Mini-Workshop on Commissioning of
X-Ray Free-Electron Lasers
 April 18-22, 2005, DESY Zeuthen, Germany

Work Package 1: Injector Commissioning
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Coordinators:

D. Dowell, SLAC (Chair) +1-650-926-2494
S. Schreiber, DESY +49-40-8998-4360

Ideas:

The injector portion of the commissioning workshop will concentrate on three basic areas:
  1. Installation and machine startup. In this portion of the working session we will review injector startup strategies and characterization of the various injector components. This should include, for example, a discussion of the diagnostics necessary to measure the drive laser's spatial and temporal distributions with good resolution, as well as the RF measurements required to assure the gun and accelerator sections are operating within specifications. Diagnostics and controls for stable operation at various repetition rates are of interest, especially RF resonance control of the gun when operating at both low- and high-average powers.
  2. Optimization procedures and techniques. Once the injector is up and running it will be necessary to optimize its operation. To be discussed are the procedures used to adjust the injector parameters in order to achieve the design operating point. The interplay between diagnostics and modeling is important to guarantee the injector behaves according to simulations and to efficiently guide the operator in the large parameter space. The participants are asked to describe the various online tools they already use or will need to aid in the optimization and their procedures for optimizing the machine.
  3. Analysis techniques. Two approaches to data analysis will be discussed. The first concentrates on the standard methods used obtain the projected transverse and longitudinal emittances as well as other beam properties such as energy and energy spread. For example, quadrupole scan and three-screen emittance measurements fall into this category. The participants are asked to describe their methods for analyzing image data, including background subtraction, noise filtering, determination of the rms beam widths and fitting techniques. The second portion of this discussion will concentrate on new and novel techniques such as tomography, the analysis of transverse deflecting cavity data for slice emittance, and other methods to determine phase space distributions. Here the desire is to go beyond the simple representation of beam properties by emittance and peak current, and discuss methods for measuring the distributions in transverse and longitudinal phase spaces. In both cases, measured and simulated image data will be provided for the participants to analyze before the workshop.
The participants are requested to perform their data analyses in advance to be prepared to discuss their results during the workshop. Suggestions for problem topics are welcome, but please contact the working group chairmen as soon as possible so they can be included in the work package.

Thanks for Your participation in this important workshop!

Problem Descriptions:

Injector Problem 1: Analysis of view screen data for beam sizes vs. quadrupole strength to obtain the transverse emittance. The motivation is to verify that the correct emittance is being determined by measuring it on three very different screen materials, at different locations and with and without dispersion. The spectrometer bend plane is vertical while the plane of the emittance data is horizontal. Consider the beam line configuration with component parameters as shown in the following drawing. The beam kinetic energy is 30 MeV with negligible energy spread. Images have been collected on view screens consisting of OTR, YAG and a phosphor at the spectrometer screen as functions of Quad$npbs;2. The data taking system has generated a SDDS text file which contains the relevant parameters of the quadrupole current and the image names. The text file lists in columnar form the image filename, an image flag (1 for background, 0 for beam), Quad 2 current, etc. The image file format is TIF. The data files can be down loaded from folder transverse_data.

The problem is to use your standard techniques for correcting the background and producing beam profiles to produce the horizontal rms beam sizes with error bars as functions of Quad 2 strength for each of the three screens. Then fit this data to obtain the horizontal rms emittance determined by each screen location at the entrance to Quad 2.

NOTE: The 183.7 cm dimension is an error. The correct distance from the YAG screen to the entrance of the spectrometer is 70.61 cm. The working group discussion will entertain solutions with both dimensions.



Get pdf version of image.

Injector Problem 2: Analysis of energy spread data to obtain longitudinal beam parameters. The goal is to determine the beam matrix for the longitudinal phase space from energy spectra measured at the spectrometer screen vs. the linac phase. In this problem the assumptions used in the analysis are important and should be clearly explained. The beam line configuration is the same as for the previous problem, however in this case the motivation is to determine the beam matrix parameters for the longitudinal phase space. The mean energy of the beam and rms energy spread vs. the linac phase should be plotted along with a fit to the longitudinal beam matrix parameters determined at the entrance to the linac section. The data again consists of a text file in SDDS format giving the images associated with each linac phase, and the files are located in folder: energy_data

Injector Problem 3: Tomography analysis of energy spectra to reconstruct the longitudinal phase space. Effective compression of the bunch at high energy forces us to understand the details of the longitudinal phase. While the transverse deflector cavity in the LCLS injector will provide this information directly, it is also important to develop tomography techniques for instances where a deflector is not available. The same beam line configuration as above is again used as well as the data of Problem 2. The goal is the reconstruction of the longitudinal phase space at the entrance of the linac section, along with a description of the assumptions and issues related to the technique.

