Applications of Microwaves to Antiproton Control

Abstract

A major achievement in particle accelerator physics has been the invention of stochastic cooling, a method which increases the density of beams of rare particles, like antiprotons, by several orders of magnitude. The beam circulates in a storage ring where it is sampled by electromagnetic devices which detect and correct the statistical fluctuations in position and energy. The efficiency is related to the sampling resolution which is itself associated with the system frequency bandwidth, a few gigahertz in practice. The coupling structures are made of electrode arrays connected by combiner or splitter networks. The dynamic range may exceed 150 dB yet fulfilling stringent linear characteristics. At the detection stage, the thermal noise is reduced using cryo-electronic techniques. At the other end of the amplification chain, solid state amplifiers delivering up to 100 watts CW power have been preferred to travelling wave tubes for reasons of phase linearity, lifetime and economy. The performances and technological aspects of the microwave systems are discussed by the example of the CERN antiproton project, ACOL. Invited paper, 17th European Microwave ConferenceRome, Italy, 7th-10th September 1987Geneva, Switzerland July 1987 APPLICATIONS OF HICROWAVES TO ANTIPROTON CONTROLB. Autin, G. Carron, F. Caspers, L. Thorndahl* ABSTRACT A major achievement in particle accelerator physics has been the invention of stochastic cooling, a method which increases the density of beams of rare particles, like antiprotons, by several orders of magnitude. The beam circulates in a storage ring where it is sampled by electromagnetic devices which detect and correct the statistical fluctuations in position and energy. The efficiency is related to the sampling resolution which is itself associated with the system frequency bandwidth, a few gigahertz in practice. The coupling structures are made of electrode arrays connected by combiner or spli tter networks. The dynamic range may exceed 150 dB yet fulfilling stringent linear characteristics. At the detection stage, the thermal noise is reduced using cryo-electronic techniques. At the other end of the amplification chain, solid state amplifiers delivering up to 100 watts CW power have been preferred to travelling wave tubes for reasons of phase linearity, lifetime and economy. The performances and technological aspects of the microwave systems are discussed by the example of the CERN antiproton project, ACOL.

Thousandfold improvement in the measured antiproton mass

“…At the CERN Antiproton Accumulator, for example, antiprotons were recently held 11 days without adding or extracting antiprotons, with a particle loss rate corresponding to a storage lifetime of 1.4 months in the rest frame of the energetic antiprotons. 17 Based upon calculated annihilation cross sections at low energy, 18 our containment lifetime limit above requires a background gas density less than 100 atoms/ cm 3 . For an ideal gas at 4.2 K this corresponds to a pressure less than 5xl0~1 7 Torr.…”

The status of stochastic cooling

“…There has been great progress in the design of low-noise broadband systems [12], [13], [14] and the ampliers developed for the AC and the FERMILAB debuncher are in fact formidable`HIFI systems' with an unprecedented combination of low noise, large bandwidth, high amplication and ultra-linear phase response characteristics.…”

“…An example of a resonant pick-up is the resonant cavity with a Q 10 4 employed in ICE to observe and to cool in momentum a beam of less than 100 particles (using only a single Schottky`line'). Another less extreme case is thè super-electrode' arrangement [13] used in the AC. It may be thought of as 2 loop couplers connected in series by a cable of length =2 at mid-band.…”

Electromagnetic detectors

“…This has been applied in the CERN antiproton accumulator 13 where the reduced bandwidth arrays were desired to match power' amplifier bandwidths. The electrode unit consists of two loops in series.…”