Storage Ring PETRA Research Articles

Long term experience on the superconducting magnet system for the CELLO detector

A large superconducting magnet system has been installed and is currently operated at the PETRA storage ring (Desy/Hamburg) for the CELLO detector. This system has been carried out as a joint collaboration of CEN/, Saclay and ITP/Karlsruhe and includes as main components a large thin wall solenoid cooled by force flow in a pipe bonded to the winding, two bath-cooled compensating solenoids, a 450 W liquifier-refrigerator unit and all connecting lines and appropriate control equipment designed for long-term automatic operation. The system has been in operation for nearly two years with continuous runs exceeding three months and has provided considerable technical experience.

Two-photon excitation of the tensor mesonf 0(1270)

We have measured charged particle pair production in two-photon scattering at thee + e − storage ring PETRA. While the main source of such events is the production of lepton pairs, the presence of an additional process is clearly indicated by the measured invariant mass distribution of the two particles and their angular distributions. We determine that the excess is mainly due to the decayf 0(1270)→π+π-. We derive a width Γ(f 0→γγ)=3.2±0.2±0.6 keV (statistical and systematic).

New synchrotron lab in Hamburg

The electron synchrotron and the e+e− storage ring DORIS at the German Electron‐Synchrotron laboratory DESY, in Hamburg, have been providing experimenters with synchrotron radiation beams for more than a decade. With the increased demand for synchrotron radiation sources in recent years, and the transfer of high‐energy‐physics concentration at DESY from DORIS to the new, more energetic e+e− storage ring PETRA, it was decided at the end of 1977 to expand considerably the synchrotron radiation capabilities of DORIS. The recent ceremonial dedication of the new Hasylab marked the realization of this decision.

The TASSO gas and aerogel Cherenkov counters

We describe the gas and erogel threshold Cherenkov counters built for the TASSO experiment at the DESY e +e − storage ring PETRA. The counters are arranged in two diametrically opposed groups as part of the two hadron arms. The gas counters contain Freon 114 and CO 2 respectively; 128 ellipsoidal mirrors focus the Cherenkov light through funnels onto Philips 5″ photomultipliers coated with wavelength shifter. β = 1 charged particles are detected with at least 99.9% efficiency. The aerogel counters are of the diffusing wall type. They have a sensitive area of 12 m 2, divided into 32 cells and use a total of 192 RCA Quantacon 5″ photomultipliers. The average aerogel refractive index is around 1.025. The efficiency for β = 1 charged particles is 98%. Design considerations, prototype evaluation, construction details, and performance of the final counter system are described.

Fast Beamprofile Measurement

The paper deals with a set-up utilizing synchrotron light which allows a fast measurement of beam width and beam height. The most important component of this device is a combination of an image-converter tube with an electron multiplying dynode system. The scan velocity is between .1 and .3 mm/μs and could be made even faster. This makes possible the measurements of acceptance, beam emittance, dynamical change of beam position and change of transverse beam dimensions during an accelarating cycle in an electron synchrotron. The device has also been used to measure fast cross section changes in the PETRA storage ring.

A New Generation of High Power CW-Klystrons for Accelerator and Storage Ring Application, Practical Experience and Aspects for Future Developments

In the PETRA storage ring of the DESY laboratory at Hamburg, a new generation of 600 kW, 60 % efficiency, modulating anode equipped cw high power 500 MHz klystrons has successfully passed its first two-year period of routine operation. Based on this experience, a development program is under way at Valvo Hamburg trying to push the state of the art to the 1 MW cw 70 % efficiency level. In addition to 500 MHz, the program includes klystrons with other frequencies in the 300 to 1000 MHz range.

High Voltage DC Power Supplies for RF-Klystron-Transmitters in Accelerators and Storage-Rings

For klystrons operating in high duty-cycle or cw-modes, the power supplies must meet specific requirements beyond ordinary power supply characteristics. Typical klystron beam voltages range between 40 and 80 kV. Capacitor banks are necessary to avoid rf-phase fluctuations related to beam voltage fluctuations. Hence the stored energies are very high, typically around 20000 Joules. In case of arcing the klystrons can withstand only energies of up to approx. 20 Joules. Therefore crow bar systems are of vital interest in klystron transmitter power supplies. This paper describes design of the PETRA storage ring klystron power supplies and the operational experience.

Reduction of the Horizontal Antidamping in the Desy Electron Synchrotron

In the DESY electron synchrotron the horizontal betatron oscillations are antidamped because of the isomagnetic combined-function lattice. Since the main task of the synchrotron is to supply electrons and positrons at the highest possible injection energy for the storage ring PETRA, a reduction of the horizontal antidamping would be very advantageous for the following reasons: - smaller horizontal beam emittance improves injection efficiency in PETRA - injection energy for PETRA could be 8 GeV instead of 7 GeV - the repetition rate of presently 50 Hz could be reduced to 12.5 Hz without affecting the accumulation rate in PETRA. This would have further advantages for the operation of the synchrotron. Using the existing backleg windings of the magnets, the antidamping can be reduced as measurements show. Adding quadrupoles to the synchrotron magnet lattice would allow to introduce horizontal damping. The variation of the horizontal beam size during acceleration is shown.

Behaviour of large cylindrical drift chambers in a superconducting solenoid

We describe the construction and behaviour of a set of cylindrical drift chambers operating inside a superconducting solenoid with a central magnetic field of 1.3 T. The chambers are part of the 4 π detector CELLO at the e +e − storage ring PETRA in Hamburg. The chambers were designed without field shaping to keep them as simple as possible. In order to parametrize accurately the nonlinear space-time relation, we used a computer simulation of the drift process in inhomogenous electric and magnetic fields. With such a parametrization we achieved a resolution of 210 μm, averaged over the whole drift cell and angles of incidence up to 30°.

