Some Thoughts About Possible Measurements with SR at DaFne R. Kersevan, CERN-TE-VSC-VSM Meeting in Frascati, 14/10/2016

Introduction: Some thoughts about the analysis and proposal of possible measurements on DAFNE’s SR beamlines are discussed; The reference document is: R. Cimino et al., “Synchrotron radiation studies at LNF DAFNE-L laboratories of reflectivity/photoelectrons/photo induced desorption in collaboration with CERN-TE-VSC-VSM”, July 25th, 2016, referenced here as “the paper”; The paper concludes that both wiggler and bending magnet beamlines could be used for different kinds of measurements which are all potentially in the interest of CERN in the framework of several projects and design studies, most notably HL-LHC and FCC-hh/FCC-ee; In the following we outline a (very) preliminary analysis, based on partial knowledge of the DAFNE machine parameters and optics, which highlights some of the crucial points discussed in the paper; We also present some arguments of “complementarity” with past, present, and future experiments carried out at other research laboratories in the framework of other CERN collaborations;

Wiggler beamline DXR1: The paper reports the following wiggler parameters and photon flux spectrum: We have made a model with the ray-tracing code SYNRAD+ of the generation of SR by the DAFNE wiggler (as per data provided by M. Boscolo, LNF-INFN, personal communication, scaled to 1.71 T peak-field (the original data file being peaked at 1.64 T)):

Wiggler beamline DXR1: DAFNE wiggler SYNRAD+ model: +/- 200 mrad, circular arc, +/- 5 cm tall, placed around the central point of the wiggler trajectory; 1 A beam current; 2x200 1-cm-wide facets at 10 m distance:

Wiggler beamline DXR1: Zooming into the +/- 3 mrad (H) cone of radiation as mentioned in the paper (rectangle 1-2-3-4); Good agreement with flux spectrum within 6 mrad (H) rectangular cone (see arrow):

Wiggler beamline DXR1: Although the critical energy for FCC-hh at 50 TeV is much higher than the 296 eV of the DAFNE wiggler, it is nevertheless very likely that a future FCC-hh will have to spend a considerable amount of time at lower beam energies, during commissioning: The several-hours-long energy ramping time from 3.3 to 50 TeV will need also to be stable and void of beam- and cryo-instabilities driven by vacuum effects and SR;

Wiggler beamline DXR1: These measurements would be complementary to those that we have already made and will make again at KEK’s Photon Factory (M. Ady, CERN, PhD thesis EPFL, May 2016, http://cds.cern.ch/record/2157666 ), at a higher critical energy of 4 keV;

Wiggler beamline DXR1: These measurements would be also complementary to those are planned to be made next year at the ANKA light source in the framework of the EuroCirCol collaboration, at a critical energy of 6.2 keV, close to the one of FCC-hh at 50 TeV (4.3 keV); ANKA can reproduce quite well also the SR power density of FCC-hh at 50 TeV, ~ 30 W/m

XUV1 and XUV2 bending magnet beamlines: The interest for the bending magnet beamlines, as per the paper, resides mainly in the possibility to perform SEY measurements, which are vital for both HL-LHC and FCC-hh (and FCC-ee as well, for the e+ ring and the full-energy booster ring as well); In particular the possibility of concentrating a low-power photon beam generated along the bending magnet over a large horizontal arc (17 mrad) and integrated over a large vertical aperture (6 mrad) onto a small sample area of the order of 1 mm2, is potentially interesting in order to speed-up the conditioning time and the scrubbing for e-cloud studies: it could provided crucial data about some of the many parameters which play a role in the e-cloud simulation codes (e.g. PYcloud); These measurements would be complementary to those that are going to be carried out soon by R. Cimino et al. at BESSY-II, in the framework of the EuroCirCol study; CERN must make a choice (HL-LHC), or state a preference (FCC-hh and –ee), for e- cloud mitigation surface treatments, such as: Sputtered thin films of amorphous-carbon and NEG (eventually also HTS films); Laser-engineered surface structures; Clearing electrodes; Chamber/beam-screen materials and photon absorber geometries; The possibility to use monochromators and perform accurate energy-dependent photon-induced-desorption and -electron yield measurements is also interesting, as there is a lack of such measurements for practical surfaces (i.e. other than single- crystals);

Conclusions: It is certainly in CERN’s interest to be able to carry out measurements at DAFNE’s SR beamlines; If successful, all these measurements could represent for years to come a milestone achievement in the fields of vacuum and accelerator technology, mirroring what the campaigns of similar measurements for LEP, SSC, and LHC did in the past (see bonus slides), which left some voids in the determination of some important parameters.

Bonus slides: