The Cryogenic Current Comparator (CCC) for beamlines is designed for the non-destructive, highly sensitive, and absolute measurement of bunched (AC) and un-bunched (DC) beam current of charged particle in the nA range using the external magnetic field of the beam. Niobium based CCCs are running at the CERN-Antiproton Decelerator (beamline diameter of 100 mm) and are tested at the CRYRING@ESR. CCCs of the xD-series (extended dimension) can support the new facility for antiproton and ion research (FAIR) at GSI (Gesellschaft fur Schwerionenforschung) in Darmstadt with a 150 mm beamline diameter. The large FAIR-Nb-CCC-xD has an inductance of 80 mu H. An effective way to increase the sensitivity is to increase the inductance of the pickup coils. The two first CCCs of the new Sm-series (smart & small) have overall inductances of 200 and 300 mu H. This work describes the individual development steps, starting with the superconducting pickup coils. For CCCs with a flux concentrating core in the pickup coil, the subsequent current noise of the CCC is determined by the cores parameter. On the basis of low-temperature LsRs-measurements on pickup coils, it is shown how the fluctuation-dissipation theorem (FDT) can be used to infer the current noise of the CCC. For the first time a white noise of 1 pA(rms)/root Hz could be achieved. A superconducting, meandering shield filters the circular magnetic field and suppresses interference fields. Through step-by-step setup and measurements, it follows how this affects CCC system parameters. Finally, it was possible to measure current impulses below 1 nA(pp) in the laboratory.

The superconducting, heavy ion synchrotron SIS100 is the core of the new FAIR facility at GSI, Darmstadt, Germany. Its unique design is dedicated to the acceleration of intermediate charge state heavy ions. Several new technical approaches assure the stabilization of the vacuum dynamics and the minimization of charge related beam loss. Beside high intensity heavy ions, SIS100 will accelerate all ions from Protons to Uranium, and in spite of the fact that superconducting magnets are used, SIS100 shall be as flexible in ramping and cycling as a normal conducting synchrotron.

Cryogenic Current Comperators (CCC) are an innovative concept for non-destructive measurements of nA currents caused by moving charged particles in beam lines. Classical CCC designs consist of a toroidal pickup coil around a highly magnetic permeable core inductively coupled to a Direct Current Superconducting Quantum Interference Device (DC-SQUID) in combination with a meander shaped superconducting shield. Previous experiments have shown that increasing the inductance of the pickup coil by utilizing a larger amount of the same ring core material reduces the noise density by the square root of the inductance change. We introduce a novel prototype, the Dual-CCC (DCCC), which doubles the pickup inductance in respect to the previous design by adding a second identical core with a second pickup coil and SQUID, which can be read out independently. The combined output exhibits a current sensitivity of about 2 pAHz(-1/2) in the white noise region.

We report on a novel concept and prototype development of a coreless SQUID-based charged-particle beam monitor as a non-destructive diagnostic tool for accelerator facilities. Omitting the typically used pickup coil with a high magnetic permeability core leads to a significant improvement in low-frequency noise performance. Moreover, a revised shielding geometry allows for very compact and rather lightweight device designs. Based on highly sensitive SQUIDs featuring sub-micron cross-type Josephson tunnel junctions, our prototype device exhibits a current sensitivity of about 6 pA Hz−1/2 in the white noise region. Together with a measured shielding factor of about 135 dB this opens up the way for its widespread use in modern accelerator facilities.

