1 PS Days - Evian / MV The SPL : a High-Power Superconducting H – Linac at CERN  Motivations  Applications  Design features  Improvements  Conclusions M. Vretenar for the SPL Study Group: B. Autin, K. Bongardt, R. Cappi, F. Caspers, E. Chiaveri, R. Garoby, F. Gerigk, H. Haseroth, C. Hill, A. Krusche, D. Kuchler, M. Lindroos, A. Lombardi, R. Losito, M. Poehler, H. Ravn, M. Sanmarti, H. Schönauer, M. Silari, J. Tückmantel, M. Vretenar SPL SPL = Superconducting Proton Linac

2 PS Days - Evian / MV The SPL - Motivations   to improve the quantity and quality of the proton beams provided by the PS Complex  advantages for the LHC  production of intense secondary beams for the Neutrino Factory and other users   to modernise the injectors with standard equipment   to use the LEP Superconducting RF system The LEP SC-RF system: 288 SC cavities in 72 cryostats (812 meters!), 44 klystrons

3 PS Days - Evian / MV The SPL - Applications  High-brightness injector for the PS (factor 3 in beam brightness, higher intensity for all users)  Proton driver for a Neutrino Factory (with accumulator / compressor rings in the ISR, 4 MW beam power)  Driver for a second generation radioactive beam facility (SuperISOLDE)

4 PS Days - Evian / MV The SPL - Main parameters (1) All details in the SPL Yellow Report (Conceptual Design of the SPL) CERN m

5 PS Days - Evian / MV Main parameters (2) 2.2 GeV:  LEP cavities (  =1) are efficient for W>1GeV  Reduced space charge tune shift in the PS for injection energies > 1.4 GeV (present PSB)  Efficient pion production for the Neutrino Factory for W > 2 GeV 75 Hz : for intense beams, a high rep. rate reduces charge per pulse (possible only with linacs!), limit given by power efficiency LEP cavities TTF 11 mA : optimum distribution of klystrons, same current as LEP2

6 PS Days - Evian / MV The SPL - Main Design Features H- source, 25 mA 16.5% duty Fast chopper (2ns) Cell-Coupled DTL, 352 MHz new SC cavities at  =0.52, 0.7, 0.8 RF system: all at 352 MHz, combination of tetrodes and LEP klystrons Careful beam dynamics design, large apertures to avoid halo formation and beam losses (50M particles + mismatch  OK)

7 PS Days - Evian / MV The Chopper accumulator bucket  Travelling wave electrostatic deflector, meander line to match beam and wave velocity  Used to create gaps in the linac bunch distribution between accumulator buckets  Needs very short rise/fall times (2 ns !) to avoid partially deflected bunches  Development of pulser

8 PS Days - Evian / MV The Drift Tube Linac  MeV: “classic” Alvarez linac  MeV: Cell Coupled DTL concept The quadrupoles are taken out of the drift tubes Short (2-gaps) DTL cavities are connected by off- axis coupling cavities. Advantages of the CCDTL:  Higher shunt impedance (less power)  Simple access and alignment for the quadrupoles  Relaxed mechanical tolerancies (lower cost)  One klystron per string of cavities  FODO focusing is maintained

9 PS Days - Evian / MV The Superconducting Linac To standardise construction, * 3 families of cavities optimised for different betas * cavities are grouped in cryostats *  =0.8 cavities in LEP cryostats

10 PS Days - Evian / MV The SC cavities for  < 1 The  =0.7 4-cell prototype  CERN technique of Nb/Cu sputtering for  =0.7,  =0.8 cavities (352 MHz): excellent thermal and mechanical stability (very important for pulsed systems) lower material cost, large apertures, released tolerances, 4.5  K operation with Q = 10 9  Bulk Nb or mixed technique for  =0.52 (one 100 kW tetrode per cavity)

11 PS Days - Evian / MV Pulsing of the SC cavities  The LEP RF is CW, pulsing (75 Hz, 2.2 ms) a SC system is an additional complication. Problems: low power efficiency due to long cavity filling times high sensitivity to vibrations: “small” mechanical vibrations (external, or Lorentz force) large detuning (high Q!) large V and  errors solutions (under study): appropriate feedback loops, reduce number of cavities per RF unit, debunching to minimise  W at ring injection.

12 PS Days - Evian / MV SPL Design - Beam Dynamics Goal: beam loss below 1 W/m to avoid activation of components (0.5 2 GeV) Beam size evolution in the SC linac (aperture  200 mm) matched case strongly mismatched case 100% rms 100%  Careful beam dynamics design to avoid halo formation:  minimise effects of mismatched beam  eliminate sources of mismatch  simulations with 50M particles (1/6 of bunch !)  Conclusion: no loss or halo seen in the simulations

13 PS Days - Evian / MV Layout on the CERN site Linac + klystron gallery parallel to the fence of Meyrin site (Route Gregory)  Economic trench excavation  Geological advantages (tunnel on“molasse”, no underground water)  Minimum impact on the environment (empty field)  Simple connection to PS & ISR via existing tunnels  Use some of the old ISR infrastructure (electricity, cooling)

14 PS Days - Evian / MV SPL Layout - Tunnels * “Cut and cover” technique * >8 meters of earth for shielding * tunnel on the molasse * linac slope 1.4%

15 PS Days - Evian / MV SPL Layout - connections to PS, ISR * 2 bunching/debunching sections and 230m drift to increase beam length to 180 ps and to reduce energy jitter coming from SC cavity vibrations * only 100m of line before connecting to the existing tunnel network * easy connection to ISOLDE (old and new)

16 PS Days - Evian / MV Improvements to the present design with respect to the present reference design (Yellow Report), some points can be improved, with the aim of: - reducing the power consumption (40 MW for 4 MW beam power, i.e. 10% conversion efficiency) - reducing the cost of the machine DESIGN IMPROVEMENTS  New design with repetition frequency down to 50 Hz, increased current and/or pulse length  Re-optimised layout of SC section  Dare to reduce the apertures to reduce cost of the machine ?  Design a room-temperature alternative structure for the expensive  =0.52 SC section HARDWARE TEST IN 2001  Test of LEP klystrons in pulsed mode  Test of SC cavities in pulsed mode  Construction and tests of a chopper pulser prototype  High Power test of a CW DTL model, collaboration with CEA/Saclay

17 PS Days - Evian / MV Conclusions  43% of the cavities, 60% of the cryostats and all the klystrons of LEP can be used for a 2.2 GeV pulsed H – Linac.  A 2.2 GeV, 4 MW beam power linac at CERN would allow the PS to produce beams of high intensity and quality, and makes possible the production of muons for a Neutrino Factory and of other secondary beams.  The design of the linac has been outlined  This machine fits nicely on the CERN site

18 PS Days - Evian / MV