LINAC developments for heavy ion operation at GSI and FAIR

Abstract

The first cavity of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217 MHz multi gap Crossbar H-mode structures (CH) has been already commissioned at high acceleration gain. The worldwide first beam test with a superconducting multi gap CH-cavity was a milestone of the R&D work of HIM and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project, substituting GSI-UNILAC as a heavy ion high duty factor Linac. Recently the first two of four fully equipped cw-Linac cryomodules are in procurement. To meet the future FAIR science requirements higher beam intensity has to be achieved in the present GSI-accelerator complex. In the last years ion source developments, in particular for the high current Vacuum Arc Ion Sources (VARIS), were concentrated on heavy elements, as Bi and Pb, aiming for stable routine ion source operation at a sufficient rep. rate and high production efficiency. Stripping is a key technology for all heavy ion accelerators. After upgrade of the supersonic N 2 -gas jet implementation of high current foil stripping, recently a new H 2 gas cell, using a pulsed gas regime synchronized with arrival of the beam pulse has been developed. An enhanced stripper gas density as well as a simultaneously reduced gas load results in an increased stripping efficiency, while the beam emittance remains the same. A new record beam intensity (11.1 emA) for 238 U 28+ beams at 1.4 MeV/u has been achieved, applying the pulsed high density H 2 -stripper target to a high intensity 238 U 4+ beam from the VARIS ion source. Further ion source developments have been accomplished recently providing for sufficient heavy ion beam intensities at the High Current Injector Linac. A machine investigation program has been performed in 2020. The focus was to optimize the entire FAIR injector chain for high intensity heavy ion beam after the successful implementation of different upgrade measures. Besides a dedicated operation mode applying UNILAC, as a heavy ion Linac, at a synchronous phase significantly lower than 30 degrees for high intensity proton beam, could be established. Thus, UNILAC is able to deliver a sufficient proton beam intensity for the FAIR commissioning phase, when the FAIR-proton Linac is not yet available.

Advanced basic layout of the HElmholtz LInear Accelerator for cw heavy ion beams at GSI

“…The GSI UNILAC will be upgraded to supply the FAIR facility currently under construction with short high-intensity heavy ion pulses [25][26][27][28][29][30][31]. In future, the HELIAC will then meet the requirements of users, including those from SHE research, for long pulses with the highest possible power density.…”

Beam dynamics and cavity design of an 8 MeV CW IH-DTL for SYSU-PAFA

“…Therefore, in order to limit the emittance growth, the APF cavities are usually not designed to be too long. Due to the advantage of no magnets inside the cavity and the transverse focusing ability can be improved by optimizing the distribution of synchronous phases, the APF beam dynamics scheme is widely adopted by many different accelerator-based facilities, such as the Advanced Proton Therapy Facility (APTRON) in China [19], the Muon Linac at J-PARC [20], the Heavy Ion Medical Accelerator Center (HIMAC) in Japan [21], and Helmholtz Linear ACcelerator (HELIAC) at GSI in Germany [22]. All the APF-DTLs of these facilities adopt IH structure and accelerate particles with high acceleration efficiency and have been in good operation so far, demonstrating the feasibility and superiority of the APF beam dynamics scheme.…”

How Simply One Can Considerably Improve Performance of the Gas Stripper at the GSI UNILAC (Proposal)

“…In this article, we propose a simple method to considerably improve the performance of the gas stripper setup at the GSI Universal Linear Accelerator (UNILAC) in Germany. A detailed description of the design and operation of the GSI gas stripper reader can be found elsewhere, for example, in [4][5][6][7][8][9][10][11][12][13][14], as well as links between them. Therefore, in this article, we provide only a short description.…”