Design Principals for ILC- Positron Targets Peter Sievers-CERN-ESS POSIPOL 2013,Argonne P.Sievers/POSIPOL131

1.Introduction Review of Pendulum, Rotating Wheel and Trolling Targets for the Hybrid System (Crystal + Target, 10 kW, Ref: PHD-Thesis of Chenghai XU, IHEP-Beijing) and the Truely Conventional System (35 kW, Ref: Omori….). Still: 5 Hz, each Burst contains 13 Bunches, each Bunch with a duration of 0.6 μs and separated by 3.3 ms. Deposited Average Power: 10 kW and 35 kW (tbc) for Hybrid and Conventional Targets, respectively. Thermal shock for both. For Polarized Positrons: 1 m diameter, fast rotating Ti- Wheel, 4.5 kW, beam at 5 Hz, 1 ms Pulses, no thermal shock. P.Sievers/POSIPOL132

2.Pendulum, Wheel and Trolling Targets for the Hybrid and truely conventional Systems. As reported at POSIPOL 2011/12, for the hybrid system, the heat of 10 kW can be removed from a pendulum with a target width of 13 cm or, more comfortably, from a wheel with a diameter of cm, both cooled either by water or He. For larger powers (35 kW) for the truely conv. target the width of the pendulum will have to be enlarged (Study under way by Omori-San et al.) P.Sievers/POSIPOL133

The Pendulum P.Sievers/POSIPOL134

One Example of a Trolling Target Try to minimize the pivot of the bellows: P.Sievers/POSIPOL135

Comparison of Pendulum and Trolling Target P.Sievers/POSIPOL136

Comparison of Pendulum and Trolling Target Beam at 5 Hz, pulse duration 40 ms, required velocity, to prevent pile up: 3 m/s. Pendulum and trolling target oscillate at 2.5 Hz with an amplitude of +/- 20 cm. With a lever arm of 1 m, the bellows pivot at +/- 11 degr. The movement of the pendulum has to be locked to the beam pulses. The trolling target not. The effective target width for the pendulum is 12 cm, while for the trolling target it is 119 cm! Trolling target easier to cool than pendulum at high powers. P.Sievers/POSIPOL137

Rotating Wheel Diameter 40 cm, rotating at 2.5 Hz. P.Sievers/POSIPOL138

Granular Rotating or Trolling Target P.Sievers/POSIPOL139

How to Fight Thermal Shock? W-bulk material, edge cooled by water, may brake due to shock and thermal stress. The thermal contact between the W-target and the water cooling may be lost. Subdivide the W-bulk into smaller components, like spheres. Efficient cooling. Less shock and thermal stress. But this requires containment (windows) of the target and the cooling fluid, passing between the spheres. Bulk W-target wrapped into a Graphite container, which confines the W-target, even when broken, and which itself resists to the thermal load. Such a target was used for the CERN-P-bar source. 3 mm W-rods were inserted into the center of a 30 mm diameter C-cylinder. Average power 1 kW, rep. Rate 0.5 Hz. P.Sievers/POSIPOL1310

P-BAR TARGET CERN P-BAR TARGET: W rods in graphite container P.Sievers/POSIPOL1311

Broken W, but confined by graphite. W rods are 3 mm diam. P.Sievers/POSIPOL1312

W-Rods, confined by a Graphite Jacket. W-rods of about 10 mm diameter contained in a C-jacket with a wall thickness of about 5 mm and arranged around a wheel with 40 cm diameter. Requires good timing with the beam. Requires higher velocity of about 4-5 m/s (216 rpm) and good stability of the rotation: Δv/v.(t/T)< 8 x t is time over which velocity is drifting. T is time/turn; T=0.28s P.Sievers/POSIPOL1313

P.Sievers/POSIPOL1314 BulkRods

3.Fast Rotating Wheel for Polarized Positrons 4.5 kW, 5 Hz, 1 ms pulse duration: small shocks! To spread the energy deposition from the γ- beam over 10 cm, needs a velocity of 100 m/s. With a diameter of the wheel of 1 m, it rotates at 32 Hz, about 2000 rpm. Principal lay out: see previous sketches. Needs good mechanical support, no vibration. Bearings outside the vacuum, one or two rotating seals. P.Sievers/POSIPOL1315

