easily be changed. During the hold phase, the plasma dynamics is studied by means of the analysis of the induced charge signals detected at the walls of the confining cylinders; at the end of the hold phase an axially integrated density distribution is obtained by accelerating the particles towards a phosphor screen (kept at a positive potential of few kV), and detecting the emitted light by means of a high sensitivity CCD camera.

![Schematic of the ELTRAP Malmberg-Penning trap and of its diagnostic system: the sectored cylinders S2 and S4 allow to detect the plasma rotation. The source connections, the amplification circuitry and the phosphor screen for the optical diagnostic are shown. The polarization layer of the phosphor screen has also been used as a charge collector.[]{data-label="fig1"}](FigEltrap.eps)

The confined plasma                            -5-

      In 2006 petitioners proposed and respondent accepted an installment

agreement, which was established on November 6, 2006 (with respect to their

1995, 1996, 1999, 2000, 2001, 2002, 2003, and 2004 income tax liabilities). The

record reflects that petitioners began paying on this plan in December 2006. On

April 13, 2009, respondent determined that petitioners were no longer in

installment agreement status.4 On April 23, 2009, respondent issued a notice of

intent to levy with respect to petitioners’ 1995, 1996, 1999, 2000, 2001, 2002,

2003, and 2004 income tax liabilities.

      On August 28, 2009, the parties entered