Beam diagnostic developments for fair*

The FAIR (Facility for Antiproton and Ion Research) accelerator complex is currently designed and projected at GSI. The unique features of the main machine SIS100, like e.g. the acceleration of high intensity beams of 2.5×10 protons and 5×10 Uranium ions, the operation close to the space charge limit leading to a large tune spread and the extreme UHV conditions of the cryogenic system for fast ramped superconducting magnets, impose challenging demands on the beam diagnostic components. This contribution describes the general concept of beam diagnostics for FAIR and reports on the present status of prototype studies. Exemplarily the achievements for a novel type of dc transformer, beam position monitors and the ionization profile monitor are discussed and first measurements with prototype setups are presented. FAIR ACCELERATOR COMPLEX Presently GSI entered the final planning phase for the international FAIR project [1]. The existing GSI accelerators, UNILAC and SIS18, together with a new high-current proton LINAC will act as injectors. In its final stage FAIR will consist of two heavy ion synchrotrons (SIS100, SIS300) and four storage rings (CR, RESR, NESR, HESR). The main features of FAIR are: acceleration of all ion species from protons to Uranium, high currents of primary beams, generation of radioactive beams for fixed target experiments or injection in storage rings, as well as antiproton production, accumulation and storage ring experiments. For the planned large variety of physical experiments the multiplexed operation of the whole facility with different settings for ion species, energy etc. on a pulse-to-pulse basis, has been an important design criterion. In this contribution we focus on diagnostics for the fast ramped superconducting synchrotron SIS100 and the high energy beam transport section of FAIR. REQUIREMENTS FOR DIAGNOSTICS A set of general strategies has been considered in order to facilitate the construction of the facility with worldunique complexity. A main paradigm is the facility-wide standardization of diagnostic devices. Even though the requirements of the synchrotrons and storage rings differ, it is planned to use identical diagnostic installations wherever applicable. Standardization also covers the front-end software FESA [2] as an integrative platform for all diagnostic devices at FAIR. Concerning the hardware it is planned to use commercially available components to a maximum extent, in order to reduce manpower and spares inventory. FAIR beam parameters impose strict requirements for all diagnostic devices. A strong constraint with regard to mechanics is the extreme UHV condition down to 5×10 mbar in SIS100. In this main synchrotron, high currents (up to the space charge limit) of primary beams in low charge states will be stored and accelerated with a large incoherent tune spread of up to ΔQ≈0.5. An important prerequisite is the precise beam alignment since in certain locations the synchrotron acceptance is limited to 6 times the rms beam width. For the High Energy Beam Transport section of FAIR the acceptance is even lower, four times the rms beam width. The goal for diagnostics in transport lines and storage rings is to achieve a high resolution and low detection limit. Additionally, the HEBT diagnostic devices have to deal with slow and fast extracted beams, respectively. Due to the requirement for online measurements and in order to prevent device destruction at high beam intensities, non-intercepting diagnostics is preferred and focused on in this contribution. BEAM CURRENT MEASUREMENT Novel DC Current Transformer (NDCCT) For the GSI-built synchrotron DCCT, it was found that at high beam currents (>70mA) and bunch frequencies around 1.2 MHz the feedback loop of the DCCT loses control and the setting of the correct working point becomes unreliable. Therefore an alternative device based on state-of-the-art sensor technology is presently under development at GSI [3]. The NDCCT makes use of integrated GMR sensors (giant magneto-resistance) inside the gap of a split flux concentrator (amorphous alloy or ferrite toroid). The GMR signals are corrected and amplified by a differential pre-amplifier. Additionally, an AC transformer path is implemented by a secondary winding. Special requirements for the NDCCT are: low noise characteristic, high resolution (~100 μA), capability to measure beam currents from 100 μA to 150 A (2 A DC), bunch frequency up to 5 MHz, long-term zero-point stability and high absolute accuracy. The utilized GMR sensor (AA-0002, Nonvolatile Electronics Co.) consists of 4 meandered resistors and 2 flux concentrators, building up a Wheatstone bridge. Studies on the frequency response revealed that the sensor circuitry spans inductive loops and, above a certain threshold frequency, the frequency response of the GMR sensor becomes disturbed. The upper frequency threshold was found to be a result of macroscopic effects like unwanted induced voltages in the sensor, eddy currents and skin effects in the GMR's NiFe-layer, leading to a reduced bridge voltage above the cut-off frequency of 1 MHz, as depicted in Fig. 1. The GMR frequency response is shown for different core materials (CMD5005, ___________________________________________ *Work partly supported by EU-FP6 DIRAC-phase1, -secondary-Beams WEOA04 Proceedings of DIPAC09, Basel, Switzerland 01 Overview and Commissioning