First results from PETRA provide new aspects of the basic structure of matter

First experimental results from the new large positron-electron storage ring PETRA have been obtained during the first half of 1979. To describe these results a short summary of the present understanding of the basic structure of matter is given. The most recent results are compatible with the existence of gluons, the field quanta of the nuclear force. The possible existence of a quark-lepton-symmetry has led to search for a sixth quark, the t-quark, but no evidence has been seen up to the highest energies of 31.6 GeV.

Search for narrow resonances in e +e − annihilation at petra

We have performed a search for narrow resonances in the center of mass energy range from 29.90 to 31.46 GeV using the e +e − storage ring PETRA at DESY. We present the total cross section for hadron production and an upper limit for resonance production, indicating that no bound state of charge- 2 3 quarks exists in this energy range.

Hadron production from photon-photon interactions in the CM energy range from 1 to 5 GeV

We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e +e − storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.

X-ray and γ-ray sources: A comparison of their characteristics

A comparison of the various source characteristics, in particular the available fluxes of radiation in the X-ray/γ-ray region from (1) high power rotary anode X-ray generators, (2) radioactive γ-ray sources and (3) high energy electron storage rings will be presented. Some of the specific characteristics and possible applications of synchrotron radiation as a source will be discussed in detail, together with problems associated with the monochromatization of the continuous radiation in the X-ray/γ-ray region. The new high energy machines PEP at Stanford, the 8 GeV storage ring CESR at Cornell and the PETRA storage ring in Hamburg, which will soon come into operation provide a spectrum of high intensity radiation reaching well above hv photon = 100 keV. Thus e.g. at the PETRA e + − e − storage ring with E = 18 GeV and an electron current of 20 mA a photon flux of 8 × 10 10 photons/s · eV · mrad 2 of highly collimated and pulsed radiation will be available at the critical photon energy ϵ c = 75 keV. We will also discuss briefly the possibilities of using ondulators (wigglers), and laser-electron scattering for constructing high repetition rate tunable γ-ray sources. Finally we mention the potentials of using the powerful spontaneous emission of γ-quanta by relativistic channeled particles.

Electric Power and Cooling Systems for PETRA

For 19 GeV operation the PETRA storage ring and its experiments need 25 MW of electric power. The different power distribution systems at medium voltage and low voltage level are described. For powering the PETRA magnet system individual high precision dc-power supplies are employed, all centrally located near the PETRA control room. Details will be given about the magnet circuits and the rf-power supplies. Water cooling of the PETRA magnets, vacuum chambers and rf-components is made by 2 systems consisting of pumps, heat exchangers etc and concentrated in 2 cooling centers together with a cooling tower and a cooling spray pond. Cooling equipment for individual experiments is located near the experiments. Utilization of part of the electric energy for heating is provided.

First observation of hadron production in e +e − collisions at 13 and 17 GeV CMS energy with the pluto detector at petra : Pluto Collaboration

First results from the magnetic detector PLUTO at the new e +e − storage ring PETRA are shown. The ratio R of the cross section for hadron production to that for μ-pair production has been measured to be R = 5.0 ± 0.5 at 13 GeV and 4.3 ±0.5 at 17 GeV. Both values have an additional systematic error of 20%. The events show a typical 2-jet structure. The mean transverse momentum approaches a constant value with increasing energy implying a shrinkage of the jet opening angle.

PIA, the Positron Intensity Accumulator for the PETRA Injection

The storage ring PETRA is designed to store 4.1012 electrons and positrons in 2xfour 500 MHz rf buckets. Since the intensity of the positron linac is about 2.107 particles per 500 MHz bucket, 2.105 bunches are required for injection and accumulation in PETRA. In order to get reasonably short filling times the storage ring DORIS presently is acting as an intermediate bunch accumulation facility. This scheme has been successfully in operation since September 1978. Now the increased demand for elementary particle physics and for synchrotron radiation experiments at DORIS has motivated the construction of the small 450 MeV intermediate storage ring PIA, located between the positron linac and DESY. The circumference is 28,8 m. About 1 . 109 positrons will be injected at a rate of 50 Hz. A first harmonic cavity (10,4 MHz) accumulates positrons in a 0,8 m long bunch which is further compressed to 0,25 m length by a 12th harmonic rf system (125 MHz) for injection into the DESY 500 MHz system. After acceleration to 6,5 GeV in DESY single positron bunches are injected into PETRA.

Bench Measurements of the Energy Loss of a Stored Beam to Vacuum Components

Since 1975 measurements of higher order mode losses have been carried out at DESY. The method in use had been proposed by J. Rees and M. Sands): Short current pulses (2 σ = 100 psec) on a thin coaxial wire simulate a relativistic particle bunch. Changes in the bunch shape allow the determination of energy losses due to higher mode excitation. Measurements on simple cavity structures agree well with calculations. Results for a large variety of vacuum structures in the PETRA storage ring are given including structures, the losses of which can no longer be easily calculated. For these structures the results of the measurements described here are the only source of information for improvements.

The Electron-Positron Storage Ring Petra, Plans and Status

Construction of the Electron-Positron Storage Ring PETRA was authorized October 20, 1975. At present most of the civil engineering work is completed and ring installation work is under way. All major components are on order and series production of bending magnets, quadrupoles, vacuum chambers and rf-resonators has started. Start-up of the machine is planned with a fourfold symmetry configuration with four active beam-beam interaction points. Five experimental facilities have been recommended for the first round of experiments scheduled to begin mid 79.