Injector Problem 4: Tomography analysis of transverse beam shapes to reconstruct the transverse phase space. The motivation for this problem are similar to Problem 3, that is, to reconstruct the details of the transverse phase space distribution, to go beyond the standard comparisons of projected emittance. Again the same configuration is used and the data set will be the same as in Problem 1. The suggested data set is that for the YAG view screen, with the objective of obtaining a reconstruction of the projected transverse phase space at the entrance to Quad 2. The issue concerning the sufficiency of this type of data to obtain a faithful reconstruction should be discussed.

Injector Problem 5: Three screen emittance measurement for the LCLS layout. The beam is at 135 MeV. The images were generated using PARMELA but adding background noise. The distributions were ideal for some cases but modified for others. The three screens are separated by 186.2 cm and are WS01, WS02 and WS03 as labeled in the file name. Series s, d and dd have different emittance values Images are 420×560 ; the noise levels and pixel sizes vary;

Series s1: pixel size 10 µm
Series s2: pixel size 20 µm
Series s3: pixel size 10 µm
Series s4: pixel size 10 µm

Series d1: pixel size 10 µm
Series d2: pixel size 20 µm

Series dd1: pixel size 10 µm

Injector Problem 6: We simulate the horizontal slice emittance measurement for the LCLS layout. The transverse cavity gives a transverse kick (equivalent to +/- 0.75 mrad from head-to-tail). The QE03 quadrupole is scanned in 11 data points from 0.7 to 1.2 around the nominal value. The nominal value is k = -7.309955 m-2. QE03 has an effective length of 10.8 cm. The images are given at WS02 which is 254 cm from the center of QE03. The beamline is described as

TCAV, z = 1147 cm, transverse deflecting cavity
Drift, z = 1147 cm to z = 1151.7 cm  
QE03, z = 1151.7 cm to z = 1162.52 cm, k = -7.309955 m-2
Drift, z = 1162.52 cm to z = 1191.72 cm  
QE04, z = 1191.72 cm to z = 1202.52 cm, k = 6.196657 m-2
Drift, z = 1202.52 cm to z = 1411.12 cm  
WS02, z = 1411 cm  

Series ee1 : pixel size 20 µm
Series ee2 : pixel size 10 µm

PITZ1 Benchmark Problem: The problem is simultaneous simulation of a consistent set of measurements obtained during a PITZ1 run. The suggested measurements were done mainly during one shift (night shift August 17, 2004) and the measured electron beam properties are close to the optimum obtained at PITZ1.

The motivation is to understand beam dynamics features in the photo injector by means of simultaneous simulations of various beam measurements:
  1. Phase scan - measurement of the beam charge vs. rf gun (launch) phase
  2. Measurement of rms beam size vs. rf gun phase (reference phase check)
  3. Longitudinal momentum measurements
  4. Emittance measurements using slit scan technique - analyzed data and individual images of the beam and the beamlets for various main solenoid currents are available.
Auxiliary data on the cathode laser properties (transverse and temporal profiles) and some stability issues (charge and position jitter) are available as well.
The goal is the reconstruction of the electron beam phase space details.
The emittance measurement technique as well as the photo injector optimization strategy and procedure could be discussed.
More detailed description and data are located at:
http://www-zeuthen.desy.de/~kras/PITZProblem.html/PITZbenchmark.html

Presentation Equipment:

Provisions for presenting talks from a CD or a PC laptop are available as wells as using the old overhead projector.

Documents:

Icon  Name                    Last modified      Size  Description
[DIR] Parent Directory                             -   
[   ] WP1_image1.pdf          28-Mar-2005 15:55   29K  
[DIR] energy_data/            17-Feb-2005 09:25    -   
[DIR] simulation_data/        16-Feb-2005 10:56    -   
[DIR] transverse_data/        17-Feb-2005 09:25    -
Content Owner: D. Dowell, SLAC
Page Editor: H.-D. Nuhn, SLAC

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