Gajendra Kumar Sahoo's Homepage             

Deutsches Elektronen Synchrotron(DESY) Homepage

PETRA III Extension Optics - MADx Input Files
Previous works on Orbit & Dispersion Correction, and others

At PETRA III, Deutsches Elektronen Synchrotron (DESY), Hamburg.

PETRA-III is a 3rd generation synchrotron light source commissioned with electron beam energy of 6 GeV and 100mA stored current at betatron tune values of 36.12 and 30.28. The horizontal beam emittance is 1 nmrad while a coupling of 1% amounts to a vertical emittance of 10 pmrad. The machine is dedicated to users for experiments from 14 beam lines with 30 end-stations. The storage ring is presently being modified to incorporate 12 new beam lines including a Superlumi beam line from dipole radiation. PETRA operates with several filling modes, such as 40, 60, 480 and 960 bunches with a beam current of 100 mA.

FORTRAN 95 Code - codf : for simulation of slow and fast orbit correction.

Since the vertical beam sizes are ~5–10 micron in the low gap undulators sections the beam position stability requirement in the vertical plane is between 0.5 and 1 micron whereas the stability requirement in the horizontal plane is more relaxed. Here determination of golden orbit in the presence of magnetic field errors and magnet misalignments and correction of vertical spurious dispersion is discussed. A scheme of slow and fast orbit correction using the SVD algorithm has been developed. The distribution of monitors and the location of slow and fast correctors are reported. Estimations of the parameters of the fast orbit feedback have been derived from present measurements on PETRA II.

FORTRAN 95 Code - codc : for simulation of dispersion function correction.

The spurious vertical dispersion, arising due to the misalignment and rotational errors of the magnets in the storage rings dedicated for synchrotron radiation sources are highly undesirable in the low emittance machines, as this contributes to the vertical beam size of the photon beam. This is a matter of concern in PETRA III, a 6GeV positron storage ring with a horizontal beam emittance of 1nm.rad and 1% emittance coupling. Here the local and/or global vertical dispersion correction in the ring after getting a corrected orbit with combined horizontal dispersion correction of the perturbed lattice are discussed. The global vertical dispersion is corrected using the vertical corrector magnets used for orbit correction and 12 skew quadrupole magnets are used at three locations viz. two damping wiggler sections and the new octant with DBA cells, with a pair of skew quadrupoles on either side to correct locally without disturbing the dispersion out side. A SVD method can also be used considering the BPMs (Beam Position Monitors) on either side of insertion devices using skew quadrupoles to minimize the vertical dispersion in those locations so that the vertical emittance can be maintained at a desired value.

MATLAB-2010 Code - ormdrm.m : for simultaneous orbit and dispersion function correction.

The low emittance is achieved with proper correction of horizontal dispersion to its theoretical values in the arcs as well as dispersion free sections. The spurious vertical dispersion, arising due to misalignment and rotational errors of the magnets is also duly corrected as this contributes to the vertical beam size of the photon beam. Here we discuss the method taken to correct the horizontal dispersion using a combined orbit and dispersion correction scheme. In the vertical plane the same procedure can be used as that of horizontal plane or only the dispersion can be corrected using dedicated skew quadrupoles to millimeter level after orbit correction has been done.

Java Code - dispersioncorrection.jar; Displauncher.jnlp : for online simultaneous orbit and dispersion function correction via Java Web Applications.

Java Code - meoc.jar; MEOClauncher.jnlp : for analysis of Post-Mortem data via Java Web Applications.

During a user run unscheduled beam dumps triggered by Machine Protection System may occur. In many cases the reason can be identified but in some it remains undetected. Though the beam is lost some signature is left in the ring buffers of the 226 BPM electronics where last 16384 turns just before the dump are available for post-mortem analysis. Scrutinizing turn by turn orbits and the frequency spectrum measured at a BPM can improve understanding of such a beam loss and may help to increase the efficiency of operation by eliminating the sources. Here we discuss in detail the functionality of a Java GUI used to investigate the reasons for unwanted dumps. In particular, the most effective corrector method is applied to identify correctors that might have perturbed the golden orbit leading to violations of the interlock limits.

Java Code - pscTransientRecorder.jar; pscTRlauncher.jnlp : for analysis magnet PS transients via Java Web Applications.