In view of the upcoming FAIR project (Facility for Antiproton and Ion Research) several long-term development projects had been initiated with regard to diagnostic devices for beam current measurement. The main accelerator of FAIR will be the fast ramped superconducting synchrotron SIS100. Design parameters of SIS100 are acceleration of 2×10 protons/cycle to 29 GeV for the production of antiprotons, as well as acceleration and slow extraction of p to U ions at 10 ions/s in the energy range of 0.4-2.7 GeV/u and extraction times of up to 10 s. For high-intensity operation non-intercepting devices are mandatory, thus the developments presented in this contribution focus on purpose-built beam current transformers. First prototype measurements of a dc current transformer based on a Tunnelling Magneto Resistance sensor are presented, as well as recent achievements with a SQUID-based Cryogenic Current Comparator. FAIR ACCELERATOR FACILITY Presently, the technical layout of the FAIR accelerator complex is being finalized and civil construction of the accelerator tunnel will start soon. FAIR consists of the fast-ramped superconducting synchrotron SIS100, the high-energy beam transport system (HEBT) interconnecting the synchrotrons with the pBar-Target for production of anti-protons, the super-fragment separator (SFRS) for the production of rare isotopes, the collector ring (CR) for stochastic pre-cooling of rare isotopes and anti-protons, and the high-energy storage ring (HESR) for internal target experiments [1]. Existing GSI accelerators serve as injectors for the FAIR machines. Primary goal of the novel facility is the production of heavy ion beams with unprecedented intensities close to the space charge limit of the synchrotron. The workhorse of FAIR will be SIS100, designed to produce up to 5 10 U ions/s with energies of 400-2700 MeV/u. Particles will be extracted either in single bunches of e.g. 30 ns as required for the production of anti-protons, or as slowly extracted beam with extraction times of several seconds for the radioactive ion beam program of FAIR. For effective usage of the accelerator chain a multiplexed machine operation is foreseen which will allow to provide beams to up to four different physics experiments inside one machine super-cycle. Especially the planned high-intensity operation calls for a reliable online transmission control system. Beam current transformers will be the main source of intensity signals along the accelerator chain. Each section of the FAIR complex has special requirements and, ideally, beam current transformers are purpose-built instruments for each use case. REQUIREMENTS FOR BEAM CURRENT MEASUREMENT The accelerator control system of FAIR will require the measurement data of beam current transformers for various applications. Besides regular transmission monitoring, operating and archiving systems will monitor the beam currents during injection, accelerating ramp and during fast and slow extraction to calculate extraction efficiencies online. This is done e.g. to prevent recurring beam losses leading to unnecessary activation of machine components. Additionally, the planned machine protection system requests the generation of a ‘beam-presence flag’ and a ‘setup-beam flag’ from the current transformer signals. The setup-beam flag identifies beam settings that are used for preliminary test runs and accelerator commissioning, typically performed at low beam intensities. A signal threshold is monitored for beam current monitors along the related accelerator chain to verify the conditions for the setup-beam flag. The beam-presence flag on the other hand identifies machine settings that have previously been validated for high-current operation of the machine. In this state the online transmission control based on transformer signals is set to very small tolerance bands to protect the accelerator chain from potential beaminduced damages. Since many years commercial solutions for beam current transformers are available on the market. However, for special use cases, demanding e.g. for very high dynamic range of beam intensities, or the measurement with ultra-high sensitivity in the nanoampere range, purposebuilt transformers are required. TUNNELING MAGNETO RESISTANCE DC CURRENT TRANSFORMER The goal of the research project for a novel DC current transformer (DCCT) was to create an instrument that allows for precise online measurement of accelerated and stored beams with a large dynamic range of beam intensiProceedings of IBIC2016, Barcelona, Spain TUPG50 Charge Monitors and Other Instruments ISBN 978-3-95450-177-9 461 C op yr ig ht © 20 16 C C -B Y3. 0 an d by th e re sp ec tiv e au th or s ties (μA to 150 A) and bunch frequencies up to 5 MHz. Due to its design the present GSI-built DCCT shows faulty signals at beam currents of >70 mA with bunch frequencies around 1.2 MHz, which will be standard operating parameters for SIS100. The novel DCCT is based on the clamp-on amperemeter design, consisting of a split toroid, which facilitates dismounting, e.g. for vacuum bake-out. The toroid is made from amorphous VITROVAC 6025F and acts as a flux concentrator. In the present design a beam current of 1 A leads to an induction of 80 μT in both gaps of the toroid, cf. Fig. 1. Two magnetic sensors are placed inside the toroid gaps and give a direct measure of the magnetic field inside the toroid. A number of different B-field sensor types were studied for the usage inside the novel DCCT. Figure 1: Schematic layout of the novel DCCT. The DCCT development consists of three major steps. Firstly, different types of commercially available magneto-resistance (MR) sensors were tested and an amplifier PCB was developed for the most appropriate sensors. In a subsequent step the MR sensor signal was used as input for a zero flux feedback loop. MR Sensor Study and Noise Analysis For the detection of low magnetic fields two main types of MR sensors are available: Giant Magneto-Resistance (GMR) and Tunnel Magneto-Resistance (TMR) sensors. The functional structure is identical for all MR sensors and the field measurement is based on the change of the electrical resistivity of a thin film structure in the presence of an external magnetic film. In the standard layout four thin film resistors form a Wheatstone bridge. Whereas the GMR has two shielded resistors in the bridge causing unipolar output, the TMR has a bipolar output. For the application inside a novel DCCT the bipolar output is desirable because it facilitates to upgrade the device with a ‘zero-flux’ feedback loop. For a theoretical noise analysis the performance of MR sensors was evaluated using the detectivity D as optimization parameter: , where SV is the output noise power spectral density [V/ Hz] and RBV is the sensitivity of the magnetic field sensor [V/T]. The total output noise power spectral density SV is given by the summation of all uncorrelated noise contributions, i.e. thermal shot noise, flicker noise, thermal magnetic noise and magnetic flicker noise. Separate PCBs were produced for each MR sensor and noise spectra were measured inside a magnetic shield. Best results were obtained with an MMLP57FD TMR-sensor [2] with a measured detectivity of D=15.6 nT/ Hz, thus the novel DC current transformer was named tunnelling magneto resistance DCT (TDCT). Stretched Wire Tests Three different PCBs were selected for a test setup consisting of a stretched wire carrying a DC current placed in the center of the split toroid. The sensors were mounted inside the 10 mm air gaps of the split toroid and the whole setup was covered with a mu-metal box to attenuate external magnetic fields. Figure 2 depicts the measurement results for the selected MMLP57FD sensor leading to a minimum detectable DC current of 62 μA [3]. Figure 2: Stretched wire measurement with TMR-sensor MMLP57FD, note the good linear response.

