Choppers Comparison of three schemes of choppers is made 2.5 MeV and 2.1 MeV beam energies are considered Presented by Boris Shteynas May,

Content Several schemes of chopper are studied Two schemes with vertical kicks ( and ) from Eliana’s presentation on April 8 th and a scheme, proposed by John Staples (initially with horizontal kicks, but for comparison purposes changed to vertical kicks) are presented All schemes were considered in TraceWin with current In all three schemes 325MHz bunchers are used Initial conditions and optimal apertures are found All schemes considered under the same conditions with beam energy 2.1MeV. New parameters of elements in lattices are found

Initial conditions for 2.5 MeV beam for chopper #1(+-+-) and chopper #2 (+--+).

Chopper 1(+-+-): 3σ-Envelope 5 MHz Phase advance: x –140, y -180, l -90 Voltage=0 V Voltage=210 V* Losses 100%Losses ≈0.6% Here and in the whole presentation “Voltage” means potential difference between axis and chopper plates. Potential difference between two plates of kicker is two times bigger.

Chopper 1(+-+-): Losses. 210V and

After 2 nd scraperBefore 3d scraper Chopper 1(+-+-): Y-Y’ and X-Y

Chopper 1(+-+-): particles density. 210V and

Losses ≈0.6% Losses 100% Chopper 1(+-+-): Energy=2.1 MeV,current=5 Voltage=0 V Voltage=175 V

Chopper 1(+-+-): Losses. Energy 2.1 MeV Voltage=175V

Comparison of lattices of chopper 1 for 2.5 and 2.1 MeV 2.5 MeV2.1 MeV Phase advance x,y,l (deg)140, 180, 90152, 170, 94 Effective gap voltage (V) Structure period (m)2.6 Apertures of scrapers (mm) T/m N Magnetic field gradients Input parameters for 2.1 MeV :

Chopper 2(+--+): Envelopes of passed and chopped beam. Energy= 2.5 MeV, Voltage=235 V, Current=5 Asymmetric diaphragm is implemented in TraceWin by means of command BEAM_ROT. Losses 100% Losses ≈0.4%

Chopper 2(+--+): Energy=2.1 MeV,current=5 Voltage=220 V Losses≈0.4% Losses=100%

Staples’s chopper: initial conditions

Staples’s chopper: Voltage=325 V. Phase advance between 2 kickers is 180 Passed and chopped beam Losses≈0.3% Losses=100% Apertures are almost 2 times bigger than in choppers 1 and 2

Current: 5 MHz Norm.emittances (x,y,z): 0.25, 0.25, 0.3 mm*mrad Distribution is generated in 3.4σ Voltage needed for 100 % losses * Losses of passed beam Losses of chopped beam for 200 V Losses of chopped beam for 175V Chopper 1210 V0.6%99.8%97.8% Chopper 2235 V0.4%99.8%99.2% Energy=2.5 MeV Voltage needed for 100 % losses Losses of passed beam Losses of chopped beam for 200 V Losses of chopped beam for 175V Chopper 1175 V0.6%(100%) Chopper 2220 V0.4%99.7%99.0% Staples325 V0.3%96.4%93.8% Energy=2.1 MeV *If distribution is generated in 6.1σ this values become 218 V and 270 V respectively

Summary New initial conditions are found Optimal voltages are determined on the base of Gaussian distribution generated in 3.4σ 2.1 MeV beam energy is considered. New optic parameters of all elements and apertures in lattices are found.

Backup Slides

Voltage=200 V, 5 mA Losses 99.8% Chopper 1(+-+-): 3σ-Envelope 5 MHz Voltage=0 V

Losses (200 V) Losses = 99.8%

Chopper 2 ( ), 200V Losses 99.8%

Chopper 2 ( ), 235V with asymmetric diaphragm (implemented in terms of command BEAM_ROT in TraceWin) Losses=0.35% (mostly because of apertures of kickers 2 and 3)

RMS Emittance Un-chopped beam in chopper 1 (Voltage=0V) Un-chopped beam for chopper2 (Voltage=235V)

Staples’s chopper: Voltage=325 V

Transition to 2.1 MeV. Unkicked beam.

Chopped beam. Chopper 1 (+-+-).Voltage 175 V. Emittance (x,y,z): 0.25, 0.25, 0.3 Current 5 mA

Chopper 1(+-+-): Gradients.Energy=2.1 MeV

Chopper 1+SSRO matching GAP tripletsol SSR0 2 solenoids and a gap introduced for matching. TraceWin also varied last gap of the chopper and the last quad in the last triplet.

Chopper 1+SSR0 matching. Envelopes

Chopper 1+SSR0 matching. Partran

Chopper 1. Losses