Barth, W.

Clemente, G.

Schlitt, B.

Vinzenz, W.

GSI Repository

GSITemplate2007 Status of the High-Energy Linac Project at GSI B. Schlitt, G. Clemente, W. Barth, and W. Vinzenz GSI, Darmstadt, GermanyTo assure reliable operation for FAIR, a new high-intensity heavy-ion injector linac for SIS18 (high-energy (HE) linac) was proposed as replacement for the existing post-stripper linac at the GSI UNILAC. A linac for short beam pulses, low repetition rate, and fixed end energy is under investigation. The first proposal [1, 2] included to extend the pre-stripper to 3 MeV/u to achieve higher charge states around U38+ behind the gas-stripper and the linac end energy was boosted to 22 MeV/u. Recently, a less ambitious solution was favoured without an extension of the pre-stripper linac and keeping U28+ for acceleration along the new HE linac and in SIS18 (Fig. 1, Table 1). Six 108 MHz IH-type drift-tube linac cavities within a total length of about 24 m accelerate the ions up to 11.4 MeV/u as provided by the existing linac. Fast pulsed quadrupole triplet lenses suitable for multi-beam opera-tion are used for transverse focusing in between the IH cavities (Fig. 2). Quadrupole magnets inside the cavities should be avoided. This new HE linac solution is less expensive as the previous one and the existing gas-stripper section does not need to be shifted to a new loca-tion. The new solution leaves plenty of space within the existing UNILAC tunnel available for future linac energy upgrades (Fig. 1). In addition, alternative solutions to the present nitrogen gas stripper, like carbon foil strippers [3], a plasma stripper [4], and the use of low-Z gases like hy-drogen at the gas stripper [5] are being investigated in order to generate higher charge states.   RF Systems A preliminary study for 108 MHz, 1.8 MW high-power amplifiers for short-pulse low duty cycle operation was performed in collaboration with industrial partners. It is based on a TH558SC tetrode from THALES Electron Devices which is widely used worldwide for broadcast as well as for scientific applications. Thus, there is no known risk concerning the long-term availability of this tube for the coming decades. Pilot studies concerning solid-state driver amplifiers and amplifier supply units based on state-of-the-art technologies as well as for a modern digi-tal low-level RF (LLRF) system were started. Outlook Design and construction of a prototype IH cavity as well as of a prototype RF amplifier are planned for 2013 –15, followed by high-power RF tests and beam tests at GSI. Tests of a digital LLRF system on loan from an in-dustrial partner are planned at GSI for 2013.  References [1] B. Schlitt, G. Clemente, W. Barth, and W. Vinzenz, in: GSI Scientific Rep. 2011, p. 296. [2] B. Schlitt et al., in: Proc. HIAT2012, p. 191. [3] H. Vormann et al., this report. [4] C. Teske, Y. Liu, S. Blaes, and J. Jacoby, Physics of Plasmas 19, 033505 (2012). [5] B. Schlitt, H. Vormann et al., this report.   Figure 1: The proposed new 108 MHz high-energy (HE) linac within the existing UNILAC tunnel at GSI. -40-30-20-100102030400 500 1000 1500 2000 2500Beam Axis  /cmTransv. Beam Envelopes / mm Figure 2: Hor. (red) and vert. (green) 99 % beam enve-lopes for a 20 mA U28+ beam along the HE linac. Table 1: Main design parameters of the proposed linac Design ion species 238U28+  Design beam current (pulse) 15 mA Max. mass / charge ratio 8.5  Input beam energy 1.4 MeV/u Output beam energy 11.4 MeV/u Total acceleration voltage 85 MV Linac length ca. 24 m RF frequency 108.4 MHz Beam pulse length ≤ 100 µs Beam repetition rate ≤ 4 Hz RF duty factor ≤ 1 % No. of IH-DTL cavities 6  Cavity length 1.6 – 3.5 m Max. RF power / cavity  (incl. beam loading) 1300 kW  PHN-SIS18-ACC-14 GSI SCIENTIFIC REPORT 2012270 FAIR@GSI

Status of the High-Energy Linac Project at GSI

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Status of the High-Energy Linac Project at GSI

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