processing method are demonstrated in this work. Positive and negatives ions with maximum concentrations of 106–107 cm−3 have been found at 10–80 mm distance behind the plasma zone. On the basis of the revealed distributions for different gas mixtures, the physical model of the observed phenomena is proposed. The model illustrates the capability of the virtual ion emitter formation behind the discharge gap and the presence of an extremum of the electrical potential at the distance of approximately 10−2–10−1 mm from the grounded electrode.

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“…[ -jak X ~+curl bJ (7) Since it is desired that E (t) be real, a i defined as an odd function of w, so that the imaginary parts of the in tegrals ill cq. 6 and 7 vanish , since they arc odd functions of w.…”

Section: Noise Spectrummentioning

confidence: 99%

“…The potential distribution within a conducting diode has been thoroughly investigated by Fry [7] and Langmuir [8], among others. However, Fry limited his investigations to the case where the potential has a minimum.…”

Section: Rigorous Solutionmentioning

confidence: 99%

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Noise spectrum of a diode with a retarding field

Freeman¹

1949

J. RES. NATL. BUR. STAN.

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A general expression for the noise-power spectrum generated by t he random emission of electrons of arbitrary trajectori es within a wavegu ide is obtained. A n ume rical solut ion of t he potential distribution within a plane d iode is effected , and a famil y of curves from wh ich the potential di stribu t ion may be obtained is graphed. A graphical co mparison bet ween several actual potential distribution s and Von Laue's solu tion is gi,·en. The above resul ts are u t ili zed to derive t he equ ivalent mean-square fl uctuation current du e to the space charge w ith in a diode for two cases of potential d istribution, namely, t he linear di s tribution, and t hat di stribu tion which occur at the neighborhood of the beginning of the retarding field. For t he case of t he li near potent ial distribution, the equivalent no ise temperatu re of the diode con ductance is sho\\'l1 to be eq ual to th e cathode tempe ratu re.

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The Thermionic Current between Parallel Plane Electrodes; Velocities of Emission Distributed According to Maxwell's Law

Cited by 89 publications

References 0 publications

A novel electron gun for inline MRI‐linac configurations

A novel electron gun for inline MRI‐linac configurations

Spatial distribution of the electrical potential and ion concentration in the downstream area of atmospheric pressure remote plasma

Noise spectrum of a diode with a retarding field

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