Forces Centrifugal acceleration b with R=0.5m, ω=200 s -1 : b= 20,000 m/s^2. When a mass of 1 g is missing, e.g. a bubble in the water, this disequilibrates the wheel with a radial force of 20 N, i.e. 2 kg! The wheel has to be very well equilibrated! Centrifugal force tries to « explode » the rim of the wheel radially. This creates a circumferential stress in the rim, if not retained by spokes: σ = ρ x v^2 = 45 MPa in Ti. Traction in the spokes not negligible. Static radial pressure in the cooling water due to centrifugal force along the spokes. At the rim of the wheel: 5 MPa, 50 bars! Coriolis force: the cooling water is flowing radially through the spokes: with a water velocity of about 6 m/s. This creates a circumferential acceleration on the water of 2,400 m/s^2, about 12% of the centrifugal acceleration. P.Sievers/POSIPOL1316

Radiation Cooled, Fast Wheel To evacuate 4.5 kW from the rim of the wheel, its surface has to be increased! With a radiating surface of the rim of about 6000 cm^2, an emissivity of 0.8 of both sides and T(1) = 670 K (370 oC) and T(2) = 300 K (20 oC): Evacuated power 4.58 kW. The rim of the wheel must resist at such temperatures T(1) to the centrifugal forces! No cooling fluid inside the vacuum. Opens option: No rotating seal! But bearings and motor rotator inside the vacuum. Magnetic bearings and drives have been developed by FZJ-Juelich for fast rotating choppers for neutron beams inside vacuum. A slow, radiation cooled Graphite wheel is in operation in a d.c.- beam at PSI: Ø=0.45 m; 1 turn/s; power 50 kW; operating temperature 1700 K. P.Sievers/POSIPOL1317

Radiation Cooled Wheel P.Sievers/POSIPOL1318

Radiation Cooled Hanging Wheel P.Sievers/POSIPOL1319

Non Contact Labyrinth Rotating Seal Such rotating seals serve to transmit cooling fluids into rotating wheels, with air around it. Have or can they be used for sealing vacuum against air? P.Sievers/POSIPOL1320

Magnetic Forces and Heating of the Wheels, induced by the Flux Concentrator Studies have been made previously. It is a rather complex issue. In the t.c. and hybrid wheel, eddy currents are induced mainly by the short magnetic pulses of 1-2 μs, and not much by the rotation (3 m/s). Using small spheres is equivalent to laminating, it helps. Eddy currents in the Be-windows? In the high resistive, fast Ti-wheel, eddy currents are mainly due to the high velocity (100 m/s), and less due to the long pulse of 1 ms. Laminating the Ti with sheets of about 1 mm thickness could help. P.Sievers/POSIPOL1321

4. Conclusion For all systems (tr. conv., hybrid and polarized positrons) need moving targets. For the tr. c. and hybrid systems, velocities of the targets of 2-3 m/s are required to avoid pile up of the heating by individual bunches (0.6 μs duration and separated by 3.3 ms). Thermal shock is a common problem for tr. c. and hybrid targets. Water cooled W-bulk material may crack and cooling will fail. W-rods, packed into a C-container, may crack, but are kept in place. Water cooling could be possible. Granular targets will survive better the shocks, but they need He as a cooling fluid with containing windows. P.Sievers/POSIPOL1322

Truely Conv. and Hybrid Targets To evacuate the average power and to provide sufficient cooling surface, target widths of well above 0.1 m and up to about 1 m should be envisaged. For pendulum and trolling targets, no rotating seals: Requires bellows, pivoting through an angle of +/ degrees at 1-3 Hz. Organic bellows, protected by shielding. Better lifetime? Make them easily replacable! Rotating wheel: comfortable target width of about 1 m (diameter 0.4 m) and rotating at 2.5 Hz. Organic rotating seals, protected by shielding. P.Sievers/POSIPOL1323

Target for Polarized Positrons Fast rotating 1 m wheel for polarized positrons: requires good engineering to maintain a force- free rotation. Ferro-fluid seals not trivial and under investigation. No-contact labyrinth seal may be an option? Water cooling has to designed carefully. Cooling of the wheel by radiation: no rotating seal! But needs rotating (magnetic) bearings and magnetic drive motor, to run in vacuum! P.Sievers/POSIPOL1324

Future R + D Find expertise in Industry: Turbines for jet-planes. Cryo-technology. Space-technology. Formula-1 racing cars. Get waepons industry interested in ILC instead of war. Get the FUNDING! P.Sievers/POSIPOL1325

THANK YOU FOR YOUR ATTENTION P.Sievers/POSIPOL1326