A new Cryogenic Current Comparator with eXtended Dimensions (CCC-XD), compared to earlier versions built for GSI, is currently under development for a non-destructive, highly-sensitive monitoring of nA-intensities of beams for larger beamline diameters planned for the new FAIR accelerator facility at GSI. The CCC consists of a: 1) flux concentrator, 2) superconducting shield against external magnetic field and a 3) superconducting toroidal coil of niobium which is read out by a 4) Superconducting Quantum Interference Device (SQUID). The new flux concentrator (1) comprises a specially designed highly-permeable core made of nano-crystalline material, in order to assure low-noise operation with high system bandwidth of up to 200 kHz. The superconducting shielding of niobium (2) is extended in its geometric dimensions compared to the predecessor CCC and thus will suppress (better -200 dB) disturbing magnetic fields of the beamline environment more effectively. For the CCD-XD readout, new SQUID sensors (4) with sub-μm Josephson junctions are used which enable the lowest possible noiselimited current resolution in combination with a good suppression of external disturbances. The CCC-XD system, together with a new dedicated cryostat, will be ready for testing in the CRYRING at GSI in spring 2017. For the application of a CCC in the antiproton storage ring at CERN a pulse shape correction has been developed and tested in parallel. Results from electrical measurements of two components (1 and 4) of the new CCC-XD setup will be presented in this work.

Non-perturbative measurements of low-intensity charged particle beams are particularly challenging to beam diagnostics due to the low amplitude of the induced electromagnetic fields. In the low-energy antiproton decelerator (AD) and the future extra low energy antiproton rings at CERN, an absolute measurement of the beam intensity is essential to monitor the operation efficiency. Superconducting quantum interference device (SQUID) based cryogenic current comparators (CCC) have been used for measuring slow charged beams in the nA range, showing a very good current resolution. But these were unable to measure fast bunched beams, due to the slew-rate limitation of SQUID devices and presented a strong susceptibility to external perturbations. Here, we present a CCC system developed for the AD machine, which was optimised in terms of its current resolution, system stability, ability to cope with short bunched beams, and immunity to mechanical vibrations. This paper presents the monitor design and the first results from measurements with a low energy antiproton beam obtained in the AD in 2015. These are the first CCC beam current measurements ever performed in a synchrotron machine with both coasting and short bunched beams. It is shown that the system is able to stably measure the AD beam throughout the entire cycle, with a current resolution of 30 nA .

DC Current Transformers (DCCTs) are known since decades as non-intercepting standard tools for online beam current measurement in synchrotrons and storage rings. In general, the measurement principle of commonly used DCCTs is to introduce a modulating AC signal for a pair of ferromagnetic toroid. A passing DC ion beam leads to an asymmetric shift of the hysteresis curves of the toroid pair. However, a drawback for this measurement principle is found at certain revolution frequencies in ring accelerators, when interference caused by the modulating frequency and its harmonics leads to inaccurate readings by the DCCT. Recent developments of magnetic field sensors allow for new approaches towards a DCCT design without using the modulation principle. This paper shows a review of different kinds of usable magnetic sensors, their characteristics and how they could be used in novel DCCT instruments.

