High quality beam genera1on in density downramp injec1on and its early applica1ons

Transcription

1 2017 FEACT-II Science Workshop October, 2017 SLAC, Menlo Park, CA High quality beam genera1on in density downramp injec1on and its early applica1ons Xinlu Xu, Thamine Dalichaouch, Weiming An, Shiyu Zhou, Fei Li, Wei Lu, Mark Hogan, Chan Joshi and Warren Mori UCLA/SLAC/THU 10/19/2017

2 Outline Introduc1on Physics behind density downramp injec1on Ø Injec1on process Ø How this injec1on process leads to low emipance? - Transverse decelera1on process Ø How this leads to low energy spread? low slice energy spread break the longitudinal phase mixing low projected energy spread - remove the ini1al energy chirp Ø Scaling law and X-FEL simula1ons Conclusions

3 Introduc1on High quality beam genera1on in plasma wakefield accelerators Ø emipance 2I B= 5D Brightness Ø current n,x n,y Ø energy spread (slice and projected) X-FEL at LCLS1: 0.4 / < 1P A/m2 /rad Emma et al., Nature Photonics 4, (2010).

4 Introduc1on Downramp Injec1on S. Bulanov 2 et al. (1998), and H. Suk 3 et al. (2001) studied the injec1on process using 1D analysis. 1 T. Katsouleas, Phys. Rev. A 33, 2056 (1986); 2 S. Bulanov, et al., Phys. Rev. E 58, R5257 (1998); 3 H. Suk, et al., Phys. Rev. Lett. 86, 1011 (2001);

5 Introduc1on Downramp Injec1on S. Bulanov2 et al. (1998), and H. Suk3 et al. (2001) studied the injec1on process using 1D analysis. 1T. Katsouleas, Phys. Rev. A 33, 2056 (1986); 2S. Bulanov, et al., Phys. Rev. E 58, R5257 (1998); 3H. Suk, et al., Phys. Rev. Lett. 86, 1011 (2001);

6 Outline Introduc1on Physics behind density downramp injec1on Ø Injec1on process Ø How this injec1on process leads to low emipance? - Transverse decelera1on process Ø How this leads to low energy spread? low slice energy spread - broken longitudinal phase mixing low projected energy spread - remove ini1al energy chirp Ø Scaling law and X-FEL simula1ons Conclusions

7 The par1cle velocity z Injec1on Condi1on: z ph r i 0.5r m =4 =4

8 z =1 The par1cle velocity z 2(1 + ) large p 1+p 2? +(1+ )2 or is close to -1 The Possion-like Equa1on P. Mora and T. M. Antonsen Jr, Physics of Plasma 4, 217 (1997); W. Lu et al., PRL 96, (2006)

9 The phase velocity For a plasma wake (z, t) = vph (z, t) = p (z)(z/vd 1 t) vd (d p /dz) p 1 (vd t For the tail of the nonlinear wake1, d p1 vph vd (1 4 ) dz 8 1W. d p 1 1/2 dz Lu et al., PRL 96, (2006) ph 1.5 np0 z) np0

10 Outline Introduc1on Physics behind density downramp injec1on Ø Injec1on process Ø How this injec1on process leads to low emipance? - Transverse decelera1on process Ø How this leads to low energy spread? low slice energy spread - broken longitudinal phase mixing low projected energy spread - remove ini1al energy chirp Ø Scaling law and X-FEL simula1ons Conclusions

11 Transverse Decelera1on The transverse force on the sheath plasma electrons F r = F d + F i + F e D F -- D F e = (r/2)(1 z)de z /d is from the plasma electrons. In most of the wake, d 2 0 d 2 = de z d = 1 2 At the very rear of the wake, d 2 0 d 2 1 W. Lu et al., PRL 96, (2006)

12 Transverse Decelera1on The transverse force on the sheath plasma electrons F r = F d + F i + F e W. Lu et al., PRL 96, (2006)

13 High brightness beam genera1on The trajectories of the injected electrons in downramp injec1on: =1,n p,h =1.5n p0,l= 20c/ p0 Enlarged View

