G. Carron

30 GHz Power Production in CTF3

One of the major objectives of CTF3 (CLIC Test Facility) is the production of 30 GHz power for the high-gradient testing of CLIC accelerating structures. To this end a dedicated beam line, power generating structure and power transfer line have been designed, installed and commissioned. 52 MW of 30 GHz power with a pulse length of 74 ns and a repetition rate of 16 Hz were delivered to the high-gradient test area. This will allow operation of test accelerating structures in the first CTF3 run of 2005 up to the nominal CLIC accelerating gradient of 150 MV/m and beyond the nominal pulse length. The system is described and the performances of the CTF3 linac, beam line and the rf components are reviewed.

Measurement of antiproton lifetime using the ice storage ring

Antiprotons have been stored in the ICE Storage Ring and held for 85h with the help of stochastic cooling. We set a limit of at least 32 h for the antiproton lifetime (in its rest frame).

Observation of transverse quadrupole mode instabilities in intense cooled antiproton beams in the AA

In the CERN Antiproton Accumulator (AA) a breathing mode type of instability has been identified as an intensity-limiting mechanism in cooled stacks. The more well-known dipole-mode instabilities are adequately controlled by the existing damper system. With the aid of a quadrupole pickup it was possible to observe transverse modes in the beam at frequencies (n-2Q). The instabilities occur only at certain emittance and intensity thresholds and are believed to be caused by uncleared pockets of ions trapped in the beam potential. A quadrupole kicker was added to the machine so that these modes could be excited, and beam transfer functions were measured for each of the possible modes. Feedback can be applied to actively damp the quadrupole modes. The best solution has been to rid the machine of the remaining ion pockets gradually by improving the clearing, by the careful choice of tunes, and even by shaking the beam.<<ETX>>

Antiproton lifetime measurement in the ice storage ring using a counter technique

Abstract Results are presented of the search for an antiproton decay into an electron and a neutral pion. Using a stacking scheme based on stochastic cooling an average of 7000 antiprotons was accumulated and stored in the ICE ring for 10 days. No experimental evidence for such an antiproton decay was found. The following lower limit for the antiproton lifetime has been established in the antiproton rest frame: τ > BR × 1700 h at 90% confidence level (CL), where BR is the branching ratio for this decay channel.

Experiments on Stochastic Cooling in ICE (Initial Cooling Experiment)

Recent experiments on stochastic cooling have resulted in cooling rates several orders of magnitude higher than obtained previously in the ISR. Two cooling systems reduce betatron oscillations. A third system reduces momentum spread, using the so-called filter method. The favourable signal-to-noise ratio of this method has led to cooling times (e-folding of peak density) of 15 s with 7.107 protons in ICE. Betatron cooling times are longer due to the lower signal-to-noise ratio. Simultaneous cooling in all three planes has yielded lifetimes of about 100 h, a value consistent with losses caused by single scattering on the residual gas. The existing stochastic cooling theory has been confirmed.

Recent Experience with Antiproton Cooling

Improvement of transverse stochastic cooling in cases where the pick-up-to-kicker distance is not optimal may be obtained by using a transmission-line filter that causes opposite phase shift at alternating Schottky sidebands. Improvement of the horizontal stack-core cooling in the Antiproton Accumulator by using a pickup at a zero dispersion location is planned; the filter technique will make this possible. The improvement of the signal-to-noise ratio in the 250-500 MHz stack tail termination resistors is discussed, as well as some problems caused by undesired modes perturbing the pickup response.

Beam Optics Studies on the Antiproton Accumulator

The CERN Antiproton Accumulator (AA) was designed to accumulate 6 x 1011 antiprotons per day, using the stochastic cooling technique. Its construction was completed within two years and the first beam circulated in early July 1980. This paper describes the conceptual design of the lattice and how multipole shim corrections were applied to develop the large betatron and momentum design acceptances. We also report how a sequence of such corrections, based on optics studies with proton beams, have been applied to the point that the machine is now approaching design performance.

Demonstration of two-beam acceleration and 30 GHz power production in the CLIC Test Facility

The Compact Linear Collider (CLIC) Test Facility (CTF II) at CERN has recently demonstrated Two-Beam power production and acceleration at 30 GHz. With 41 MW of 30 GHz power produced in 14 ns pulses at a repetition rate of 5 Hz, the main beam has been accelerated by 28 MeV. The 30 GHz RF power is extracted in low impedance decelerating structures from a low-energy, high-current “drive beam” which runs parallel to the main beam. The average current in the drive-beam train is 25 A, while the peak current exceeds 2 kA. Crosschecks between measured drive-beam charge, 30 GHz power and main-beam energy gain are in good agreement. In this paper, some relevant experimental and technical issues on drive-beam generation, two-beam power production and acceleration are presented.

RF hardware development work for the CLIC drive beam

It is foreseen that the transfer structures (CTS) of the drive linac will produce 40 MW, 11.4 ns, 30 GHz RF power pulses for acceleration purposes in the CLIC main linac. Extensive model work, using the beam simulating wire method, has been undertaken in order to study the properties of the CTS with oversize models working at 8.6 GHz. At present a real size Cu 30 GHz CTS is under construction for beam tests in the CLIC Test Facility. A second Cu structure is in preparation for power testing with an MIT 33 GHz FEL power source. Further work is the development of power phase shifters and, inspired by the SLAC SLED-II studies, investigation into the use of longer RF pulses (than 11.4 ns) from the CTS (by a factor 3-4) combined with pulse compression. With longer RF pulses the drive beam bunchlet generation should become easier since the total drive beam charge of 7.04 /spl mu/C would be distributed over more bunchlets.<<ETX>>

Applications of Microwaves to Antiproton Control

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.