During a user run the Machine Protection System (MPS) may trigger an unscheduled beam dump if transients in the current of magnet power supplies are detected which are above permissible limits. The trigger of MPS stops the ring buffers of the 226 BPM electronics where the last 16384 turns just before the dump are stored. These data and transient recorder data of Magnet Power Supply Controllers are available for a post-mortem analysis. Here we discuss in detail the functionality of a Java GUI used to investigate the transient behavior of the differences between set and readout values of different power supplies to find out the responsible power supply that might have led to emittance growth, fluctuations in orbits or beam dumps seen in a post-mortem analysis.

FORTRAN 95 Code - makSingle.f95 : Conversion of MADx input file to Sixtrack input file.

Java Code - OdiaBotam.V2.jar : It is a library of buttons, panels and labels to be used for development of Java Applications.

This gives a 3D look and can be painted with different styles by selecting pMode and the text can be written in different styles with tMode. The buttons are : oButton, oRoundButton, oOvalButton, oToggleButton or oOvalToggleButton. These can be placed on oPanel. For labels oLabel can be used. Click over below links to visualise these buttons, panel and labels.

FORTRAN 95 Code - lattice.f95 : Prepares text files fort.51 and fort.52 for ploting of Twiss functions along with the lattice structure from output of MADx using Origin or gnuplot.

Java Code - TuneDiagram.jar : This Java Applications plots the Tune Diagram for PETRA III storage ring.

Java Code - MultiTrack.jar : This Java Applications tracks particles for many turns in presence of magnetic multipoles in a ring.

At INDUS-I and II, Raja Ramanna Centre for Advanced Technology (RRCAT), Indore.

Since 1984 working in the field of electron beam dynamics in Alternating Gradient Accelerators e.g. design of weak focussing and strong focussing electron storage rings. I was involved in lattice design of the 20-700 MeV synchrotron, 450 MeV electron storage ring of INDUS-1 Synchrotron Radiation Facility. The lattice for synchrotron is a FODO with six periods and 28.44m circumference. Whereas, the magnetic lattice of INDUS-1, consists of four superperiods; each has a dipole magnet with field index of 0.5 and two doublets of quadrupoles. Some lattices with Triple Bend Achromat, Expanded Chasman-Green and few other types were studied as candidate lattice for a 2.5GeV, 300mA electron storage ring for synchrotron radiation, INDUS-2. For the study of these lattices a computer program ESRO was developed.

FORTRAN 95 Code - ESRO : Electron Storage Ring Optics.

FORTRAN 95 Code - xy : To plot xy plots in gr85 type terminal and output with HPGL for plotters.

FORTRAN 95 Code - ut : Utjwalata to compute spectral brilliance of Synchrotron Light Sources.

FORTRAN 95 Code - liti : LifeTime to compute beam life time of stored beam.

Effect of coulomb scattering on low energy machines was studied. The computer programs have also been written for the calculation of beam lifetime, the spectral brilliance and angular dependence of radiation. Some studies were made on the variation of beam emittance during the acceleration cycle of the synchrotron.

Actively involved in the commissioning of the INDUS-1 synchrotron radiation facility. A 20MeV, 25mA, 1μs long pulse from the classical microtron is injected to the synchrotron. A peak current of 40mA at the injection energy lasting for 25ms was observed. The synchrotron was operated at the injection energy to measure the beam optical parameters such as tunes, beta functions, apertures, chromaticity etc. The trials to accelerate the electrons to higher energies commenced in June'95 and a successful acceleration to 480MeV with a beam current of 1.8mA was achieved in September'95 and further improved to 11mA.

