HIGH POWER CYCLOTRONS FOR THE NEUTRINO EXPERIMENTS DAEδALUS AND ISODAR

DAEδALUS (Decay At rest Experiment for δcp At a Laboratory for Underground Science) has been proposed to measure the value of the CP violating phase δ through the oscillation of low energy muon antineutrinos to electron antineutrinos. With a single large detector, three accelerators at different distances enable the oscillation to be measured with sufficient accuracy. We have proposed the multi-megawatt DAEδDALUS Superconducting Ring Cyclotron (DSRC) as the means of producing the 800 MeV 12 mA protons required, through the acceleration of H+2 ions with highly efficient stripping extraction. The system comprises an ion source, a LEBT, and an injector cyclotron which feeds into the main ring. The injector cyclotron can also be used for a separate experiment, IsoDAR (Isotropic Decay At Rest) in which low energy protons produce Li. This gives a very pure electron antineutrino source which can be used to measure, or rule out, short range oscillation to a sterile neutrino. We describe recent developments in the designs of the injector and the booster, and the prospects for the two experiments. INTRODUCTION: THE CONCEPTS The DAEδDALUS collaboration [1, 2] proposes to determine the value of the weak CP violating phase δ through measurements of the oscillation νμ → νe at different distances. Due to the size and cost of suitable neutrino detectors, this is achieved though having multiple low-energy neutrino sources. The current design has 800 MeV proton accelerators at distances of 1.5, 8 and 20 km, with powers of 1.0, 1.6 and 4.8 MW. Each accelerator operates on a 20% duty cycle. A suitable high current proton cyclotron design has been reported previously[3, 4, 5]. This paper reports on recent progress[6, 7]. CHOICE OF BEAM PARTICLE: H 2 We propose to use H+2 ions, accelerated to a total energy of 1.6 GeV (800 MeV per proton). This ion is chosen to enable extraction from the cyclotron, where the orbits are ∗R.Barlow@hud.ac. uk too close to easily accomodate a septum, using a foil to strip the electron. A second advantage over protons is the reduction in the effects of space charge, which plays a pivotal role in the injector. Large-scale particle simulations [8] show that the injector cyclotron is space charge dominated but that a 5 mA beam current can be extracted with tolerable beam losses on the septum. (By contrast, in the ring cyclotron, no space charge induced beam loss is observed during acceleration and extraction.) Space charge effects can be quantified using the generalised perveance, K = qI 2πǫ0mγβ showing that H+2 has half the effect compared to protons. The use of H+2 imposes more stringent vacuum requirements : below 10 rather than 10 torr, to reduce losses from dissociation due to gas collisions. Also the high rigidity of the high energy, high mass particle means that high field strengths are needed, requiring a superconducting magnet. Lorentz stripping should not be a problem even in these high fields, as the H+2 ion is considerably more tightly bound than the alternative H− ion (2.8 eV rather than 0.7 eV). However not all H+2 molecules produced by the ion source are in their ground state, and dissociation from an excited state requires appropriately less energy. Some states are long lived (compared to the time spent in the accelerator) and could be Lorentz stripped in the 6T magnetic field, which would produce unacceptable beam losses. We do not know what mixture of states is produced by the ion source, and we are starting an experimental programme to measure this. If there is a problem then the H+2 can be cooled by mixing with molecules of an inert neutral gas, such as Helium. This is being investigated using the ORNL facility. There is also a possibiity that when the H+2 interacts in the foil it produces H neutral hydrogen atoms, which would also result in losses. Assumng a phase acceptance of ±10◦, and a factor of 2 due to bunching in the LEBT, the source is required to deliver 50 mA of H+2 . The Versatile Ion Source (VIS), designed and built at INFN-LNS (Catania) should achieve this. It is an off-resonance 2.45 GHz microwave discharge source[9] and can produce beams with emittance of order MOPFI071 Proceedings of IPAC2013, Shanghai, China ISBN 978-3-95450-122-9 446 C o p y ri g h t c ○ 2 0 1 3 b y J A C o W — cc C re a ti v e C o m m o n s A tt ri b u ti o n 3 . 0 (C C -B Y -3 .0 ) 04 Hadron Accelerators