Abstract A design study, named $${\text {ESS}}\nu {\text {SB}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtext>ESS</mml:mtext> <mml:mi>ν</mml:mi> <mml:mtext>SB</mml:mtext> </mml:mrow> </mml:math> for European Spallation Source neutrino Super Beam, has been carried out during the years 2018–2022 of how the 5 MW proton linear accelerator of the European Spallation Source under construction in Lund, Sweden, can be used to produce the world’s most intense long-baseline neutrino beam. The high beam intensity will allow for measuring the neutrino oscillations near the second oscillation maximum at which the CP violation signal is close to three times higher than at the first maximum, where other experiments measure. This will enable CP violation discovery in the leptonic sector for a wider range of values of the CP violating phase $$\delta _{{\mathrm{CP}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>CP</mml:mi> </mml:msub> </mml:math> and, in particular, a higher precision measurement of $$\delta _{{\mathrm{CP}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>CP</mml:mi> </mml:msub> </mml:math> . The present Conceptual Design Report describes the results of the design study of the required upgrade of the ESS linac, of the accumulator ring used to compress the linac pulses from 2.86 ms to 1.2 μs, and of the target station, where the 5 MW proton beam is used to produce the intense neutrino beam. It also presents the design of the near detector, which is used to monitor the neutrino beam as well as to measure neutrino cross sections, and of the large underground far detector located 360 km from ESS, where the magnitude of the oscillation appearance of $$\nu _{e }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>ν</mml:mi> <mml:mi>e</mml:mi> </mml:msub> </mml:math> from $$\nu _{\mu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>ν</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> </mml:math> is measured. The physics performance of the $${\text {ESS}}\nu {\text {SB}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtext>ESS</mml:mtext> <mml:mi>ν</mml:mi> <mml:mtext>SB</mml:mtext> </mml:mrow> </mml:math> research facility has been evaluated demonstrating that after 10 years of data-taking, leptonic CP violation can be detected with more than 5 standard deviation significance over 70% of the range of values that the CP violation phase angle $$\delta _{{\mathrm{CP}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>CP</mml:mi> </mml:msub> </mml:math> can take and that $$\delta _{{\mathrm{CP}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>CP</mml:mi> </mml:msub> </mml:math> can be measured with a standard error less than 8° irrespective of the measured value of $$\delta _{{\mathrm{CP}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>CP</mml:mi> </mml:msub> </mml:math> . These results demonstrate the uniquely high physics performance of the proposed $${\text {ESS}}\nu {\text {SB}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtext>ESS</mml:mtext> <mml:mi>ν</mml:mi> <mml:mtext>SB</mml:mtext> </mml:mrow> </mml:math> research facility. 

/pdf/the-european-spallation-source-neutrino-super-beam-ezgfmlty.pdf

The European Spallation Source neutrino super-beam conceptual design report

Experiments comparing an internal and an external antenna H− source at the Spallation Neutron Source with and without cesium revealed key performance differences which provide insight to the source physics and will guide the development of an RF H− source at the ISIS Neutron Source. RF power sweeps were taken for each of these cases, for which the total charge, electron to H− ratio, and H− extracted per kW are all studied and plotted. At around 40 kW and typical hydrogen flow and cooling parameters, cesiated sources output 35 mA square beam pulses where uncesiated sources output 15 mA. At these settings, the beam pulse for the internal source initially overshoots, while it is flat for the external source. This observation is discussed with the difference in coupling between the antenna, the plasma, and the outlet. Sweeps of pulsed RF repetition rate and the collar temperature only affected cesiated sources, which is attributed to surface processes affecting the H− production only in the presence of cesium. Possible future experiments using a fast optical measurement and modifications to the gas flow into the external source’s plasma gun and by removal of the collar assembly in uncesiated operation are discussed.

A comparison of SNS internal and external antenna source performance with and without cesium.

High brightness, negative hydrogen ion sources are used extensively in scientific facilities operating worldwide. Negative hydrogen beams have become the preferred means of filling circular accelerators and storage rings as well as enabling efficient extraction from cyclotrons. Several well-known facilities now have considerable experience with operating a variety of sources such as RF-, filament-, magnetron- and Penning-type H- ion sources. These facilities include the US Spallation Neutron Source (SNS), Japan Proton Accelerator Research Complex (J-PARC), Rutherford Appleton Laboratory (RAL-ISIS), Los Alamos Neutron Science Center (LANSCE), Fermi National Accelerator Laboratory (FNAL), Brookhaven National Laboratory (BNL), numerous installations of D-Pace (licenced by TRIUMF) ion sources used mainly on cyclotrons and, most recently, the CERN-LINAC-1 injector. This report first summarizes the current performance of these ion sources in routine, daily operations with attention toward source service-periods and availability metrics. Sustainability issues encountered at each facility are also reported and categorized to identify areas of common concern and key issues. Recent ion source improvements to address these issues are also discussed as well as plans for meeting future facility upgrade requirements.