INDUS-1, the 450 MeV electron storage ring for VUV radiation was declared commissioned on 14.06.99 by the Atomic Energy Commission, Chairman Dr. R. Chidambaram. The first stacking of two bunches that extracted out of three bunches from Synchrotron, took place on 22.04.99 with accumulation of 4.2mA; and within a month and half, a stored current of 113mA was achieved against the design of 100mA. In the beginning, the stored current was limiting in build up due to the gas scattering that released on photo desorption process due to intense synchrotron radiation. On gradual cleaning by radiation the vacuum condition was improved and it resulted increase in stored current. The machine was commissioned at the tune point of (1.73, 1.45), where the beam current of 113mA was achieved in ~12minutes. Later on we investigated other tune points for better accumulation rates and the beam lifetimes associated in those possible operating points. At the tune point of (1.69, 1.31), it is possible to accumulate electrons at much faster rate and it is just 100mA in three minutes. In present scenario with an average vacuum pressure of 40nTorr the beam lifetime is ~45 minutes at 100mA and it is more than one hour at 50mA. The beam lifetime is still higher at lower currents, as the vacuum is comparatively one order lower. A maximum of 203mA current was accumulated in INDUS-1, while the accelerated current in Synchrotron was ~ 2-5 mA.

The beam optical parameters such as tune values, natural chromaticities etc. were measured by using RF knock out method in horizontal and vertical planes at these two operating points. It is found that the natural chromaticity is negative in horizontal plane and positive in vertical plane.

Visited and worked in the international laboratories such as Elettra, Sincrotrone Trieste, Trieste, Italy for a period of 6 months under the BOYSCAST(Better Opportunities for Young Scientists in Chosen Areas of Science and Technology) FELLOWSHIP SCHEME 1988-89; Adone, LNF dell'INFN, Frascati, Rome and ENEA, Rome for a week. Visited CERN, Geneva for a week and KEK, Tsukuba, Japan for a week.

At ANKA (Renamed as KARA - Karlsruhe Research Accelerator), Karlsruhe Institute of Technology (KIT), Karlsruhe.

I was posted as a Guest Scientist in the field of Commissioning of High Energy Electron Storage Rings at Forschungsgruppe Synchrotronstrahlung (FGS), Forschungszentrum Karlsruhe, Germany from 19th January 2000 till mid of July 2001. The active participation in commissioning of 2.5GeV electron storage ring Angströmquelle Karlsruhe (ANKA) and the other theoretical works under taken there are reported in the following paragraphs.

In ANKA during June 2000 we could ramp 50-70 mA up to 2.5 GeV with a lifetime of 2-3 hours. As the injection of higher current (>90mA) into the ring was limited by gas scattering and trapped ions, it was decided to implement gap in filling structure of bunches. In July, this filling structure pushed the injection limit too more than 140mA. Till date a maximum of 303mA has been injected to the storage ring at 500MeV. In a single train (a pulse of 30 bunches or 60 ns) it was observed that one can inject a current of 207mA which is 7mA per bunch. While accelerating greater than 200mA, it is found that the beam is lost due to trip in RF cavities due to vacuum interlock in these. This happens that as the degassing rate increases at high energies at high currents due to intense synchrotron radiation due to the process of photo desorption. We could store a maximum of 196mA at 2.5GeV, whereas in practice we store a current of 160-180mA in regular operations. The injection so far achieved is 16mA/minute.

The investigation of feasibility of ANKA machine to operate in a mini-β configuration was initiated with an idea not to change the defocussing quadrupole near the dipole in the long drift section. With different doublets and triplets the mini-β solutions were obtained. The results show that above mentioned quadrupole needs strength higher than specified. So, one has to modify this quadrupole too. In practice, a doublet with modified lengths and a triplet with similar lengths were taken for investigation of mini-β solutions. The solutions of such structures were discussed with a doublet in the long drift section, an extra quadrupole in the long drift section, a triplet in the long drift section.

The modification of the lattice functions from 17.5, 7.2m to 0.3, 2m in both the planes in the long drift section while the short drift section is kept untouched, is accomplished by modifying the lengths of the doublet in the long drift section. A drift of 4.6m is still available for utilisation for insertion devices. The lattice functions were calculated using ESRO at the selected tune point of (8.80, 3.28), where the beam emittance was reduced further from 91nm.rad to 82nm.rad.

• Shri Samarendra Das, MCA, Devi Ahilya Vishwa Vidyalaya, Indore project on Application of Fractals in ViSc( Scientific Visualisation), 1992
• Shri Samir Dubey, A student of M.Sc(Physics), DAVV, Indore did his Summer Training Project on Study of Orbit Stability in Synchrotrons, 11 August 1994
• Shri Pradeep Kant, Beam Dynamics Section, CAT, Indore for his M.Sc degree by research on Design of beam transfer line for the food irradiation microtron, 2002