Field ionization characteristics of an ion source array for neutron generators

Abstract

Low-energy beam transport studies supporting the spallation neutron source 1-MW beam operationa) Rev. Sci. Instrum. 83, 02B727 (2012); 10.1063/1.3681125 Novel methods for improvement of a Penning ion source for neutron generator applicationsa) Rev. Sci. Instrum. 83, 02B309 (2012); 10.1063/1.3670744 Development of ion sources from ionic liquids for microfabrication J.A new deuterium ion source is being developed to improve the performance of existing compact neutron generators. The ion source is a microfabricated array of metal tips with an integrated gate (i.e., grid) and produces deuterium ions by field ionizing (or field desorbing) a supply of deuterium gas. Deuterium field ion currents from arrays at source temperatures of 77 K and 293 K are studied. Ion currents from single etched-wire tips operating under the same conditions are used to help understand array results. I-F characteristics of the arrays were found to follow trends similar to those of the better understood single etched-wire tip results; however, the fields achieved by the arrays are limited by electrical breakdown of the structure. Neutron production by field ionization at 293 K was demonstrated for the first time from microfabricated array structures with integrated gates. V C 2013 AIP Publishing LLC. [http://dx.

Studies of a prototype linear stationary x-ray source for tomosynthesis imaging

“…f Applied fields are well below those for bulk breakdown of the thermal SiO 2 insulator. g The cathode tips have been shown to regularly support nearly 100X the field stress associated with electron emission fields (Johnson et al 2013).…”

Nanofabricated Low-Voltage Gated Si Field-Ionization Arrays

“…While un-gated NW and nanowhiskers in [11], [32] demonstrated ultra-low ionization voltages, gated FIAs have the advantage of using different voltages for ionization and acceleration. Gated FIAs based on W-coated Si tips from Sandia National Laboratories (SNL) and Mo Spindt cathodes from SRI International demonstrated improved FI at lower temperatures of 77 K [3], [24]. The bias needed to achieve similar FOM values in this work, were significantly smaller (<200 V) as illustrated in Fig.…”

“…Data collected from previous works on gated FIAs [3], [16], [24], un-gated CNT forests [35], dense Au NW [32], and undoped-Si nanowhiskers [11] have been used to calculate FOM values at V meas as illustrated in Fig. 10.…”

“…S INCE the first observation of field ionization by Müller [1] in 1957, devices that can field-ionize gas molecules have found applications in mass spectrometry [2], neutron sources [3], gas sensors [4], field ion microscopy [5] and scanning helium ion microscope [6]. The field ionization (FI) mechanism consists of a valence electron from a gas atom or molecule tunneling across a potential barrier, into a vacant electron state in a pointed electrode called here an "ionizer" [7].…”

“…A high aspect ratio nanowire (NW) current-limiter is integrated with the tip to regulate the current, hence compensating for the tip fabrication non-uniformity [20]. This NW can also increase the path length between the gate and the ionizer, which increases the breakdown voltage [3], [21]. Low voltage dielectric breakdown can also be circumvented by employing a mesa structure, which is formed by a highly anisotropic etch in conjunction with a thick oxide (>2 µm) holding the contact pads [21].…”