Negative hydrogen ion sources for particle accelerators: Sustainability issues and recent improvements in long-term operations

Ion sources produce beams used in accelerators and other applications. Both development and use of ion sources need beam diagnostics to probe the plasma processes and beam formation for optimization purposes and to produce beam parameters needed for transport tuning. These diagnostics include beam intensity measurements usually carried out with Faraday cups or inductive pickups, magnetic separation, profile measurements with scintillation screens and wires, and phase space measurements with different types of emittance scanners.

Ion beam intensity and phase space measurement techniques for ion sources.

The ISIS spallation neutron and muon facility is undergoing an upgrade to the negative hydrogen (H−) linac preinjector with the addition of a medium-energy beam transport (MEBT) line. A fast electrostatic sweep chopper is included in the MEBT and will notch the linac bunch train at the synchrotron frequency. The MEBT and chopper will increase the beam transport efficiency significantly, reducing the output H− current requirements from the ion source. As such, a long-lifetime, noncesiated, RF-driven, external-antenna H− ion source based on the successful CERN Linac4 and SNS designs is constructed, which will improve facility uptime and reliability. This paper will highlight the latest developments on the MEBT before focusing on the RF ion source. The RF ion source must deliver 35 mA of H− beam current in pulses 400 μs long at a 50 Hz repetition rate, with transverse normalized 4 rms emittances less than 1.2 π mm mrad. The beam current and emittance are within the reach of a noncesiated H− source, whereas operating at relatively high duty cycles presents challenges in terms of thermal management, which this paper will address.The ISIS spallation neutron and muon facility is undergoing an upgrade to the negative hydrogen (H−) linac preinjector with the addition of a medium-energy beam transport (MEBT) line. A fast electrostatic sweep chopper is included in the MEBT and will notch the linac bunch train at the synchrotron frequency. The MEBT and chopper will increase the beam transport efficiency significantly, reducing the output H− current requirements from the ion source. As such, a long-lifetime, noncesiated, RF-driven, external-antenna H− ion source based on the successful CERN Linac4 and SNS designs is constructed, which will improve facility uptime and reliability. This paper will highlight the latest developments on the MEBT before focusing on the RF ion source. The RF ion source must deliver 35 mA of H− beam current in pulses 400 μs long at a 50 Hz repetition rate, with transverse normalized 4 rms emittances less than 1.2 π mm mrad. The beam current and emittance are within the reach of a noncesiated H− source, whereas o...

/pdf/a-pre-injector-upgrade-for-isis-including-a-medium-energy-2nd414h01t.pdf

A pre-injector upgrade for ISIS, including a medium energy beam transport line and an RF-driven H− ion source

A project to design and construct an RF-driven long-lifetime volume production ion source producing 30 mA of H− with 50 Hz repetition rate and 1.5% duty factor at 35 keV energy for the ISIS Neutron and Muon Source has been started at Rutherford Appleton Laboratory. The development of the new ion source aims at replacing the caesiated Penning-type surface plasma ion source that has served the ISIS facility since 1980s. The design of the ion source is based on recent developments at CERN demonstrating 30 mA H− in volume mode with less than 50 kW of RF-power but at lower repetition rate of 0.8 Hz. This paper describes the physics design of the ion source and the status of the project. The magnetic field, extraction optics, RF system and preferred plasma ignition scheme are discussed in detail.

The RF H− ion source project at RAL

Linac4, the new CERN Hinjector to the Proton Synchrotron Booster, has been commissioned and has delivered a beam intensity and quality calculated to be sufficient to produce the standard beams for LHC and the high intensity beams for ISOLDE when connected. The beam current is nevertheless half of what is foreseen and the problem has been identified at the low energy end, between the extraction and the matching to the RFQ. The Linac4 test stand is being used to address this issue by testing different extraction geometries and different plasma generators. A fast method to access the current in the RFQ acceptance has been put in place. This paper reports the results of the measurements obtained so far.

/pdf/activities-at-the-linac4-test-stand-55q0ts53s6.pdf

Activities at the Linac4 Test Stand

/pdf/linac4-source-extraction-and-low-energy-beam-transport-study-1ey1nvmx90.pdf

Linac4 source extraction and low energy beam transport study

Linac4: Reliability Run Results and Source Extraction Studies

After the second LHC long shutdown, Linac4 will become the new injector for proton beams to CERN’s chain of accelerators. It has been commissioned at a maximum beam current of 25 mA, below the initial specification of 40 mA. At present, the beam current delivered by the linac is limited by the pre-injector. Previous investigations have found that this is due to the emittance of the H− beam extracted from the ion source exceeding the acceptance of the RFQ. Detailed measurements of the beam parameters provided by the ion source at a dedicated test stand confirmed these earlier findings. By extending and adjusting the simulation model implemented using IBsimu, an agreement to the measured emittance values was obtained. An analysis of the simulation results shows that the larger-than-expected emittance is a result of aberration at the extraction electrodes. These are due to a plasma meniscus significantly more convex than predicted by the earlier simulation. Three modifications to the extraction gap were proposed to achieve a shift of the plasma meniscus back towards a more concave position. Two of the changes—a shorter extraction gap and a larger bore diameter—result in significant decreases of the emittance as confirmed by experiments.

/pdf/beam-characterization-of-linac-4-s-iso3-3j7wc0w4bg.pdf

Beam Characterization of Linac 4's ISO3

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