dorsal/arxiv
View SchemaThe Diffraction Model and its Applicability for Wakefield Calculations
| Authors | P. Huelsmann, W. F. O. Mueller, H. Klein |
|---|---|
| Categories | |
| ArXiv ID | physics/0008091 |
| URL | https://arxiv.org/abs/physics/0008091 |
| Journal | eConf C000821 (2000) MOE06 |
Abstract
The operation of a Free Electron Laser (FEL) in the ultraviolet or in the X-ray regime requires the acceleration of electron bunches with an rms length of 25 to 50 micro meters. The wakefields generated by these sub picosecond bunches extend into the frequency range well beyond the threshold for Cooper pair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown, that the superconducting cavities can indeed be operated with 25 micro meter bunches without suffering a breakdown of superconductivity (quench), however at the price of a reduced quality factor and an increased heat transfer to the superfluid helium bath. This was first shown by wakefield calculations based on the diffraction model. In the meantime a more conventional method of computing wake fields in the time domain by numerical methods was developed and used for the wakefield calculations. Both methods lead to comparable results: the operation of TESLA with 25 micro meter bunches is possible but leads to an additional heat load due to the higher order modes (HOMs). Therefore HOM dampers for these high frequencies are under construction. These dampers are located in the beam pipes between the 9-cell cavities. So it is of interest, if there are trapped modes in the cavity due to closed photon orbits. In this paper we investigate the existence of trapped modes and the distribution of heat load over the surface of the TESLA cavity by numerical photon tracking.
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"abstract": "The operation of a Free Electron Laser (FEL) in the ultraviolet or in the\nX-ray regime requires the acceleration of electron bunches with an rms length\nof 25 to 50 micro meters. The wakefields generated by these sub picosecond\nbunches extend into the frequency range well beyond the threshold for Cooper\npair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown,\nthat the superconducting cavities can indeed be operated with 25 micro meter\nbunches without suffering a breakdown of superconductivity (quench), however at\nthe price of a reduced quality factor and an increased heat transfer to the\nsuperfluid helium bath. This was first shown by wakefield calculations based on\nthe diffraction model. In the meantime a more conventional method of computing\nwake fields in the time domain by numerical methods was developed and used for\nthe wakefield calculations. Both methods lead to comparable results: the\noperation of TESLA with 25 micro meter bunches is possible but leads to an\nadditional heat load due to the higher order modes (HOMs). Therefore HOM\ndampers for these high frequencies are under construction. These dampers are\nlocated in the beam pipes between the 9-cell cavities. So it is of interest, if\nthere are trapped modes in the cavity due to closed photon orbits. In this\npaper we investigate the existence of trapped modes and the distribution of\nheat load over the surface of the TESLA cavity by numerical photon tracking.",
"arxiv_id": "physics/0008091",
"authors": [
"P. Huelsmann",
"W. F. O. Mueller",
"H. Klein"
],
"categories": [
"physics.acc-ph"
],
"journal_ref": "eConf C000821 (2000) MOE06",
"title": "The Diffraction Model and its Applicability for Wakefield Calculations",
"url": "https://arxiv.org/abs/physics/0008091"
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