Karlheinz Schindl

Shaping of Proton Distribution for Raising the Space-Charge of the CERN PS Booster

The intensity of the PS Booster is limited by space-charge defocusing forces which create a spread in the betatron tunes of up to ΔQ ≃ 0.5. Shaping of the transverse and longitudinal distributions was used for accommodating more particles in a given working area and enabled the Booster to accelerate 2 × 1013 protons per pulse, twice the design intensity. Modifying the RF potential well by an experimental second-harmonic cavity yields beam intensities and densities well beyond the present performance. The corresponding PSB experiments and improvements are described and an outlook on future developments is given.

Conversion of the PS complex as LHC proton pre-injector

CERNs Large Hadron Collider (LHC) will be supplied with protons from the injector chain Linac2-PS Booster (PSB)-PS-SPS. The required transverse beam brilliance (intensity/emittance) is almost twice that of current PS beams and the LHC bunch spacing of 25 ns must be impressed on the beam before its transfer to the SPS. The scheme involves new RF harmonics in the PSB and the PS, an increase of the PSB energy, and two-batch filling of the PS. After a successful test of the main ingredients, a project for converting the PS complex was launched in 1994. Major additions are: (i) h=1 RF systems in the PSB, (ii) upgrading of the PSB main magnet supply from 1 to 1.4 GeV operation, (iii) new magnets, septa, power supplies, kicker pulsers for the PSB-PS beam transfer, (iv) 40 and 80 MHz systems in the PS, (v) beam profile measurement devices with improved resolution. A significant part of the effort is being provided by TRIUMF under the Canada-CERN co-operation agreement on the LHC.

The CERN PS complex as part of the LHC injector chain

The delivery of a beam with characteristics appropriate to the filling of the LHC (Large Hadron Collider) proton-proton collider requires that the CERN PS complex provide a beam whose transverse particle density exceeds, by a factor of three, the highest currently attained. The beam dynamics operations and the associated hardware modifications which would be required to achieve this goal are considered. The approach favored involves filling the Proton Synchrotron (PS) with two pulses from the Proton Synchrotron Booster (PSB) and requires and RF quadrupole (RFQ2) as a preinjector for the linac (LINAC2), an increase of the PSB extraction energy and additional RF systems, both in the PSB and PS.<<ETX>>

Beam Dynamics Experiments in the PS Booster

The main problems encountered on the way to 1013 ppp have been emittance blow-up and coherent instabilities. The observations and counter measures are described in the text.

A Method for Increasing the Multiturn Injection Efficiency in AG Proton Synchrotrons by Means of Skew Quadrupoles

An increase of the injection efficiency due to linear coupling [already known at the Cosmotron in 19531)] is shown to work in AG Proton Synchrotrons for QH - QV = P. The system is in operational use at the CERN Proton Synchrotron Booster (PSB) to reach intensities above 1013 ppp. An intensity increase of 20% is achieved at the expense of a slight vertical blow-up, which is however not noticeable for high-intensity beams as their emittance is already increased because of an integer stop-band. In this paper a comprehensive model is presented, which describes the efficiency as a function of several parameters, such as the coupling strength, injection geometry and Q-values. Provided enough vertical acceptance is available, the same scheme may be profitable for other accelerators using betatron stacking for |QH - QV - P| < 0.1; ¿H >> ¿V.

Upgrading the CERN PS booster to 1 GeV for improved antiproton production

For efficient antiproton production, a maximum number of protons must be concentrated within one quarter of the CERN Proton Synchrotron (PS) ring before sending the beam to the production target. With the Antiproton Collector (AC) added to the Antiproton Accumulator (AA), the bunch length has to be shorter (by about 20 ns) than before to allow bunch rotation in the AC. While a more ambitious scheme providing such a beam is being implemented, a funneling method, in which beams of two rings of the four-ring Proton Synchrotron Booster (PSB) are recombined in pairs by an RF dipole that permits longitudinal interleaving of successive bunches, has been in operation since the start-up of the AC. Preliminary experiments had shown that the PS space-charge limit had to be overcome in order to make the scheme feasible. After raising the PSB output energy from 815 MeV to 1 GeV, beams of >10/sup 13/ protons compressed into one quarter of the PS ring were achieved. Related to this development, a record proton beam for fixed-target physics was accelerated in the Super Proton Synchrotron, while beam losses in the Proton Synchrotron Booster-Proton Synchrotron Ring (PSB-PS) line were reduced.<<ETX>>

Simultaneous Dynamic Compensation of Stopbands and Multipurpose Location of Correction Lenses in the CERN PS Booster

Three 3rd order stopbands, amongst them the structural 3Qv = 16 (= number of lattice periods), are compensated simultaneously for the first 100 msec of the acceleration cycle. The location of the correction multipoles was optimized for all relevant resonance harmonics. The ultimate QH-QV working area still being uncertain, all stopbands up to order four as well as 3rd order crossing point were considered when choosing the locations of the new sextupoles and octupoles, eight per type and ring. A solution providing ideal locations for pairs of lenses applying to almost all harmonics was found. Experiments dealing with compensation of 3QV = 16 are described. With simultaneous dynamic correction of 2QH + QV = 14, QH + 2QV 15 and 3QV = 16, high intensity beams of a transverse density hitherto unknown in the PS Booster were obtained.

Emittance preservation in the PS complex

As the LHC injectors have to provide bright beams, all the potential sources of emittance blow-up must be eliminated. One such source arises from the mismatch of the betatron focusing at the interface of a transfer line with a circular machine. Measurements and corrections of this effect have been performed in the line downstream of the linac where space charge plays an important role and between the booster and the PS ring where four beams are recombined and have to be matched simultaneously.

Acceleration of lead ions in the CERN PS Booster and the CERN PS

The new CERN Heavy-Ion Accelerating Facility implies besides a new linac also important modifications of existing accelerators. They are imposed by the low speed and the low intensity of the ion beam and, crucially at low energy, by the short lifetime of the partially stripped ions due to charge exchange with the atoms of the residual gas. Once the optimum charge state (Pb/sup 53+/) and energy of the injector (4.2 MeV/u) had been chosen, the operational pulse-to-pulse variability (PPM) of particle species and intensities in the PS and its four-ring Booster (PSB) dictate the main beam parameters.

R.F. Beam Recombination ("Funnelling") at the CERN PSB by Means of an 8 MHz Dipole Magnet

For filling the Antiproton Accumulator ring, the beam in the PS must be concentrated within one quarter of its circumference. A first step is to inject as much beam as possible into two groups of five PS buckets each occupying one quarter of its periphery. For this purpose, beams from the 4-ring injector synchrotron (PSB) are recombined in pairs by means of an RF dipole magnet which permits longitudinal interleaving of successive bunches. Each PSB bunch being slightly under 180° in length, two of them can fit into a (stationary) PS bucket. It is shown that the use of a sinusoidal deflecting field instead of the ideal square wave results in only a modest growth of the transverse emittance of the recombined beams. The increase of longitudinal emittance by a factor of ~ 3, inherent to the scheme is also acceptable for the PS machine. We discuss the beam dynamics aspects, the construction of the 8 MHz, 250 gauss meter deflecting magnet and the experimental results.