diff --git a/Grid/threads/Accelerator.cc b/Grid/threads/Accelerator.cc
index 9c40f538..32a6693e 100644
--- a/Grid/threads/Accelerator.cc
+++ b/Grid/threads/Accelerator.cc
@@ -8,6 +8,7 @@ void     acceleratorThreads(uint32_t t) {accelerator_threads = t;};
 
 #ifdef GRID_CUDA
 cudaDeviceProp *gpu_props;
+cudaStream_t copyStream;
 void acceleratorInit(void)
 {
   int nDevices = 1;
diff --git a/Grid/threads/Accelerator.h b/Grid/threads/Accelerator.h
index a8c91aa8..fa4d1dc0 100644
--- a/Grid/threads/Accelerator.h
+++ b/Grid/threads/Accelerator.h
@@ -105,6 +105,7 @@ void     acceleratorInit(void);
 #define accelerator_inline __host__ __device__ inline
 
 extern int acceleratorAbortOnGpuError;
+extern cudaStream_t copyStream;
 
 accelerator_inline int acceleratorSIMTlane(int Nsimd) {
 #ifdef GRID_SIMT
@@ -213,9 +214,13 @@ inline void *acceleratorAllocDevice(size_t bytes)
 inline void acceleratorFreeShared(void *ptr){ cudaFree(ptr);};
 inline void acceleratorFreeDevice(void *ptr){ cudaFree(ptr);};
 inline void acceleratorCopyToDevice(void *from,void *to,size_t bytes)  { cudaMemcpy(to,from,bytes, cudaMemcpyHostToDevice);}
-inline void acceleratorCopyDeviceToDevice(void *from,void *to,size_t bytes)  { cudaMemcpy(to,from,bytes, cudaMemcpyDeviceToDevice);}
 inline void acceleratorCopyFromDevice(void *from,void *to,size_t bytes){ cudaMemcpy(to,from,bytes, cudaMemcpyDeviceToHost);}
 inline void acceleratorMemSet(void *base,int value,size_t bytes) { cudaMemset(base,value,bytes);}
+inline void acceleratorCopyDeviceToDeviceAsynch(void *from,void *to,size_t bytes) // Asynch
+{
+  cudaMemcpyAsync(to,from,bytes, cudaMemcpyDeviceToDevice,copyStream);
+}
+inline void acceleratorCopySynchronise(void) { cudaStreamSynchronize(copyStream); };
 inline int  acceleratorIsCommunicable(void *ptr)
 {
   //  int uvm=0;
@@ -289,7 +294,10 @@ inline void *acceleratorAllocShared(size_t bytes){ return malloc_shared(bytes,*t
 inline void *acceleratorAllocDevice(size_t bytes){ return malloc_device(bytes,*theGridAccelerator);};
 inline void acceleratorFreeShared(void *ptr){free(ptr,*theGridAccelerator);};
 inline void acceleratorFreeDevice(void *ptr){free(ptr,*theGridAccelerator);};
-inline void acceleratorCopyDeviceToDevice(void *from,void *to,size_t bytes)  { theGridAccelerator->memcpy(to,from,bytes); theGridAccelerator->wait();}
+inline void acceleratorCopyDeviceToDeviceAsynch(void *from,void *to,size_t bytes)  {
+  theGridAccelerator->memcpy(to,from,bytes);
+}
+inline void acceleratorCopySynchronise(void) {  theGridAccelerator->wait(); }
 inline void acceleratorCopyToDevice(void *from,void *to,size_t bytes)  { theGridAccelerator->memcpy(to,from,bytes); theGridAccelerator->wait();}
 inline void acceleratorCopyFromDevice(void *from,void *to,size_t bytes){ theGridAccelerator->memcpy(to,from,bytes); theGridAccelerator->wait();}
 inline void acceleratorMemSet(void *base,int value,size_t bytes) { theGridAccelerator->memset(base,value,bytes); theGridAccelerator->wait();}
@@ -394,7 +402,8 @@ inline void acceleratorFreeShared(void *ptr){ hipFree(ptr);};
 inline void acceleratorFreeDevice(void *ptr){ hipFree(ptr);};
 inline void acceleratorCopyToDevice(void *from,void *to,size_t bytes)  { hipMemcpy(to,from,bytes, hipMemcpyHostToDevice);}
 inline void acceleratorCopyFromDevice(void *from,void *to,size_t bytes){ hipMemcpy(to,from,bytes, hipMemcpyDeviceToHost);}
-inline void acceleratorCopyDeviceToDevice(void *from,void *to,size_t bytes)  { hipMemcpy(to,from,bytes, hipMemcpyDeviceToDevice);}
+inline void acceleratorCopyDeviceToDeviceAsynch(void *from,void *to,size_t bytes)  { hipMemcpy(to,from,bytes, hipMemcpyDeviceToDevice);}
+inline void acceleratorCopySynchronise(void) {  }
 inline void acceleratorMemSet(void *base,int value,size_t bytes) { hipMemset(base,value,bytes);}
 
 #endif
@@ -435,7 +444,8 @@ inline void acceleratorMemSet(void *base,int value,size_t bytes) { hipMemset(bas
 accelerator_inline int acceleratorSIMTlane(int Nsimd) { return 0; } // CUDA specific
 inline void acceleratorCopyToDevice(void *from,void *to,size_t bytes)  { memcpy(to,from,bytes);}
 inline void acceleratorCopyFromDevice(void *from,void *to,size_t bytes){ memcpy(to,from,bytes);}
-inline void acceleratorCopyDeviceToDevice(void *from,void *to,size_t bytes)  { memcpy(to,from,bytes);}
+inline void acceleratorCopyDeviceToDeviceAsynch(void *from,void *to,size_t bytes)  { memcpy(to,from,bytes);}
+inline void acceleratorCopySynchronize(void) {};
 
 inline int  acceleratorIsCommunicable(void *ptr){ return 1; }
 inline void acceleratorMemSet(void *base,int value,size_t bytes) { memset(base,value,bytes);}