14 High brightness beam genera1on Λ=1, n p,h =1.5 n p0, L=20 c/ω p0

15 Outline Introduc1on Physics behind density downramp injec1on Ø Injec1on process Ø How this injec1on process leads to low emipance? - Transverse decelera1on process Ø How this leads to low energy spread? low slice energy spread - broken longitudinal phase mixing low projected energy spread - remove ini1al energy chirp Ø Scaling law and X-FEL simula1on Conclusions

16 Low slice energy spread - Rela1ons between z i and ξ f 8 =1, np,h =1.5n p0, L=20c/ p0 [c/ p0 ] z i [c/ p0 ] Longitudinal phase mixing 1 is broken! Slice energy spread ~ O(0.1) MeV! 1 X. L. Xu, et al., PRL 112, (2014).

17 Low projected energy spread play with the chirp E z L ramp Ini1al energy chirp can be removed when and at this op1mized distance.

18 Low projected energy spread play with the chirp 900 Evolving Driver: =4, z= r=c/ p0, n=c/ p0, 1.5 np0->n p0 (L=250 c/ p0), Te=10 ev 635 EEbb [MeV] [MeV] z [c/ ] p z [c/ p0 ]

19 Outline Introduc1on Physics behind density downramp injec1on Ø Injec1on process Ø How this injec1on process leads to low emipance? - Transverse decelera1on process Ø How this leads to low energy spread? low slice energy spread - broken longitudinal phase mixing low projected energy spread - remove ini1al energy chirp Ø Scaling law and X-FEL simula1ons Conclusions

20 Scaling law I ε n, τ and σ r B σ E /E n Q e - Beams n p0 0 n p0-0.5 n p0 1 n p0 0 n p0 1 n p0-0.5 Ramp Length 1 AcceleraOon Distance 2 Plasma n p0-0.5 n p0-0.5 Take 1.5 n p0 à n p0 (L=250 c/ω p0 ) as an example: Injected beam Plasma n p0 [cm -3 ] I [ka] ε n [nm] τ [fs] σ r [um] B [A/m 2 / rad 2 ] 1 For fixed density change; 2 To remove the energy chirp. E [MeV] σ E /E Q [pc] e e e e-3 14 n p0 [cm-3] Density change [cm -3 ] L ramp [mm] L acc [mm] e e

21 Injector for an X-FEL I [ka] σ r [um] σ z [um] ε n [um] Q [nc] E b [GeV] Driver beam 34 (Λ=4) n p,h [cm -3 ] n p0 [cm -3 ] L ramp [mm] L acc [mm] IniOal T [ev] Plasma 1.5e18 1e (250 c/ω p0 ) E b = 620 MeV ˆEb = B~4e18 A/m 2 /rad 2

22 X-FELs Driven by Plasma Accelerators High quality beam genera1on Matching Plasma Matching + Quadrupoles Radiator l=0.30mm L=5.7mm 4 quads, ~300 T/m Codes: OSIRIS ( + QuickPIC) elegant Genesis 1.3

23 FEL radia1on sor X-ray Undulator: λ u =0.5 cm, K=1 1 à λ r =3.6 nm Genesis 1.3 Simula1on Results 1 : ~10 spikes 1 S. Reiche, Nucl, Instrum. Methods Phys. Res., Sect. A 429, 243 (1999).

24 Conclusions We studied the injec1on dynamics in downramp injec1on in the 3D blowout regime and found high quality (high current, low emipance, low slice and projected energy spread) electron beams can be generated with suitable parameters. By combing the plasma matching sec1on and quadrupoles, this high quality beam can be transported to the undulator to drive a X-FEL.

25 Thanks!

26 Plasma Matching Sec1on Characteris1c l=0.30 mm, Total L=5.7 mm Before Matching sec1on Arer Matching sec1on ~0.3 mm ~6 mm

27 Magne1c transport lines L1 L2 L3 L4 Parameters Value L1 [m] 0.3 L2 [m] 0.9 L3 [m] 0.9 L4 [m] 0.9 K1 [m -2 ] 28.1 K2 [m -2 ] K3 [m -2 ] 16.4 K4 [m -2 ] * Width [m] 0.1 * corresponding to 270 T/m