Dominant electromagnetic modes of a tape helix loaded in a conducting cylindrical waveguide

Abstract

The paper is concerned with identifying the dominant electromagnetic modes of a tape helix loaded in a conducting waveguide. Two distinct regions of operation of the helix are found. For knu rh<1(knu :free space wavenumber; rh:helix radius), the helix supports slow as well as fast waves, while for knu rh>1, it supports only fast waves. For each region separate asymptotic formulae have been derived. These have also been verified experimentally. Since the exact dispersion relation for a helix is extremely complex these formulae serve to eliminate the associated computational problems. Moreover, a helix in a waveguide supports a large number of fast wave modes. This makes the simplified formulae for fast waves extremely important since these isolate the dominant fast wave directly.

Studies on microwave-induced plasma production using helical slow-wave structures

“…A detailed theoretical analysis of tape and slotted helices loaded inside waveguides (for use in plasma production) can be found in [21] and [22]. Here we shall summarize the major conclusions for large diameter helices only (2nr h /X v > 1; r h : helix radius; A,,: free-space wavelength of the microwave).…”

“…(These have been designated as RC and NRC in the table.) The values of A.,, given in the table for each helix, have been computed at 2.45 GHz, the frequency of our microwave source [21], [22].…”

“…Theoretically, the slow-wave mode of helices in free space [16]- [18], as well as their modes inside a waveguide [19], [20], have been analyzed in detail. In some recent studies [21], [22], the dispersion relations of a tape helix (mathematical idealization of a wire helix) and a slotted helix-loaded waveguide were simplified considerably to yield asymptotic formulae for the wavenumbers of the slow and fast (V plt > c) dominant waves (termed as the SDW and FDW, respectively) of the system. In addition, the field patterns corresponding to these modes were also computed [22], from which the dominant field components of these modes can be identified.…”

High-density plasma production using a slotted helical antenna at high microwave power

“…It is well known that slow-wave structures like the slotted line antenna [1][2][3][4][5][6] and slotted helical antenna [7][8][9][10][11][12][13][14][15][16][17][18] are quite effective for plasma production. To optimize the use of these structures for plasma production purposes, detailed theoretical and experimental studies were undertaken for the slotted line antenna [4][5][6] and the helical antenna [14][15][16][19][20][21]. In these studies, it was established that plasma production efficacy, using these structures, can be maximized by exciting the slow-wave modes (v ph < c;v ph : phase velocity; c: speed of light in vacuum) of these structures efficiently.…”

Feed optimization for the slotted line antenna for high-density plasma production

“…Ganguli SWM [ 13]- [ 15]. It therefore becomes important to identify the field configurations of the SWM and excite this mode in isolation (i.e., with little or no power being coupled to the fast wave modes).…”