The FAIR facility will provide intense primary beams of protons and heavy ions, or secondary beams of antiprotons and rare isotopes. The operation includes fixed-target experiments or subsequent facilities of independent storage rings and experiment beam lines. The particle beams greatly differ in ion species, energy, intensity, time structure, spot size and stopping power. Therefore, transverse beam profile measurements require a careful choice of detector type for each location in order to cope with the large dynamic range and operational demands. This contribution presents the actual status of FAIR detector developments for intercepting devices (SEM-grids, multi-wire proportional chambers, scintillating screens) as well as non-intercepting beam induced fluorescence monitors and ionization profile monitors. Recently, promising results were obtained with an 11.4 MeV/u Uranium beam in measurements of optical transmission radiation emitted from thin metal foils. The boundaries for the application area are described and basic detector parameters are summarized. FAIR BEAM PARAMETERS The main objectives of the upcoming FAIR (Facility for Antiproton and Ion Research) accelerator complex are to provide high-intensity ion beams, to generate beams of rare isotopes, as well as the production and storage of anti-protons [1]. Because the existing GSI accelerators Unilac and SIS18 will serve as injectors for FAIR a longterm upgrade program had been initiated including an extensive upgrade of beam diagnostic devices for the requirements of high-intensity operation. The foreseen FAIR standard operation modes require e.g. that Unilac routinely injects 510 U in a 150 μs macropulse into SIS18 as a booster synchrotron. From SIS18 the beam will be injected into the fast ramped superconducting heavy-ion synchrotron SIS100, the main accelerator of the future FAIR complex. SIS100 will deliver high-energy high-intensity protonand heavy ion beams near the space charge limit. The requirements for the experiments with radioactive ion beams include acceleration of up to 410 U ions/s to end energies of 400-2700 MeV/u, either in single bunches of 30-90 ns, or as slowly extracted beam with extraction times of several seconds. For the production of anti-protons 2.510 protons per pulse will be accelerated to 29 GeV with a repetition rate of 0.1 Hz and an output bunch length of 50 ns. It is clear that the large variety of beam parameters along the FAIR accelerator chain requests for well-matched diagnostic devices. Moreover, the high-energy beam transport lines (HEBT) have to be designed for the transport of ion beams with a large range of parameters. Because of the multiplexed experiment operation, the beams principally might differ on a pulse-by-pulse manner in ion species, energy, intensity, time structure and transverse beam width. The interconnection of the existing SIS18 to SIS100 has a magnetic rigidity of 18 Tm and will transport slowly and fast extracted beams in the intensity range 110310 particles per pulse. Beams to and from the storage rings will be transported by 13 Tm and 100 Tm beam lines, but also here a large range of beam intensities of 10-10 particles per pulse is planned. Additionally, the aperture has a range of 100-150 mm, which sets up additional requirements with regard to the mechanical layout of beam profile monitors. INSTRUMENTATION FOR BEAM PROFILING For the broad range of parameters adequate instruments for beam profile detection have been developed at GSI in the past years. Devices are divided into intercepting instruments, like SEM-grid, multi-wire proportional chamber (MWPC) or scintillating screens (SCR), that are specifically used for beam optimization procedures and non-intercepting devices, like beam induced fluorescence monitors (BIF) or ionization profile monitors (IPM) that allow for online profile measurements. Table 1: Typical Parameters during Test Measurements for Development of FAIR Instrumentation Device Ion Energy [MeV/u] Detection Threshold [Part./Pulse] Spatial Resol. [mm] SEMGrid U 11.4 510 <1

Online monitoring of low intensity (below 1 μA) charged particle beams without disturbing the beam and its environment is crucial for any accelerator facility. For the upcoming FAIR project a beam monitor based on the Cryogenic Current Comparator principle with an enhanced resolution was developed. The main focus of research was on the low temperature properties of the ferromagnetic core material of the superconducting pickup coil. The pick-up coil transforms the magnetic field of the beam into a current that is detected by a high performance low temperature dc Superconducting QUantum Interference Device (LTS-DC-SQUID). The penetration of the pick-up coil by interfering magnetic fields is highly attenuated by a meander shaped superconducting shielding. The Cryogenic Current Comparator is able to measure DC beam currents, e.g. as required for slow extraction from a synchrotron, as well as bunched beams. In this contribution we present first results of the improved Cryogenic Current Comparator working up to now in a laboratory environment.

To cope with the demands of FAIR for UNILAC highcurrent operation, non-intercepting beam diagnostics is mandatory. A new diagnostic for transverse beam profile measurements, the Beam Induced Fluorescence monitor (BIF) was developed. After the first BIF installation in 2008 (Unilac section US1), three new monitors were installed (Unilac section UA4 and transfer-line sections TK2 and TK6) and several upgrades were performed to make the monitors more reliable and easier to use for the upcomming handover to operation. For FAIR several BIF monitors are destined for p-Linac, HEBT and SFRS and it is foreseen to realize all slow controls by Siemens SPS and FESA-based software.

Since 15 years the MAPS has been an indispensable tool for daily operation of the UNILAC, to visualize t he actual beam current of the UNILAC macropulses at given locations being measured by 45 beam current transformers (BCTs). It also shows an overlay of the beam cur rent signal with each related gate pulse, to allow for checks and adjustments of the integration timing. Additionally, synchronous information about the gated-average beam current as measured by the selected transformers along the beam path is displayed, thus an online display of 2 BCTs and the related ion transmission can be observed.