Superconducting Quadrupoles inside the HERA Experiments M. Bieler, DESY, LHC LUMI 05 Workshop, Arcidosso, September The HERA Interaction Region - The ZEUS Detector - The Quadrupoles

The HERA Interaction Region 920 GeV Protons 27.5 GeV Electrons

ZEUS Detektor p e Vorwärts-Kalorimeter Rückwärts-Kalorimeter Zentrales-Kalorimeter Solenoid Magnet Zentrale Driftkammer CTD Mikrovertex-Detektor

GG

GO

As part of the HERA luminosity upgrade, 6 superconducting Interaction Region quadrupoles were delivered, accepted, and are in service. These 6 layer magnets were designed to include the main quadrupole focus, a skew quad, a normal and skew dipole, and a final sextupole layer. Because of the physical space constraints imposed by the existing detector region components, the DESY magnets were of necessity designed to be very compact. In addition, they are also are required to operate within the solenoidal detector fields at the collision points, so all construction materials had to be non magnetic. Two types of DESY magnets were fabricated. The first, designated as G0, was a two meter long, constant radius magnet. The second, designated GG, is a one meter long, tapered tube, with a continuously increasing field strength from the lead end towards the collision point. From Design Parameters

Magnet Parameters GO Magnets GG Magnets I(A)Field(T)GradientL eff I(A)Field(T)GradientL eff Circuit at 31mm (m) at 45mm (m) Quad T/m T/m1.33 hor. Dipole Skew Quad T/m T/m1.04 vert. Dipole Sextupole T/m T/m

The GG Magnet

The GO Magnet 3.7m 17cm75cm

The GO Magnet

Cross Section of the GO Magnet 4K He Return 40K He 3mm Beam Pipe 5mm Coil Support Tube (102mm ID) Coil Layers 3mm He containment (144mm OD) Slotted G-10 Spacer Stainless Support Key 60mm 90mm 39mm 39mm for magnet and cryostat

Magnet Production at BNL - 11 axis wiring machine - 6 layers - Ultrasonic wire bonding - Pattern modulation to correct for field errors in lower layers - 5 circuits

Radial Magnet Design Kapton Insulation Coils in Substrat S-Glas Kompression LHe at 4K Ca. 2mm Quadrupole Dipole Sextupole Skew Quad Coil Support Tube (5 mm) Outer Helium Tube (3 mm) Coils ca. 11 mm GO:

„6 around 1“ Cable 51  m Filament:8  m Cu/NbTi: 1.8:1

The ‘End Can’

Cryogenics Heat load at 4KHeat load at 40K Magnet(Watt) H1, GO28117 H1, GG29108 ZEUS, GO50104 ZEUS, GG31146 Measured static heat loads for the magnets and transfer lines (dynamic heat load: 6 – 15 W/m). The magnet coils are cooled with supercritical single phase helium between 4K and 4.4K whereas the beam pipe is cooled between 40K and 80K.

Problems with GG and GO Water: The temperature of the outer magnet surface was so low, that water was condensing on the magnet, dripping down into the detector. Solution: Armaflex for thermal insulation, plastic bag to collect the water. Magnet position: Inner tip of the magnet supported by steel cables or hydraulic movers. Exact position of the tip can not be surveyed. Magnetic forces between the magnet and the experiment’s solenoid move the magnet by 1 mm during the energy ramp. Solution: Electron orbit feedback system. Cryogenics: Pressure drop in the magnets 3 times higher than expected. Solution: Additional circulation pumps.

References Brück et al, Operational Experience with the new Superconducting luminosity upgrade magnets at HERA, ICEC 19, Grenoble, France, 2002