Rainer Wanzenberg

Status and future developments of the wake field transformer experiment

Abstract Future e + e − linear colliders with center-of-mass energies of 2 TeV need high average accelerating gradients to be built within a reasonable length. The gradients required by colliders at this energy range can be economically provided by resonant wake field transformers. At the wake field experiment at DESY a 20 cm long transformer section was investigated. The basic ideas are reviewed and the most recent results are presented in this paper. Furthermore an overview of the present status of research concerning the proposed next stage of a multibunch driver linac with superconducting cavities and long wake field transformer sections is presented.

Insulation of a hollow beam gun

The authors are investigating the possibility of accelerating particles with a high gradient in a wake-field transformer. They focus on the short-pulse, high-current hollow-beam gun being developed for this experiment and especially on the insulation problems. A laser-driven gun that works in a solenoid field of 0.2 T was chosen. At a cathode voltage of 100 kV, the gun produces a hollow beam of 109-cm diameter with a space-charge-limited current of 100 A over a pulse length of a few nanoseconds. The cathode voltage is limited by vacuum breakdown, caused by electrons, emitted from the cathode and from the surfaces of optical elements between the electrodes. >

Wake computations for undulator vacuum chambers of PETRA III

At DESY it is planned to convert the PETRA ring into a synchrotron radiation facility, called PETRA III. The wake fields of a tapered transition from the standard vacuum chamber to the small gap chamber of the insertion devices contribute significantly to the impedance budget of PETRA III. The computer codes MAFIA and PBCI have been used to determine the loss and kick parameters of the tapered transition. PBCI is a recently developed parallelized, fully 3D wake field code, which used a purely explicit, split-operator scheme to solve the Maxwell equation in the time domain.

Wake Field Acceleration, a Way to TeV e+ e- Collisions

Future e + e -- accelerators in the energy range above 1 TeV will be linear colliders with a high accelerating gradient. For creating the high gradient, new concepts are investigated, such as wake field acceleration, which need driver beams with high current and short bunches. At DESY an experiment with a Wake Field Transformer has been set up, where electromagnetic wake fields of a highly charged hollow driver beam are spatially focussed, and the resulting high longitudinal electric field is used for the acceleration of a second beam. The basic idea, the layout of the experiment and the results are presented. In a stage-1 experiment several bunches, each of 50 to 100 nC charge, have been produced and accelerated to an energy of 6.5 MeV and bunched down to a length of 3–4 mm. Using longer bunches of 1 cm, a gradient of 8 MeV/m has already been measured in a short Wake Field Transformer section.

Hollow beam dynamics in the DESY wake field accelerator

The characteristic requirements for studies of an intense hollow electron beam do not permit the use of simulation codes usually used for linac or storage ring design. At DESY, two special codes have been developed for this purpose: WAKTRACK, a tracking code which includes arbitrarily shaped external fields and collective effects and TBCI‐SF, a 2‐1/2 dimensional, fully relativistic particle‐in‐cell code used for studies of the ring shaping and bunching process. TBCI‐SF also includes arbitrarily shaped static or dynamic fields. Both computer codes will be discussed and applications for the Wake Field Transformation Linac will be indicated.