To improve the performance of the Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI), an upgrade is ongoing (referred to as SLS 2.0), 2021-2025, that includes the complete renewal of the storage ring, providing about 40 times lower emittance in user operation mode and therefore an enhanced brightness. SLS 2.0 imposes very strict requirements in terms of field quality and magnetic alignment on more than 1000 magnets, which are being produced and magnetically qualified. For the first time a light source will operate with a combination of three types of magnets: i) NdFeB based permanent magnets; ii) Electro-magnets; iii) 5-T Nb-Ti superconducting longitudinal gradient dipoles (installed in the second phase of the machine upgrade). This article provides an overview of the project's progress with respect to the design and production aspects of the magnets, the assembly and measurement strategy, and the challenges associated with series magnetic tests requiring 10 -3 relative accuracy level.

Following the spectacular success of the third-generation light source over the past decades, a few new-generation light sources based on the multibend achromat (MBA) scheme have come into operation. Other such facilities are also under construction while existing ones are being upgraded. Likewise, the Swiss Light Source, which has been in operation for more than 20 years at the Paul Scherrer Institute, is to be upgraded with the present storage ring being replaced by an MBA low-emittance ring. A natural emittance of 158 pm at a beam energy of 2.7 GeV is achieved for a storage ring of comparatively short circumference, 288 m, providing a gross straight section of 83.6 m. The objectives of the upgrade were met under tight constraints by the application of two novel concepts: the introduction of both a longitudinal gradient and a reverse bend into the unit cell and pushing the superperiodicity to the number of arcs, effectively with ``pseudosymmetry.'' A detailed account of the MBA design and its expected performance is presented and the experience gained is highlighted with the aim to facilitate next-generation light source lattice design.

Lu-Ping Zhou,1, 2, 3, 4, ∗ Xiao-Jie Ni,4 Zaher Salman,4 Andreas Suter,4 Jing-Yu Tang,1, 2, 3 Vjeran Vrankovic,5 and Thomas Prokscha4, † 1Institute of High Energy Physics, CAS, Beijing 100049, China 2University of Chinese Academy of Sciences, CAS, Beijing 100049, China 3Spallation Neutron Source Science Center, Dongguan 523803, China 4Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland 5Paul Scherrer Institute, Division of Large Research Facilities, CH-5232 Villigen PSI, Switzerland (Dated: February 1, 2022) Abstract The μE4-LEM beamline at Paul Scherrer Institute (PSI, Switzerland) is a special muon beamline combining the hyprid type surface muon beamline μE4 with the low energy muon facility (LEM) and delivers μ+ with tunable energy up to 30 keV for low-energy muon spin rotation experiments (LEμSR). We investigate a possible upgrade scenario for the surface muon beamline μE4 by replacing the last set of quadrupole triplet with a special solenoid to obtain 1.4 times original beam intensity on the LEM muon moderator target. In order to avoid the muon beam intensity loss at the LEM spectrometer due to the stray magnetic field of the solenoid, three kinds of solenoid models have been explored and the stray field of the solenoid at the LEM facility is finally reduced to the magnitude of the geomagnetic field. A more radical design, "Super-μE4", has also been investigated for further increasing the brightness of the low energy muon beam, where we make use of the current μE4 channel and all sets of quadrupole triplets are replaced by large aperture solenoids. Together with the new slanted muon target E, at least 2.9 times the original muon beam intensity can be expected in the Super-μE4 beamline. Our work demonstrates the feasibility of upgrading surface muon beamlines by replacing quadrupole magnets with normal-conducting solenoids, resulting in higher muon rates and smaller beam spot sizes.

Institute of High Energy Physics, CAS, Yuquan Road 19B, Beijing 100049, China University of Chinese Academy of Sciences, CAS, Yuquan Road 19A, Beijing 100049, China Spallation Neutron Source Science Center, Dongguan 523803, China Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland Paul Scherrer Institute, Division of Large Research Facilities, CH-5232 Villigen PSI, Switzerland

The PROSCAN project at the Paul Scherrer Institute (PSI/Switzerland) involves a number of innovative elements in tumor treatment. Apart from the compact superconducting dedicated proton cyclotron COMET, a fast energy degrader and laminated magnets in the beam lines, including the newly conceived Gantry 2, will enable rapid energy changes of the proton beam to modulate the range of the scanning pencil beam in three dimensions over the tumor volume. The last multifunctional 90deg bending magnet of the Gantry 2 transport system is not only the largest of the three gantry bending magnets, but also the most challenging element because of its dynamical eddy current effects during ramping and the reduction of these effects with a special arrangement of laminated parts in the pole of the magnet. The design of the three Gantry 2 bending magnets and measurements of the magnet field and the dynamic behavior of the two 58deg bending magnets are presented.

At the Paul Scherrer Institute (PSI/Switzerland) a new proton gantry for cancer treatment is planned. A fast 3 dimensional scanning technique of the tumour volume is one of the medical highlights of this new gantry. The gantry will be driven by the new COMET proton cyclotron, which will deliver a cw proton beam. The energy of this beam will be adjusted by a fast degrader device. All beam line magnets should follow the energy changes of the degrader as fast as possible. Therefore the eddy current effects in the laminated bending magnets of the beam line and the gantry must be reduced by an appropriate magnet design. The paper shows measurements and numerical simulation of the dynamic behaviour of the fast switched bending magnets and design schemes for eddy current reduction in the bending magnets.