Diagnostics for multiple frequency heating and investigation of underlying processes

Abstract

The development of new facilities routinely challenges ion source designers to build and operate sources that can achieve ever higher beam intensities and energies. Electron cyclotron resonance ion sources have proven to be extremely capable in meeting these challenges through the production of intense beams of medium and high-charge state ions. As performance boundaries are pushed, source stability becomes an issue as does the technology required to meet the challenge. Multiple frequency heating, the simultaneous use of two or more plasma heating frequencies, is a powerful tool in meeting the simultaneous need of intensity and stability. Relatively straightforward to utilize, the technique has been employed at numerous facilities to increase beam current and achievable charge state while also stabilizing the plasma. Its application has expanded the operational boundaries of existing and next generation sources, demonstrating that these devices have not yet achieved their full operational potential. To better understand the underlying physics, the diagnostics used to probe the source operational boundaries and the plasma properties have become increasingly sophisticated. In concert with detailed modeling, they are beginning to provide insight into the heating mechanism and, with that, the prospect of future advances.

Gas mixing and double frequency operation of the permanent magnet quadrupole minimum-B electron cyclotron resonance ion source CUBE-ECRIS

“…With double frequency heating the CSD is also observed to shift towards higher charge states and the obtained performance improvements are in line with those reported for conventional ECRISs for high and medium charge states (see e.g. [8,9,14,15]). In all cases the best high charge state beam currents were achieved using the maximum available microwave power.…”

“…Another method to improve the high charge state performance is multiple frequency operation, first demonstrated by Xie and Lyneis [8]. In this method, microwaves at two or more discrete frequencies are simultaneously injected into the plasma, which provides improved plasma heating, mitigation of plasma instabilities and improved ion confinement times [9,10]. In the work presented here the applicability of these two methods was probed experimentally by studying their effectiveness in improving the high charge state performance of CUBE-ECRIS.…”

Diagnostics of highly charged plasmas with multicomponent 1+ ion injection

“…Similarly to the n e and E e values, a range of solutions is obtained for the characteristic times, and in lieu of additional constraints (e.g., the cutoff density [24] for n e ) the range may be very broad. There is evidence from both simulations and experiments that highly charged ions originate from the same plasma volume near the central axis of the plasma chamber [8,9,[25][26][27][28] and, consequently, these ion populations probe the same plasma conditions, i.e., they have a common n e E e value. We may thus take the intersection of two or more solution sets of highly charged ion populations which constrains the results on the aforementioned physical basis.…”

An Innovative Superconducting Magnetic Trap for Probing β-decay in Plasmas

“…Historically, this can be considered the first non-conventional method of plasma heating outside the scheme traced by the standard model. Since 1994, the socalled two-frequency heating (TFH) has been used Vondrasek [16] to improve the highly charged ions production by feeding the plasma with two (or more) electromagnetic waves at different frequencies instead of one. From the above considerations and also considering the non conventional PANDORA plasma chamber dimensions with respect to the state of the art ECRISs in the world Leitner [4], it has been decided that the RF injection system will be composed of three lines by employing:…”