• K. Honkavaara, B. Faatz, J. Feldhaus, S. Schreiber, R. Treusch
  DESY, Hamburg
• J. Roßbach
  Uni HH, Hamburg

The free-elec­tron laser user fa­cil­i­ty FLASH at DESY, Ger­many has been up­grad­ed. The up­grade start­ed in au­tumn 2009 after al­most 2 years of a very suc­cess­ful sec­ond user pe­ri­od. The beam en­er­gy is in­creased to 1.2 GeV by in­stalling a 7th su­per­con­duct­ing ac­cel­er­at­ing mod­ule. The new mod­ule is a pro­to­type for the Eu­ro­pean XFEL. Among many other up­grades, 3rd har­mon­ic su­per­con­duct­ing RF cav­i­ties are in­stalled in the in­jec­tor. The main pur­pose is to flat­ten and - to a cer­tain ex­tend - to shape the lon­gi­tu­di­nal elec­tron beam phase space im­prov­ing the dy­nam­ics be­hav­ior of the beam. The seed­ing ex­per­i­ment sFLASH is being com­mis­sioned, an im­por­tant step for­ward to es­tab­lish seed­ed FEL ra­di­a­tion for user ex­per­i­ments. After the on­go­ing com­mis­sion­ing, the 3rd user pe­ri­od will start this sum­mer. In many as­pects FLASH will be an FEL with a new qual­i­ty of per­for­mance: a wave­length ap­proach­ing the car­bon edge and the water win­dow, tun­able pulse width, and with thou­sands of puls­es per sec­ond. This re­port sum­ma­rizes the re­cent­ly fin­ished up­grade of FLASH and re­ports on the re­sults of the on­go­ing com­mis­sion­ing and the ex­pect­ed per­for­mance as a free elec­tron laser user fa­cil­i­ty.

Slides

• S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch
  DESY, Hamburg

The free-elec­tron laser fa­cil­i­ty FLASH at DESY, Ger­many fin­ished its sec­ond user pe­ri­od sched­uled from Novem­ber 2007 to Au­gust 2009. More than 300 days have been de­vot­ed for user op­er­a­tion, a large part of beam­time has been al­lo­cat­ed for ma­chine stud­ies for fur­ther de­vel­op­ments, in­clud­ing beam­time for XFEL and ILC R&D. FLASH pro­vides trains of fully co­her­ent 10 to 50 fem­tosec­ond long laser puls­es in the wave­length range from 40 nm to 6.8 nm. The SASE ra­di­a­tion con­tains also high­er har­mon­ics; sev­er­al ex­per­i­ments have suc­cess­ful­ly used the third and fifth har­mon­ics. The small­est wave­length used was 1.59 nm. We will give a sum­ma­ry of the ex­pe­ri­ence from two years of user op­er­a­tion at FLASH.

• B. Faatz, N. Baboi, V. Balandin, W. Decking, S. Düsterer, J. Feldhaus, N. Golubeva, T. Laarmann, T. Limberg, D. Nölle, E. Plönjes, H. Schlarb, S. Schreiber, F. Tavella, K.I. Tiedtke, R. Treusch
  DESY, Hamburg
• J. Bahrdt, R. Follath, M. Gensch, K. Holldack, A. Meseck, R. Mitzner
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
• M. Drescher, V. Miltchev, J. Roßbach
  Uni HH, Hamburg

FLASH has been a user fa­cil­i­ty since 2005, de­liv­er­ing ra­di­a­tion in the wave­length range be­tween 7 and 47 nm using the SASE prin­ci­ple. In order to in­crease user beam time and im­prove the ra­di­a­tion prop­er­ties de­liv­ered to users, a major ex­ten­sion of the user fa­cil­i­ty called FLASH II has been pro­posed by DESY in col­lab­o­ra­tion with the HZB, which is a seed­ed FEL over the pa­ram­e­ter range of FLASH. As log­i­cal con­tin­u­a­tion, the HHG de­vel­op­ment pro­gram start­ed with sFLASH, will re­sult in di­rect seed­ing. Be­cause in the fore­see­able fu­ture there will prob­a­bly not be HHG seed lasers avail­able at high rep­e­ti­tion rates down to wave­lengths of 4 nm, a cas­cad­ed HGHG scheme will be used to pro­duce short wave­lengths. After a first de­sign re­port, the pro­ject now en­ters its prepa­ra­tion phase until the de­ci­sion for fund­ing will be taken. Dur­ing this time, the FLASH beam pa­ram­e­ters after the pre­sent up­grade 2009/2010 will be char­ac­ter­ized and the pre­sent de­sign will be re-eval­u­at­ed and ad­just­ed. In ad­di­tion, com­plete start-to-end sim­u­la­tions will com­plete the sim­u­la­tions which have been per­formed so far, in­clud­ing a com­plete de­sign of the ex­trac­tion area.

• A. Willner, S. Düsterer, B. Faatz, J. Feldhaus, H. Schlarb, S. Schreiber, F. Tavella
  DESY, Hamburg
• S. Hädrich, J. Limpert, J. Rothhardt, E. Seise, A. Tünnermann
  Friedrich Schiller Universität, Jena
• J. Roßbach
  Uni HH, Hamburg

The per­for­mance of fourth gen­er­a­tion light sources is of in­ter­est in many fields in na­ture sci­ence. Dif­fer­ent seed­ing schemes for FELs are under in­ves­ti­ga­tion to im­prove tim­ing sta­bil­i­ty, pulse shape and spec­trum of the am­pli­fied XUV or X-ray puls­es. One of the most promis­ing schemes is di­rect seed­ing by high-har­mon­ic gen­er­a­tion (HHG) in gas. A seed­ed free elec­tron laser with a tune­able wave­length range from 10 to 40nm and a bunch fre­quen­cy of up to 100 kHz (1 MHz up­grad­ed), as pro­posed for FLASH II (col­lab­o­ra­tion HZB/DESY), makes high de­mands on the HHG seed source con­cern­ing con­ver­sion ef­fi­cien­cy and sta­bil­i­ty. How­ev­er, the most chal­leng­ing task is the con­cep­tion of a laser sys­tem with a rep­e­ti­tion rate of 100 kHz (1 MHz up­grad­ed). The key pa­ram­e­ters for this laser am­pli­fi­er sys­tem are pulse en­er­gies of 1-2mJ and sub-10fs pulse du­ra­tion. We re­port on the de­vel­op­ment sta­tus of the re­quired laser sys­tem for the seed source and give an overview of first con­cepts for the HHG tar­get setup which can com­ply with the re­quire­ments of a new seed­ed FEL at DESY.