The effect of beam excitation on the HERA electron-beam lifetime disruption

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The electron beam of HERA is subject to disruptions of the beam lifetime. The prevailing conjecture is that this is due to dust particles trapped by the beam within quadrupoles magnets. Good lifetime can be recovered temporarily by beam excitation. This has been predicted by theory and simulation and was confirmed by experiment for HERA and PETRA electron beams. During HERA electron machine studies in Dec 1995 the lifetime was increased from ht o h with an injection kicker at a kick rate of Hz over a period of 10 minutes at energy GeV and at current mA. Similarly, the lifetime was improved from h to h with a feedback kicker sweeping from frequencies near or above the beam tunes kHz kHz to low frequencies Hz at a sweep period of ms. The local discrete decrease of electron loss rates in loss monitors located near arc quadrupoles and of global loss rates in background and electron detectors at experiments H1 and ZEUS correlated with discrete beam lifetime im- provements during the beam excitation procedures - pro- viding further support for the trapped dust particle explana- tion of the HERA electron beam lifetime problem. The fre- quency of all loss monitor and detector events was greatly reduced during the excitation procedures. Further lifetime disruptions were however observed to recur after the exci- tation "cleaning" procedures were concluded, especially at desired operation currents mA. The kicking proce- dure, loss rate observations, and agreement with theory are presented.
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